A ninvestigatio n o f panicl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 61) . I lowever , th e peak o f eac hprofil e estimate db y th e numerica l dat ai s muc hclose r t o th e pip e inne r wal l (th e negativ e x direclion ) tha n tha t i n th e experimenta l data . Fo r U a yprofile s o n th e x axis , bot hth e experimenta l an dnumerica l dat adispla y asimila r decreasin g tendenc y o f U a yfro m th e pip e oute r

wal l to th e pip e inne r wal l (alon g th e negativ e x direction ) at eac hsection . Th e U a y . profile s ar e muc hflatter , whic hi s show n b y th e narrowe ddifferenc e o f U a yamon g th e differen t point s o n th e x axis . However , th e numerica l profil e o f U a yha s awide r

fla t to p regio n tha n th e experimenta l profil e o f U a ydoe s a t

th e sectio n O D an d2D , fo r th e experimenta l cross-sectiona l distribution s o f

U a ywit hth e fastes t

velocit y i n Figur e 4. 5 ar e thinne r tha n thos e ofth e numerica l result s i n Figur e 4.6 . Figur e 4.1 0 show s th e experimenta l an dnumerica l profile s o f U r aan dU a yi n th e z axis . Th e symmetrica l featur e alon g th e z axi s i s show n i n bot hth e experimenta l an dth e numerica l profile s o f Ua x an dU a ya t

eac hsection . Th e profil e pea k o f an dth e botto mo f U a yar e locate dat

th e poin t z=0 . Anothe r

observe dagreemen t fo r U a xo r U a yi s th e simila r

profil e shap e betwee n th e experimenta l an dth e numerica l profile s downstrea mo f th e sectio n OD , I n general , U Mi s faste r i n th e pip e centr e tha n i n th e pip e lef t (th e z negativ e axis ) an drigh t side s (th e z positiv e axis) . B y contrast , U a yi s faste r i n th e pip e tw o side s tha n i n th e pip e centr e alon g th e z axis . However , th e profil e shap e o f

U a xan dU a yha s muc hdiscrepanc y o n th e sectio n OD , althoug hthei r experimenta l an dnumerica l profile s sho w asimila r variatio n tendency . A t th e sectio n OD , th e experimenta l profil e o f U a xsho w ashar p pea k at th e poin t

z=0 , wher e th e numerica l profil e o f U a xshow s afla t

top . An dth e numerica l profil e o f U a yi s ver y fla t

wit hamino r

dro p fro mth e pip e tw o side s t o th e pip e centr e alon g th e z axis . I n contrast , th e experimenta l profil e o f U a y show s adee p minimu mi n th e centr e regio n aroun dz= 0 wher e U a yi s slowes t i n th e z axis . Comparin g th e one-dimensiona l profile s i n Figur e 4. 9 an dFigur e 4.1 0 wit hth e two-dimensiona l cross-section s distributio n i n Figur e 4.5~4.8 , w e ca n se e tha t th e discrepancie s betwee n th e experimenta l an dnumerica l profile s o f U a xan dU a yi n th e x axi s an dth e z axi s at th e sectio n O D ar e mainl y cause db y th e fac t tha t th e numerica l position s ofth e highes t velocit y regio n o f

U „ an dth e horsesho e centr e o f U a ydiffe r

fro mth e correspondin g position s measure db y experiments .

6 5


# VES01710 0Chapter - 1 l-.\pcrimcnla l studie s o f cross-sectiona l characteristic s o f ai r velocit y i n pipe s U/<U > profile s O n th e z axi s U/l i profile s O nth e zaxi s 6 D 6 D

3 TM | 5 0. 8

4 D 0. 6 1. 2 4 D

x * ° i

2 D 0. 6 1. 2 2 D 3 0

OD 0. 6 1. 2 OD

C F D L D A

- 1 -0. 6 -0. 2 0. 2 0. f

Z/ R 0. 8 : CF O ^ LD A

- 1 -0. 6 -0. 2 0. 2 0. 6 1

z/ R Figur e 4.I 0 Profile s o f U „ an dU a ) . alon g th e z axi s a t fou r selecte dvertica l cross-section s ( < U a x > i s th e mea n absolut e valu e o f U„ ; U , i s th e ai r

conveyin g velocit y lOm/s )



### 4. 3 CONCLUSION S Th e tw o calculate dtransfor mmatrices , fo r th e horizonta l an dvertica l pip e flo w measurement s respectively , wer e use dt o arrang e th e shiftin g coordinate s o f th e travers e syste mwhic hcarrie d th e LD Aprobe s t o acces s measuremen t cross-section s i n th e horizonta l pip e an dth e vertica l pip e behin dahorizontal-vertica l 90 ° ben d(R/D= l .3) . O nth e tw o horizonta l cross-sections , th e experimenta l dat ao f th e axia l ai r

velocit y (U a x ) revea l a n annula r

nature . Bot hth e profile s o f U u xo n th e y axi s an dth e z axi s agre e wit hth e empirica l one-sevent hpower-la w profile . O n th e eigh t vertica l cross-section s fro m0 D t o 7D , th e

6 6


# VES01710 1A n investigatio n o f particl e dynamic

s i n adilut e phas e pneumati

c conveying syste

m horseshoe-lik e feature i s displaye d o n each cross-sectiona l distributio n o f the axia l ai rvelocit y ( U a y ) . Uay , i s slowe rinsid e th e horsesho e clos e t

o th e pip e inne rwal l and U a yi s faste ri n th e regio n aroun d th

e pip e oute rwall . Th e differenc e o f U a ybetwee n insid e an d outsid e o f the horsesho e graduall y decreases a tfurthe rdownstream section s from OD . A secondary flow i s reveale d i n th

e cross-sectiona l distribution s o f th e radia l ai rvelocit y (U a x ) , especiall y o n th e sectio n OD . Thi s secondary flow include s tw o circulation s symmetrica l alon g the z axis . Hence , a vertica l cross-sectio n ca n b e classifie d into three region s o f th e mi d stri p an d the tw o sectors outsid e th e strip , accordin g t o Ua x directions . O n each section , th e secondary flow o n the mi d stri p i s divide d int

o two a tth e pip e oute rwall . On e subflo w i s accelerate d toward s the pip e inne r wal l alon g th e pip e lef twal l an d th e othe ralon g th e pip e rightwall . The n tw o subflow s are mixe d a tthe regio n clos e t

o the pip e inne rwall . Th e directio n o f th e mixe d flo w i s change d toward s the pip e centre (i n th

e positiv e x direction) . Befor e reachin g th e pip e centre , the mixe d flo w i s accelerate d t

o obtai n it

s maximu m magnitud e o f U a xi n th e positiv e x direction . The n U Ki s decelerate d t

o approach zer o a

tth e pip e oute rwall . Thus , th e lef tsubflo w with th

e mixe d flow form s th e circulatio n i n th e counter-clockwis e direction . Th e rightsubflo w wit h th e mixe d flow form s anothe rcirculatio n i n th e clockwis e direction . However , a tth e furthe rdownstream section s o f 4 D t o 6D , th

e secondary flow become s weak , fo rth e magnitud e o f

Ua x graduall y decreas e an d th e differenc e o f

Ua x between the mi d stri p an d its tw o side s i s narrowed .
A compariso n o f

the experimental datab y LD A an d th e numerica l results b y CF D indicate tha t bot h o f the m o n th

e x axi s an d th

e z axi s sho w asimila rshap e fo rthe axia l ai rvelocit y (U a y ) an d th e horizonta l ai rvelocit y (Uax) .

6 7



# VES01710 2

# Chapte r5 Experimenta l investigatio n of Particl e Dynamic s i n a Dilut

e Pneumati c Conveyin g Syste m usin g

th e Extende d LD A Techniqu e

This chapterpresents experimental results obtained

by using the extended LDA technique introduced In Chapter

3, for the quantitative assessment of particle dynamic behaviour in the horizontal

and vertical legs ofthe dilute pneumatic conveying system shown in Figure 3.2. Three kinds of glass beads were selected

to simulate the pulverized coal and biomass pellets transported in a dilute pneumatic conveying system. Detailed information on the cross-sectional spatial

distributions of

the axial particle velocity and

particle numberrate is reported. In the horizontal part, the experimental data on a series of

cross-sections clearly illustrate two uniform fluid patterns, annulus structure and stratified configuration, which describe the cross-sectional distributions of

particle velocity and particle numberrate respectively. In the vertical pipe behind

an elbow R/D=1.3, a horseshoe shape characterizes the cross-sectional distribution of

axial particle velocity for all three types of

glass beads on the section OD, close to the elbow outlet. The development of cross-sectional

distributions of particle numberrate indicates that particles with high inertia would be de-entrained

from the rope formed in a bend.



### 5. 1 FLUI D CONDITION S AN D MEASUREMEN TPARAMETER S Th e objective s o f

th e experimenta l investigatio n ar e particl e dynami c propertie s lik e particl e velocity , particl e numbe rrat e an d thei rspatial distributio n ove rapip e cross-section . Al l o f them hav e been measure d b y employin g th e extende d techniqu e o f Lase rDopple rAnemometr y (LDA ) whic h was discusse d i n Chapter3 . Th e experimenta l task s include d the measuremento f the cross-sectional distribution s o f particl e velocit y an d particl e numbe rrat e fo rdifferen tparticl e size s a s wel l a s the assessmentofth e effec to f particl e siz e o n th

e turbulenc e intensit

y o f the soli d phas e i n th

e horizonta l an d vertica l parts o f th e dilut e pneumati c conveyin g syste m whic h i s displaye d i n Figur e 3.2 . Experiments were performe d unde rth e dilute flow regim e wit h three differen tsize s o f glas s bead s an d smoke . Thre e type s o f glas s bead s wer e selecte d t o b e transporte d i n pipe s b y air , whic h were t

o simulat

e the dilut e gas-soli d flow o f pulverize d coa l o rbiomas s pellets . Accordin g



# VES01710 3( liaplc r5 experimenta l studie s o f particl e dynamic s b y LD A l o th e criterio n o f

similarit y ol ' Stoke s Numbe r a s introduce di n Chapte r 2 , th e firs t

typ e o f glas s bead s (les s tha n 50pm ) an dth e secon d(70-110pm ) correspon dt o pulverize dcoa l withi n 0~110um , a s use di n powe r stations . Th e thir dgrou p (180~300pm ) represent s wood-chip s aroun dI m msize . I n addition , smok e wa s use dt o trac k th e ai r phas e o f

th e flo w i n th e LD A experiments .

" f ii '°2 0 3

0 4 0 E O 8 0 7 0 0 0 9 0 IO 0 11 0 ! " 2

0 3 0 4 0 S O ffl /

0 B O 9 0 10 0 11 0
(a) b y mas s (b ) b y numbe r Figur e 5. 1 Particl e distributio n fo rth e secon d typ e o f glas s beads . A s fo r th e secon dgrou p o f glas s beads , it s rea l densit y an dbul k densit y ar e 255 0 kg/m 3 an dbul k densit y 156 9 kg/m 1 respectively . Thes e bead s wer e als o sorte dusin g 5 differen t siev e meshe s (38 , 45 , 75 , 9 0 an d106pm ) o n ahig hefficien t electric-magneti c shaker . Th e distribution s ofth e mas s rati o an dparticl e numbe r ar e show n i n Figur e 5.1 . I n producin g thes e results , thre e particl e sampl e volume s o f

600ml , 400m l an d200m l wer e sieve dove r tw o hours . Accordin g t o th e mas s distributio n (i n Figur e 5.1a) , mos t particle s ar e locate di n th e rang e 90-106p man dth e correspondin g mas s i s abou t 90% . I f

mes hsiz e wa s considere da s th e mea n diamete r o f particle s groupe di n thi s mesh , th e particl e numbe r media n diamete r

shoul db e 9 0 p mwher e th e particl e cumulativ e numbe r

rati o i s mor e tha n 50 % (a s show n i n Figur e 5,1b) . Thes e measure dresult s agre e wit hth e siz e precisio n o f 90 % i n rang e o n th e dat ashee t o f glas s bead s provide db y th e compan y Wor f

Glaskugel n Gmb H (2008) .

6 9A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 

### 5. 2 DETERMININ G TH E PROPE R SAMPL E RAT E O F LD A I nsectio n 3.4 , w e hav e discusse dth e reaso n wh y th e sampl e frequenc y o f LD Ashoul db e a

t leas t equa l t o o r

greate r tha n l/t rai n(t m i „ i s th e minimu mtempora l interva l betwee n tw o adjacen t particles) . Sinc e particl e signal s recorde db y LD A ar e discrete , ther e i s n o theoretica l Nyquis t frequenc y fo r

acontinuou s signa l an dasuitabl e samplin g frequenc y o f LD A mus t

b e experimentall y investigate dunde r differen t

flui dconditions .
I ngeneral , th e frequenc y variatio n o f particle s a t

apoin t ca n b e describe da s th e loca l particl e numbe r rate , particl e velocit y o r particl e mas s flo w rate . Amon g thes e thre e parameters , particl e numbe r rat e i s th e mos t

prope r an deviden t

paramete r

fo r expressin g particl e loca l frequenc y variation , fo r

i t ca n b e directl y obtaine db y countin g ever y availabl e burs t signa l recorde db y L D Aaccordin g t o th e LD Aprincipl e discusse di n sectio n 3.1.1 . Subsequently , at ameasuremen t point , particl e numbe r rat e agains t

th e differen t

sampl e rat e o f

LD A ca n b e deduce dfro m countin g burs t

signals . Wit hregar dt o astead y gas-soli dflo w wit haconstan t soli dloadin g ratio , th e faste r

th e sampl e rat e o f

LDA , th e large r

th e availabl e burs t

signal s tha t

ca n b e recorded , whic hresult s i n ahighe r particl e numbe r

rate . I f w e observ e tha t

particl e numbe r

rat e i s n o longe r increase dwit hth e samplin g rat e o f LD Abeyon dacertai n value , th e curren t particl e numbe r

rat e show s th e maximu mfrequenc y variatio n o f particle s a t

th e measuremen t

poin t unde r th e curren t flui dconditions . Thus , th e suitabl e sampl e rat e o f LD Ashoul db e selecte da s large r tha n thi s maximu mfrequency .
T o exten dth e abov e discussio n relatin g t o apoint , t o th e whol e spac e o f apneumati c conveyin g system , th e prope r

sampl e rat e o f

LD Afo r

measuremen t

i n ahorizonta l o r

vertica l pip e wil l b e determine dwhe n th e highes t loca l frequenc y variatio n o f gas-soli dflo w i s acquired . Du e t o gravit y settling , soli dphas e concentratio n i n th e botto mregio n o f th e horizonta l part s i s highe r tha n i n othe r

parts , eve n ignorin g th e effec t o f elbow s i n th e pneumati c conveyin g syste ma s show n i n Figur e 3.2 . Whe n th e prope r sampl e rat e o f

LD Ai s obtaine db y experiment s a t th e botto mregio n o f

th e horizonta l leg , thi s sampl e rat e wil l b e suitabl e fo r measurement s a l othe r spac e i n th e syste ma s well .
I nou r LD A experiments , th e secon dtyp e o f glas s bead s (70-110u.ni) , whic hwa s use dt o determin e th e suitabl e sampl e frequenc y o f LDA , wa s conveye db y a n ai r conveyin g velocit y 1 2 m/ s wit hsoli dmas s loadin g rati o (1.6 % kgs 'Vkgs" 1 ) a t th e maximu minjectio n spee do f th e screw-feeder , Eleve nsampl e rate s o f LD A wer e evaluate da t 1 5 sampl e point s o n eac hy coordinat e i n th e lowe r hal f o f apip e cross-sectio n (30 0 m mawa y fro mth e elbo w inlet) . Th e measure ddat ao f

particl e numbe r

rat e a t eac hsampl e poin t

b y th e differen t

sampl e rat e wer e

7 0



# VES01710 5Chapter 5 experimenta l studie s o f particl e dynamic s b y LD A show n i n Figur e 5.2 .

150 0 y~0 m m 1000 •S 50 0 200 0 S 1500

- 100 0 y=-7. 5 m m

50 0 1 0 2 0 3 0

z(mm ) 4 0 1 0 1 5 2 0 z(mm ) 2 5 3 0 400 0 300 0 200 0 100 0 y=-1 5 m m

0 1 0 2 0 3 0

z(mm ) 4 0 100H z 300H z 500H z 800H z 1kH z 2kH z 3kH z 4kH z 5kH z Figur e 5.

2 Particl e numbe rrate agains tth e sampl e rat e o f LD A on th e sectio n 300m m away fro m the elbow inle tai rvelocit y 12m/s , soli d loadin g rati o abou t1.6% Comparin g thes e thre e diagram s i n Figur e 5.2 , w e notic e tha t th e highe r

th e sampl e rat e is , th e mor e particle s ar e counted . An dw c als o se e tha t particl e numbe r

rat e varie s spatiall y accordin g t o th e differen t

sampl e rat e o f

LDA . A t

alo w sampl e rat e equa l t o o r les s tha n 50 0 I Iz , particl e numbe r rat e i s almos t

th e sam e at

50 0 count s pe r

secon da

t th e differen t

sampl e point s o n thre e differen t

y coordinate s a s show n i n th e thre e sub-diagram s o f Figur e 5.2 , It

i s clea r tha t a500 1 I z sampl e rat e o f

LD Ai s to o lo w fo r

experiments . Particl e numbe r rat e unde r

thi s sampl e rat e doe s no t displa y it s spatia l variatio n du e t o gravit y settling . Increasin g th e sampl e rate , w e ca n se e tha t particl e numbe r

rat e i s als o increase dno t onl y fro mpip e wal l t o pip e centr e alon g th e z axi s bu t als o toward s th e pip e botto m(alon g y negativ e axis) . However , particl e numbe r rat e a t eac h sampl e poin t

i s n o longe r

increase drapidl y an dit s valu e retain s onl y anarro w fluctuatio n whe n th e sampl e rat e o f

LD Ai s mor e tha n 4 kHz . A s such , 4 kH z i s considere da s th e maximu m frequenc y variatio n o f particle s o n th e sampl e lin e (y=-15mm ) unde r th e curren t

flui dconditions .
I n practice , 1 0 kH z wa s empiricall y selecte da s th e sampl e rat e o f LD Ai n ou r

experiment s wit h consideratio n o f

th e possibilit y o f

particl e numbe r

rat e (large r

tha n 4000 , bu t

les s tha n 10000 ) at point s clos e t o pip e botto munde r th e flui dcondition s o f soli dmas s loadin g rati o 1.6 % kgs 'Vkgs" ' at a12m /s ai r conveyin g velocit y i n atj>75m mpipe .

7 1



# VES01710 6A ninvestigatio n ol " particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m I naddition , fo r

LD A i s asingl e poin t instrument , ameasuremen t ove r eac hcross-sectio n consume dabou t

7 0 minute s fo r

ameasuremen t

interva l ove r

on e secon da t

ever y sampl e point . Th e 1 0 kH z sampl e rat e ofl.D Awil l ensur e th e recordin g th e maximu m10 k numbe r

ofth e dat a set (Up, , i I , ... . N ] a t eac hpositio n i n on e second . Her e U pca n b e on e componen t o f th e particl e velocit y a t

th e measuremen t

positio n dependin g o n th e optica l arrangemen t o f th e LDA , Ni s th e actua l tota l numbe r o f particle s crossin g th e sampl e poin t withi non e secon d(N<10k) , whic hi s define da s th e particl e loca l numbe r rate . Thu s th e particl e mea n velocit y at asampl e poin t (x , y , z ) i s give n b y 1 , v
wher e {u p x , u p y , u p / f ar e thre e particl e velocit y component s an d< > represent s a n appropriat e average . Th e particl e root-mean-squar e (RMS ) fluctuatio n velocit y i s calculate da s averagin g th e square ddifferenc e betwee n atime-serie s o f loca l velocitie s an dit s mea n valu e a t asampl e point . I t ca n b e describe db y

wher e <U' P '' > i s als o representativ e o f th e granula r

temperatur e 0 whic hi s proportiona l t o th e squar e o f

arando mvelocit y wit hwhic hth e particle s oscillat e abou t amea n hydrodynami c velocit y (Campbell , 1990) . The n particl e turbulenc e intensit y i s expresse da s (5.3 )
Usin g th e equation s outline dabove , th e experimenta l dat awil l b e analyze dt o displa y th e cross-sectiona l propertie s o f particl e dynamic s alon g th e horizonta l an dvertica l part s o f th e experimenta l rig . 

### 5. 3 EXPERIMENTA L RESULT S O N PARTICL E DYNAMIC S I N A HORIZONTA L PIP E I n Chapte r

4 , w e hav e demonstrate dho w t o measur e th e cross-sectiona l velocit y o f ai r phas e b y usin g th e pre-calculate dtransfor mmatri x t o matc heac hshif t coordinat e o f

th e travers e syste m wit hth e actua l spatia l positio n o n th e measuremen t region . Similarly , th e cross-sectiona l propertie s o f th e soli dphas e lik e particl e velocity , particl e numbe r rat e an dgranula r

temperatur e wer e als o investigate db y mean s o f LD Awit ha1 0 kH z sampl e rate . O neac hcross-section , atota l o f 104 7 sampl e point s wa s designe dt o represen t th e distributio n ove r th e whol e region . Thes e wer e accesse dthroug hshiftin g th e three-dimensiona l travers eChapte r 5 Experimenta l studie s o f particl e dynamic s b y LD A syste mofth e LDA . Consequently , eac hsectio n ha s bee n meshe dint o th e 104 7 loca l subregions . Th e followin g subsection s wil l presen t th e experimenta l result s o f thre e type s o f

glas s bead s (<50um ; 70-110p man d1X0~300pm ) i n th e horizonta l pip e respectively . 5.3. 1 Feature s ofth e measure d parameter s a tatypica l poin t Amon g th e experimenta l result s ofth e secon dtyp e o f glas s bead s (70-110pm) , Figur e 5. 3 show s th e variation s o f

th e thre e component s o f th e particl e velocit y measure dat atypica l positio n o n th e cross-sectio n eigh t pip e diameter s (8><75mm) upstrea mo f th e elbo w inlet . Th e typica l positio n i s locate dat (0 , 25 , 0 ) m mwhic hi s marke da s th e re dcros s show n i n th e righ t han dsid e o f Figur e 5. 3 an di s relativ e t o th e referenc e coordinat e locate dat th e sectio n centre . Eac h velocit y componen t

i s adiscret e tim e serie s recorde db y LD Aan dfluctuate s aroun damea n value , fo r ther e i s n o clea r

increasin g o r

decreasin g tren di n Figur e 5.3 . However , th e variatio n o f {U p x } i s muc hstronge r

wit hacovarianc e o f 0.32 . Th e covarianc e value s o f {U p y } an d{U p z } ar e 0.1 1 an d0.0 5 respectively .

Nvalue s o f

aparamete

r 4 8 fo r U p x 66forU p y 14forU p z Covarianc e 0.3 2 for U p x 0.1 1 for U p y 0.0 5 for U

60 0

T(ms ) Figur e 5.3 Th e measure d particl e velocity a tasampl e poin ti n thre e axe s (U a =12m/s ; particle s withi nth e siz e rang e 70

— 110pm ) I n Chapte r

3 , w e hav e discusse dth e refractio n effec t o f th e curve dpip e wal l whic hmake s th e identica l cross-poin t

(at whic hthre e pair s o f thre e colou r

beam s o f

th e LD A intersect ) separat e whe n th e crossin g poin t i s move dint o th e pipe . Th e measurement s o f th e thre e component s o f {Up X } , {U p y } an d{U p z } ar e no t coinciden t

i n location , sinc e th e actua l crossin g point s ofth e thre e colou r

beam s ar e (0 , 25.10 , -1.67 ) m mfo r th e blu e beam s (U p x ) , (0 , 24.98 , 1.08 ) m mfo r th e gree n beam s (U p y ) an d(0 , 25.01 , 0.92 ) m mfo r th e violen t

beam s (U p 7 ) . The y ar e groupe daroun d th e typica l poin t

(0 , 25 , 0 ) withi na2m mdistance .

7 3



# VES01710 8A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m Th e tota l numbe r

o f measure ditem s fo r eac hparamete r

i n on e secon di s considere da s th e particl e numbe r

rate . Here , th e set s JU p x } , {U p y ( an d{V pr } ove r

on e secon dconsis t

o f 48 , 6 6 an d1 4 item s separately . Thus , th e measure dparticl e numbe r rate s ar e define da s 48 , 6 6 an d1 4 pe r second . Therefore , w e wil l us e th e statisti c time-average dvalue s o f {U p x } , {U p y } , {U p z } an dparticl e numbe r rat e K t o describ e th e overal l variabilit y o f soli dphas e i n aloca l subregio n whic hi s represente db y atypica l point . 5.3. 2 Characterizin g th e experimenta l dat ao n apip e cross-sectio n

Contou r o f th e mea n { U} m/ s <l 1 3 >1
1 0

-

'•

3 12. 5 1 2 -4 0 -2 0 0 2 0 4 0

z(mm ) Contou r o f th e mea n { U} m/ s

0.0 1

-4 0 -2 0 0 2 0 4 0

z{mm ) I o b V

-4 0 -2 0 0 2 0 4 0

z(mm ) Contou r o f particl e numbe r

ral e {N }

I o

-4 0 -2 0 0 2 0 4 0

z(mm ) Figur e 5.

4 Cross-sectiona l flo w pattern s describe d b y the distribudon s o f particl e mea

n velocitj ' an d particl e numbe rrate respectivel y (U a =12m/s ; particle s withi n the siz e rang e 70~T10pm ) Figur e 5. 4 display s th e time-average dvalue s o f experimenta l dat ao n th e sectio n eigh t pip e diameter s upstrea mo f th e referenc e poin t

15m mbefor e th e elbo w inle t i n th e horizonta l pipe . Amon g th e fou r

diagram s i n Figur e 5.4 , th e spatia l distributio n o f th e time-average dparticl e axia l velocit y |U p x } clearl y form s a n annula r distribution , i n whic hth e particl e axia l velocit y decrease s fro mth e centr e o f th e sectio n t o th e wall . W e cal l thi s kin do f flui dpatter n a n annula r cross-sectiona l pattern . Moreover , fo r th e sam e gas-soli dflo w o n th e section , w e als o observ e

7 4Chapte r 5 l:\perimenla l studie s o f particl e dynamic s b y LD A tha t th e particl e numbe r

rat e i s represente db y astratifie ddistributio n layere dfro mth e pip e to p t o th e bottom . Thi s strat i fie dconfiguratio n clearl y expresse s th e phenomeno n o f gravit y settlin g du e t o th e gravit y forc e i n ahorizonta l pipe . Asl o a n iso-lin e o f th e stratificatio n reduce s i n heigh t alon g th e y axi s fro mth e pip e right-han dt o left-han dsid e alon g th e z positiv e direction , whic h mean s tha t

th e particl e numbe r rat e i s large r

i n th e z negativ e fieldtha n i n th e z positiv e regio n unde r th e condition s o f

th e identica l y coordinate . Thi s inhomogeneou s distributio n o n th e z axi s ma y b e cause db y th e particle s initia l conditions , a s i n th e experiment s the y wer e horizontall y injecte dalon g th e z negativ e directio n b y ascre w feeder . Thus , th e particle s wil l posses s a n initia l velocit y i n th e z negativ e directio n afte r bein g injected , whic hresult s i n a n initia l tendenc y o f th e particle s to mov e toward s th e z negativ e direction . A s fo r th e othe r

tw o particl e velocit y components , {U p y } an d{U p z j , thei r cross-sectiona l distribution s d o no t

hav e an y clea r

pattern , especiall y fo r th e contou r

o f {U p y } . I n general , th e time-average dvalue s o f {U p z } ove r

th e whol e sectio n ar e positive , whic hshow s th e overal l tendenc y o f

particle s t o mov e towar dth e z positiv e direction . However , th e time-average dvalue s o f {U p y } ma y b e positiv e o r negativ e an dhav e arando mdistributio n o n th e section . Therefore , w e wil l us e th e parameter s o f {U p s } , th e correspondin g granula r temperatur e {0 } an d particl e numbe r

rat e {N } t o analyz e th e cross-sectiona l experimenta l dat aalon g th e flui d directio n i n th e followin g sections . 5.3. 3 Th e developmen to f cross-sectiona l flui d pattern s i n ahorizonta l pip e Unde r th e condition s o f

ai r conveyin g velocit y 12m/ s an dsoli dmas s loadin g rati o 1.6 % an da sampl e rat e 1 0 kH z fo r Lase r Dopple r

Anemometry , th e experimenta l measurement s fo r th e secon dtyp e o f

glas s bead s (70-110pm ) wer e performe da t aserie s o f

pip e cross-section s upstrea mo f

th e elbo w inle t

a s show n i n Figur e 5.5 . Th e referenc e cross-sectio n i s define da s O D whic hi s 15m mbefor e th e elbo w inlet . Th e origi npoin t o f ever y loca l coordinat e syste mlocate s at th e centr e o f

th e pip e cross-section . Th e experimenta l result s o f time-average dparticl e axia l velocitie s {U p v } , granula r temperatur e {© } an dparticl e numbe r rat e {N } o n eac hcros s section s ar e visualize di n th e sam e ro w i n Figur e 5.6 . Th e cross-sectiona l evolutio n o f thes e thre e parameter s i s subsequentl y displaye dfro mth e sectio n 7 D t o I D alon g th e flui ddirection . Wit hregar dt o cross-sectiona l flui dpatterns , o n ever y sectio n fro m7 D t o ID , th e annula r contou r

structur e o f

{U p s } an dth e stratifie dcontour s o f )N } ar e als o clearl y observed , resemblin g th e result s show n i n Figur e 5.4 . Thus , gas-soli dpip e flo w fo r soli dphas e wit hStoke s numbe r les s tha n 3. 6 coul db e treate da s eithe r annula r

flo w o r

75



# VES01711 0A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m stratifie dflow , describin g contour s o f particl e axia l velocit y o r particl e numbe r

rat e respectively .

Figur e 5.5 Th e sketch o f eigh tmeasuremen tcross-section s alon g th e horizonta l pip e Despit e th e genera l similarit y o f flui dpattern s amon g th e cross-sections , th e shape , are aan d centr e o f

th e annula r

cor e (th e fastes t

region ) fo r

[U p xj var y alon g th e flui ddirection . Moreover , th e centr e o f

eac hcor e i s obviousl y no t situate dat

th e correspondin g cross-sectio n geometri c centr e o f

th e cross-section , whic hresult s i n axia l asymmetr y fo r th e {U p x J cross-sectiona l distribution . Considerin g th e developmen t o f th e varianc e o f

{U p x } o r

granula r

temperatur e {©} , w e ca n se e a n analogou s shap e o n eac hsection . Basically , th e varianc e o f fluctuatio n o f

{U p x } i s smalle r i n th e right-u p regio n o f across-section , whic hmean s asteadie r gas-soli dflo w tha n i n th e othe r

parts . Fo r

th e developmen t

o f particl e numbe r

rat e {N} , asimila r

layere dconfiguratio n i s observe dfo r

th e cross-sectiona l distributio n o f particl e numbe r

rat e o n eac hsection . Bu t a n iso-lin e o f

particl e numbe r

rat e varie s i n actua l positio n wit hadecreasin g tren dfro mth e lef t t o th e righ t

(alon g th e z axis ) o f eac hcross-section . Thi s phenomeno n show s th e effec t o n th e behaviou r

o f th e downstrea mgas-soli dflo w cause db y th e manne r o f feedin g particles , sinc e th e particle s hav e mino r initia l velocitie s o n th e z negativ e axi s whe n the y ar e injecte db y th e scre w feede r fro mth e pip e righ t

sid e t o th e pip e centre . Notice : Th e origi npoin t (O ) locate s a t the centre o

f the O D sectio n

7 6



# VES01711 1Chapte r 5 Experimenta l .studie s o f particl e dynamic s b y LD A {II } rn/ s a l the auctio n k =7 D {<- ) } a t the sectio n x=7 D {H) a t the sectio n x=7 D

-4 0 -2 0 0 20 4 0 -4 0 -2 0

z(mm j 2 0 4 0 -4 0 -2 0 { U } m/ s a

t the sectio n x=6 D z{mm) {0 } a t the sectio n x=6D z(mm ) {H} a t th e sectio n x=6D

-4 0 -2 0 0 20 4 0 -4 0 -2 0 0 2 0 4 0

2(rnm ) 2(mm) { U } m/ s a

t the sectio n x = 5 D {0 } a t th e sectio n x=5 D -4 0 -2 0 0 2 0 4 0 z(mm ) {N > a t th e sectio n x=5 D

-4 0 -2 0 0 20 4 0

?(mm ) m/ s a t the sectio n x-4 D -4 0 -2 0 0 2 0 4 0 z (mm ) { 0 } a tth e sectio n x=4 D {N } a t the sectio n x=4D

-4 0 -2 0 0 2 0 4 0

z{mm ) { U } m/ s a l th

e seclio n x=3 D 0 2 0 4 0 -4 0 -2 0 ;(mm) {(- ) } a t th e sectio n x=3 D z(rnm ) {N } a t the sectio n x=3 D

-4 0 -2 0 0 20 4 0

z (mm ) z(mm)

(Figur e 5. 6 Continue ) 2 0 4 0 -4 0 -2 0 0 z(mm )

7 7



# VES01711 2A l linvestigatio n o i particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m ( U } m/ s a

t the sectio n x=2D { 0 } a t th e sectio n x=2 D

•40 -20 0 2 0

z(mm t ( U } m/ s a

t the sectio n x=1 D 0 2 0 z{mm) ( 0 } a t the sectio n x

= 1 D {N } a t the sectio n K=2

D

-4 0 -20 0 2 0 4 0

z(mrn ) -4 0 -20 0 2 0 4 0 z(mm ) 0 2 0 4 0 z(mm ) {N } a t th e sectio n x=1 D

-4 0 -20 0 20 4 0

z(mm ) Figur e 5. 6 Cross-sectiona l distribution s o f th e mean value s o f {U pv } an d th

e granula r temperatur e {© } (unit : m ! /s 2 ) a s wel l a s particl e numbe r{N } a ta n ai rconveyin g velocit y 12m/ s Accordin g t o th e char t o f Geldar t fo r classificatio n o f

fluidizatio nbehaviou r (a s show n i n Figur e 2.2) , th e thre e kind s o f glas s bead s use di n th e experiment s ca n b e characterize db y thei r retentio n properties . Th e firs t

typ e i s les s tha n 50pm , withi nwhic hglas s bead s les s tha n 20p mo r withi n 20~50pn i respectively , correspon dt o Grou p C material s (wit hver y goo dpermeability ) o r Grou p Amaterial s o n th e Geldar t chart . Th e secon dtyp e o f glas s bead s withi n70-110p mals o correspond s t o Grou p A materials , whic hhav e goo dretentio n propertie s an dar e suitabl e fo r dens e phas e pneumati c conveyin g a s well . A s fo r th e thir dtyp e o f

glas s bead s rangin g fro m1 8 0 t o 300pm , the y ar e equivalen t t o Grou p B material s wit hver y poo r ai r retentio n capabilit y an d ca n de-aerat e rapidl y whe n th e suppl y o f fluidizin g ai r

i s shut-off . Th e empirica l minimu m conveyin g ai r

velocitie s i n dilut e phas e suspensio n flo w ar e abou t 10~12m/ s fo r

transportin g Grou p A materials , 13~16m/ s fo r Grou p B material s an daroun d3~4m/ s fo r Grou p C material s (Mill s D.,2004) .
Sinc e th e thre e kind s o f glas s bead s (densit y 255 0 kg/m' ) hav e bee n use dt o simulat e th e flo w o f pulverise dcoa l (0-110pm , densit y 155 0 kg/m 3 ) an dbiomas s pellet s (size < 1.0mm , density<80 0 kg/m 3 ) , thes e pulverise dcoa l an dbiomas s pellet s ar e effectivel y Grou p A materials . Bu t fo r hig h densit y an dlarge r

granula r

biomass , th e classificatio n i s Grou p B . Here , ou r experiment s mainl y focu s o n Grou p A materials . It i s ver y meaningfu l t o stud y particl e dynami c behaviou r i n dilut e phas e pneumati c transportatio n unde r th e minimu mai r

conveyin g velocity . I n thi s way , i t ca n b e see n whethe r

th e tw o cross-sectiona l flui dpattern s i n th e abov e discussion s represen t th e regim e

7 8Chapte r 5 L\pcrimcnta l studie s o f particl e dynamic s b y LD A

o f dilut e phas e pneumati c conveyin g i n lo w ai r velocity . Ther e follow s ase t o f experimenta l result s o n th e sam e serie s o f cross-section s (a s show n i n Figur e 5.5 ) unde r a n ai r conveyin g velocit y o f

lOm/ s i n th e horizonta l pipe . 

### 5.3.3. 1 Glas s bead s les s tha n 50|j m (th e firs t type )
Glas s bead s o f

th e firs t

typ e ar e les s tha n 50p mi n diamete r an dthei r

Stoke s Number s ar e als o les s tha n 3.6 . O n th e whole , thes e kind s o f particle s hav e agoo dabilit y t o follo w th e ai r flow . Fo r thes e fin e particles , th e correspondin g particl e numbe r rat e i s drasticall y large r tha n th e othe r

tw o type s unde r

th e sam e soli dmas s loading . I n orde r t o kee p th e sam e sampl e rat e 1 0 kH z o f LD A fo r th e thre e type s o f

glas s beads , th e soli dmas s loadin g rati o forth e firs t typ e i s onl y 1/1 0 tha t o f th e othe r

tw o type s whos e soli dmas s loadin g ratio s ar e abou t 1.9 % unde r

a n ai r conveyin g velocit y o f

lOm/ s i n o)75m mpipe . Figur e 5. 7 an d5. 8 visualiz e th e cross-sectiona l experimenta l dat ao f th e firs t

typ e o f glas s bead s o n th e section s fro m7 D t o OD . I n orde r t o mak e thes e experimenta l dat ao n differen t section s comparable , th e axia l particl e velocit y an dth e particl e numbe r rat e ar e separatel y normalize db y ai r conveyin g velocit y (U a ) an dth e tota l numbe r rat e (ZN ) o n eac hcross-section .
I n Figur e 5.7 , th e developmen t o f th e cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {U px /Un } i s illustrate dalon g th e flui dflo w direction . Th e contour s o f {U p x /U a } apparentl y displa y asimila r annula r

form , especiall y o n th e section s fro m7 D t o ID . I n thes e contours , eac hannula r cor e wit ha n iso-lin e valu e o f 1. 2 i s aroun dth e sectio n centr e wit hasligh t deviatio n toward s th e z positiv e axis . Th e iso-lin e valu e o f {U p x /U a } show s clearl y decreasin g tendenc y fro mpip e centr e t o pip e wall . Bu t th e are awithi na n iso-lin e ma y b e differen t dependen t

o n th e detaile dcross-section . Althoug hth e annula r for mi s als o show n i n th e contou r o f {U p x /U a } o n th e sectio n OD , th e ke y differenc e wit hthos e o n th e othe r section s lie s i n tha t

th e annula r cor e i s shifte dbeyon dth e pip e centr e an dit s iso-lin e valu e i s increase da s 1. 3 o n th e sectio n OD . Thi s differenc e mus t b e cause db y th e effec t o f th e ben do n th e upstrea mflui dflow , fo r th e sectio n O D i s 15m mupstrea mfro mth e ben dinlet . O n th e whole , i n term s o f th e similarit y amon g th e cross-sectiona l distribution s o f {U p x /U a } , th e dilut e suspensio n flo w o f glas s bead s o f th e first typ e ca n b e treate da s bein g full y develope dan dstead y i n th e horizonta l pip e befor e on e pip e diamete r

o f th e bend .

7 9



# VES01711 4A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

Figur e 5.

7 Developmen to f

cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {U px /U a } o f

th e firs ttyp e o f

glas s bead s (<50um) unde ran ai rconveyin g velocity U a =10m/s an d th e soli d mas s loadin g rati o 0.19% .

8 0



# VES01711 5Chapte r 5 Lxperimcnta l studie s ofparticl e dynamic s b y LD A

4 0
2 0

-2 0
-4 0 4 0 , 2 0

-2 0
-4 0 4 0
2 0

-2 0
-4 0 4 0 2 0

-2 0
-4 0 7 D Natura l logarith mo f th e dimensionles s particl e numbe r rat e {ln(N/£N) }

- 4 0 r

- 7

• 6 t 5 D

9 •95

2 D '- 6 #

O D -AA .

tl tr.

-5 0 •S -7 ' V

0 z(mm ) 2 0

-2 0
-4 0 4 0
2 0

-2 0

2 0

-2 0
-4 0 6 D •9

4 D

1 D

-5 0 0

4mm ) 5 0

5 0 - 9 - 8 - 7 - 6 - I e \ x=-9 , -8,-7,-6,-5,- 4 nx10" 4 ,n=2,4,10,25 , 68,18 4 Section s Tota l (N}(x10 5 ) 0 D 3.1 3 1 D 4.6 9 2 D 9.4 0 4 D 3.9 8 5 D 6.3 8 6 D 4.6 0 7 D 3.2 7 - 4 - 3

Figur e 5.8 Developmen tof cross-sectiona l distribution s o f th e dimensionles s particl e numbe r rat e {ln(N/£(N)) } of

th e firsttyp e o f

glas s bead s (<50pm ) unde ran ai rconveyin g velocity L i 11 =10m/

s an d the soli d mass loadin g rati o 0.19% . B y contrast , Figur e 5. 8 show s th e cross-sectiona l distribution s o f th e natura l logarith mo f th e

8 1



# VES01711 6A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m dimensionles s particl e numbe r rat e jln(N/X(N)) } fro mth e sectio n 7 D t o OD . Th e contour s o f particl e numbe r

rat e |N | i n Figur e 5. 8 no t onl y generall y illustrat e th e stratifie dconfiguratio n o n eac hsection , bu t

als o clearl y sho w th e differen t layere dshap e o f

eac hcontou r

varyin g alon g flui d direction . O n th e sectio n 7D , th e larges t valu e ofparticl e numbe r rat e i s i n th e regio n clos e t o th e bottom-left

o f th e section . The n thi s regio n graduall y expand s toward s th e sectio n botto munti l th e sectio n 5D . Th e contou r iso-lin e o f

-7 , whic hi s correspondin g t o lOxlO" 4o f th e tota l particl e numbe r rate , remain s nea r

th e centr e (y=0 ) o f th e pip e unti l th e sectio n ID . Bu t th e region s layere db y iso-line s sho w som e fluctuations . Thi s fluctuatio n indicate s th e differen t frequenc y o f particle-wal l collisio no n eac hsection . Du e t o gravity , particle s wit hsmal l Stoke s Numbe r stil l hav e afallin g tendency . A s such , th e large r th e regio n wit hmaximu mparticl e numbe r rat e mean s th e mor e th e particle s ar e concentrated , whic hma y caus e ahighe r frequenc y o f

particle-wal l collision . Whe n particle s ar e re-suspende dtoward s th e pip e centr e du e t o th e Saffma n forc e an d th e effec t

o f particle-wal l collision , th e regio n wit hth e maximu mparticl e numbe r rat e o n th e nex t adjacen t sectio n wil l b e decreased . Thi s variatio n als o show s tha t th e gas-soli dpip e flo w o f th e firs t typ e o f glas s bead s i s heterogeneou s an dunsteady , whic hi s contrar y t o th e resul t deduce db y th e variation s o f

{U p x / U a } . Therefore , th e gas-soli dflo w forme db y th e firs t typ e o f glas s bead s show s stead y an dunstead y stat e simultaneousl y dependen t o n whic hparameter s ar e use dt o vie w it . 

### 5.3.3. 2 Glas s bead s withi n th e rang e 7 0 t o 11 0 |it n (th e secon d type )
Th e secon dtyp e o f

glas s bead s rang e from7 0 t o 11 0 p man dth e correspondin g Stoke s Numbe r varie s withi n10-28 . Compare dwit hth e firs t type , glas s bead s o f th e secon dtyp e hav e highe r inertia l propertie s an dthe y usuall y kee p thei r ow n trac k

rathe r tha n followin g flui dlik e th e particle s o f

th e firs t

type . Unde r

a n ai r conveyin g velocit y o f lOm/ s an dsoli dmas s loadin g rati o 1.9% , th e measure dexperimenta l dat ao n th e section s fro m7 D t o I D (a s show n i n Figur e 5.5 ) ar e illustrate di n Figur e 5. 9 an dFigur e 5.10 .
I n Figur e 5.9 , a n annula r for mi s als o observe do n eac hcross-sectiona l distributio n o f th e dimensionles s axia l particl e velocit y {U p x / U a } o f th e secon dtyp e o f

glas s bead s (70-110pm) . Overall , thi s annula r

form , i n whic hth e axia l particl e velocit y decrease s fro mth e annula r cor e t o th e pip e wall , resemble s tha t show n i n Figur e 5.7 . Bu t th e iso-lin e valu e an dpositio n o f th e annula r cor e ar e differen t

i n th e tw o figures . Fro mth e sectio n 7 D t o ID , eac hcentr e o f th e annula r core s wit ha n iso-lin e valu e o f 1.3 5 i n Figur e 5. 9 i s beyon dth e pip e centre , whic hi s differen t

fro mth e observatio n tha t ever y centr e o f

th e annula r

cor e wit ha n iso-lin e valu e o f 1. 2 i s shifte dtoward s th e z positiv e axi s i n Figur e 5.7 . I n th e mai n strea mregio n o f eac hcross-section , th e value s o f

iso-line s fro mpip e centr e t o pip e wal l ar e large r i n Figur e 5. 9 (1.35-1.0 ) tha n thos e

8 2



# VES01711 7Chapte r 5 Kxperimcnta ! studie s o f particl e dynamic s b y LD A i nFigur e 5. 7 (1.2-0.8) . Thus , th e area-average daxia l particl e velocit y o f th e secon dtyp e o f

glas s bead s shoul db e faste r tha n (ha

t ofth e firs t

typ e o f glas s bead s o n th e section s fro m7 D t o ID . Th e dimensionles s axia l particl e velocity { U X /U a } 4 0 r- 4 0 : —

V " -6 0 -4 0 -2 0 0 2 0 4 0

z{mm ) Figur e 5.9 Developmen to f cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {U pl /U, } ofth e secon d typ e o f glas s bead s (70~110u.m ) unde ran ai rconveyin g velocity U a =10m/s an d th e soli d mass loadin g rati o 1.9% .

8 3



# VES01711 8A ninvestigatio n oi'particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m Nalura l logarith mo f

th e dimensionles s particl e numbe r rat e {ln(N/£N) } 4 0 •3 S D 

# 4F

-4 0 4 0

-40 40

-40 40

- 1 D

-40 -20 0 2 0

z(mm ) -40 4 0

e* , x =-9,-8,-7,-6,-5,- 4 Ox10"\n=2.4 . 10,25,68 . 18 4 Section s Total{N)(,10 s ) 1 D 3.5 1 2 D 3.9 1 3 D 1.9 4 4 D 19 0 50 1.9 5 6 D 1,8 0 7 D 1.9 2 Figur e 5.1 0 Developmen to f cross-sectiona l distribution s o f the dimensionles s particl e numbe r rat e Jln(N/X(N)) } o f

th e secon d typ e o f

glas s bead s (70~110u.m ) unde ran ai rconveyin g velocity U a =10m/s an d th e soli d mass loadin g rati o 1.9% . Similarly , th e stratifie dconfiguratio n observe di n Figur e 5. 7 ca n b e als o foun di n Figur e 5.10 , whic hdi.splay s th e developmen t o f cross-sectiona l distribution s o f th e dimensionles s particl e numbe r rat e (ln(N/S(N)) } fo r th e secon dtyp e o f

glas s bead s (70-110pm) . Thi s layere dfeatur e demonstrate s the phenomeno n o f gravit y settlin g du e t o gravit y forc e whic hmake s particle s concentrat e clos e t o the botto mregio n i n ahorizonta l pipe . O n th e section s fro m7 D t o ID , th e stratifie diso-line s o f

eac hcross-sectiona l distributio n o f (ln(N/I(N)) } i n Figur e 5.1 0 ar e differen t



# VES01711 9Chapter 5 hxperimenla l studie s ofparticl e dynamic s b y LD A fro mthos e i n Figur e 5.8 . A compariso n o r the mshow s tha

t th e tota l numbe r

o f layer s i n Figur e 5.1 0 i s mor e than that

i n Figur e 5. 8 wit hthe sam e interva l o f 0.5 . An dthe maximu mvalu e o f )ln(N/X(N)) } occur s a

t the left-botto mo f

eac hsectio n i n Figur e 5.8 . In contrast , th e maximu mvalu e o f |ln(N / I(N)) j i n Figur e 5.1 0 i s nearl y clos e t o th e botto mcentr e o f eac hsectio n wit hlittl e deviation s toward s th e left-han dside . Third , ih e iso-lin c wit hth e valu e of-7 , whic hi s correspondin g t o lOxlO" 4 o f the tota l particl e numbe r rate o f eac hsection , varie s aroun dth e pip e centr e lin e o f y=0m mfro mth e sectio n 7 D to I D i n Figur e 5.7 . Thi s correspondin g iso-lin e i n Figur e 5.1 0 i s belo w bu t clos e t o th e pip e centr e lin e o f

y=0mm . 

### 5.3.3. 3 Glas s bead s withi n th e siz e rang e 180~300|j m (th e thir d type )
Glas s bead s i n th e thir dtyp e var y withi nth e siz e rang e I80~300pm . Figur e 5.1 1 show s th e experimenta l dat ameasure db y LD Ao n th e cross-section s fro m7 D t o 1 D (a s show n i n Figur e 5.5 ) unde r a n ai r conveyin g velocit y o f 1 Om/ s an dsoli dmas s loadin g rati o 1.9% . A s fo r cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {U p «/U a } , th e annula r featur e i s no t

apparentl y show n i n Figur e 5.11 , whic hi s compare dwit htha t i n Figur e 5. 7 o r Figur e 5.8 . Wit hth e sam e interva l valu e o f 0.5 , th e spatia l distributio n o f {U p x / U a } o n eac h sectio n i n Figur e 5.1 1 ca n b e divide dint o th e inne r circl e an dth e oute r

rin g b y th e iso-hn e o f 1.2 . Unlik e th e othe r

tw o type s o f

glas s beads , ther e i s n o annula r cor e wit hth e maximu mvalu e o f { U p x / U a } fo r

th e thir dtyp e o f

glas s bead s i n Figur e 5.11 . Th e area s bounde dwit hth e valu e o f a n iso-lin e large r

tha n 1. 2 ar e jus t

randoml y distribute dwithi nth e inne r circl e o f

eac hsection . Sinc e th e maximu mvalue s o f {U p x / U a } ar e separatel y 1.2 , 1.3 5 an d1. 4 fo r th e first, th e secon d an dth e thir dtype s o f glas s beads , thi s denote s a n interestin g phenomeno n tha t large r glas s bead s hav e obtaine dfaste r maximu maxia l particl e velocit y unde r th e sam e ai r

conveyin g velocity . Accordin g t o th e experimenta l result s o f Tsju i e t

al . (1982) , ai r

flo w turbulenc e wa s reduce db y plasti c particle s o f

amea n siz e 210|j m(th e rang e I00~400pm ; densit y 1000kg/m 3 ) . A s such , th e kinemati c energ y o f ai r flo w o r

ai r velocit y ma y b e increase ddu e t o th e lessenin g turbulen t energy . Thus , a n increasin g ai r velocit y woul dals o mak e th e secon dan dth e thir dtyp e o f glas s bead s accelerat e faster .
Nevertheless , th e abov e explanatio n nee dt o b e confirme db y th e furthe r experimenta l data , especiall y th e simultaneou s measuremen t dat ao f

tw o phas e velocitie s i n gas-soli dpip e flo w wit h differen t

particl e size .

8 5



# VES01712 0A ni mcsligatio n o f panicl e dynamic s i n adilut e phas e pneumati c conveyin g syste m Relativ e velocitie s ofth e axia l particl e velocit y { U/ U } 4 0 • — - 4 0

z(mm ) Figur e 5.1 1 Developmen to f cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {Upj/U a } o f

th e thir d typ e o f

glass bead s (180~300um ) unde ran ai rconveyin g velocity U a =10m/s an d th e soli d mas s loadin g rati o 1.9% .I haplc r 5 l.xpcrimenta l studie s ofparlicl e dynamic s b y LD A Natura l logarith mo f

th e dimensionles s particl e numbe r rate {ln(N/iN ) J 4 0 ---.- 1 4 0

Figur e 5.1 2 Developmen to f cross-sectiona l distribution s o f the dimensionles s particl e numbe r rat e {ln (N/ E (N)) } o f

the thir d typ e of

glas s bead s (180~300(nm ) unde ra

n ai rconveyin g velocity U a =10m/s an d th

e soli d mas s loadin g rati o 1.9 % A s fo r th e thir dtyp e o f

glas s beads , Figur e 5.1 2 show s th e developmen t o f cross-sectiona l distribution s o f

th e dimensionles s particl e numbe r rat e {ln(N/X(N)) j fro mthe sectio n 7 D t o ID .

8 7A ninvestigatio n ol'particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m Compare dwit htha i i n Figur e 5. 8 an dFigur e 5.10 , th e stratifie dconfiguratio n ca n b e stil l observe do n eac hsectio n i n Figur e 5.12 . Wit hthe sam e interva l o f {ln(N / 2(N))} , th e tota l laye r i n Figur e 5.1 2 (th e thir dtyp e o f

glas s beads ) i s large r lha n tha i i n Figur e 5. 8 (th e first typ e o f glas s beads) , bu t

les s than tha i i n Figur e 5.1 0 (th e secon dtyp e o f glas s beads) . Th e iso-lin e wit hth e valu e of-7 , whic hi s correspondin g t

o lO x 10" ' ofth e tota l particl e numbe r rat e o f eac hsection , i s awa y fro mth e pip e centr e lin e o f y=0m man dvarie s aroun dth e heigh t o f 1/ 4 pip e diamete r

fro mth e pip e bottom . I n addition , the distributio n o f

iso-line s o f

{ln(N / X(N)) } doe s no t

strictl y decreas e fro mth e to p t o th e botto mo n eac hsectio n i n Figur e 5.12 . Th e region s wit hth e relativ e large r values , clos e t o th e maximu mvalu e o f jln(N / I(N))} , i s no t

onl y locate di n the pip e botto mbu t als o foun daroun dth e pip e to p wall . Thi s phenomeno n i s no t

show n i n Figur e 5. 8 o r Figur e 5.10 . Moreover , ther e exist s som e symmetr y alon g the pip e vertica l centr e lin e o f z=0m mi n Figur e 5.12 . Thi s symmetri c propert y i s differen t fro mth e experimenta l result s observe di n Figur e 5. 8 an dFigur e 5.10 . I t indicate s tha t

th e inerti aeffec t

o n dynami c behaviou r

o f glas s bead s i n th e thir dtyp e i s muc hstronger .



### 5. 4 PARTICL E DYNAMI C BEHAVIOU R I N A VERTICA L PIP E DOWNSTREA M O F A 90 ° ELBO W Th e ropin g phenomeno n i s on e o f grea t interes t i n pneumati c conveyin g research . I t occur s i n a ben dan dresult s i n particle s bein g concentrate dwithi nasmal l portio n o f on e pip e cross-sectio n at th e bend , a s wel l a s i n th e pip e downstrea mo f th e bend , du e t o particl e inertia . Consequently , i t i s ver y importan t

t o stud y th e Rop e disintegratio n processin g afte r aben dbefor e dua l o r tripl e branche s ar e use dt o delive r particle s i n acontrollabl e wa y t o th e variou s burner s i n apulverize d fue l (PF ) boiler . Furthermore , th e extende dtechniqu e o f Lase r Dopple r

Anemometr y ha s bee n applie dt o determin e no t onl y th e spatia l chang e i n th e particl e velocit y distributio n bu t als o t o characteriz e th e particl e segregation , a s show n b y particl e numbe r rate , i n abend .
A s fo r th e characteristic s o f ai r flo w i n avertica l pip e downstrea mo f abend , experimenta l an d numerica l dat ao f

cross-sectiona l distribution s o f th e axia l ai r

velocit y {U a y } an dth e horizonta l ai r velocit y {U M } hav e bee n discusse di n Chapte r 4 . Th e cross-sectiona l distributio n o f th e axia l ai r velocit y \U ay \ o n th e sectio n 0 D display s ahorsesho e shape , wher e {U a y } i s slowe r insid e (pip e inne r

wall ) an dfaste r

outsid e (pip e oute r

wall) . Thi s featur e ca n b e stil l observe do n th e furthe r downstrea msections . Bu t th e differenc e o f

{U a y } betwee n insid e an doutsid e th e horsesho e tend s t o b e lessened . Moreover , asecondar y flo w describe db y {U a x( i s forme do n th e sectio n O D an dgraduall y become s wea k til l i t ha s completel y disappeared .

8 8



# VES01712 3Chapte r 5 1-AperimeMa l studie s o f particl e dynamic s b y LD A

Nulice : Th e origi

n poin t(O ) locates al 'h e centr e o f th e O D sectio n

Figur e 5.1 3 Th e arrangemen to f measuremen tcross-section s i n th e vertica l pip e I n th e followin g sections , th e experimenta l dat ao f thre e type s o f

glas s beads , pneumaticall y transporte dfro mahorizonta l pip e sectio n throug ha n elbo w (R/DH.3 ) int o aconnectin g vertica l pipe , hav e bee n measure db y th e extende dtechniqu e o f Lase r Dopple r

Anemometr y discusse di n Chapte r 3 . A tota l o f

seve n cross-section s alon g th e vertica l pip e ar e schematicall y illustrate di n Figur e 5.1 3 an dth e referenc e cross-sectio n (OD ) i s abou t 15m mawa y fro mth e elbo w outlet . Th e distanc e betwee n tw o adjacen t cross-section s i s equa l t o on e pip e diameter . 5.4. 1 Glas s bead s les s tha n 50u, m (th e firsttype ) Wit hregar dt o th e firs t typ e o f glas s bead s (<50pm) , th e experimenta l dat ameasure db y LD Ao n th e cross-section s fro mO D t o 6 D i n th e vertica l pip e ar e illustrate di n Figur e 5.11 , Figur e 5.1 2 an dFigur e 5 . 1 3 fo r th e dimensionles s axia l particl e velocit y {U p y / U a j , th e dimensionles s horizonta l particl e velocit y {U p x /max(abs(U p ! J) } an dth e dimensionles s particl e numbe r rat e jln(N/'Z(N)) } respectively , unde r a n ai r conveyin g velocit y lOm/ s an dsoli dmas s loadin g rati o 0.19% .

8 9A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

I n Figur e 5.14 , th e horsesho e shap e ca n b e foun do n eac hcontou r o f {U p y / U a } fromth e sectio n O D t o 4D . Thi s featur e i s simila r t o tha t show n i n contour s o f th e axia l ai r

velocit y {U a y } i n Figur e 4.5 . Generally , th e axia l particl e velocit y {U p y [ i s faste r o n th e outsid e portio n o f th e horsesho e (toward s pip e oute r wall ) tha n tha t

o n th e insid e portio n o f th e horsesho e (toward s pip e inne r wall) . A t

th e furthe r

downstrea msection s o f 5 D an d6D , th e horseshoe-shape dfeatur e n o longe r exist s an dth e cross-sectiona l distribution s o f {U p y / U a } hav e develope dint o anothe r patter n wher e asmal l regio n wit hth e slowe r {U p y } i s surrounde daring wit hth e faste r {U p y } . I n addition , th e regio n wit hth e slowes t {U p y } o n asectio n i s clos e t o th e pip e right wal l (th e z positiv e direction ) behin dth e sectio n I D an dit s are ai s graduall y enlarge dfro mth e sectio n 1 D t o 5D . A simila r

distributio n ca n b e foun dbetwee n th e contou r o f {U p y / U a } o n th e sectio n 5 D an d tha t o n th e sectio n 6D . Als o th e maximu mvalu e o f {U p y / U a j o n bot hsection s i s decrease da s 1 fro m1. 3 o n th e sectio n OD . Th e similarit y suggest s tha t gas-soli dflo w o f

th e firs t

typ e o f glas s bead s begi n t o b e stead y fro mth e sectio n 5D . Wit hregar dt o th e dimensionles s horizonta l particl e velocit y {U p x /max(abs(U p x )) } o f th e firs t typ e o f glas s bead s (<50u.m) , Figur e 5.1 5 show s th e developmen t o f th e cross-sectiona l distributio n o f

{U p v /max(abs(U p x ))}fro mth e sectio n O D t o 6 D i n th e vertica l pip e downstrea mo f abend . I t

i s ver y clea r

tha t th e secondar y flo w o f th e firs t

typ e o f glas s bead s show n i n Figur e 4. 7 (fo r th e singl e ai r

phase ) ca n b e als o observe di n Figur e 5.15 . O n eac hsection , w e assum e th e pip e inne r

wal l a s th e star t

position , wher e th e secondar y flo w run s toward s th e pip e oute r wal l wit hadecreasin g tendenc y o f {U p x } . Whe n th e secondar y flo w reache s a t th e pip e oute r

wall , { U p x } i s clos e t o zero . The n thi s secondar y flo w change s it s flui ddirectio n fro mth e x positiv e axi s t o th e x negativ e axi s an di t i s develope dint o tw o subflow s whic hru n toward s th e pip e inne r wal l wit ha n acceleratio n alon g th e pip e lef t wal l an dth e pip e righ t wal l respectively . A s such , th e secondar y flo w form s tw o subcirculation s o f on e counter-clock-wis e an don e clock-wis e separately . Fro mth e sectio n O D t o 6D , th e ke y differenc e betwee n secondar y flow s i s tha t th e regio n wit hth e positiv e maximu m{U p x /max(abs(U p x )) J i s graduall y shifte dfro mth e pip e inne r wal l t o th e pip e centr e an dth e tota l numbe r o f iso-line s i s reduced .

" 0



# VES01712 5Chapte r 5 L.xpcrimenla l studie s o f particl e dynamic s b y LD A

4 0 Dimensionles s axia l particl e velocit y {U p y /U a } O D 2 0

-2 0 -40 4 0 r f . • OQ 5 ' ' '

2 D 2 0

-20 - -40 4 0 - OS's" 

# 4

4 D 2 0 -

-20
-4 0 4 0 6 D 20

-20 • 

# 7 1 D 2 0

-2 0 -4 0 4 0 3 D 2 0

-2 0 -4 0 4 0 5 D 2 0

-2 0
-4 0 ' 1

-5 0 0 5 0

z(mm)

0. 2 0. 4 0. 6 0. 8 1 1. 2 U=10(m/s )

-4 0 -5 0 0

z(mm) 5 0 Figur e 5.1 4 Developmen to f cross-sectiona l distribution s o f th e dimensionles s axia l particl e velocit y {U p y /U„ } o f

the firsttyp e o f

glas s bead s (<50u,m ) unde ra

n ai rconveyin g velocit y U a =10m/s an d th

e soli d mass loadin g rati o 0.19 % i n th e vertica l pip e behin d a n elbow (R/D=1.3 )

9 1



# VES01712 6A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

4 0

2 0 O D

-2 0 j -4 0 i 4 0 ; 2 0

-2 0 2 D

-4 0 • 4 0

2 0

-2 0

2 0 4 D Th e dimensionles s horizonta l particl e velocit y {U p x /max(abs(U p x )) }

tu s 9 > 

# 4

6 D

-2 0

-4 0 (

' / \ U 

### v \ 

### (

V ,

-5 0 0 z(mm ) 4 0

2 0

-2 0

2 0

-2 0

2 0

-2 0 1 D

3 D

5 D

-4 0 -5 0 

# ' US

. ) Z

3 % & Pe

0 6 'O ,

- 1 -0. 5 0

z(mm )

0 5 0

5 0 Section s Maximu mabsCU^XnVs )

O D 2.2 6 1 D 2.1 4 2 D 1.7 1 3 D 1.6 1 4 D 1.4

4 5 D 1.2

4 6 D 1.4 8 Figur e 5.1 5 Developmen to f cross-sectiona l distribution s o f th e dimensionles s horizonta l particl e velocit y {U ps /max(abs(U ps )) ) o f th e firs ttyp e o f

glas s bead s (<50um) unde ra n ai rconveyin g velocit y U a =10m/s an d th e soli d mas s loadin g rati o 1.9 % i n the vertica l pip e behin d a n elbow (R/D=1.3 )

9 2



# VES01712 7Chapte r > Hxpcrimcnta l studie s o f particl e dynamic s b y LD A

4 0 Natura l logarith mofth e dimensionles s particl e numbe r rat e (ln(N/i(N)) } 40 , iO D - 7 ? 20 ) 'Jo '

-20 1 

# t

-4 0 4 0 2 D -8 . 2 0

-2 0
-4 0 t 4 0 r 4 D 2 0

-2 0

-40 ! 4 0 , 6 D 2 0

-2 0 '% :r. aMMHMta ^

. " 7 - 7 - 5

-4 0 -5 0 0

z(mm) 2 0

-2 0

2 0

-2 0

2 0

-2 0 1 D

- 8 - 6 3 D
• f f

-4 0 5 D

-5 0 0

z(mm ) 5 0

5 0 -1 0 - 9 - 8 - 7 - 6 - 5

e* , x=-9,-8 , -7,-6,-5,- 4 nx10" 4 ,n=2,4.10,25,68,18 4 Section s Tota l (N) (10 5 ) 0 D 54 0 1 D 2.5 7 2 D 4.9 8 3 D 5.1 5 4 D 4.5 4 5 D 3.6 8 6 D 3.3 5 Figur e 5.1 6 Developmen to f cross-sectiona l distribution s o f the dimensionles s particl e numbe r rat e {N/S(N) } ofth e firs ttyp e o f glas s bead s (<50pm) unde ran ai rconveyin g velocit y U o =10m/s an d th e soli d mass loadin g rati o 1.9 % i n the vertica l pip e behin d a n elbo w (R/D=1.3 )

9 3Al ) investigatio n ol ' particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m Figur e 5.1 6 display s th e experimenta l dat ao f th e dimensionles s particl e numbe r ral e jln(N / L(N))| , whic hi s normalize db y th e summatio n o f particl e numbe r

rat e o n eac hsection , fro mth e sectio n O D t o 6 D i n th e vertica l pipe . Overall , th e featur e o f stratifie dconfiguratio n o r an y othe r

unifor mpatter n ca n no t b e observe do n cross-sectiona l distribution s o f {ln(N / S(N)) } i n Figur e 5.16 . O n the sectio n OD , referrin g t o the horsesho e shap e o f (U p y / U a } a s show n i n Figur e 5.14 , w e ca n se e tha t th e relativel y dens e particl e numbe r rat e wit hth e iso-lin e valu e o f - 6 i s positione dclose dt o th e outsid e portio n o f th e horsesho e (th e pip e oute r wall) . I n contrast , th e regio n wit hth e smalle r valu e (-7 ) o f

jln(N/X(N)) } i s locate di n eithe r th e pip e left-inne r

o r right-inne r

wall . O n th e sectio n ID , th e contou r o f {ln(N/X(N)) } resemble s wit htha t o n th e sectio n OD . Bu t

th e are awithi na n iso-lin e ma y b e shifted . A t furthe r downstrea msections , th e contour s o f

{ln(N/X(N)) } are develope dto b e randoml y distribute dwit hn o clea r shape . O n th e sectio n 5 D o r

6D , th e regio n wit hth e highe r relativ e densit y {ln(N/X(N)) ) i s show n at th e pip e right-inne r

wal l wit hth e smalles t valu e o f

{U p y / U a } . O n th e whole , th e rop e o f relativ e dens e particl e numbe r

rat e forme di n th e ben dha s stil l no t disperse db y th e sectio n 6 D fo r th e firs t

typ e o f glas s bead s transporte db y a1 Om/ s ai r conveyin g velocit y an dsoli dmas s loadin g rati o 0,19 % .

5.4. 2 Glas s bead s withi n th e siz e rang e 70~110u, m (th e secon d type ) Experiment s usin g th e secon dtyp e o f glas s bead s wer e performe dt o measur e cross-sectiona l distribution s o f

th e axia l particl e velocit y {U p y } , th e horizonta l particl e velocit y {U p „ j an d particl e numbe r

rat e {N } o n th e sam e serie s o f cross-section s a s discusse di n th e proceedin g section . Unde r

flui dcondition s o f ai r conveyin g velocit y lOm/ s an dsoli dmas s loadin g rati o 1.9% , th e experimenta l dat ao n cross-sectiona l distribution s o f thre e parameter s fro mth e section s O D t o 6 D ar e show n i n Figur e 5.17 , Figur e 5.1 8 an dFigur e 5.1 9

A s fo r th e dimensionles s axia l particl e velocit y {U p y / U a } , Figur e 5.1 7 show s th e developmen t o f it s cross-sectiona l distribution s i n th e vertica l pip e downstrea mo f th e bend . Th e horseshoe-shape dfeatur e ca n b e als o observe do n th e contour s o f {U p v / U a } fro mth e sectio n O D t o 4D , bu t

i t i s n o longe r

apparen t

o n th e contour s o f

{U p y /L' a J at

th e furthe r

section s o f

5 D an d 6D . Howeve r

th e contou r

shap e o f

{U p y / U a } i s identica l t o tha t o n th e sectio n 6D , whic h indicate s astead y stat e o f gas-soli dflo w fo r

th e secon dtyp e o f

glas s bead s afte r

th e sectio n 5D . A l l th e abov e observation s hav e agoo dagreemen t wit hthos e observe di n Figur e 5.1 4 fo r th e first typ e o f glas s beads . A t

apoin t o n eac hcross-section , th e axia l particl e velocit y ofth e firs t typ e i n Figur e 5.1 4 tend s t o b e th e correspondin g loca l axia l ai r velocit y i n Figur e 4.5 . Bu t i t i s les s tha n tha t ofth e secon dtyp e i n Figur e 5.17 . Thi s phenomeno n show s th e inerti aeffec t o n particl e dynamics , sinc e th e first typ e (<50pm ) ha s asmalle r Stoke s Numbe r

tha n th e secon dtyp e

9 4Chapte r s Lxper i mental studie s ofparticl e dynamic s by LD A (70- 1 10pm ) does . A s such , afte r bein g accelerate db y th e fastes t ai r flow , th e secon dtyp e o f glas s bead s woul dretai n it s stat e wit hahig hvelocit y an dth e firs t typ e tend s t o follo w th e curren t loca l ai r Ho w whe n bot hglas s bead s ente r int o aregio n wit hlowe r ai r velocity . Figur e 5.1 8 show s th e developmen t o f cross-sectiona l distribution s o f th e dimensionles s horizonla l particl e velocit y (U p x /U a } fro mth e sectio n O D t o 6D . Clearly , th e characteristi c o f secondar y flo w i s als o show n i n Figur e 5.8 , especiall y a t th e section s o f

2 D t o 6D . Compare d wit hthos e i n Figur e 5.15 , th e featur e o f secondar y flo w i s no t clea r i n th e contour s o f

{U p x /U a } o n th e sectio n O D an dI D i n Figur e 5.18 . Bu t w e ca n stil l se e th e increasin g tendenc y o f th e magnitud e o f

{U ^/th, } toward s th e x negativ e axi s alon g th e pip e left-han dwal l an dth e pip e right-han dwal l respectively . I n addition , fo r th e secon dtyp e o f glas s beads , th e magnitud e o f {U p x /U a } i n Figur e 5.1 8 i s generall y large r i n th e x negativ e directio n tha n i n th e x positiv e direction . Bu t

th e magnitud e o f

{U p x /U a } i n th e x positiv e directio n obviousl y increase s fro mth e sectio n O D t o 6D . B y contrast , fo r th e first

typ e o f

glas s beads , th e magnitude s o f {U p x /U a } i n bot hx direction s ar e nearl y equa l o n eac hcross-sectio n (a s show n i n Figur e 5.15) . Wit hregar dt o th e dimensionles s particl e numbe r rat e {N /Z (N)) , Figur e 5.1 9 show s the developmen t

o f it s cross-sectiona l distribution s fro mth e sectio n O D t o 6D . O n th e sectio n OD , th e rop e ofth e regio n wit hth e maximu m{N /'Z (N) } i s show n a

t th e pip e oute r

wall . Additionally , a stratifie dconfiguratio n show s that (N /X (N) } decrease s fro mth e pip e oute r wal l t o th e pip e inne r wall . Thi s stratificatio n featur e wa s no t foun di n thebehavou r o f th e first typ e o f glas s bead s i n Figur e 5.16 . A t th e furthe r

section s downstrea mo f OD , th e tota l contou r numbe r o f (N/£(N) } graduall y decrease s whil e bot hth e dens e regio n wit hth e maximu m{N /Z (N) } of- 6 an dth e dilut e are awit hth e minimu m {N /Z (N) i of- 9 ar

e smalle r

an dsmaller . I n particular , downstrea mo f the sectio n 4D , the dens e regio n wit hth e iso-lin e valu e of- 6 i s lessene dlik e acurve dstri p locate daroun dth e pip e left-inne r wal l an d the cross-sectiona l distribution s o f {N/X (N) } are develope dint o asimpl e pattern i n whic harelativel y dilut e regio n wit hthe iso-lin e valu e o f - 8 i s surrounde db y arelativel y dens e regio n wit hth e iso-lin e valu e o f - 7 ove r the mai n are aofth e sectio n 5 D an d6D .
Therefore , th e gas-soli dflo w o f th e secon dtyp e o f

glas s bead s ca n b e considere da s bein g stead y downstrea mo f

th e sectio n 4D , accordin g t o th e similaritie s o f cross-sectiona l distribution s o f {Upy/L' a } an d|N /Z (N)} . I n addition , th e developmen t o f th e cross-sectiona l distribution s o f |N /Z (N) } indicate s tha t th e rop e ofth e secon dtyp e o f glas s bead s i s stil l retaine dunti l th e sectio n 6D , wher e adens e regio n wit hth e maximu m{N /Z (N) | i s locate da t the pip e left-inne r

wall .

95



# VES01713 0A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

Figur e 5.1 7 Developmen to f cross-sectiona l distribution s o f th e dimensionles s avia l particl e velocit y {U p v /U 0 ( o f

th e secon d typ e o f

glas s beads (70~110nm) unde ra n ai rconveyin g velocity U a =T0m/s an d th

e soli d mass loadin g rati o 0.19 % i n th e vertica l pip e behin d an elbo w (R/D=1 .3 )

9 6



# VES01713 1Chapte r 5hxperimenta l studie s ofparticl e dynamic s b y LD A

Figur e 5.1 8 Developmen to f cross-sectional distribution s o f the dimensionles s horizonta l particl e velocit y {Up S/max(abs(U ps )) } o f th e secon d typ e o f glass bead s (70~110u.m ) unde ran ai r conveyin g velocit

y U a =10m/s an d th e soli d mass loadin g rati o 1.9 % i n th e vertica l pip e behin d a n elbow (R/D=1.3 )

9 7



# VES01713 2A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

4 0 Natura l logarith mo f th e dimensionles s particl e numbe r rat e {ln(N/l{N)) } O D 20

-2 0

-4 0 4 0 * . 6

2 D 2 0

-2 0

-4 0 4 0 3* .

- 6

4 D 2 0

-2 0 -
-4 0 • 4 0 6 D 2 0

-20 -40 -5 0 • A

/ a '

z(mm ) 4 0 1 D -7& \2 0

-2 0 >

5 - 6

# 4 ^

-4 0 < 4 0 , 3 D 2 0

-2 0

-4 0 4 0 Jo

5 D 2 0

-2 0 3 5- s - 1

-4 0 -5 0

5 0 0 z(mm ) -1 0 - 9 - 8 - 7 - 6 - 5 e \x=-9,-8,-7,-6,-5,- 4 n x 10" 4 ,n=2,4 , 10,25,68 , 18 4 Section s Tota l {N

) (10 5 ) 0 D 2,5 5 1 D 2.6 4 2 D 2.3 8 3 D 2.3 6 4 D 2.5 4 5 D 3.1 3 6 D 2.9 4 5 0

Figur e 5.1 9 Developmen to f cross-sectiona l distribution s o f th e dimensionles s particl e numbe r rat e {N /X (N) } o f

th e secon d typ e o f

glas s bead s (70~110um) unde ran ai rconveyin g velocit y U a =10m/s an d th

e soli d mas

s loadin g rati o 1.9 % i n the vertica l pip e behin d an elbow (R/D=1.3 )

9 8



# VES01713 3Chapte r 5 Kxpcr i menial studie s ofparticl e dynamic s b y LD A 5.4. 3 Glas s bead s withi n th e siz e rang e 180~300u, m (th e thir d type ) Th e experiment s wer e performe dusin g th e thir dtyp e o f glas s bead s withi nth e siz e rang e 1 X0~300pm , whic hwer e transporte di n th e pip e b y a n ai r conveyin g velocit y lOm/ s wit hasoli d mas s loadin g rati o 1.9% . Th e experimenta l dat aar e plotte di n Figur e 5.20 , Figur e 5.2 1 an dFigur e 5.2 2 respectively . A s fo r th e dimensionles s axia l particl e velocit y {U p y / U a } , Figur e 5.2 0 show s th e developmen t o f it s cross-sectiona l distribution s fro mth e sectio n O D t o 6 D i n th e vertica l pip e downstrea mo f th e bend . I n general , th e horseshoe-shape dfeatur e i s observe di n contour s o f {U p y / U a ) befor e th e sectio n 3D . Furthe r

downstream , aclea r shap e ca n n o longe r b e observe do n contour s o f {U p y / U a } o nth e section s o f

4 D t o 6D , wher e {U p y / U a| i s muc hmor e randoml y distribute dan dha s alarge r valu e (mor e tha n 1 ) i n th e mai n are ao f across-section . Comparin g Figur e 5.2 0 wit hFigur e 5.1 4 (th e first typ e glas s beads ) an dFigur e 5.1 7 (th e secon dtyp e o f glas s beads ) a s wel l a s Figur e 4. 5 (ai r flow) , w e lis t

thei r ke y differenc e an dsimilarit y i n Tabl e 5.1 . Tabl e 5. 1 Comparison s o f th e axia l velocity distribution s i n avertica l pip e downstream o f aben d amon g thre e type s o f glas s bead s an d ai rflow A i r flo w « U a / U a } ) Glas s bead s ({U r y / U „ [ ) A i r flo w « U a / U a } ) Th e firs t typ e (<50um ) Th e secon dtyp e (70-11 0 urn ) Th e thir dtyp e (180-30 0 nm ) Stoke s Numbe r - <3. 5 10-2 8 >3 5 Horseshoe-shape dfeatur e observe do n th e section s fro mO D t o 7 D fro mO D t o 4 D fro m0 D t o 4 D fro mO D t o 2 D

o n th e sec t io n 6 D Regio nwit hth e smalles t axia l velocit y clos e t o th e pip e right-inne r

wal l th e pip e righ t wal l th e pip e left-inne r

wal l th e pip e left wal l o n th e sec t io n 6 D Th e value s o f

iso-lin e i n th e mai n are ao f

th e sectio n 6 D >= 1 >=0.9 5 >=!. ! >-1. 2

Obviously , th e horseshoe-shape dfeatur e i s acommo n characteristi c i n contour s o f th e axia l velocit y {U„/U a ) o r

{U a ) / U a } i n th e vertica l pip e downstrea mo f aben dfo r

bot hai r

flo w an d gas-soli dflo w o f

thre e type s o f

glas s beads . Thi s featur e i s stil l observe da t th e sectio n 7 D fo r

ai r flow , B y contrast , i t

disappear s at

th e downstrea mo f

th e sectio n 4 D fo r

th e first an dsecon dtype s o f glas s bead s an dat th e downstrea mo f th e sectio n 2 D fo r th e thir done . Therefore , thi s horseshoe-shape dfeatur e mus t b e forme ddu e t o th e ben deffec t whic hchange s ahorizonta l flo w o f ai r o r gas-soli dint o th e vertica l one . Th e differen t dispersio n position s o f th e horsesho e indicat e tha t

particl e Stoke s Numbe r influence s th e cross-sectiona l pattern s o f lU a y / U a } i n a vertica l pip e behin da n elbow . I n addition , fo r th e axia l particl e velocit y o f thre e type s o f

glas s bead s o n th e mai n are ao f th e sectio n 6D , i t

show s tha t

alarge r

glas s bea dha s ahighe r axia l

9 9A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

Figur e 5.2

0 Developmen to f

cross-sectional distribution s o f th e dimensionles s axia l particl e velocity {U p y /U 0 [ o f

th e thir d typ e of

glas s bead s (180~300um ) unde ra n ai rconveyin g velocit y U a =10m/s an d soli d mass loadin g rati o 0.19 % i n the vertica l pip e behin d an elbow (R/D=1.3 )

10 0Chapte r S hxpcr i menta

l studie s ofparticl e dynamic s b y LD A

4 0 Th e dimensionles s horizonta l particl e velocity { U/max(abs( U )) } O D

2 D

4 D 

# 1

6 D

-2 0 i

-4 0 -5 0 WgMm 

# t

f 

# v V

o z(mm ) 5 0 4 0

2 0

-2 0

2 0

-2 0

-4 0 4 0

2 0

-2 0 1 D

* 1

3 D

5 D

-4 0 -5 0

- 1 -0. 5 

# •4

o z(mm ) 5 0

0. 5 Section s Maximu mabs(Ly(rrVs ) 0 D I D 2 D 3 D 4 D 5 D 6 D 2.0 2

2.1 5 1.3 7 1.9 3 0.9 3 1.1 8 2.0 7 Figur e 5.2 1 Developmen to f cross-sectiona l distribution s ofth e dimensionles s horizonta l particl e velocit y {Upj/max(abs(U pj )) ( o f th e thir d typ e o f glas s bead s (180~300um) unde ran ai r conveyin g velocit

y U a =10m/s an d th e soli d mass loadin g rati o 1.9 % i n th e vertica l pip e behin d an elbow (R/D=1.3 )

10 1



# VES01713 6A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m

Contour s ofth e dimensionles s horizonta l particl e velocit y {U p x /max(abs(U p x )) ! fro mth e sectio n O D t o 6 D ar e displaye di n Figur e 5.21 . Unlik e thos e o f th e othe r

tw o type s o f

glas s beads , eac h contou r o f th e thir dtyp e doe s no t sho w th e featur e o f secondar y flo w i n th e vertica l pip e downstrea mo f

th e bend . Overall , ther e i s n o clea r for mshow n i n contour s o f {U p x /max(abs(Up X )) j o n th e section s o f OD , I D an d6D . Bu t asimila r

structur e ca n b e see n o n th e section s fro m2 D t o 4D . Contour s o f {U p x /max(abs(U p x )) } o n thes e section s illustrat e tha t a stri p i n th e middl e o f th e sectio n divide s i t int o thre e part s alon g th e x axis . Basically , {U p x /max(abs(U p x )) } i s almos t zer o i n th e stri p an dnegativ e i n bot hside s o f th e strip . Moreover , th e magnitude s o f

{U p x /max(abs(U p x )) } hav e n o significan t discrepanc y o n al l sections , especiall y o n th e sectio n 6D , wher e {U p x /max(abs(U p x )) } i s almos t homogenousl y distribute d wit havalu e o f

zer o ove r

mos t o f th e are ao f

th e section . Compare dwit hFigur e 5.1 5 an dFigur e 5.18 , th e ke y differenc e lie s i n th e lac k o f structur e o f

secondar y flo w i n Figur e 5.21 . Thi s indicate s tha t

ai r secondar y flo w (th e horizonta l ai r velocity ) ha s muc hmor e influenc e o n th e firs t an dth e secon dtype s o f glas s bead s tha n o n th e thir done .
Th e evolutio n o f

cross-sectiona l distribution s o f th e dimensionles s particl e numbe r rat e (N/Z(N) } i s show n i n Figur e 5.22 . Generally , ther e i s n o unifor mo r clea r patter n i n an y contour s o f {N/Z(N) j fro mthe sectio n O D to 6D . I n mos t region s o f

awhol e section , (N/Z(N) } ha s arelativ e smal l valu e o f

- 7 o r -8 , whic har

e correspondin g t o 1 0 o r 4 xlO" 4ofth e tota l particl e numbe r rat e o n thi s section . Th e rope , whic hi s forme db y th e regio n wit hth e maximu mparticl e rate , i s th e mos t frequentl y bu t sporadicall y locate dalon g th e pip e lef t wal l an deac hregio n onl y occupie s asmal l fractio n simila r to severa l discret e circle s o n th e whol e section . Thi s i s differen t fro mth e experimenta l result s observe d i nFigur e 5.1 6 an dFigur e 5.1 9 fo r th e firs t

an dth e secon dtype s o f glas s beads , fo r

bot htype s o f

glas s bead s a t leas t hav e aclea r

for mshow n i n th e contour s o f {N/£(N) } o n the sectio n OD . Thi s differenc e amon g thre e type s o f glas s bead s als o indicate s lha t particl e inerti aplay s an importan t influenc e o n particl e dynami c propertie s i n avertica l pip e downstrea mo f abend , fo r

the thir dtyp e o f

glas s bead s wit hthe larges t

Stoke s Number s tend s t o retai n thei r previou s state a

t th e elbo w outlet , whe n the y ente r int o the vertica l pip e fro mth e elbow . An dth e othe r tw o type s wil l b e easil y influence dt o follo w th e curren t

loca l ai r

flo w i n th e sam e proces s fro mth e elbo w t o th e vertica l pipe .

10 2



# VES01713 7Chapte r 5 Kxperimenta l studie s o f particl e dynamic s b y LD A Natura l logarith mofth e dimensionles s particl e numbe r rat e {ln(N/£(N)) } 4 0 , - - 4 0

-40 ; -40 ' ' 4 0 . -5 0 0 5 0

Figur e 5.2

2 Developmen to f

cross-sectiona l distribution s o f the dimensionles s particl e numbe r rat e jN/X(N) } o f

th e thir d typ e o f

glas s bead s (180~300p.ni) unde ra n ai rconveyin g velocit y U,=10m/

s an d the soli d mas

s loadin g rati o 1.9 % i n th e vertica l pip e behin d an elbo w (R/D=1.3 )

10 3A ninvestigatio n ofparticl e dynamic s i nadilut e phas e pneumati c conveyin g syste m 

### 5. 5 DISCUSSIO N AN D COMPARISO N 5.5. 1 Th e discrepanc y betwee n ai rvelocit y an d particl e velocit y i n th e horizonta l pip e Davi dMill s (2004b ) state dtha t th e particl e velocit y woul dtypicall y b e abou t 80 % o f

th e ai r conveyin g velocit y i n ahorizonta l pipelin e i n dilut e phas e conveyin g an dabou t 70 % i n vertica l upwar dflow i n apipeline , whic hca n b e expresse di n term s o f asli p rati o o f

particl e velocit y ove r ai r conveyin g velocity . Thi s statemen t i s base do n th e concep t tha t particl e velocit y shoul db e lowe r tha n tha t

o f th e conveyin g air , sinc e th e mechanis mo f conveyin g i s on e o f dra g forc e i n dilut e phas e conveying . However , h e di dno t describ e th e relate dmethod s fo r particl e velocit y measuremen t

o r experimenta l data .

0. 6 j 0. 4 0. 2 0 -0. 2 -0. 4 -0. 6

0. 6 Smoke , mea n U IU =1. 1 p x a First , mea n U IU =1. 1 p x a Second , mea n U III =1. 2 p x a Third , mea n U / U =1. 3

p x a Ideal air , mea n U/ U =1. 0

0. 7 0. 8 0. 9 U/ U p x a 1. 1 1. 2 1. 3 1. 4 Figur e 5.2

3 Th e vertica l profil e o f axia l mean velocit

y fo rfou rtype s o f

particle s a

tth e sectio n I D i n th e horizonta l pip e (U a =10m/s , ai rconveyin g velocity ; First : glas s bead s less tha n 50pm ; Second : glas s bead s withi n 70—11 0 urn ; Third : glas s beads withi n 180-30 0 pm) . S o far , mos t

cite dexperimenta l dat ao f particl e velocit y i n horizonta l pipe s ar e expresse da s a one-dimensiona l profil e alon g th e gravit y forc e directio n ( y axis) . I n orde r t o mak e aconvenien t compariso n wit hothe r relate dwork , w e re-plotte dth e experimenta l dat ao n th e horizonta l sectio n I D fo r thre e type s o f

glas s bead s a s wel l a s smok e i n th e one-dimensiona l profile s show n i n Figur e 5.23 . Compare dwit hth e one-sevent hpowe r profil e o f

idea l turbulen t

flo w (Robe r

e t al. , 2004) , w e ca n obviousl y se e tha t bot hprofile s o f

smok e an dth e first

typ e o f

glas s bead s hav e a goo dagreemen t

wit htha t

o f idea l ga s flo w an dthe y ar e nearl y identica l onl y wit hmino r

10 4Chapte r S l.xperimenln l studie s ofparticl e dynamic s b y LD A discrepancies , sinc e bot hth e first typ e o f

glas s bead s (<50pm ) an dsmok e particle s hav e asmal l Stoke s numbe r

(<3.6 ) whic hgive s agoo dabilit y to follo w th e flo w o f th e transportin g air . B y contrast , th e profile s o f th e secon d(70- 1 10pm ) an dth e thir d(I80~300p.m ) type s o f glas s bead s sho w asignifican t

discrepancy . Th e mea n valu e o f U p ,/U a , i s 1.1 , 1.1 , 1. 2 an d1. 3 fo r smoke , th e first, th e secon dan dth e thir dtype s o f glas s bead s respectively . Thi s indicate s tha t th e mea n axia l particl e velocit y o f

particle s wit hlarge r siz e i s greate r

tha n tha t

o f th e smalle r

particles , whic h mus t resul t fro mhig hinerti ao f th e large r

particles . Sinc e th e empirica l one-sevent hpowe r la w state s tha t

th e rati o o f

th e averag e velocit y t o th e centrelin e velocit y varie s fro m0.7 9 t o 0.8 7 i n a full y develope dflo w i n asmoot hpipe , thi s mean s that flui dvelocit y a t

th e pip e centr e i s abou t 1. 3 o r 1. 2 lime s large r

tha n th e mea n velocity . Consequently , particle s wit hhig hinerti awoul d retai n thei r

origina l velocitie s whe n accelerate di n th e fastes t regio n o f

flui do r

du e t o particle-particl e collisions . W e ca n i n fac t se e tha t

th e axia l particl e velocitie s fo r th e secon dan d thir dtype s o f

glas s bead s ar e faste r tha n tha t

o f ai r phas e a t

aloca l point , especiall y i n th e regio n clos e t o th e pip e wall . I n addition , w e als o notic e tha t th e maximu mrati o o f th e axia l particl e velocit y t o ai r

conveyin g velocit y measure s abou t 1.4 , whic hi s large r tha n tha t

o f 1. 3 estimate d b y th e one-sevent hpowe r law . Th e possibl e reaso n ma y b e th e kinemati c energ y o f ai r flo w increase ddu e t o turbulen t energ y lessene db y large r micro-particle s lik e th e thir dtyp e o f glas s beads . c=2. 5

10.0 0 15.00 20.00 25.0 0 30.0 0 tO.OO 15.0 0 20.0 0 25.00 30.0 0 10.0 0 15.0 0 20.0 0 25.0 0 30.0 0 35.0 0 Fig . 7 . Developmen t

o f vertica l profile s o f

particl e phas e propertie s alon g ahorizonta l glas s pip e fo r differen t

panicl e mas s loading s l(i=(0 ) 0.3 , (O ) 0. 5 an d(• ) 0.7 , superficia l ga s velocit y (j',-2 3 m/s) . (a ) Particl e concentratio n i n kg/m ! ; (b ) axia l mea n particl e velocit y i n m/s : ic) axia l particl e velocit y fluctuation i n m/s ; (d ) numbe r mea n particl e diamete r i n Figur e 5.2

4 Experimenta l dat ao f Hube ran d Sommerfel d (1994 ) fo rflo w i n ahorizonta l pip e b y Phas e Dopple rAnemometr y unde rai rconveyin g velocitj ' 23m/ s fo rglas s bead s wit h a mea n siz e 40p m Wit hregar dt o particl e velocit y measurement s i n ahorizonta l pipe , Figur e 5.2 4 show s th e experimenta l dat ao f Hube r an dSommerfel d(1994 ) usin g Phas e Dopple r Anemometr y (PDA) . Apparently , th e maximu mparticl e velocit y i s abou t 30m/s , whic hi s 1. 3 time s faste r tha n th e ai r conveyin g velocit y 23m/s . The y di dno t giv e an y explanation . The n Kussi nan dSommerfel d (2002 ) publishe dthei r experimenta l dat aobtaine db y measurin g th e particl e velocit y o f glas s bead s wit hmea n siz e 100p mi n ahorizonta l channe l usin g PDA , a s show n i n Figur e 5.25 . Here ,

10 5



# VES01714 0A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m particl e velocit y i s clearl y slowe r tha n ai r

velocit y excep t

fo r th e boundar y regio n an dth e maximu mrati o ofparticl e velocit y t o ai r conveyin g velocit y i s abou t 1.0 . 1 O n

0. 4

0. 0 0. 5 1 2
Fie. . 6a-c . Vertica l profile s lo r ai r an d100-u mparticle s wit h f' a v =I9. 7 ni/ s fe r

th e lo w roughnes s cas e (Rl) : ahorizonta l mea n velocitie s o f

ai r ati dparticles ; b horizonta l componen t o f nil s velocit y fluctuation ; c vertica l componen t o f rm s velocit y fluctuation [open symbols*, air ; closed

symbols: particles ) Figur e 5.2 5 Th e experimenta l dat aobtaine d b y Kussi n an d Sommerfel d (2002 ) i n th e horizonta l channe l usin g PDA . Figur e 5.2 6 show s th e experimenta l dat ao f Tsuj i e t

al . (1982 ) fo r

flo w i n ahorizonta l pip e unde r a n ai r conveyin g velocit y o f 15m/ s an dat

differen t

soli dloadin g ratios . The y extende dth e standar dtechniqu e o f LD At o measur e simultaneousl y th e velocitie s o f ai r phas e an dsoli dphas e b y discernin g th e amplitude s o f Dopple r

Signal s scattere db y th e particle s (plasti c pellet s wit h mea n siz e 200p man ddensit y 100 0 kg/m 3 ) an dth e seedin g particle s (ammoniu mchlorid e wit h mea n siz e 0.6pm) . Thei r experimenta l dat asho w tha t th e profile s ofparticl e velocit y ar e clos e t o thos e o f

th e ai r phas e at

th e differen t

soli dloadin g ratios . Th e value s o f particl e horizonta l velocit y t o ai r

conveyin g velocit y ar e les s tha n 1.3 .

F igur e It . Mea nvelocit y distribution s o f ai r an d0 2 m mparticles ; (o ) ".» . = 6 m/s ; (t ) 1 0 m/s ; (c) 15m/« . Figur e 5.2 6 Tsuji' s experimenta l dat a(1982 ) b y LD A i n ahorizonta l pip e

10 6



# VES01714 1Chapte r 5 l-Aperimenta l studie s o f particl e dynamic s b y LD A Figur e 5.2 7 show s on e se t o f th e experimenta l dat ameasure db y Yilma z an dLev y (2001 ) wh o use dalibre-opti c prob e t o measur e time-average dloca l particl e velocities , concentration s an d mas s lluxe s fo r

pulverised-coa l particle s (90 % les s tha n 75pm ) i n ahorizonta l pipe . Thei r experimenta l dat asho w tha t th e maximu mrati o o f particl e velocit y t o ai r conveyin g velocit y i s les s tha n 1.2 . Accordin g t o th e experimenta l dat ai n th e figure s o f 5.15 , 5.16 , 5.1 7 an d5.18 , th e previou s experiment s o f

measurin g particl e velocit y i n ahorizonta l pip e mainl y focuse do n asingl e typ e o f particl e wit hvaryin g differen t ai r conveyin g velocitie s o r changin g soli dloadin g ratios . Unde r th e sam e flui dconditions , experiment s usin g th e sam e material s wit hdifferen t size s lik e ou r experiment s ar e stil l scarce .

1 0 To p D = 0.154

m U „ = 2 0 m/ s •

— - 1.0 0 0.5 0 » 0.3 3 i l 

# f

- 

# /

Botto m 0, 0 0. 5 1, 0 1. 5 Fig , + Effec t

o f solid s loadin g rati o ( fi Y (a ) panicl e velocit y profile s Figur e 5.27 Experimenta l dat ao f Yilma z an d Lev y (2001) , obtaine d b y usin g Optical-Fibr e velocinictr y

10 7



# VES01714 2A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 5.5. 2 Particl e dynamic s i n th e vertica l pip e downstrea m o f arigh tangl e elbo w O nth e sectio n OD , z= 0

1 

## ro 3 j C Lj = > 0.5 !
1 O. l Firs t Secon d Thir d : iI 0. 6 0. 4 0. 2 0 -0. 2 -0. 4 -0. 6 -0. 8 - 1 x/ R

_1500 = • o I C ! o ] § 1000 ; i s I | r so o O L

—i'.. ^ ... . 1 0. 8 0. 6 0. 4 0. 2 0 -0. 2 -0. 4 -0. 6 -0. 8 - 1 x/ R Figur e 5.2 8 Profile s o f th e axia l particl e velocit y {U p , ) an d particl e numbe rrat e jN J alon g th e x axi s on th e sectio n 0 D i n th e vertica l pip e downstrea m o f the righ tangle d elbow . (U„=10m/s , ai rconveyin g velocity ; First : glas s bead s o f siz e les s tha n 50pm ; Second : glas s bead s withi n th e siz e rang e 70-11 0 pm ; Third : glas s bead s withi n th e siz e rang e 180-30 0 pm ; R : pip e radiu s 37.5mm) . I n orde r t o compar e wit hth e previou s works , Figur e 5.2 8 show s profile s ofth e axia l particl e velocit y an dparticl e numbe r rat e fo r

thre e typ e o f

glas s bead s alon g x axi s (z^0 ) fro mth e sectio n 0 D o f th e vertica l pipe . Th e profil e dat ao f {U p y [ wer e extracte dfro mFigur e 5.14 , Figur e 5.1 7 an dFigur e 5.20 . Th e profil e dat ao f {N } wer e obtaine dfro mFigur e 5.16 , Figur e 5.1 9 an dFigur e 5.22 . Her e th e x positiv e axi s point s t o th e pip e oute r wall . Th e sectio n 0 D i s abou t 15m mawa y fro mth e elbo w outlet . Compare dwit hcontour s o f !U p y / U u } an d{ln(N/I(N)) | i n Figur e 5.1 4 t o Figur e 5.22 , th e {Upy{profil e doe s no t illustrat e th e horseshoe-shape dfeatur e i n cross-sectiona l distributio n o n th e sectio n O D fo r

thre e kind s o f

glas s beads . Bu t

th e profil e o f

eac h{U p y } show s th e decreasin g tendenc y fro mth e pip e oute r wal l t o th e inne r

wal l (alon g th e x negativ e axis) , whic hi s simila r t o tha t observe di n th e correspondin g cross-sectiona l distributions . I n addition , th e axia l particl e velocit y o f

th e thir dtyp e o f

glas s bead s i s large r tha n tha t

o f th e othe r

tw o types , whic hindicate s th e inertia l effec t

o n particl e velocity , sinc e particle s wit hhig hinerti ashoul dkee p thei r initia l

10 8



# VES01714 3C'haplc r 5 Hxperimenla l .studie s o f panicl e dynamic s b y LD A velocitie s rathe r

tha n easil y follo w th e carrie r fluid . A s fo r

th e profile s o f

particl e numbe r

rat e { N] . th e profil e o f

th e secon dtyp e o f

glas s bead s reveal s tha t th e dus t

rop e forme di n th e ben di s clos e t o th e pip e oute r wall . Bu t

w e ca n no t

clearl y se e th e rop e fro mth e profile s o f th e firs t

an d thir dtype s o f

glas s beads . However , th e region s wit hahig hdensit y o f particle s ofth e firs t an d thir dtype s ca n b e observe do n thei r cross-sectiona l distribution s o f {N} . S o far , thre e previou s paper s whic hexperimentall y stud y particl e dynamic s i n avertica l pip e behin dapip e ben dhav e bee n searched . Figur e 5.2 9 show s th e profile s o f th e axia l particl e velocit y an dparticl e concentratio n a t th e positio n 0.1 mawa y fro mth e elbo w outlet . Thes e dat a wer e measure db y Hube r an dSommerfel d(1994 ) wh o use dPD A t o stud y th e degre e o f segregatio n o f

glas s bead s wit hmea n siz e 40p munde r 1 4 an d21m/ s ai r

conveyin g velocit y wit h soli dloadin g rati o 0. 5 i n avertica l pip e behin da n elbow . Her e th e pip e oute r wal l locate s a

t z=0mm . Thei r

experimenta l dat ao f particl e concentratio n profil e displa y th e rop e locate da t th e regio n clos e t o th e pip e oute r wal l an dth e minimu mvelocit y a t th e pip e oute r

wal l correspond s t o th e velocit y o f

th e dus t

rop e slidin g alon g th e wall . The y though t i t migh t b e cause db y momentu mlosse s fro mparticle-wal l an dinter-particl e collisions . Howeve r thi s i s differen t

fro m tha t observe di n Figur e 5.12 , whic hshow s tha t particle s withi nth e rop e regio n no t onl y hav e th e maximu mparticl e numbe r rat e bu t

als o hav e th e highe r velocities . Th e regio n wit hth e maximu m axia l particl e velocit y locate s at th e insid e o f

th e horsesho e shap e o f th e cross-sectiona l distributio n o f

{U p y } o n th e sectio n OD . Thi s featur e i s als o observe di n bot hFigur e 3.2 0 an d 3.2 1 fo r ai r phas e experimenta l dat aan dnumerica l results . Moreover , glas s bead s wit hmea n siz e 40p mo r

les s tha n 50p mhav e alo w Stoke s Number , whic hindicate s tha t thei r profile s shoul d sho w th e feature s o f

th e ai r phase . 30.0 0 20.0 0

20.0 0 40.0 0 80.0 0 SO . i tt a m m .0

0 i i n m m (£/,-(0 ) U m/

s an d (A ) 2

1 m/s ) ben d radiu s o f R/D-25* stainles s steel pipe , particl e mas s loadin g -0. 5 Figur e 5.2

9 Profile s o f

th e axia l particl e velocity an d particl e mas s concentratio n (Hube ran d Sommerfeld , 1994 )

10 9



# VES01714 4A l l investigatio n o f particl e dynamic s i nadilut e phas e pneumati c conveyin g syste m Anothe r tw o experiment s wer e performe db y Yilma z an dLev y (1998 , 2001) . The y use da fibre-optic prob e t o measur e lime-average dloca l particl e velocities , concentratio n an dmas s fluxes ove r

cross-section s i n avertica l pneumati c conveyin g lin e followin g a horizontal-to-vertica l elbo w unde r arang e o f

conveyin g ai r

velocitie s an dsolid s mas s loadings . I n thei r experiments , pulverize dcoa l wit hmea n diamete r 75p man dtru e densit y 168 0 kg/m 3 wer e conveye dwit hsoli dloadin g rati o 0.3 3 t o 1 unde r ai r velocitie s fro m1 5 t o 30m/s . Sinc e thei r lates t experimenta l dat ai n 200 1 include dth e ol dresults , Figur e 5.3 0 show s thei r measuremen t

result s a

t th e positio n clos e t o th e elbo w outle t (z/D=l) . Compare dwit hRuber' s dat ai n Figur e 5.29 , th e profile s o f particl e concentratio n i n Figur e 5.3 0 sho w ahig hparticl e mas s concentratio n clos e t o th e oute r wal l (alon g th e x negativ e axis ) fo r fou r differen t

fluidconditions . Obviously , thi s findin g i s clos e t o ou r experimenta l dal aofparticl e numbe r rat e show n i n Figur e 5.19 . Bu t

th e profile s o f

th e axia l particl e velocitie s ar e onl y limite dwithi nashor t distanc e x/ D les s tha n 0. 3 an dther e i s n o dat afo r th e lef t

space . Th e author s di dno t presen t

an y reaso n fo r this .

Figur e 5.3

0 Profil e o f

th e axia l particl e velocity an d particl e concentratio n a tth e positio n o f z/D= l unde rdifferen tflui d condition s (Yilma z andLevy , 2001 )


### 5. 6 SUMMAR YAN D CONCLUSION S Pneumati c conveyin g o f granula r

material s i s on e o f th e mos t

importan t

application s i n man y industries . I

t i s essenlia l an dnecessar y t o characteriz e particl e dynamic s i n differen t component s

11 0



# VES01714 5Chapte r5 Experimenta

l studie s o f particl e dynamic

s by LD A

o f apipelin e t

o explor e th e mechanis m o f pneumati c transport . In thi s chapter, th e extende d LD A techniqu e discusse d i n Chapte r3 wa s applie d t o stud y cross-sectiona l feature s o f three type s o f glas s beads i n ahorizonta l pip e an d i n avertica l pip e behin d a n elbow .
I n th e horizontal pipe , th e experimenta l dat asho w tha

tth e cross-sectiona l flow patterns o f th e soli d phas e i n the gas-soli d pip e flow (glas s bead s les s tha n 110pm ) can b e classifie d b y annula r flow describin g the axia l particl e velocit y contour s an d stratifie d flow characterisin g particl e numbe rrat

e distributio n ove racross-section . Howeve rth e positio n o f th e annula rcor e an d the value s o f

iso-line s ar

e dependen to n particl e siz e an d var y alon g th e flui d streamwis e direction . B y contrast, these tw o flow pattern s ca n b e stil l observe d fo rthe thir d typ e o f glas s bead s (180~300p.m) , bu

tthei rcharacteristic s ar e notclea rlik e thos e fo rth e othe rtw o type s o f glas s beads ,
I n th e vertica l pip e afte ra n elbo w (R/D=1.3) , ahorsesho e shap e feature has bee n foun d o n cross-sectional distribution s ofth e axia l particl e velocit y fo ral l three type s o f glas s bead s o n the sectio n O D clos e t

o the elbo w outlet . A tthe furthe rdownstream sections , the horseshoe-shape d feature i s graduall y distorte d unti l i tcompletel y disappears . Th e distanc e fo rtota l disintegratio n i s about4 D fo rthe firsttyp e o f glas s beads , 2 D fo rth e secon d typ e and I D fo rth e thir d one . A s fo rparticl e numbe rrate , it s cross-sectiona l distributio n o n the sectio n O D show s tha tarop e i s forme d a

tth e pip e oute rwal l wher e the maximu m particl e numbe rrat e occurs . O n th

e whole , the rop e forme d b y the firsttyp e o f glas s bead s ca n b e stil l observe d a tthe sectio n 6D . Fo rthe secon d typ e o f

glas s beads , th e rop e wil l disintegrate fro m the sectio n 4 D accordin g t o the similaritie s between cross-sectiona l distribution s o f {U P y /U a } an d {ln(N/£(N))} . Overall , the ropin g characteristi c i s no tobviousl y show n i n th e gas-soli d flow ofth e thir d typ e o f glas s beads afte rth e sectio n OD . Al l o f thes e indicat e tha

trope s forme d from large rparticle s dispers e more easily , fo rreasons perhap s relate d to thei rhighe rinertia .
Moreover , th

e currentexperimenta l datahav e bee n compare d wit h several previou s experimenta l publications . Thes e comparison s revea l tha tther e exist s muc h discrepanc y betwee n them . Thi s discrepanc y may b e cause d b y possibl e factor s o f differen tinstrument s an d differen tfluid condition s a

s wel l a s differen texperimenta l rigs . Consequently , furthe rexperimental studie s wil l b e necessar

y t o measure mor e granula rmaterial s unde rarange o f fluid condition s fo r understandin g th

e mechanis m o f

pneumati c conveying .

I l l



# VES01714 6

# Chapte r 6 Visualizatio n an d Measuremen t of Cross-sectiona l Characteristic s o fSoli d Phas e i n a Dilut

e Pneumati c Conveyin g Syste m

In applications of

dilute pneumatic conveying, the two important parameters ofparticle diameter and solid volume fraction have been intensively studied in numerous experiments and numerical simulations. But

local information on theirspatial distribution in pipes has scarcely been reported to date, especially overhorizontal pipe cross-sections. This chapterpresents a video & image processing method of measuring particle diameterand solid volume fraction through analyzing particle tracks and positions in frames of a video. Using a high definition camcorder, the behaviourqf

the solid

phase is recorded

when particles cross a pipe cross-section which is highlighted

by a light

sheet produced

by a halogen lamp. On every frame in a video, the instantaneous particle positions, particle diameter and the local

solid fraction over

the pipe cross section can be extracted. The corresponding time-averaged values can also be calculated through averaging data on all frames in a specific interval. The experimental results suggest

that the gas-solid

flow in a dilute pneumatic conveying system is always heterogeneous and unsteady. The parameterof

particle mass mean size is superiorto particle numbermean size for statistically describing the unsteady properties ofgas-solid pipe flow.



### 6. 1 INTRODUCTIO N Pneumati c conveyin g system s ar e widel y applie d t

o proces s granula rmaterial s i n man y industria l fields . A pneumati c conveyin g pipelin e syste m typicall y consists o f horizonta l an d vertica l sections a

s wel l a s connectin g elbows . Consequently , there exis tdifferen tphysica l phenomen ai n differen tpart

s o f apip e line . Fo rexample , gravity settlin g occur s i n horizonta l pipes . Ropin g happen s i n an elbo w du e to acentrifuga l forc e whic h make s particle s concentrate into arope . Obviously , gas-soli d pip e flow i s s o complicate d tha tunderstandin g o f

it s mechanis m i s stil l underdevelopment . Man y feature s hav e stil l t o b e investigated , especiall y loca l informatio n o n soli d phas e velocit y an d particl e diamete ran d frequenc y distributio n ove rth e pip e cross-section . Thes e parameter

s ar e importan ti n the desig n o f systems t

o ensure eve n soli d distributio n between amai n ductan d th e branche s into whic h i tdivides . Fo rexample , i n Co-firin gA n investigatio n o f particle dynamic

s i nadilut

e phas e pneumati

c conveyin

g syste m applications , estimatin g th e spatial distribution s o f pulverize d coa l an d biomas s granula rbefor e a splitte ri s an essential step i n determinin g ho w to spli tmixe d fue l i n acommo n transportatio n pipeline . I n Chapters 3 , 4 an d 5 , w e extende d the currentLase rDopple rAnemometr y (LDA ) techniqu e fo r pip e flow measurementan d use d i tt o explor e particl e behaviou rove raserie s o f cross-section s alon g th e horizonta l pipe . Th e experimenta l results demonstrate d tw o kind s o f cross-sectiona l flow patterns : annula rstructure an d astratifie d configuration , describe d b y particl e velocit y an d particl e numbe rrat

e respectively . Sinc e LD A i s amono-poin tinstrumentwit h ahig h sampl e rate , itonl y provide s informatio n a tasingl e spatial poin ti n aflo w field. Consequently , the measure d cross-sectiona l patterns o f soli d phas e measurement s representparticl e time-average d characteristic s wit h the assumptio n tha tgas-soli d pip e flow i s steady i n time . However , thi s assumptio n ignore s flow phenomen adominate d b y spatial structure , whic h mus tb e determine d b y measurin g flui d parameters o n awhol e field simultaneously . I ti s acumbersom e tas kt o measur e aparamete rove rawhol e field b y usin g apoint-wis e instrument . I n orde rt o investigate simultaneou s particl e behaviou rove rapip e cross-section , usin g alight-shee ttechniqu e with imag e processin g i s agoo d choice . Thi s i s acommo n flow visualizatio n method . I n thi s technique , aligh tbeam (lase ro rothe rligh tsource ) i s forme d into ashee tusin g cylindrica l lenses . Thi s ligh tsheeti s use d fo rsectionin g an d illuminatin g flo w t o for m aplana rmeasurementregio n where flui d characteristic s ca n b e extracte d fro m analyzin g video s o rphoto s recorde d b y aCC D o rcamera .
Th e ai m o f

flo w visualizatio n i s t o mak e flo w patterns visibl e b y addin g smoke , oi l o rfine particle s t

o trace fluid motion . Thi s kin d o f techniqu e has ha d alon g developmen thistory . Fo r example , Reynold s demonstrated tha tpip e wate rflo w coul d b e classifie d a s lamina ro rturbulent b y it s Reynold s Number . Thi s resul twa s deduce d through observin g th e dy e strea

kwhe n som e dy e was injecte d into apip e flow. Anothe rwel l know n experimen twas conducte d b y Ludwi g Prandtl , wh o investigate d unsteady separated flows behin d wing s an d othe robjects i n awater tunnel b y utilizin g flow visualizatio n technique s (Sabersky e tal , 1999) . However , result s obtaine d b y earl y flow visualizatio n technique s were qualitativ e description s o f the flow field ratherthan quantitative dat asuc h a s flow velocity . Wit h progres s i n the hardware o f optic s an d electronic s a

s wel l a s nove l theorie s o ralgorithm s i n flui d mechanic s an d signa l processin g ove r the pas ttw o decades , som e traditiona l visualizatio n technique s hav e bee n develope d o rar e unde r developmen tinto newe radvance d instrument s lik e Particl e Image Velocimetr y (PIV) , Particl e Trac kVelocimetr y (PTV ) an d Electrica l Capacitanc e Tomograph y (ECT) . whic h ca n b e employe d fo rquantitativ e measuremento f comple x instantaneous velocit y field s no tonl y i n a

11 3



# VES01714 8Chapte r6 - Visualizatio n particl e cross-sectional characteristic s i n ahorizonta l pip e singl e phas e flo w bu tals o i n multiphas e flows (Dyakowsk i e tal. , 2000 ; Datt ae

tal. , 2007) . I n previou s literature relate d t o flow visualizatio n application s i n gas-soli d pip e flow, Hesselin k e tal . (1998 ) reviewe d th e influenc e o f digita l computers o n th e classica l method s o f flow visualization . H e thoughttha tth e mos tstrikin g an d promisin g o f thes e technique s were optica l tomograph y an d gradientimaging , whic h allowe d th e interio ro f

flow s t

o b e probe d an d visualize d usin g line-of-sigh ttechnique s applie d from differen tdirections . O n the othe rhand , sheet-illuminatio n technique s provide d powerfu l means t o visualiz e the interio ro f flows. Particl e trackin g wa s an intuitivel y attractiv e metho d fo rmakin g velocit y measurements , bu tcar e shoul d b e exercise d whe n attemptin g t o determin e derivativ e data . S o far , developin g an d applyin g tomograph y technique s b y usin g differen timag e media , suc h a s ultrasonic , nuclea rmagneti c resonance , y-ray/X-ray , electri c capacitance/resistance , ar e stil l currenttopic s i n flui d measurement . A s fo rultrasoni c tomography , Brow n (1996 ) develope d a laboratory devic e t

o identif

y the gas-soli d flow mod e i n apipe . Hi s experimental results indicate d tha tameasurementfrequency i n exces s o f 1 MH z an d particl e diamete rgreatertha n 1mm wer e necessary . Warsito e tal . (1999 ) an d Utom o e tal . (2001 ) als o use d thi s techniqu e fo rmeasurin g the time-average d cross-sectiona l distributio n o f ga s an d soli d holdup s i n aslurry bubbl e column . A doughnut-shape d macroscopi c flow schem e was observe d to representth e cross-sectiona l distribution s fo rthe ga s holdup . Particle s mainl y distribute d t o the centre o f

th e doughnuti n th e column . Correspondingly , Dyakowsk i e tal . (2000 ) overviewe d the principl e o f electrica l tomograph y method s an d thei rapplication s fo rinvestigating , monitorin g an d controllin g wetan d dr y granula rconveyin g systems . Usin g electrica l capacitanc e tomograph y (ECT) , Ra o (2001 ) investigate d instantaneous an d time-average d concentratio n distribution s o f larg e particle s ove ra pip e cross-sectio n unde rdifferen tflo w regimes . Eve n i n homogeneou s ai rflow , the contou ro f particl e concentratio n i s lik e astratifie d flow. In hi s experiments , polyethylen e particle s (mea n siz e 2.8m m wit h 112 3 kg/m 3density ) wer e transporte d i n a40.4m m PV C pip e b y conveyin g ai r a t28.6m/

s velocity . Lauren te tal . (2002 ) propose d adirec tapproac h to discriminatin g annula r from stratifie d flo w through analyzin g capacitanc e dat arathe rtha n processin g the image s recorde d b y ECT . It s genera

l ide afo rflo w pattern classificatio n relie d o n finding geometrica l propertie s i n aframe correspondin g t o aseto f

capacitanc e measurements . Azzopard i e tal . (2008 ) use d atwin-plan e EC T system t o monito rthe flow rat e o f pulverise d coa l (mas s media n diamete r 61pm ) transporte d b y ai ri n 36.8m m diamete rpipe . Th e experimenta l results indicate d tha tthere were tw o type s o f

systemati c fluctuations i n the time series o f mas s flo w rat

e an d concentratio n an d th e cross-sectiona l distributio n o f soli d showe d tha

tthe coa l was concentrate d aroun d th e pip e wall . Ther e ar

e als o many othe rpapers investigatin g th e influenc e o f factor s suc h a

s wal l

11 4



# VES01714 9A n investigatio n ofparticl e dynamic

s i n adilut

e phas e pneumati

c conveyin

g syste m roughness , pip e diamete ran d soli d mas s loadin g o n cross-sectiona l particl e concentratio n profiles , whic h ar

e summarize d b y Fokee re tal . (2005 ) an d Fuch s e tal . (2007 ) . Sinc e reconstructio n algorithm s use d fo rinvertin g ase to f measure d dat

ato map materia l distributio n insid e asenso r ar e agrou p o f

nonlinea requations , result s deduce d from linea rapproximation s t o the nonlinea r equation s woul d resul ti n pooraccuracy . A s wel l a

s tomographi c techniques , ther e are als o man y studie s o f gas-soli d pip e flow usin g digita l imagin g methods , whic h ca n b e applie d t o directl y extrac

tinformatio n lik e particl e diameter , particl e concentratio n an d thei rdistributio n from one o rserie s o f gas-soli d flow images . Amon g thes e studies , Hube re tal . (1994 ) introduce d alaser-ligh tshee ttechniqu e t

o measure particl e concentratio n distributio n ove rawhol e pip e cross-sectio n through analyzin g th e ligh t intensitie s scattered b y particle s o n image s take n b y CCD . Since the ligh tshee tintersecte d the pip e a t45 ° with respec tto th e pip e axis , the experimental datawere no tove rarightangle d cross-section . Kadamib i e tal . (1998 ) extende d th e Particl e Imagin g Velocimetr y (PIV ) techniqu e fo rparticl e diamete rmeasurementan d studie d th e Gaussia n distribute d intensit y variatio n acros s the dept h o f th e ligh tshee

tan d th e optical dept h o f field. Fo ragive n PI V ligh tshee tilluminatio n setup , th e poin tsprea d functio n o f the optica l syste m shoul d b e les s tha n 10 % o f th e image d particl e diameter . Additionally , i ti s essential to ensure an image d particl e occupie s a tleas t3 pixel s t o obtai n a n accurat

e siz e estimate . Similarly , Miyazak i etal . (1999 ) als o use d PI V t o study particl e motio n (glas s beads , 2.9~3.9mm ) i n gas-soli d spira l flo w i n ahorizonta l tub e an d L i e t al . (2000 ) investigate d particl e behaviou r(polyviny l chlorid e an d polyethylen e particle s with mean siz e 3.13m m an d 4.26m m respectively ) i n ahorizonta l dilute swirlin g pip e flow. Hi s experimental results indicat e thatth e particl e concentratio n profile s exhibi tsymmetri c distribution s with respectto th e pip e axi s an d ahighe rparticl e concentratio n appears nearth e wal l i n th e acceleratio n region . Morimot o e tal . (2003 ) propose d atuf tgri d metho d combine d with aimag e processin g techniqu e t o visualiz e th e characteristic s o f apneumati c type ultr afine powde rclassifier . Caicede o e tal . (2003 ) studie d bubbl e characteristic s a s functio n o f

th e gas velocit y i n arwo-diinensiona l fluidized be d b y usin g digita l imag e analysis . Cate re tal . (2005 ) introduce d ametho d o f usin g low-cos tCC D combine d with an electrostati c velocit y mete rt o measur e particl e diameter , siz e distributio n an d mas s flo w rat e i n adilute pneumati c conveyin g system . Th e features o f particle-wal l collisio n an d the bouncin g o f particl e durin g pneumati c conveyin g i n th

e dilut e phas e hav e bee n visuall y analyze d b y means o f digita l imag e technique s (Sommerfel d e

tal . 1999 ; Vasque z e tal . 2008) .
Accordin g t

o th e abov e discussions , i ti s clea rtha tonl y afe w studies hav e bee n dedicate d t o measurin g cross-sectional characteristic s o f th e soli d phas e i n gas-soli d pip e flow, especiall y

115



# VES01715 0Chapte r 6 Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e Ihere i s alac k

o f paper s describin g th e measuremen t o f particl e spatia l distributio n o f th e soli d phas e ove r

awhol e pip e cross-section . I n thi s chapter , avide o & imag e processin g metho dthat instantaneousl y measure s particl e diamete r an dparticl e concentratio n ove r ahorizonta l pip e cross-sectio n a s wel l a s th e characteristic s o f thei r time-average dvalue s b y usin g ahig h definitio ncamcorde r

an dapowerfu l haloge n ligh t box , i s introduced .

Figur e 6. 1 Sketche s o f experimenta l rig an d optica l arrangemen tfo rexperiments


### 6. 2 EXPERIMENTA L SETU P AN D FLO WCONDITION S Figur e 6. 1 sketche s th e experimenta l ri g i n whic hal l th e experiment s wer e performed . I h e pipelin e o f

th e apparatu s include s a4 mlon g horizonta l sectio n connecte dt o a2 mlon g vertica l pip e throug hahorizontal-to-vertica l elbow . On e T-typ e piec e wa s installe dt o connec t ascre w feede r wit hth e pipeline . I n orde r t o lesse n th e effec t o f electrostati c charging , al l pip e meta l connector s ar e earthed . Th e ai r flo w provide db y acentrifuga l fa n varie s fro m5~42m/s . Unde r th e conditio n o f

1 0 m/ s ai r conveyin g velocity , th e maximu mvalu e o f soli dloadin g rati o i s abou t 1.6 % fo r

glas s bead s (siz e withi n180~300um , densit y 255 0 kg/m 3 ) injecte db y th e scre w feeder . Th e measuremen t

11 6A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m regio n i s locate do n ahorizonta l pip e cross-sectio n 240m mupstrea mo f th e elbow' s inle t

o r 3.60 mdownstrea mfro mth e scre w feede r injectio n position . Whe n gas-soli dflo w passe s throug h thi s section , particle s ofth e soli dphas e ar e illuminate dusin g ashee t o f ligh t approximatel y 2m m thic k produce db y a500 w quart z haloge n lam p box . Th e ligh t ray s ar e arrange dt o b e perpendicula r

t o th e pip e axi s wit hth e shee t cuttin g acros s th e pipe . Particle s withi nth e ligh t shee t ar e image dusin g ahig hdefinitio n JV C GZ-IID 7 camcorder , whic hi s mounte do n atripo d t o focu s o n th e measuremen t regio n centre . Th e camcorde r axi s intersect s th e ligh t shee t at abou t a45 ° angle , whic hi s depicte di n th e su b diagra mo f Figur e 6.1 . Th e JV C GZ-HD 7 i s atapeles s camcorde r an dha s th e feature s o f 10 x optica l zoom , 1/ 5 inc h C C D sensor , optica l imag e stabilize r an d2. 7 inc hcolou r LC D It

ca n recor d2 5 hig hqualit y frame s (1920x108 0 pixels ) pe r second . It s shutte r

spee dvarie s fro m1/ 2 t o 1/4000 11 ' o f

asecon d an dth e apertur e fro mf/1. 8 t o f/8.0 . It ha s als o a60G B uni t har ddis k

whic hca n stor e five hour s vide o a t ful l hig hdefinition . Th e vide o i s store di n extende dMPEG- 2 transpor t strea mfiles, commonl y know n a s M2TS , whic hi s define da s aTO D file extensio n i n JV C GZ-HD7 . Here , MPE Gstand s fo r

Movin g Picture s Exper t Group , th e committe e o f industr y whic hcreate dth e standard . Transpor t

strea m(M2TS ) i s acommunicatio n protoco l fo r audio , vide o an ddat awhic h i s specifie di n MPEG-2 , an dwhic hmake s extensiv e us e o f motio n compensate dpredictio n t o eliminat e redundancy . Th e mos t significan t

extensio n o f

MPEG- 2 ove r

MPEG- 1 i s a n improvemen t

i n option s withi napictur e tha t ca n b e use dt o perfor mmotio n compensate d predictio n o f

interlace dsignals . MPEG- 1 treat s eac hpictur e a s acollectio n o f sample s fro mth e sam e momen t

i n tim e (know n a s frame-base dcoding) . MPEG- 2 ha s mode s i n whic hth e dat aca n eithe r b e predicate dusin g on e motio n vecto r t o giv e a n offse t

t o apreviou s fram e o r tw o vector s givin g offset s t o tw o differen t fields (Digita l T V Group , 2008) . Therefore , usin g JV C GZ-IID 7 wil l obtai n mor e ra w vide o dat awit hhig hspatia l resolution .
I nthi s study , fl. 8 apertur e an dl/250 s shutte r spee dwa s empiricall y selecte dfo r ou r experiments . Whe n particle s passe dthroug hth e expose darea , atwo-minut e vide o o f thei r behaviou r

wa s recorde dfo r

ever y flo w condition . Instantaneou s o r time-average dloca l informatio n o n particl e diamete r

an dparticl e concentratio n wa s extracte dfro mthes e videos . I n th e followin g sections , w e wil l discus s th e relate dvide o & imag e processin g algorithm s an dth e experimenta l results . 

### 6. 3 VIDE O & IMAG E PROCESSIN G SYSTE M Sinc e dat arat e i s on e o f th e ke y parameter s i n transmittin g aserie s o f hig hdefinitio n frames , th e forma t o f Movin g Pictur e Expert s Group-I I (MPEG2 ) i s implemente dt o cod e th e particl e video s i nth e JV C GZ-H 7 camcorder . Th e procedur e o f dat aprocessin g i n thi s stud y wil l b e divide dint o

11 7



# VES01715 2Chapte r o Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e tw o mai n routine s o f vide o decodin g processin g an dimag e processin g respectively , whic har e sketche di nFigur e 2 . Onc e th e experimenta l video s hav e bee n obtained , th e first ste p i s t o decod e (h e MPEG 2 video s int o Audi o Vide o Interfac e (AVI ) forma t (Clark e et

al . 1995) . A n AV I vide o consist s o f

serie s o f

uncompresse dbitma p frame s (BM Pimages ) i n whic hth e coordinat e o f a pixe l i s directl y matche dt o th e correspondin g poin t i n th e measuremen t region . The n an individua l fram e o r

severa l consecutiv e frame s i n avide o ca n b e extracte dfo r furthe r imag e processin g at

th e nex t

stage . 

### f

D«rco>3jn g mmit o J
wm p

padicl e fro misnagpe s Labellin g particle s b y numbe r 1 Statistica l processing 

# T

v Figur e 6.

2 Flo w char to f

vide o an d imag e processin g I n general , al l vide o & imag e algorithm s use di n thi s researc har e implemente dusin g



# VES01715 3A niiivcsiigalio no f panicl e dynamic s i n adilut e phas e pneumati c conveyin g syste m MATLAB7. 0 wit hImag e Processin g Toolbox , als o incorporatin g som e routine s describe di n Nixo n(2002) . I n th e procedur e o f processin g asingl e image , th e first ste p i s t o determin e th e boundar y o r

pip e wal l s o a s t o reduc e th e nois e cause db y th e dat aoutsid e th e pipe , sinc e th e measuremen t

regio n i s onl y on e par t o f aframe . The n muc ho f th e othe r

unwante dnois e ca n b e filteredb y subtractin g areferenc e image , whic hi s take n befor e injectin g particle s int o th e pipe . I n thi s way , onl y th e dat awithi nth e boundar y o r insid e th e pip e i s kep t an dth e res t

i s se t t o b e background . Accordin g t o Otsu' s metho d(1979) , th e greyscal e imag e converte dfro ma n origina l tru e colou r

fram e i s change dint o abinar y imag e b y implementin g Otsu' s operator . Thi s produce s abinar y imag e (whit e particl e region s o n ablac k background ) whic hcontain s particl e informatio n read y fo r sizin g an dcounting . I n orde r t o identif y ever y separat e particle , eac h regio n o f

whit e pixel s wil l b e labele dwit hadifferen t number . Th e numbe r o f pixel s containe di n eac hlabele dregio n i s equivalen t t o th e projecte dtrac k o f aparticle' s motio n i n th e measuremen t regio n ove r

l/250s . 

### 6.3. 1 Principle

of decoding

a MPEG-2

video

Figur e 6.

3 Thre e type s o f

picture s i n avide o strea m (re d colou rarro w mean s bidirectional ) Th e forma t

o f th e hig hdefinitio n vide o recorde db y JV C GZ-HD 7 conform s t o MPEG- 2 hig h profil e an di s store di n extende dMPEG- 2 transpor t strea mfiles. JV C provide s th e softwar e calle dCyberlin e PowerDirecto r 5 NE , whic hi s use dt o conver t transpor t

strea mfiles t o progra m strea mfiles i n standar dMPEG- 2 format , whic hca n b e replaye dan dedite db y usin g commo n algorithm s fo r

MPEG-2 . Thi s i s apopula r codin g an ddecodin g standar dfo r digita l compressio n o r decompressio n o f

audi o an dvide o signals . A MPEG- 2 vide o remove s bot hspatia l an d tempora l redundancie s b y usin g compressio n algorithm s base do n th e Discret e Cosin e Transfor m fo r motio n estimatio n an dcompensation . Ther e exis t thre e kind s o f

frame s i n aMPEG- 2 vide o strea m(a s show n i n Figur e 6.3) , whic har c Intra-code d(I) , Predicative-code d(P ) an d Bidirectionall y predicated-code d(B ) pictures . I-picture s ar e code dwithou t referenc e t o othe r pictures . Thi s i s periodicall y applie dt o provid e acces s point s wher e decodin g ca n begin . P-picture s represen t

th e differenc e betwee n th e curren t pictur e an dth e referenc e pictur e an dar e usuall y compresse dfo r reducin g vide o strea mredundancy . I n addition , B-picture s ca n us e th e previou s an dnex t

I

- o r P-picture s fo r

motion-compensation , an doffe r th e highes t

degre e o f compressio n (Tudor , 1995) .

11 9



# VES01715 4Chapte r 6 Visualb.atio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e

I n aMPKG- 2 video , it s strea mi s organize da s aGrou p o f Picture s (GOP ) whic har e composit e o f 1- . P

- an dB-pictures . A typica l l:P: B pictur e rati o i n aGO Pi s 1:3:8 , an datypica l displa y orde r o f GO Pis : B , B 2hB 4B 5 Pr , B 7 B 8P 9B, 0B u P, 2 wher e th e subscript s mea n position s i n th e origina l video . Th e encode r reorder s th e picture s int o th e followin g sequence :
I 3 B i B 2P ( lB 4 B 5 P 9 B 7 B g P1 2 Bh i B1 1 Unde r thi s configuration , i f th e decode r

encounter s aP-picture , it s motio n predictio n i s wit h respec t t o th e previousl y decode d1

- o r P-picture ; i f

th e decode r

encounter s aB-picture , it s motio n predictio n i s wit hrespec t t o th e previousl y tw o decode dI

- o r P-pictures .
I n a n encodin g process , eac hpictur e i n avide o strea mi s divide dint o 16x1 6 macrobiocks , whic h consis t o f a2x 2 arra y o f

block s (eac ho f

whic hcontain s a n 8x 8 arra y o f pixels) . Macrobiock s specif y colour s usin g aluminanc e channe l t o represen t saturatio n (colou r

intensity) , an dtw o chrominanc e channel s t o represen t hue . A red , gree n an dblu e (RGB ) signa l ca n b e equivalentl y expresse da s luminanc e (Y ) an dchrominanc e (UV ) components . Fo r astandar ddefinitio n video , MPEG- 2 stream s ar e encode di n th e commo n samplin g structur e o f 4:2:0 , whic hmean s a macrobloc k

usin g fou r

block s fo r

th e luminanc e channe l an don e bloc k fo r eac ho f

th e tw o chrominanc e channels . Eac ho f th e I- , P

- an dB-picture s ar e processe db y a2-dimensiona l Discret e Cosin e Transfor m(DCT) , whic hca n separat e apictur e int o part s wit hvaryin g visua l importance . Th e DC T coefficient s ar e quantize dt o reduc e th e numbe r o f bit s neede dt o represen t them . Th e run-lengt hencode r scan s th e DC T matri x i n azig-za g orde r t o consolidat e th e zero s i n th e matrix . Finally , th e outpu t o f th e run-lengt hencoder , motio n vecto r data , an dothe r information , ar e Huffma n code dt o furthe r reduc e th e averag e numbe r o f bit s pe r dat aitem . Th e compresse dstrea mi s sen t t o th e outpu t

devic e (Drak e e t

al . 2005) . Correspondingly , th e proces s o f decodin g aMPEG- 2 vide o i s essentiall y performe dusin g th e invers e encodin g process . Th e inpu t strea mi s Huffma n an drun-lengt hdecoded , resultin g i n quantize dDiscret e Cosin e Transfor m(DCT ) matrices . Fro mth e code dvide o stream , i t reconstruct s th e i-pictures . The n P

- an dB-picture s ar e reconstructe db y usin g th e correspondin g I-pictures , additiona l code ddat aan dmotio n vectors . A s aresult , eac hpixe l i n a n uncompresse d fram e i n adecode dMPEG- 2 vide o ha s aclea r relationshi p wit haspatia l position . Thes e uncompresse dframe s ca n b e extracte dfromth e AV I vide o fil e fo r furthe r imag e processing .

12 0



# VES01715 5A ninvestigatio n o f panicl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 

### 6.3. 2 Strategy

for processing

large volume

of uncompressed

frames

(AVI files) Wit hth e dramati c volum e expansio n o f uncompresse dframe s i n avide o file , technolog y i s neede dt o effectivel y extrac t o r brows e aspecifi c segmen t i n ashor t

time . Th e firs t

strateg y i s to eliminat e audi o infonnatio n fo r increasin g vide o rat e durin g decodin g aMPEG- 2 video . Th e secon dstrateg y performe di s t o cu t athirty-second s par t i n atwo-minut e vide o fo r eac hse t

o f flui dconditions , whic hi s carrie dou t durin g convertin g aJV C TO D fil e int o th e standar d MPEG- 2 video . Th e fil e siz e o f a30 s MPEG- 2 vide o i s usua l abou t 9 0 Mbytes . It s correspondin g decodin g file siz e i s abou t 90 0 Mbytes . Suc halarg e volum e uncompresse dfile woul dconsum e muc htim e i n bein g loade dint o compute r memor y an dbein g indexe db y fram e numbe r o r a specifi c tim e o r

interval . Th e thir dstrateg y i s t o spli t athirty-secon duncompresse dAV I file int o 3 0 su b files kep t

i n Matla b ma t

dat aformat , whic hwil l benefi t i n quickl y an dconvenientl y loadin g avide o dat afile fo r th e imagin g process . Eac hsub-fil e wil l onl y accommodat e on e secon dwort ho f

dat ao f 2 5 frame s accordin g t o th e JV C GZ-HD 7 recordin g rat e o f 2 5 frame s pe r second . Thus , w e wil l obtai n abou t 75 0 frame s wit hhig hdefinitio n (1920x102 0 pixels ) a t eac h measuremen t

sectio n withi n thirt y seconds . Frame(1 ) Framefi! )

Frame ®

Figur e 6.

4 Fou rspecifi c frame s i n an AV I vide o I nthes e experiments , al l measurement s wer e conducte di n th e ri g show n i n Figur e 6.1 . Glas s bead s withi n th e rang e 180-30 0 p m(manufacturer' s specification ) wer e conveye di n <|>75m m glas s pipe s b y a n ai r

superficia l velocit y o f lOm/s . Figur e 6. 4 show s fou r typica l frame s (5 l h , 10 1 ' 1 ,

12 1



# VES01715 6Chapte r 6 Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e 15 * an d20 n) i n aone-secon dvide o consistin g o f 2 5 frame s o n th e pip e cross-sectio n 3.7 0 m awa y fro mth e fee dposition . Al l fou r frame s clearl y displa y th e instantaneou s spatia l distributio n o f soli dphas e ove r

th e cross-section . Comparin g th e fou r frame s wit heac hother , w e clearl y observ e tha

t particl e numbe r

i s greate r

i n th e pip e lowe r

hal f tha n i n it s uppe r

half . Thi s i s th e gravit y settlin g phenomeno n i n horizonta l pipes . However , ther e ar e stil l som e particle s i n th e pip e uppe r

half , whic hindicate s tha t th e particle s ar e i n astat e o f dynami c suspensio n rathe r tha n irreversibl y depositin g o n th e pip e botto mafte r 3.70 m(whic hwoul dhappe n i f the y wer e simpl y settlin g unde r

gravity.) . Consequently , thes e picture s sho w th e heterogeneou s natur e o f soli d phas e flo w ove r

apip e cros s section . I n addition , th e tota l particl e numbe r i s als o observe dt o b e apparentl y differen t

fro mfram e t o frame . Thi s denote s th e unstead y characteristi c o f gas-soli d flo w i n tim e ove r

th e pip e section . Al l o f thes e qualitativel y demonstrat e th e heterogeneou s spatia l an dunstead y tempora l natur e o f gas-soli dpip e flo w i n adilut e pneumati c conveyin g system . I n th e nex t

section , w e wil l sho w th e extractio n o f quantativ e informatio n fro mthes e uncompresse dframes . 

### 6.3.3 Particle

diameter

and spatial position

measurement I nth e abov e section , w e hav e discusse dho w t o decod e aMPEG- 2 vide o an dobtai n th e correspondin g uncompresse dframe s whic har e hig hdefinitio n pixe l pictures . Eac hpixe l i n a fram e i s mappe dt o aspatia l positio n o n th e pip e cross-sectio n whic hi s illuminate db y th e ligh t sheet . Figur e 6. 4 show s fou r sampl e uncompresse dframe s i n a n AV I video . Befor e extractin g particl e informatio n fro mthes e pictures , i t woul db e bette r

t o manuall y determin e th e pip e inne r surfac e edg e whic hform s th e boundar y o f measuremen t

region . Wit hregar dt o th e cross-sectio n o neac hfram e o f

Figur e 6.5 , i t

i s clea r tha t th e whit e colou r

curve s whic har e highlighte db y th e ligh t shee t ar e th e pip e edges . Sinc e w e us e ahaloge n ligh t rathe r tha n alase r

ligh t source , ther e exist s asmal l divergen t angl e fo r

th e ligh t

sheet , whic hresult s i n tw o whit e curve dsegment s rathe r tha n on e continuou s ova l curv e encirclin g th e sectio n boundary . I n orde r t o eliminat e nois e fro moutsid e th e pipe , aboundar y templat e i s create dmanuall y throug hsettin g dat aa s zer o fo r eac hpixe l outsid e th e pip e an dsettin g dat aa s 1 fo r eac hpixe l insid e th e pipe . In thi s way , a n uncompresse dfram e lik e fram e (1 ) i n Figur e 6. 4 multiplie db y th e boundar y templat e result s i n th e pictur e a s show n i n Figur e 6.5 . Thu s th e measuremen t regio n o f

850x95 0 pixel s ca n b e separate dfro mth e entir e pictur e o f 1920x108 0 pixel s unde r th e curren t

optica l arrangemen t i n ou r experiments . Eac hfram e i n avide o wil l b e implemente db y alogi c AN D wit hth e boundar y templat e t o obtai n th e dat aonl y withi nth e measuremen t regio n box .

12 2



# VES01715 7A ninvcstigalio norpartici e dynamic s i n adilut e phas e pneumati c conveyin g syste m

Figur e 6.

5 Th e regio n o f

the pip e cross-sectio n o n afram e Wit hrespec t

t o th e su b imag e withi nth e measuremen t regio n i n Figur e 6.5 , i l i s atru e colou r pictur e whic hi s store di n MATLA B a s athre e dimensiona l arra y tha t define s re d(R) , gree n (G) , an dblu e (B ) colou r

component s fo r

eac hindividua l pixel . Th e colou r o f eac hpixe l i s determine d b y th e combinatio n o f th e red , gree n an dblu e intensitie s store di n eac hcolou r plan e a t th e pixel' s location . Observin g particl e image s i n Figur e 6.5 , w e ca n se e tha t particl e image s ar e muc h brighte r an dclos e t o white . I n contrast , th e colou r o f th e position s wit hn o particl e tend s toward s black . Therefore , i t i s convenien t

t o separat e particle s fro mth e backgroun di n th e pictur e accordin g t o thei r

luminanc e informatio n rathe r tha n thei r

colou r data . Th e matri x o f th e colou r pictur e i n RG B spac e wil l b e converte dint o th e spac e o f luminanc e (Y ) an din-phas e chrominanc e (I ) a s wel l a s quadrati c chrominanc e (Q ) b y usin g equalio n (6.1 ) (Bovi k Al , 2000) . 

## ~Y~ "0.29 9 0.58 7 0.11 4 

## ~R~ 

## I 

## = 0.59 6 -0.27 5 -0.32 1 

## G (6 . 0.21 2 -0.52 3 0.31 1 

## B I f al l th e component s o f th e I an dQ matrixe s ar e se t t o zer o whil e retainin g th e luminanc e matri x Y , th e tru e colou r

sub-imag e wil l b e converte dt o agreyscal e one . Figur e 6. 6 show s th e colou r sub-imag e ofth e measuremen t regio n an dit s correspondin g grayscal e pictur e converte db y usin g Equatio n (6.1) .

12 3



# VES01715 8ChaplL' r 6 Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e

(a ) colo r

imag e (b ) gra y imag e 

### Figur e 6. 6 Particl e image s o n th e pip e cross-sectio n Sinc e digita l image s ar e pron e t o avariet y o f type s o f

nois e du e t o electroni c transmissio n o r othe r processes , enhancemen t algorithm s lik e th e Wiene r filte r (Ur ne t

al . 1990 ) hav e bee n use d t o reduc e imag e nois e an dincreas e particl e contrast s i n th e pictur e fo r facilitatin g th e extractio n o f particl e information . Th e Wiene r filter i s a n adaptiv e filte r whic huse s apixelwis e adaptiv e metho dbase do n statistic s estimate dfro maloca l neighbourhoo do f eac hpixel . It s algorith mca n b e describe da s 1 M = NM

1 

### XX ("i'"2)~ v ~ (6.2 ) NM wher e r\ i s th e N-by- M loca l neighbourhoo do f eac hpixe l i n th e imag e A i n whic hai s on e element . Usin g th e estimate s o f equatio n (6.3) , apixelwis e Wiene r filte r ca n b e created . {n l 

### ,n 2 

### ) = fi+ -

o~ —v a' (a(n^n 2 

### )-/j ) (6.3 ) wher e v " i s th e nois e variance . It s valu e i s calculate dfro maveragin g al l th e loca l estimate d variance s i n aframe . Figur e 6. 7 (a ) show s th e result s o f th e gra y imag e i n Figur e 6.6(b ) denoise db y aWiene r filter.
Observin g th e ra w image s i n Figur e 6. 6 a s wel l a s th e denoise dimag e an dFigur e 6.7(a) , w e stil l notic e tha t

th e backgroun do f

eac himag e i s heterogeneou s an di s divide dint o athre e stripe d

12 4



# VES01715 9A ninvestigatio n ol " particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m region s wit hdifferen t brightness . O n th e lef t an drigh t

sid e o f th e images , th e brightnes s o f th e backgroun di s muc hhighe r tha n tha t

i n th e fiel dbetwee n tw o sides . Thi s result s fro mth e optica l arrangemen t

fo r th e measuremen t

syste mi n practice . Consequently , w e mus t reduc e th e effec t

o f a n inhomogeneou s backgroun do n convertin g agreyscal e imag e t o th e binar y one . I n othe r words , th e heterogeneou s backgroun dshoul db e separate dfro mth e particle s i n a n image , whic hca n b e realize db y usin g aMedia nFilte r (Li me t

al. , 1990) . Th e Media nFilte r i s anonlinea r

operatio n whic hi s mor e effectiv e tha n convolutio n fo r reducin g "sal t

an dpepper " nois e whil e preservin g edges . Sinc e fin e particle s ar e pneumaticall y transporte di n th e dilut e phase , thei r image s i n a pictur e ca n b e considere da s som e kin do f nois e lik e "sal t

an dpepper" . Whe n a n m-by- n Media nFilte r

i s performe do n a n imag e matri x i n tw o dimensions , eac houtpu t pixe l contain s th e media n valu e i n th e m-by- n neighborhoo daroun dth e correspondin g pixe l i n th e inpu t imag e (Nixo ne t

al. , 2002) . A s aresult , Figur e 6. 7 (b ) show s th e correspondin g resul t o f processin g th e denoise dimag e (Figur e 6. 7 (a) ) b y usin g a2 5 x 2 5 Media nFilter . Usin g thi s filter , w e hav e obtaine daseparate dbackgroun dthroug hremovin g particl e image s i n fh e denoise dpictur e o f Figur e 6.7(a) . I t

i s clea r tha t th e separate dbackgroun dimag e stil l keep s it s origina l features .

(a ) Th e denoise dimag e (b ) Th e separate dbackgroun d Figur e 6. 7 Denoisin g the imag e (a ) an d separatin g th e backgroun d (b ) Subsequently , whe n th e denoise dimag e o f Figur e 6. 7 (a ) ha s it s separate dbackgroun dimag e Figur e 6.7(b ) separated , th e subtractio n residu e i s show n i n Figur e 6. 8 (a ) i n which , whil e th e heterogeneou s backgroun dwa s removed , w e hav e obtaine dmos t o f particle s wit hsom e segment s ofth e pip e edg e o r

th e boundar y o f

th e cross-section . Sinc e th e nois e resultin g fro mshadow s an d

1 2 5Chapte r 6 Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e varian t illuminatio n i n Figur e 6. 7 (a ) ha s bee n eliminate dthroug hth e abov e subtractio n process , th e entir e imag e o f

Figur e 6. 8 (a ) ca n b e converte dfro magreyscal e imag e t o th e binar y on e b y usin g a n optima l thresholdin g process . Otsu' s metho d(Otsu , 1979 ) i s on e o f th e mos t

popula r technique s o f

optima l thresholdin g t o automaticall y perfor mhistogra mshape-base dimag e thresholdin g o r

reduc e agreyscal e imag e t o th e binar y one . Essentially , thi s techniqu e maximize s th e likelihoo dtha t

th e threshol di s selecte ds o a s t o separat e th e imag e betwee n a n objec t an dit s background . Thi s i s achieve db y choosin g athreshol dleve l tha t give s th e bes t

separatio n o f classes , fo r

al l pixel s i n a n image . Th e imag e t o b e thresholde di s assume dt o includ e tw o kind s o f pixel s whic har e classifie da s foregroun dan dbackgroun drespectively . The n i t calculate s th e optimu mthreshol dseparatin g thos e tw o classe s s o tha t thei r combine dsprea d(within-clas s variance ) i s minimal . Figur e 6. 8 (b ) show s th e correspondin g binar y imag e o f Figur e 6. 8 (a ) thresholde db y Otsu' s method . Comparin g Figur e 6. 8 (b ) wit hFigur e 6. 8 (a) , w e ca n se e tha t particl e image s ar e highlighte di n ahomogeneou s blac k background .

(a ) Eliminatin g th e backgroun d(b ) Th e binar y imag e Figur e 6.

8 Th e image wit

h its backgroun d subtracte d (a) an d it s binar y imag e (b) S o far , th e binar y imag e a s show n i n Figur e 6. 8 (b ) ha s bee n obtaine dan di s suitabl e fo r applyin g quantificatio n algorithm s t o extrac t essentia l particl e feature s suc ha s shape , siz e an dspatia l positions . Sinc e aparticl e take n b y CC D i s represente da s acollectio n o f brigh t pixel s i n a n image , i t

ca n b e classifie db y objec t descriptor s whic har e use dt o describ e th e propertie s o f th e grou p o f

pixel s formin g aparticl e image . Tw o objec t descriptor s o f

Regio n an dShape , whic h characteriz e th e arrangemen t o f pixel s withi nth e are aan dth e configuratio n o f pixel s i n th e

12 6



# VES01716 1A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g system perimete r

o r boundar y respectively , ar e use dt o describ e a n object . A regio n usuall y describe s interio r point s whic har e surrounde db y aboundar y o r perimete r

whic hi s als o ofte n calle dth e region' s contou r

o r shape . A shap e ca n b e trace db y quantifyin g th e relativ e positio n o f consecutiv e point s o n th e boundar y o f aregion . Thus , th e ke y poin t fo r tw o descriptor s lie s i n obtainin g particl e contou r o r shape .

(a) Particl e ra w imag e (b ) Connectivit y i n Chai nCode s ( c ) Particl e scale dimag e Referenc e point : star t (x , y ) Chai ncode s = {4,3,4,2,2,2,3,4,2,3,4,2,2,2,3,4,2,2,2,3,4,0,2,0,6,6,7,0,6,7,0,6,6,7,0,6,6,6,7,0,6,6,6,6,6 } Figur e 6.

9 Particl e sampl e chai n codes wit h 8-wa y connectivity template Th e metho dcalle dth e chai n cod e technique , whic hstore s th e relativ e co-ordinate s betwee n consecutiv e pixels , achieve s th e shap e o f aregio n b y analyzin g eac hpoin t o n th e boundar y i n sequenc e an dassignin g acod e t o denot e th e spatia l directio n betwee n tw o adjacen t points . Fo r 8-wa y connectivity , on e pixe l ha s eigh t possibl e relativ e relationship s wit hit s neighbors . Th e relationshi p templat e i s show n i n Figur e 6. 9 (b ) wher e eac hnumbe r o f 0- 7 i s encode da s on e o f th e majo r

compas s directions . Give nacomplet e borde r whic hi s equivalen t t o knowin g ase t

o f connecte dpoints , i f w e defin e th e firs t left-to p poin t

o f aparticl e a s th e star t positio n o r

th e referenc e point , th e chai n cod e ofth e particl e borde r i s forme db y concatenatin g th e numbe r tha t designate s th e directio n o f th e nex t

adjacen t

point s alon g a n anti-clockwis e direction . Tha t is , give n apixel , th e successiv e directio n fro mon e pixe l t o th e nex t pixe l become s a n elemen t i n th e fina l code . Thi s i s repeate dfo r eac hpoin t

unti l th e star t

poin t i s reache dagain , whe n th e shap e i s completel y analyzed . Fo r example , th e imag e o f aparticl e trac k

take n b y CC D i n Figur e 6. 9 (a) , whic hi s inverte dfro mFigur e 6. 8 (b) , i s enlarge dfo r visualizin g it s pixe l grou p a s show n i n Figur e 6. 9 (c) . Th e particle' s firs t pixe l (Po ) o n th e lef t to p positio n i s marke da s "start " whic h i s th e referenc e poin t o f encodin g th e particl e borde r chain . Accordin g t o th e 8-wa y connectivit y

12 7Chapte r 6 Visualizatio n particl e cross-sectiona i characteristic s i n ahorizonta l pip e 

### templat e show n i n Figur e 6. 9 (b) , th e directio n fro mth e star t poin t (P 0 

### ) t o th e nex t

(P| ) i s sout h (i.e . cod e 4 ) o n a n anti-clockwis e loop , s o th e firs t elemen t o f th e chai n cod e describin g th e shap e i s 2 . The n th e directio n fro mpoin t (P[ ) t o th e nex t

anti-clockwis e adjacen t poin t (P 2 

### ) i s southeas t

(cod e 3) , hithert o th e nex t elemen t

o f th e cod e i s 3 . Thi s codin g i s repeate dunti l th e 44 l h

### poin t

(P44) , whic hi s connecte dwestward s t o th e startin g poin t (Po) , s o th e las t

elemen t

(th e 4 5 t h

### clement ) o f

th e cod e i s 6 . Subsequently , th e tota l area , perimete r an dgeometri c centr e bounde db y th e Chai nCode s ca n b e deduced . I nFigur e 6. 9 (c) , th e grou p o f blac k pixel s form s th e are aofth e sampl e particl e trajector y withi n l/250 s (CC D shutte r

speed ) projecte do n th e pip e cross-section . I norde r t o simplif y th e questio n an davoi dmor e complicate dmorphologica l analysis , th e shap e o f aparticl e trajector y i s a n approximat e rectangl e whos e are a(S ) i s equa l t o th e produc t o f th e trajector y lengt h(L ) an d particl e diamete r

(D p 

### ) . I t

ca n b e define da s S = LxD p 

### (6.4 ) Fo r example , th e tota l are a(S ) ofth e particl e trajector y i n Figur e 6. 9 (c ) i s counte da s 7 8 squar e pixels . I f

th e coordinat e o f

th e star t

poin t i s assume da s (0 , 0 ) pixel , th e poin t at th e righ t

botto m o f particl e trajector y locate s a t (17 , 9 ) pixel . Thu s th e lengt ho f th e particl e trajector y i s figure d ou t b y equatio n (6.5 ) L= V (l7-0) 2 

### -(9-0) 2

### * 19.2 4 (6.5 ) Thus , th e particl e diamete r i s equa l t o

D



### - % = %.2 4 = 4

### < 6 

### ^ A n dth e coordinat e o f th e are alocate s at

(17-0 , 9-0)/ 2 = (9 , 5 ) relate dt o th e star t point . The n th e loca l concentratio n o f soli dphas e ca n b e calculate dtoo , whic hwil l b e introduce di n th e nex t sectio n fo r

applyin g th e abov e discusse dalgorithm s fo r extractin g particl e feature s o n awhol e pip e cross-section .


### 6. 4 RESULT S & DISCUSSIO N Th e experiment s wer e conducte dove r apip e cross-sectio n whic hwa s 240m mupstrea mo f th e elbo w inle t

o r th e 3.60 mdownstrea mo f th e particl e injectio n positio n i n th e ri g (show n i n Figur e 6.1) . Glas s bead s o f

siz e 180~300u man ddensit y 255 0 kg/m 3 

### (manufacturer' s specification ) wer e conveye di n <|>75m

mglas s pipe s b y a n ai r superficia l velocit y o f lOm/s . Fo r

eac hflui dcondition , w e actuall y recorde dtw o minute s vide o i n whic h30 s dat awer e cu t fo r particl e imag e analysis . Therefore , atota l numbe r o f 25x30=75 0 frames wil l b e use dfo r extractin g particl e information , accordin g t o th e sampl e rat e o f JV C GZ-HD 7 (2 5 frame s pe r second) . I n sectio n 6.3.2 , w e hav e

12 8



# VES01716 3A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m displaye dagrou p o f fou r sampl e frame s (5 t h , 10 t h , 15 11 ' an d20 t hframe ) i n Figur e 6.4 . Thes e fou r frame s wer e extracte dfro maone-secon dMPEG- 2 vide o whic hwa s als o on e thirtiet ho f th e vide o data . Observin g thes e fou r frames , w e ca n clearl y an ddirectl y se e som e qualitativ e feature s suc ha s gravit y settling , whic hresult s i n ahighe r particl e numbe r

densit y i n th e pip e lowe r hal f o f th e pip e an damor e dilut e suspensio n i n th e uppe r half . Moreover , particle s ar e distribute dove r th e whol e pip e sectio n rathe r tha n onl y i n th e pip e bottom , whic hindicate s tha t th e particle s ar e i nastat e o f

dynami c suspensio n rathe r tha n irreversibl y depositin g o n th e pip e botto mdu e t o gravit y settlin g afte r runnin g a3.7 5 mdistanc e fro mth e particl e fee dpositio n (whic hwoul d happe n i f

th e particle s wer e simpl y settlin g unde r gravity) . O n th e othe r hand , th e tota l numbe r o f particle s differ s fro mfram e t o fram e an dth e shap e o f th e particl e spatia l distributio n ove r a whol e sectio n i s als o different . Thes e kind s o f variatio n o f

particl e distributio n demonstrat e th e heterogeneou s an dunstead y characteristic s o f gas-soli dpip e flo w i n adilut e pneumati c conveyin g system .

5 0 ¥ 4 0

_ Q £ >- . > 2 0 Q C 0 3 £1 0 < D i t
0

6 0 Mea ndiamete r b y numbe r

(pm ) 16 9 17 6 20 6 19 3

0-10 0 

# I B i

100-15 0 

# I 1 11 1

150-20 0 200-25 0 250-30 0 300-35 0 D p ( u m )

| 4 0
2 0 Mea ndiamete r b y mas s (pm ) 28 5 27 9 28 8 28 3 

# I I 

# . 0-10 0 100-15 0 150-20 0 

# I 200-25 0 

# I I

250-30 0 300-35 0 D p (pm ) Figur e 6.1 0 Particl e diamete rfrequencie s b y numbe ran d b y mass o n fou rexampl e frame s Wit hregar dt o particl e quantitativ e propertie s ove r th e whol e cross-section . Figur e 6.1 0 show s th e measure ddiamete r distributio n (th e normalize dparticl e numbe r vs . particl e diamete r an dth e normalize dparticl e mas s vs . particl e diameter ) i n th e fou r frame s (5 l h , 10* , 15 l han d20 l h ) a s show n i n Figur e 6.4 . Thes e result s hav e bee n analyze db y usin g th e algorithm s o f vide o & imag e

12 9



# VES01716 4Otaple r 6 Visualizatio nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e processin g discusse di n th e previou s sections . O n th e whole , w e ca n observ e tha t th e shap e o f

th e particl e diamete r

distributio n curv e i s approximatel y conserve dove r th e fou r

exampl e frames , an dclos e t o th e specifie dparticl e distribution . Bu t th e frequency' s absolut e valu e a t ever y siz e bi nvarie s ove r

th e fou r

frames . Thi s denote s th e instantaneou s unstead y characteristi c o f gas-soli dpip e flo w at ever y moment . Fro mparticl e diamete r distributio n b y number , i t i s clea r tha t particl e diamete r

i s mainl y concentrate dwithi ntw o interval s o f les s tha n lOOu man d 175~200pm . Thei r

numbe r

fraction s ar e mor e tha n 20 % an dth e numbe r fractions i n th e othe r siz e interval s ar e les s tha n 10% . I n addition , th e mea n particl e diamete r b y numbe r

o n eac hfram e i s differen t

withi nastandar ddeviatio n o f 16.8p mfro mth e se t o f particl e mea n siz e b y numbe r (169 , 176 , 206 , 193 ) pm . O n th e contrary , ther e ar e thre e group s o f particle s whos e mas s fraction s ar e mor e tha n 10% , a s show n i n Figur e 6.10 . Comparin g thes e tw o diagrams , w e ca n se e tha t tin e particle s les s tha n lOOu monl y occup y asmal l mas s fractio n les s tha n 5% , althoug h thei r quantit y i n term s o f particl e numbe r

i s mor e tha n 20% . Considerin g particl e mea n siz e b y mas s o n eac hframe , it s measure dse t o f (285 , 279 , 288 , 282 ) ja mshow s anarro w variation , sinc e th e standar ddeviatio n o f th e se t i s onl y 3.9p mcompare dwit htha t b y particl e number . I t denote s a n invarianc e o f

particl e mea n siz e b y mass .

Th e variation s o

f tw o kind s o f

mean siz e i n asecon d 30 0 . ,

„ typ e mea n st drang e . n , Jmhp r | 25 0 +213. 1 14. 8 67. 8 by numbe r

o 279. 5 6. 8 33. 5 by mas s

20 0

15 0 1 ' 0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0 90 0 1000 tim e (ms ) Figur e 6.1 1 Th e variation s ofparticl e numbe rmea n size an d particl e mass mean size ove rI s I n orde r t o investigat e th e tempora l variation s o f particl e mea n siz e b y numbe r an dparticl e mea n siz e b y mass , thei r tempora l variation s withi non e secon dar e plotte di n Figur e 6.11 . A time-average dvalu e i s calculate db y averagin g th e correspondin g dat ao n al l frame s i n th e

13 0



# VES01716 5A ninvestigatio n o f panicl e dynamic s i n adilut e phas e pneumati c conveyin g syste m specifi c interval . Obviously , th e evolutio n o f particl e mea n siz e b y mas s (th e re dcurve ) varie s narrowl y wit hamea n valu e o f 279.5p man dastandar dvarianc e 6.8p mwithi navariatio n rang e o f 33.5pm . Correspondingly , th e evolutio n o f particl e mea n siz e b y numbe r (th e blu e curve ) varie s widel y wit hamea n valu e o f 213.1p man dastandar dvarianc e 14.8p mwithi narang e o f 67.8pm . Thi s i s simila r t o th e resul t

show n i n Figur e 6.10 . Therefore , th e paramete r o f particl e mas s mea n size , rathe r tha n particl e numbe r mea n size , i s statisticall y mor e consisten t t o describ e th e stead y characteristic s o f particl e diamete r

i n unstead y gas-soli dflow , sinc e large r particle s hav e large r

weigh t factor s tha n smalle r one s whe n th e mea n mas s flo w rat e i s calculate dove r a pip e cross-section . Usin g particl e mea n siz e b y mas s rathe r tha n particl e mea n siz e b y numbe r i s mor e suitabl e t o describ e th e statistica l propertie s o f unstead y gas-soli dflo w ove r across-section . Fo r thi s reason , th e followin g result s wil l focu s o n th e time-average dpropert y o f particl e concentratio n an dparticl e accumulatio n numbe r (define da s th e tota l numbe r o f particle s counte d i na n interval ) a s wel l a s thei r cross-sectiona l distributions . Figur e 6.1 2 show s tw o kind s o f cross-sectiona l distribution s o f particl e accumulatio n numbe r an d th e normalize dvalue s o f particl e time-average dconcentratio n ove r th e measuremen t

sectio n a

t I s an d30 s separately , whic har e totall y counte do r time-average dfro mth e correspondin g 2 5 frame s an d75 0 frame s respectively . I n general , al l o f th e fou r

diagram s i n Figur e 6.1 2 no t onl y clearl y displa y th e phenomeno n o f gravit y settin g bu t

als o sho w astratifie dflo w patter n layere db y particl e numbe r

o r particl e concentratio n ove r th e cros s section . Bu t th e contour s ove r

30 s sho w a relativel y clea r

an dunifor mstratificatio n structure , compare dwit htha t ove r 1 s , especiall y fo r

th e diagra mo f

particl e concentratio n distribution . Thi s mean s tha t th e distributio n o f

particl e numbe r o r particl e concentratio n require s th e averagin g o f mor e frame s t o produc e goo dqualit y statistica l features .
I n compariso n o f

Figur e 6.1 2 an dFigur e 6.13 , whic hi s th e contou r o f th e dimensionles s particl e numbe r rat e at th e sectio n 3 D selecte dfro mFigur e 5.12 , bot ho f the mdemonstrat e asimila r cross-sectiona l flo w patter n resemblin g astratificatio n structur e fo r th e spatia l distribution s o f particl e numbe r

an dparticl e concentratio n ove r th e cross-sectio n i n ahorizonta l dilut e gas-soli d pip e flow . However , iso-line s i n th e tw o figure s hav e differen t value s an dma y b e locate di n differen t

positions , especiall y i n th e regio n clos e t o th e pip e to p wal l wher e th e experimenta l dat a obtaine db y LD Astil l sho w th e dimensionles s {N/ln(Z(N) ) wit halarge r value .

13 1Chaple r 6 Visiinli'/atui nparticl e cross-sectiona l characteristic s i n ahorizonta l pip e

u.i l I'.'j.imt mI. iIh. i i tn.li

t numhi'i (ln| Ni.N) r

i ni s Natura

l logarith ma. Ui qdirnsncirjnlcs

s particl e numbe r {ln(N/;;N) } i n3D s

, # • - l• - s X

. 1 * f . 0. 2 • & S o

(a ) Contour s o f

th e dimensionles s particl e numbe r ove r Is an d30 s UipiJimonsionlos

s particl e ^o n centr atio n'>"( C Ihedimenslonles Eparticl o conconl/aJo

n | C l±(C ) ) (% | ovti r 30 s

(b ) Contour s o f

th e dimensionles s particl e concentratio n {Cp/sumfC^) ) ove r I s an d30 s Figur e 6.1 2 Cross-sectiona l distribution s o f th e dimensionles s particl e countin g numbe ran d th e dimensionles s particl e concentratio n ( N i s th e particl e countin g number ; Ri s th e pip e radius ; {C,, } i s th e loca l concentratio n o f soli d phase ) Natura l logarith mo f th e dimensionles

s particl e numbe r rat e {InlN/^N) }

-4 D -3 0 -2 0 -1 0 0 1 0 2 0 3 0 4 0 z|mm ) e \ X=-9 , -8
. -7 . -6 , -5,- 4 Section s Tota l {N } (*10 f ) n x 10" 4 ,n=2.4 , 10.25,68,18- 3 3 D 0 8 0 . • J. j 

# I

Figur e 6.1 3 Th e contdu ro f |ln(>J/Z(N) } o n th e sectio n 3 D measure d b y LD A (selecte d fro m Figur e 5.12 )

13 2



# VES01716 7A n investigatio n o f particl e dynamic

s i n adilut e phas e pneumati

c conveying syste

m 

# 6. 5 SUMMAR

YAN D CONCLUSION S I n thi s chapter , w e develope d avide o & imag e processin g syste m fo rmeasurin g particl e diamete r an d analyzin g th

e spatial characteristic s o f particle s ove rahorizonta l pip e cross-sectio n i n a dilute pneumati c conveyin g system . A ligh tshee tproduce d b y ahaloge n lam p bo x was use d t o illuminat e an d cutaslic e o f gas-soli d flo w ove rapip e cross-section . The n w e use d ahig h definitio n camcorde rt o recor d th e particles ' behaviou rove rth e highlighte d region . A seto f vide o algorithm s ha

s bee n develope d t

o decod e the compresse d MPEG- 2 video s into th e AV I forma tfo r furthe rimag e processing . A n AV I video , lik e adatabase , consists o f aserie s o f

uncompresse d frames . Eac h pixe l o n each uncompresse d fram e i s directl y mappe d t o aspatial poin ti n th e measurementregion . Subsequently , th e siz e an d locatio n o f eac h particl e ca n b e extracte d from ever y frame b y usin g ou rdevelope d imag e algorithms . A s fo rimag e processing , firstly, eac h colou rframe whic h i s extracte d fro m an uncompresse d AV I vide o wil l b e converte d int o th e correspondin g grey pictur e accordin g particle s luminanc e information ; Second , itwil l b e denoise d b y Wiene rfilter ; Th e thir d step i s tha tabackgroun d imag e wil l b e obtaine d throug h removin g particl e image s i n the denoise d pictur e b y usin g a25 x 25 Media n Filter . I

n thi s way , th e featur e o f backgroun d environmen tca n b e kept . Subsequently , whe n the separated backgroun d imag e i s subtracte d from denoise d image , th e heterogeneou s backgroun d wil l b e abl e t o b e removed . The n thi s grey imag e i s to b e converte d into abinar y imag e b y usin g Otsu' s method . Finally , the feature s o f ever y particl e suc h a s shape , siz e an d spatia l position ca n b e extracte d b y applyin g th e Chai n Cod e Technique , whic h store s th e relativ e co-ordinate s between consecutiv e pixels , achieve s th e shap e o f aregio n b y analyzin g eac h poin t o n th e boundary i n sequence an d assign s acod e to denote the spatial directio n betwee n tw o adjacentpoints . The n particl e diamete rdistributio n an d mea n siz e ove rasectio n ca n b e calculate d from the se to f Chai n Code .
Th e experimental result s o f particl e diamete ran d siz e distributio n o n each frame sugges ttha t gas-soli d pip e flo w i s alway s heterogeneou s i n spac e an d unstead y i n time . Accordin g t o thei r fluctuation s i n tempora l space , usin g particl e mea n siz e b y mas s i s mor e suitabl e t o statisticall y describ e the unsteady propertie s o f gas-soli d pip e flow . O n th e othe rhand , bot h the contour s o f particl e accumulatio n numbe ran d particl e time-average d concentratio n exhibi taflow pattern resemblin g astratifie d structure ove rahorizonta l pip e cross-sectio n i n gas-soli d flow. Thi s kin d o f stratifie d structur

e i s simila rt

o th e result

s explore d b y th e experimental dat ao f Lase rDopple r Anemometr y i n Chapte r5 . Bu tiso-line s may hav e differen tvalue s an d b e locate d i n differen t positions .

13 3Chapte r6 - Visualizatio n particl e cross-sectional characteristic s i n ahorizontal pip e Needles s t o say , th e curren tdevelope d vide o & imag e processin g syste m ca n b e use d to measur e th e siz e an d spatia l distributio n o f particle s mor e tha n 80u m ove rawhol e cross-sectio n i n <t>75m m pipe . Thus , thi s visualizatio n syste m wil l b e suitabl e fo rfin e particle s measuremen tb y usin g asmalle rsiz e o f pipelin e fo rexperiments . I n addition , usin g coloure d granula rmaterials , thi s syste m ca n b e develope d int o ameasuremen ttoo l fo r gas-soli d pip e flo w wit h amulti-componen tsoli d phas e b y addin g th e functio n o f discernin g particl e colour .

134



# VES01716 9

# Chapte r 7 CF D Investigatio n o f Cross-sectiona l Flo wPattern s o f Soli d phas e i n Gas-Soli d Granula r Pip e Flo w

This chapterpresents numerical predictions of

flow patterns on cross-sections along a horizontal

pipe using the Discrete Phase Model (DPM) of

Fluent 6.3.26 as well

as the latter coupled with the Discrete Element Method

(DEM) software of EDEM 1.3.1. The simulations are compared

to experimental

measurements on glass beads (size 70-110pm, solid loading ratio 1.6%) transported by 12m/sairin $75mm glass pipes. Using LaserDopplerAnemometry (LDA), the measured

contours of

the horizontal

particle velocity component show an annular structure overthe pipe cross-sections; this flow pattern can also be described as stratified flow overcross-sections, layered by particle numberdistribution. The comparisons of numerical

and experimental

cross-sectional

flow patterns of solid phase show that

there is reasonable agreement at pipe cross-sections located at horizontal

positions less than half the product of particle mean velocity and mean free fall

time in the pipe from the particle inlet. Furtheraway from the inlet, the numerical results show flow patterns which are increasingly divergent from the experimental results along the pipe in the direction of flow. This discrepancy indicates that particles'spatial

distribution in a pipe is not accurately predicted

by DPM orFluent

coupled

with DEM. Moreover, it is necessary to validate and develop numerical

models by using the latest experimental

data.



## 7.1 INTRODUCTION In Chapte r2 , the effect s o f som e macr o parameters lik e th e Saffma n forc e an d Stoke s numbe ro n pneumati c transportatio n hav e bee n investigate d usin g th e Discret e Phas e Mode l (DPM ) i n Fluen t6.2.16 . I n Chapters 4-6 , w e presente d experimental results o f soli d phas e distribution s ove raseries o f

cross-section s i n the horizonta l pip e b y usin g a n extende d Lase rDopple rA n investigatio n o f particl e dynamic s i n adilute phase pneumati c conveyin g syste m Anemometr y (LDA ) techniqu e an d developin g avisualizatio n syste m involvin g vide o recordin g an d Image processing . Thes e experimenta l result s displa y two cross-sectiona l flo w patterns ofth e soli d phase , resemblin g an annula rstructure an d stratificatio n i n ahorizonta l pipe . Th e annula r structur e represent

s th e contou ro f

particl e velocit y an d the stratifie d imag e represent s the contou r o f particl e numbe rrat

e ove rapip e cross-section . Thes e experimenta l dat aprovid e agoo d too l t o validate the availability an d limitations o f th e currentnumerica l model s fo rpneumati c conveyin g research . Generally , flo w regime s fo rhorizonta l conveyin g o f granula rmaterial s ca n b e classifie d into dilut e suspensio n flow, stratifie d flow , sedimentatio n dune flow, plu g flo w an d movin g be d flow (FAN , 1998) . Thes e flow regime s ar e usuall y observe d alon g th e pip e axi s an d eac h i s a qualitativ e ter

m depictin g th e macro-state o f gas-soli d flow . S o far , research int o soli d phas e distributio n ove rapip e cross-sectio n i s stil l scarce . Mos t numerica l an d experimental studie s onl y sho w one-dimensiona l loca l informatio n o n th e soli d phas e alon g alin e ratherthan two-dimensiona l dat aove rawhol e cros s section . Amon g thes e studies , the experimental wor ko f Tsju i (1983) , use d Lase rDopple rVelocimetr y t o measur e the velocit y o f

mixe d plasti c particles , siz e 200p m an d 3.2mm , density 1000kg/m 3 ; conveye d b y ai r o f velocity 6,1 0 an d 15m/ s i n a30.5m m diamete rhorizonta l glas s pipe . Th e vertica l profil e o f the normalize d axia l particl e velocit y becam e flattened wit h increasin g particl e siz e o rsoli d loadin g ratio , an d th

e profil e pea kwas shifte d upward s abov e the pip e centre line . Thi s i s als o confirme d b y Huber' s (1994 ) experimental dat a(glas s particl e siz e 40pm ; ai rvelocit y 2 1 m/ s an d (|)80m

m glas s pipe) . Hube rno tonl y use d Phas e Dopple rAnemometr y (PDA ) t o measure th e particl e velocity profile , bu tals o applie d th e light-shee tmetho d to measur e particl e concentratio n ove r the pip e cross-sectio n throug h analyzin g th e ligh tdensitie s scattere d b y particle s i n image s take n b y CCD . Th e contours o f particl e concentratio n ove rpip e cross-section s clearl y displa y a n annula rstructure , butthei rcor e region s wer e locate d i n th e lowe rhal f o f th e pip e du e t

o gravitational settling . Usin g Electrica l Capacitanc e Tomograph y (ECT) , Ra o (2001 ) measure d soli d phas e concentration s ove rawhol e pip e cross-sectio n i n variou s flow regimes . Th e experimental syste m wa s ar{)40.4m m PV C pip e i n whic h ai ra tsuperficia l velocit y 10. 4 ~28.6m/

s transported three larg e particl e types , whic h wer e titaniu m dioxid e (3.01mm , 1683kg/m 3 ) , brow n mustar d (1.76mm , 879kg/m 3 ) an d polypropylen e (2.8mm , 112 3 kg/m 3 ) . In the homogeneou s flo w regime , th e contou ro f time-average d particl e concentratio n (polypropylene , ai rvelocit y 28.6m/s ) showe d astratifie d structure ove rthe cross-section .
Du e t o the complexity o f gas-soli d pip e flow , particl e transportatio n i s stil l an are ao f kee n interes ti n computational fluid dynamic s studies . Mos tnumerica l simulation s i n thi s field hav e

13 6


# VES01717 1Chapte r7 CF D investigatio n o f cross-sectiona l flow pattern o f soli d phas e i n ahorizonta l pip e bee n performe d usin g the Euler/Lagrang e approach , whic h has bee n develope d into the standar d Discret e Phas e Mode l (DPM ) i n the commercia l Computationa l Flui d Dynamic s (CFD ) software packag e FLUENT . Amon g numerica l studie s o f soli d phas e spatial distributio n i n horizonta l pipes , Huber' s (1998 ) numerica l results sho w tha t40p m glas s particle s hav e agoo d ability t o follo w the flui d i n ai ro f 24m/ s superficia l velocit y i n a<J>80m m smoot

h glas s pip e an d tha tthei r trajectories ar

e distribute d ove rth e whol e pip e space . Further , Sommerfel d (2003 ) investigate d the effec to f

wal l roughnes s o n trajectorie s o f 30~700p m particle s transporte d b y 18m/ s ai ri n a 2 D channe l wit h 6 m length an d 35m m height . Th e calculate d trajectorie s o f 110p m particle s withou tconsiderin g th e effec to f wal l roughnes s indicate d tha tal l o f the m wer e concentrate d i n the channel botto m regio n afte r3 m forwar d progress , althoug h they wer e homogenousl y injecte d a tth e inlet . Althoug h there ar e som e papers o n th e stud y o f

soli d phas e distributio n ove r cross-section s o f

pip e bend s an d vertica l pip e runs , thei rresults ar e no tdiscusse d here sinc e it wa s decide d tha

thorizonta l pipe s provid e th e bes ttesto f the prediction s ofth e tw o methods .
I n th e followin g sections , th e numerica l model s an d the correspondin g parameters wil l b e introduce d firstly. The n th e experimenta l data , whic h hav e bee n measure d b y the extende d techniqu e o f

Lase rDopple rAnemometry , wil l b e summarized . Th e experimenta l results includ e contours o f

particl e velocit y an d particl e numbe rrat e o n aseries o f

horizonta l pip e cross-sections . Basin g th

e inle tcondition o f

numerica l simulation s o n the actual experimenta l data , theoretical prediction s o f

flo w patterns o n pip e cross-section s hav e bee n explore d b y usin g th e DP M optio n o f Fluen tan d Fluen tcouple d wit h EDE M respectively . The n w e discus s the limitation s o f current numerica l model s throug h analyzin g th e discrepanc y betwee n numerica l results an d the correspondin g experimental data . 

## 7.2 NUMERICALMODELS AND THEIR PARAMETERS 7.2.1 Mathematical

models In dilute pneumati c conveying , th e force s actin g o n particle s ma y b e classifie d into thre e groups : (1 ) force s du e t

o th e interfac e betwee n flui d an d particles , (2) force s du e to th e interaction s between particle s an d collision s o f particle s wit h the wall , an d (3) , force s impose d b y externa l field s such a

s gravity (Fan , 1998) . Th e force s i n the firs tgrou p normall y are th e dra g force , the Saffma n lif

tforce , th e thermophoreti c force , th e Magnu s force , th e Brownia n Forc e an d aforc e relate d t

o th e pressur e gradient . Th e force s i n the secon d grou p ar e accounte d fo ri n the particle-wal l collisio n mode l an d particle-particl e interactio n models . In th e standard DP M o f Fluent , whic h ha

s bee n introduce d i n Chapte r2 , the standard particl e motio n equatio n doe s no t includ e item s correspondin g to the Magnu s forc e an d th e forc e relate d to th e pressur e gradient . I t als o ignore s particle-particl e interaction s so a s t o reduc e th e expens e o f computation . Th e

13 7


# VES01717 2A n investigatio n o f particl e dynamic s i n adilute phas e pneumati c conveyin g syste m concep to f

parcels , whic h represent s agrou p o f

particle s with the same propertie s such a s particl e size , density an d injectio n position , i s introduce d i n DPM . Thus , DP M i n Fluen ti s modelle d t o trackaseto f

parcel s o rparticl e stream rathe rthan each individua l particl e i n th e domain . A n alternativ e approach differen tfrom DP M ha s bee n introduce d t

o develo p two-flui d continuu m model s tha

tconside rthe ga

s an d soli d phase s a s two interpenetratin g continua . The n th e mechanica l behaviou ro f the soli d phas e i s describe d b y th e discrete elemen tmetho d (DEM ) an d ai rphas e flo w structur e i s solve d usin g the traditiona l CF D method . Basically , thi s approach i s a couple d DEM-CF D calculation . In th e couple d DEM-CF D calculations , conservatio n equation s fo rth e soli d phas e ar

e n o longe rrequire d i n CF D calculation s usin g th e commercia l softwar e Fluent . Th e DE M mode l directl y calculate s th e soli d phas e terms i n th e ai rphas e equations , such a s th e momentu m exchang e coefficien tbetwee n the phases an d the mea n soli d phas e velocity . Trackin g the motio n o f individua l particle s allow s aprecis e calculatio n o f ho w th e soli d volum e associate d with thes e particle s change s wit h time .
I n ordert

o investigate th

e actual particle-particl e influences , Crappe re tal . (2005 ) use d acouple d simulatio n usin g DE M togethe rwit h FLUEN T t o study particl e characteristic s i n elbow s o f a dilute pneumati c conveyin g system , sinc e ther e exis ti n bends man y stron g particl e interactions . Similarly , Y u etal . (2005 ) als o use d the discrete elementmetho d couple d wit h computational fluid dynamic s t

o study the pneumati c transporto f polypropylen e bead s (maximu m numbe r2000 , diamete r2.8mm ) i n bot h vertica l an d horizonta l one metr e lon g pipes . Thei rnumerica l result s onl y focuse d o n soli d phas e flow alon g the pip e axi s unde rdifferen toperatin g conditions . Severa l research worker s hav e applie d th e metho d o f

combinin g DE M wit h CF D t o simulate plu g flow an d fluidize d bed s (Tsuj i etal . 1992 ; Tsuj i e tal . 1993 ; Rhode s e tal . 2001) . Here , w e us e the commercia l DE M softwar e calle d EDE M whic h was develope d b y DE M Solution s Limite d o f Edinburgh . I

tca n b e directl y couple d wit h Fluen tfo rth e simulatio n an d analysi s o f granular material handlin g an d manufacturin g operation s (Dem-solutions , 2008) . Sinc e both DP M an d DE M hav e bee n develope d t o b e standard model s i n commercia l software , th e detaile d equation s governin g th e phas e dynamic s wil l notb e replicate d here . W e onl y focu s o n selectin g the suitabl e mode l parameters . Tabl e 7. 1 an d 7. 2 lis tal l the numerica l parameter s use d her e fo rDP M an d DEM-Fluen tsimulation s respectively .

13 8


# VES01717 3Chapte r7 CF D investigatio n o f cross-sectional flow patter n o f soli d phas e i n ahorizonta l pip e Tabl e 7. 1 Numerica l parameter s forDP M simulation s Typ e Choice s Solve r •v * Segregate

d solve rwith 2"' < - Space : 3 D Unsteady simulatio n < - Tim e step : lxl0" 3 s orderdiscret e scheme

Turbulenc e model(k- e Model )

Discrete phase optio n

Gravity Wal l collisio n mode

l Mode l Constants : C m u=0.084 5 C , = 1.42C 2 =1.6 8 RN G options : Differentia l viscosit y mode l Near-wal l treatment : standar d wal l function s Interaction wit

h continuous phase Updat e DP M sources ever

y 2 5 flui d phase iterations Saffman lif

tforc e Two-wa y turbulenc

e couplin g Developin g user-defined-function s (UDF ) t o control particl e numbera

teac h positio n a

teach injectio n momen t A tota l o f 104 7 injectio n point

s whic h produce 5326 7 parcel s withi n asecond . th e negativ

e directio n o f

y axi s Value : 9.8 1 m/s 2 Elasti c collisio n mode l Restitution coefficients o f normal and tangentia l directions ar e 1 Smoot h pip e Tabl e 7.2 Numerica l parameter s fo rDEM-Fiuen tcalculation s Typ e Value s Fluen t Solve r Segregate d solve rwit

h 2 n dorderdiscret

e schem e Space : 3 D Unsteady simulatio n Tim e step : lxl0" 3 s Turbulenc e model(k

- 8 Model ) Mode l Constants : C m u=0.0845 , C , = 1.42 , C 2 =1.6 8 RN G options : Differentia l viscosity mode l Near-wal l treatment : standar d wal l function s Ful l buoyancy effect

s Gravit y th e negative directio n ofth e y axis , Value : 9.8 1 m/s 2 EDE M Particle s materia l

Particl e mea n siz e Numbe ro f

particle s Poisson' s rati o Restitutio n coefficien t Particl e factor y (particl e injectio n position ) Spherical glass bead s 90u m 5326 7 withi n asecond 0. 4 1 212 Tim e ste p Shea rmodulu s (Pa ) lxl0" 6 s 2.6x10 s

139


# VES01717 4A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 

### 7.2.2 Experimental

rig and numerical

geometry Figur e 7. 1 show s th e experimenta l ri g an dth e thre e meshe dsection s whic hschematicall y displa y th e numerica l domain . Th e domai n i s th e l mlon g horizonta l glas s pip e (((>75mm ) 90m m upstrea mo f

th e elbo w i n orde r t o compar e th e numerica l result s wit hth e experimenta l dat a withou t th e elbo w effec t

o n th e upstrea mfluid . I t ha s bee n meshe dint o 7640 0 triangula r cell s wit haboundar y laye r o f 5 cell s thickness . Gri dindependenc e ha s bee n confirme db y singl e ai r phas e flo w calculations .

Figur e 7. 1 Experimenta l ri g an d schemati c diagra m o f numerica l geometry 

### 7.2.3 Fluid conditions

at inlet Th e initia l condition s a t th e inle t

fo r numerica l simulation s ar e generate dfollowin g th e experimenta l results . Usin g th e extende dLD A techniqu e introduce di n Chapte r 3 , w e measure d th e cross-sectiona l distribution s o f ai r velocity , particl e velocit y an dparticl e numbe r rat e o n a serie s o f

pip e cross-section s withi nth e numerica l domai n whos e inle t locate s 2.9 mawa y fro mth e particl e fee dpositio n i n th e horizonta l part o f th e experimenta l ri g (a s show n i n Figur e 7.1) . In th e experiments , glas s bead s wit hmea n siz e 90p m(Stoke s numbe r 10.2 ) an ddensit y 255 0 kg/m 3 wer e pneumaticall y transporte db y ai r wit haconveyin g velocit y o f 12m/s . Th e experimenta l

14 0Chapte r 7 CF D investigatio n ol'cross-scctiona l flow patter n o f soli dphas e i n ahorizonta l pip e result s a t th e inle t

o f th e numerica l domai n ar e show n i n Figure s 7. 2 an d7. 3 fo r th e ai r an dsoli d phase s respectively .

'0. 5 4 0 2 0 bp ""- I

2 0 0 2 0 z(mm ) 0.0 1
5 O.0 P 0.01 9

-4 0 -2 0 0 2 0 Figur e 7.2. Ai rvelocit y (U „ U , an d U z ) a tinlet Figur e 7. 2 show s th e distributio n o f th e thre e component s o f ai r velocit y a t

th e sectio n x=0m m (inlet) , whic hwer e measure db y LD Ausin g smok e as seedin g particles . Th e measure dturbulenc e intensit y ofth e ai r

flo w i s abou t

3.5% . Thes e experimenta l dat awa s use da s th e velocit y profil e o f th e ai r phas e a t

th e inle t

i n th e numerica l simulations . U.. . U „ 4 0 2 0 0 -2 0 •40 -4 0 -2 0

4 0 2 0 0 -2 0 p x p y

1 3 1 2 0 2 0 4 0 z(mm )

-4 0 >-o s

0.01

-4 0 -2 0 0 2 0 4 0

z(mm ) 4 0 2 0 0 -2 0 -4 0 -4 0 -2 0 v<* > .0 > - o is K 3 -O. ^

0 2 0 4 0 z(mm ) Count s withi n1 s

30 0 4 0 2 0 0 -2 0 -4 0 -4 0 -2 0 too

'20 0900 0 2 0 4 0 z(mm ) Figur e 7.3 . Cros s sectional distribution s o f particl e velocity an d particl e numbe rrate a tinle taverage d ove rI s
Wit hregar dt o th e inle t condition s o f

th e soli dphase , th e distribution s o f particl e velocit y an d

14 1


# VES01717 6A i i investigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m particl e numbe r

rat e ar e illustrate di n Figur e 7.3 , a s measure dunde r condition s o f

1.6 % soli d loadin g rati o a

t 12m/ s ai r

conveyin g velocit y i n a<j>75m mpipe . I t

i s clea r

tha t soli dphas e a

t th e inle t i s heterogeneou s ove r th e section , sinc e particl e velocit y reduce s fro mth e centr e t o th e wal l an dparticl e numbe r

rat e increase s fro mth e to p t o th e bottom . Thu s th e numerica l simulation s shoul db e performe di n th e unstead y state . 

### 7.2.4 Experimental

cross-sectional

flow patterns

of solid phase Particl e numbe ri n 1 s 4 0
2 0

-2 0
-4 0 U p x(m/s )

" 11.S

& 1 1 ^ 40 - 2 0
0
-2 0
-1 0 100

300 50 0

^ 500 §

-4 0 -2 0 0 2 0 4 0 -40 -2 0 0 2 0 4 0

z(mm ) z(mm ) Figur e 7.

4 Th e contour s o f

particl e velocit

y U p xan d particl e coun tove rI s a tth e sectio n x=455mm
40 1
2 0 U p x < m/s >

c i . w £0 m > , o>*> . -20 1 1 -4 0 t o W* 5

# 5 -2 0
-1 0 ! Particl e numbe ri n 1 s 4 0
2 0 a

ifi . % 50 0

'50 0 90 0 -4 0 -2 0 0 2 0 4 0

z(mm ) -4 0 -2 0 0 2 0 4 0 z(mm ) Figur e 7.

5 Th e contour s o f

particl e velocit

y U p van d particl e coun tove rIs a tth e sectio n x= l 000mm .
I nChapte r

5 , th e experimenta l cross-sectiona l flo w pattern s o f soli dphas e o n aserie s o f cross-section s hav e bee n displaye dunde r th e differen t

flui dconditions . Her e tw o selecte d

14 2


# VES01717 7Chapte r 7 CTT J investigatio n o f cross-sectiona l flo w patter n o f soli dphas e i n ahorizonta l pip e sample s withi nth e numerica l domai n ar e show n i n Figur e 7. 4 an d7. 5 whic hcorrespon dt o th e mi dsectio n an doutle t ofth e numerica l domain . The y wil l b e use dt o compar e wit hth e numerica l results . A s show n i n Figure s 7.3 , 7. 4 an d7.5 , w e notic e tha t th e contour s ofparticl e horizonta l velocit y componen t

(U p x ) a

t th e thre e section s displa y acharacteristicall y annula r structure , an dthei r annula r core s o r

th e fastes t

U p sregion s ar e observe dt o b e displace dupward s abov e th e pip e centr e line . Th e contour s o f particl e numbe r

rat e o n th e thre e section s revea l acharacteristicall y stratifie dform . Consequently , th e flow pattern s o f gas-soli dflo w ove r

th e pip e cross-section s ca n b e describe da s a n annula r patter n i n term s o f horizonta l particl e velocit y componen t an da stratifie dlaye r

patter n i n term s o f

particl e numbe r

rate .



### 7.3 RESULTS

AND COMPARISONS 7.3.1 Flow

patterns

of solid phase investigated

by DPM
Usin g DP M i n Fluent , w e simulate datota l o f 5326 7 parcel s (th e uni t o f particle s i n atrajector y a t ever y tim e interval ) passin g throug hth e domai n fro m104 7 feedin g point s ove r Is . Thes e fee d point s wer e th e sam e a s th e samplin g point s i n th e experiments . Sinc e soli dmas s flo w rate s at th e fee dpoint s wer e differen t dependin g o n particl e numbe r rate , a n injectio n progra mutilisin g a user-defined-functio n (UDF ) b y usin g macro s i n Fluen t wa s develope dan dcouple dint o Fluent . Thi s determine dth e particl e numbe r injecte dfro meac hpoin t a t ever y numerica l tim e step . Fo r unsteady-stat e simulations , th e time-average dvalue s o f parameter s canno t

b e displaye db y Fluen t directly . Th e result s wer e therefor e post-processe dan dstatisticall y analyze dusin g Matlab7.0 . A selectio n o f

typica l result s i s show n i n Figure s 7. 6 an d7.7 .

14 3


# VES01717 8A i l investigatio n o l particl e dynamic s i nadilut e phas e pneumati c conveyin g syste m {LWU a } at

th e momentt=200(ms ) 4 0

2 0

-2 0 A. 1

7. 7 {U p x /U a } atth e momentt=500(ms ) 4 0 - 20

- 7 * ~ A A 0 i ^

-

> -2 0 ^ N N
-4 0 -4 0 -2 0 0 2 0 4 0

z(mm ) {IWUJatth e momentt=800(ms ) 4 0 1 -4 0 -4 0 -2 0 0 2 0 4 0

z(mm ) {<U p x /U a >}ove r

100 0 (ms ) 4 0
2 0 - 

# I 0 A. 1 2 0 1. 1

-2 0 1. 1

1 -4 0 - -4 0 -2 0 0 2 0

z(mm ) -2 0 7 -t tA. 1 A-1 7 1 j -4 0 4 0 -4 0 -2 0 0 2 0 z(mm ) 4 0

Figur e 7. 6 Contour s o f th e dimensionles s particl e instantaneou s velocitie s )TJp,/U, ) an d it s time-average d valu e {<U pv /U a > } ove r1000m s o n th

e sectio n x=455m

m obtaine d fro m simulatio n usin g FLUEN T DP M (Ua=12m/s ) Figur e 7. 6 show s thre e selecte dcontour s o f th e axia l instantaneou s particl e velocit y {U p x } an d on e time-average dcontou r {<U p x > } ove r

on e secon do n th e sectio n x=455mnt . Observin g th e firs t thre e contour s o f

particl e instantaneou s velocit y U p x , w e fin dtha t th e contou r

shape s diffe r fromeac hother . Thi s mean s that th e structur e o f

th e U p xcontou r

i s time-dependent . I n addition , w e als o notic e tha t

som e fragmente disoline s displaye di n al l fou r diagram s o f

Figur e 7.6 . Th e time-dependen t

structur e an dfragmente disoline s indicat e tha t th e gas-soli dpip e flo w i s unstead y i ntim e an dheterogeneou s i n space . Compare dwit hth e thre e instantaneou s contours , th e contou r ofparticl e time-average dvelocit y ove r I s (at th e righ t

botto mo f

Figur e 7.6 ) mor e clearl y show s th e annula r

structur e o f

gas-soli dflo w ove r th e pip e cross-section . Thi s annula r structur e i s generall y simila r

t o th e flo w patter n portraye db y th e experimenta l dat ao f particl e velocit y U p xi n

14 4


# VES01717 9Chapte r 7 CI-' D investigatio n o f cross-sectiona l flo w patter n o f soli dphas e i n ahorizonta l pip e Figur e 7. 5 an dFigur e 7.6 . Thei r differenc e result s fro mth e fac t tha t th e fastes t

regio n o r

annula r cor e i n Figur e 7. 6 i s displace ddownward s belo w th e pip e centr e line , whil e th e experimentall y locate dannula r

cor e i n Figur e 7. 5 i s shifte dupward s abov e th e pip e centr e line . However , th e numerica l annula r

patter n i n Figur e 7. 6 i s no t unifor mlik e th e experimenta l on e i n Figur e 7.5 . {<U ot> } (m/s ) o n the sectio n x = 455mmparticl e numbe r N in 1 s 4 0 . 40 . 2 0 20 ;
E nE £a

* *

* " E -20 v K ' -2 0 1 3

• ^ -4 0 . _, -4 0 to o "t o

30 0

-4 0 -2 0 0 2 0 4 0 -4 0 -2 0 0 2 0 4 0

z(mm ) z(mm) {< U > } (m/s ) on the sectio n x=1000m mparticl e numbe r Nin 1 s 4 0 - 40 , 20 2 0

1 A1 3 | o - 5| o !
-20 . , 3 p -2 0 i ,0 0 10 0

r i ^ - I -4 0 —• • - -4 0 I - - —- -t O -2 0 0 2 0 4 0 -4 0 -2 0 0 2 0 4 0

z(mm ) z(mm) Figur e 7.

7 Contour s of

th e time-average d axial particl e velocity {<U pv > } an d particl e numbe r[N } ove rIs o n two sampl e sections (x=455mm , 1000mm) obtaine d fro m FLUEN T DPIV I
Sinc e th e contour s o f time-average dparticl e velocit y U p xar e usefu l t o explor e som e characteristic s o f

gas-soli dflow, Figur e 7. 7 show s contour s o f time-average dU p xan dparticl e numbe r rat e a t tw o section s at

x-=455m man d1000m mrespectively . Comparin g thes e flo w pattern s wit hthos e a t th e inle t

indicate di n Figur e 7.3 , bot hth e annula r structur e i n term s o f U p x an dth e stratifie dshap e layere db y particl e numbe r rat e ar e stil l show n i n th e contour s a t th e x=455m msection , bu t thes e tw o characteristic s ar e distorte dt o extinctio n i n th e contour s a t th e x = 1000m msection . Thi s show s tha t th e DP M modelle dflo w patter n varie s alon g th e flui d direction .

14 5A ninvestigatio n ofparticl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 

### 7.3.2 Flow patterns

of solid phase investigated

by Discrete

Element

Method Inth e couple dFluen t & EDE M simulations , al l numerica l geometry , flui dcondition s an d boundar y condition s wer e th e sam e a s th e foregoin g one s i n th e DP M simulations . Bu t fo r particl e injectio n a

t th e inlet , particle s coul db e automaticall y injecte dwit hadifferen t mas s flo w rat e at ever y injectio n poin t throug hdefinin g "particl e factories " ove r th e inle t

rathe r tha n usin g a U D Fprogra mt o contro l th e proces s o f particl e injection . Sinc e th e soli dphas e i n th e DE M i s treate da s individua l particle s disperse di n th e flui drathe r tha n a s th e "parcels " (group s o f particle s wit hth e sam e trajectory ) use di n DPM , th e effec t o f particle-particl e interaction s an d frictio ndu e t o collision s ca n b e accounte dfo r i n detai l i n th e DE M mode l implemente dher e b y th e EDE M software . Du e t o th e nee dt o transfe r particl e location s bac k t o th e flui ddomai n at eac hflui dtim e step , an dth e larg e siz e o f domai n relativ e t o th e particl e siz e an dnumber , th e spee do f

thi s couple dsimulatio n i s rathe r slow . Typica l result s o f th e time-average dcontour s o f particl e velocit y U p xan dparticl e numbe r rat e ar e show n i n Figure s 7.8 . {< U>} (m/s ) on the sectio n x = 455m m 4 0 40 , particl e numbe r {N } i n 1 s

2 0

-2 0 2 0 ?0 0 30 0 to o 

## % 10 0 w 3o ° o • . o 10Q '§ 

## % 1 50 0 % 20

0 100 0 200 0 ,t j -4 0 .. . -4 0 -2 0 0 2 0

z(mm ) 4 0 (< U > } (m/s ) o n th

e sectio n x=1000m

m p x 4 0 , -4 0 > -4 0 -2 0

4 0 0 2 0 4 0

z(mm) particl e numbe r

{N } i n 1 s

2 0 2 0

-20

- 1 2

-4 0 -4 0 -2 0 "1 2

1 1 « 0 2 0 4 0 z(mm ) 0 , -2 0 i
-4 0 -4 0 -2 0 0 2 0 4 0

z(mm) Figur e 7.8 . Th e flo w pattern s o f particl e mean velocity an d particl e numbe ro n two sampl e sections (x=45Smm , 1000mm) obtaine d b y usin g FLUEN T & EDE M

14 6


# VES01718 1Chapte r 7 CF D investigatio n o f cross-sectiona l flo w patter n o f soli dphas e i n ahorizonta l pip e O nth e sectio n x=455mm , an annula r flow patter n o f

soli dphas e i n term s o f th e particl e velocit y horizonta l componen t (U, n ) (t o b e compare dwit hFigure s 7. 4 an d7.7 ) i s obviou s i n th e uppe r sectio n o f

Figur e 7.8 , an dth e cor e regio n i s als o displace ddownward s belo w th e pip e centr e a s i n th e DP M results . However , th e stratifie dflo w patter n observe di n Figure s 7. 4 an d7. 7 i s completel y distorte di n th e uppe r sectio n o f

Figur e 8 . A s fo r

flo w pattern s o n th e x=1000m m section , bot hth e annula r patter n an dth e stratifie dpatter n ar e skewed , an dn o clea r patter n ca n b e observe di n Figur e 7.8 . 

## 7.4 DISCUSSION

0. 5 ; 0 x = 300m m
-0. 5 -

0 9 0.9 5 1 1.05 1. 1 1,1 5 1. 2 1.2 5

1 i i 0. 5 - Q ; 0 x = 700mr n i
-0. 5

- 1 0. 8 0 . 9 1 1. 1 1. 2 1. 3 {< U »/ U ) p . a' Figur e 7. 9 Compariso n of the numerica l an d experimenta l vertica l profile s o f {<Upx>/Ua } a

t fou rdifferen tposition s alon g the flui d flo w directio n (th e continuou s blu e lin e is th e profil e a t inlet )

I n orde r convenientl y t o acces s th e evolutio n o f flo w pattern s alon g th e pipe , th e experimenta l an dnumerica l profile s o f th e dimensionles s {<U p . x >/U a ) an dparticl e numbe r ove r I s a t th e z=0m mline s at

severa l section s (x=300 , 455 , 700 0 an d1000mm ) ar e plotte di n Figur e 7. 9 an d Figur e 7.10 . U p xi s normalize db y th e mea n ai r conveyin g velocit y (U a ) whic hi s 12m/s .
I n general , profile s at th e positio n o f

x=300m mhav e agoo dagreemen t wit heac hothe r

a s wel l a s similarit y t o th e profil e at inlet , althoug hth e peak s o f bot hnumerica l profile s o f {<U p x >/U a } sho w asmal l shif t

awa y th e pip e centr e line . A t th e furthe r

downstrea mdistanc e o f x=45 5 t o 0. 8 0. 9 Inte l L D A D P M D E M

g 0
. x=1UUUrn m {< u >/u ) 1. 2 1. 3

(<U >/ U ) 1. 2 1. 3

14 7A ninvestigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m I OOOmm , ther e i s muc hdiscrepanc y amon g thes e profiles . Especiall y at th e positio n o f x1000mm , bot hnumerica l profile s o f {<U p x >/U a } hav e bee n distorted , whic har e completel y differen t

fro mth e experimenta l profil e o f {<U p x >/U a } a s wel l a s th e profil e a t inlet . B y contrast , th e experimenta l profile s o f {<U p x >/U a } ca n b e observe dt o b e simila r a t th e differen t

position s alon g th e pipe .

Particl e numbe r Nover 1 s Inlo l LD A; DP M j 1 r OE M | ! 0. 5 i 50 0 100 0 150 0 200 0 250 0

Particl e numbe r

N o\e r 1 s

50 0 100 0 150 0 200 0 Panicl e numbe r

Nover 1 s 50 0 100 0 150 0 200 0 Particl e numbe r

N o\e r 1 s Figur e 7.1 0 Compariso n ofth e numerica l an d experimenta l vertica l profile s of particl e numbe r ove rI s a tfou rdifferen tposition s alon g th e flui d flo w directio n
A s fo r particl e numbe r

counte dove r

Is , Figur e 7.1 0 show s it s numerica l an dexperimenta l profile s at

th e fou r

differen t

position s alon g th e pipe . O n th e whole , w e ca n se e tha t th e experimenta l profile s o f particl e numbe r

ar e identica l t o eac hothe r an dthe y als o jus t

var y aroun d th e profil e o f

particl e numbe r

at inle t wit hasmal l deviation . Wit hregar dt o th e numerica l profile s o f

particl e numbe r

ove r Is , ther e i s asignifican t discrepanc y amon g the malon g th e flui d flow direction . Bot hnumerica l profile s sho w tha t ther e i s a n increasin g tendenc y o f particl e numbe r alon g th e pipe , fo r

particl e numbe r

graduall y increase s at pip e botto man ddecrease s at pip e uppe r

half , eve n wher e ther e i s aver y dilut e o r empt y spac e withou t particle s i n th e pip e uppe r spac e at

th e positio n x = 1000mm .
However , experimenta l dat ai n Figure s 7.3 , 7. 4 an d7. 5 show s tha t bot hth e annula r

flo w patter n an dstratifie dparticl e numbe r distributio n follo w astead y tren dalon g th e downstrea mdirectio n i nth e whol e domain . Thi s indicate s tha t usin g DP M o r

DE M ca n onl y estimat e flo w pattern s

14 8Chapte r7 CF D investigatio n o f cross-sectiona l flow pattern o f soli d phas e i n ahorizonta l pip e properl y withi n ashortdomain . In anothe rwords , both DP M an d DE M hav e no tyielde d satisfactory result

s fo rpredictin g som e parameters relate d t o particl e spatia l distributio n i n th e gas-soli d pip e flow.
In th e previou s tw o sections , the cross-sectiona l flow patterns an d thei revolutio n i n th e downstream direction , a s calculate d usin g two numerica l methods , wer e discussed . Comparison s o f th e numerica l results wit h the correspondin g experimental dataindicat e thatnumericall y predicte d cross-sectiona l flow patterns sho w reasonabl e agreementwit h experimenta l one s onl y a tpip e cross-section s locate d withi n aspecifi c distanc e from th e inlet . A tgreate rdownstream distances , numerica l flow patterns becom e distorte d unti l the y ar e completel y differen tfrom experimental flow patterns . Thi s discrepanc y mean s tha tthe spatia l distributio n o f 38- 1 lOu m particle s bein g transporte d i n th e dilut e stat

e i n alon g horizonta l pip e i s no tproperl y estimate d b y th e curren tnumerica l methods .
Th e numerica l results o f Hube r(1998 ) showe d 40u m glas s beads ' 2 D trajectorie s o n avertica l sectio n o f

a<|>80m

m horizonta l pipe . A s woul d b e expecte d sinc e thei rStoke s Numbe rwas 2.0 , th e trajectories o f

thes e glas s bead s followe d th e flui d flow pattern . Furthermore , Sommerfel d (2003 ) numericall y investigate d trajectorie s o f fou rdifferen tsiz e glas s bead s i n a2 D horizonta l channel with 35m m heigh tan d 6 m length . Withou tconsiderin g the effec to f wal l roughness , hi s numerica l results sho w thatal l trajectorie s o f 1 lOu m particle s en d u p o n th e channe l botto m b y 3 m downstream o f

th e inlet . Thi s i s simila rt o ou rnumerica l results ofparticl e numbe ri n Figure s 7 an d 9 . T o allo w fo rth e proble m o f

irreversibl e deposition , Sommerfel d introduce d amode l o f particle-wal l collisio n whic h assume d particl e impac tangl e compose d o f th e particl e trajectory angl e an d arando m norma l distribute d componen tdue to roughness . Th e trajectorie s o f HOu m particle s were the n muc h widel y distribute d ove rth e whol e channe l spac e an d agree d with hi s experimental data .
I n summary , th

e foregoin g discussio n reveal s thatthere stil l exis tsom e effect s whic h hav e not bee n accounte d fo ri n the currentDP M o rFluen t& EDE M couplin g simulation s fo rinvestigatin g gas-soli d pip e flow. Th e mode l o f particle-wal l collisio n introduce d b y Sommerfel d wil l b e incorporate d i n futur e couplin g simulation s an d method s o f two-dimensiona l pattern recognitio n wil l replac e the curren tone-dimensiona l techniqu e t o precisel y determin e th e similarit y o f fluid pattern s o f th e soli d phas e o n aserie s o f pip e cross-sections . 

## 7.5 CONCLUSIONS Base d o n experimental dat aan d th e geometry o f th e experimental rig, flow patterns o n aseries o f

14 9A n investigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m pip e cross-section s an d thei rvertica l profile s alon g the pip e hav e bee n numericall y investigate d b y th e standard DPM s o f Fluen tan d Fluen tcouple d wit h EDEM . Thre e conclusion s ca n b e deduce d fro m th e compariso n o f numerica l an d experimental data . Th e annula rstructur e o f the particl e velocit y horizonta l componen tan d th e stratifie d structure b y particl e numbe rca n b e predicte d b y bot h Fluen tDP M an d Fluen t& EDE M withi n acertai n distance fro m th e inlet , whic h ca n b e estimate d b y th e produc tofparticl e mea n velocit y an d hal f the particl e free fallin g time . O n pip e cros s section s furthe rdownstream , th e flo w patterns modelle d are distorte d unti l the annula rvelocit y an d stratifie d particl e numbe rcharacteristic s completel y disappear . Compare d wit h th e contou ro f particl e numbe ran d its evolutio n alon g th e pip e simulate d usin g Fluen tDPM , th e dat aachieve d b y usin g Fluen t& EDE M shows tha t particle s distribute muc h widel y i n th e pip e space , rathe rthan bein g locate d clos e t o the pip e botto m afte rthey hav e bee n transporte d acritica l downstrea m distance . Thi s mean s tha t considerin g the effec to f particle-particl e interaction s i n DE M wil l improv e th e accurac y o f numerica l simulation s fo rgas-soli d horizonta l pip e flow, eve n thoug h (h e soli d phas e i s i n a dilut e state . Th e distorte d flow pattern s an d thei revolutio n profile s alon g the pip e indicate tha t particl e spatia l characteristic s foun d from experimen tar e no tproperl y estimate d b y th e current numerica l models . Thus , the micro-mechanis m o f fine particl e transporti n pipe s shoul d b e furthe rstudied . Finally , i tshoul d b e mentione d thatwor ko n developin g th e curren tnumerica l mode l usin g ou r experimental dat

ai s ongoing .

15 0


# VES01718 5

# Chapte r 8 

# Conclusion s

Co-firin g application s i n powe rstation s hav e bee n confirme d a s bein g apromisin g wa y t o reduc e C 0 2emission s ver y considerabl y whil e generatin g enoug h electricit y fo renergy demand . A demandin g taski s tha to f controllabl y distributin g afue l mixtur e o f pulverize d coa l blende d with biomas s particle s i n acommo n pipeline , whic h i s likel y t o sav e muc h investmen tas succes s woul d enabl e existin g pulverize d fue l boiler s t o b e use d fo rbiomas s exploitation . Therefore , t o addres s th e proble m o f controllabl e distributio n i n co-firin g technique s an d t o gai n a n improve d understandin g the mechanis m o f pneumati c conveying , thi s researc h into particl e dynamic s o f pip e flow wa

s undertaken .
Th e objective s o f

thi s research were , firstly, t o numericall y evaluate th e influenc e o f

variou s factor s o n th e behaviou ro f particle s o f

th e differen tmaterial s i n ahorizonta l pip e flow; secondly , t o develo p an extende d techniqu e o f Lase rDopple rAnemometr y i n orde rt o determine cross-sectiona l characteristic s o f th e soli d phas e i n th e horizonta l an d vertica l section s o f a pneumati c conveyin g system ; thirdly , to develo p anove l imagin g syste m fo rvisualizin g particl e propertie s b y usin g ahig h definitio n camcorde ro n across-sectio n illuminate d b y ahaloge n ligh t sheet ; and , finally , to mak e acompariso n o f the cross-sectiona l characteristic s reveale d b y experimen tan d those simulate d b y usin g the Discret e Phas e Mode l o f Fluen tan d th e couplin g calculation s o f

Fluen t& EDE M respectively . Conclusions o f

the experimental an d numerica l investigation s ar e detaile d below . 

# 8. 1 SUMMAR YO F RESULT S

Th e overal l result

s fro m thi s stud y cove rparticl e dynamic s i n horizonta l pip e flow an d i n a vertica l pip e flow downstream o f right-angle d elbow . Th e mai n results ar e summarise d a

s follows :A n investigatio n o f particl e dynamic s i n adilut e phas e pneumati c conveyin g syste m 1 . Critical

parameters and

particle similarity in a horizontal dilute phase pneumatic conveying system Usin g th

e Discret e Phas e Mode l i n Fluen t6.2.16 , w e hav e explore d the influenc e o f ai r conveyin g velocity , pip e roughnes s an d particl e siz e o n particl e trajectorie s i n th e boundar y region . Th e numerica l results demonstrat e tha tthe Saffma n Forc e play s a n importan trol e i n a dilut e pneumati c conveyin g system , especiall y fo rdeterminin g whethe raparticl e wil l b e re-suspende d fro m th e boundar y region . Thi s analysi s show s tha tther e exis tthree critica l parameters : (1) The critical

airconveying velocity. A highe rai rconveyin g velocit y generall y benefit s b y liftin g aparticl e highe rfrom th e boundary regio n toward s the mainstream field o f pip e flow , butth e heigh treache d i s n o longe rmuc h enhance d whe n the ai rvelocit y i s mor e tha n 30m/ s i n ou rnumerica l model . Thi s valu e i s defme d a s th e critica l ai rconveyin g velocity . (2) The critical

pipe roughness. I n th e pip e boundary region , increase s i n pip e roughnes s resul ti n aparticl e bein g abl e t o jum p t o amuc h highe rposition . However , whe n the pip e relativ e roughnes s i s mor e tha n 1.64% , the trajectorie s o f th e particl e ar

e th e sam e an d the particl e i s n o longe rlifte d muc h higher . Th e valu e o f 1.64 % i s terme d th e critica l pip e relativ e roughnes s fo rthe curren tflui d condition s o f ai rconveyin g velocit y 24m/s . (3) The critical

particle size. Basically , the bigge raparticl e is , the highe ri tca n b e suspende d i f it s siz e i s i n th

e rang e o f

10~100um . However , thi s phenomeno n n o longe rexists whe n a particl e i s large rthan 100pm . Th e valu e o f 100p m i s define d as th e critica l particl e siz e fo r th e currentfluid condition s o f ai rconveyin g velocit y 24m/s . (4) The characteristics of the dimensionless mean particulate velocity. Th e numerica l result s indicate tha

tparticl e mea n velocitie s o f th e differen tmaterial s ca n b e classifie d int o three region s i n th

e horizonta l an d vertica l directions , non-dimensionalisin g b y mean s o f th e Stokes Numbe ro rdivide d b y the termina l velocit y respectively . Particle s with aStoke s Numbe rles s than 1 hav e amea n velocit y equa l t o th e ai rconveyin g velocit y i n the horizonta l directio n an d amea n vertica l velocit y equal to the termina l velocit y i n the full y develope d region . Correspondingly , fo rlarge rparticle s wit h Stoke s Numbe rmor e than 3.5 , thei rmea n dimensionles s velocit y U p x / U a(the horizonta l particl e velocit y divide d b y ai rconveyin g velocity ) tends toward s 0. 6 i n th e horizonta l directio n an d thei rmean dimensionles s velocit y Upy/U a(the vertica l particl e velocit y divide d b y ai rconveyin g velocity ) i n th e vertica l directio n become s essentiall y zero . Th e mea n dimensionles s velocitie s o f particle s wit h Stokes numbe rbetwee n 1 an d 3. 6 are i n th e rang e o f 0.6- 1 i n th

e horizonta l directio n an d -1- 0 i n th

e vertica l directio n (as the directio n o f gravity) .
2 . The extended

technique ofLaserDoppler Anemometry

15 2



# VES01718 7Chapte r8-Conclusion s S o far , ther

e i s stil l alac ko f

paper s discussin g th e detaile d effec to f refractio n a

tthe pip e wal l an d o f

sampl e rat

e i n gas-soli d flo w measurement s usin g Lase rDopple rAnemometry . Th e refractio n effec tdu e to th e curve d surfac e o f the pip e ca n no tb e ignore d an d th e samplin g rat

e i s relate d t

o the statisticall y accurac y o f calculatin g th e time-average d valu e o f aparamete rmeasure d b y LDA , w e hav e propose d modification s to th e currentnorma l techniqu e o f

LDA , whic h has bee n validate d b y fh e compariso n o f th e profile s o f

ai rvelocit y measure d b y LD A an d th e correspondin g theoretical profil e estimate d b y th e empirica l one-sevent

h powe rla w o f

ai rvelocit y i n apipe . Thi s extende d techniqu e has bee n applie d t o measur e the cross-sectional velocit y distributio n o f the ai rphas e i n avertica l pip e downstream o f

a90 ° elbow . Th e contribution s o f the newly-developed technique s consis tof: (1) Buildine a mathematical model

forcalculating the transform matrix of the three pairs of LDA laserbeams. Th e transfor m matri x i s use d t o map th e actua l positio n o f the measurementvolum e o f LD A i n pip e flo w accordin g t o prob e angle , fo rany chang e affecte d b y shiftin g th e three-dimensiona l travers e system . (2) Determining a suitable sample rate forLDA experiments. A suitabl e sampl e rat e (10 K Hz ) fo rLD A has bee n experimentall y determine d fo r70- 1 lOu m glas s bead s conveye d b y a 12m/ s ai rvelocit y with asoli d loadin g rati o o f 1.6% i n (j>75m

m pipe . Thi s samplin g rat e applie d t

o th e experiment

s ensure s t

o accuratel y calculate th e loca l time-average d particl e velocit y a

tan y sampl e point . (3) Confirming the profile of airvelocity in a horizontal pipe. Th e experimenta l dat asho w tha tth e profil e o f

ai rvelocit y measure d b y LD A i n ahorizonta l pip e i s i n goo d agreement with the empirica l one-sevent h powe rlaw . Similarit y amon g cross-sectiona l distribution s o f th e axia l ai rvelocit y o n differen thorizonta l cross-section s indicate s th e stability o f full y develope d ga

s pip e flo w velocit y profile . Th e axia l ai rvelocit y show s an annula rdistributio n ove racross-section . (41 Cross-sectional

characteristics of the airvelocity in a vertical pipe downstream of a 90° bend. O n vertica l cross-sections , th e ai rvelocit y distributio n a tn o longe rmaintain s th e annula rvelocit y contours i n horizonta l pipes . Th e cross-sectiona l distributio n o f the axia l ai r velocity shows contours resemblin g ahorsesho e i n shap e a tth e elbo w outlet , where ai rflo w bein g faste ri n th

e regio n clos e to th e pip e bend' s oute rwal l (outsid e th e horsesho e ) than i n th e regio n insid e th

e horseshoe , i n th e pip e centre an d clos e t o the inne rwal l o f

the bend . Furthe rdownstream , the differences o f axia l particl e velocit y betwee n th e horsesho e insid e and its outsid e graduall y decrease . A compariso n o f th e experimenta l dat aan d th e numerica l result s generate d b y usin g CF D indicat e tha tbot h o f them sho w simila rresults o f ai rvelocit y evolutio n i n th e horizonta l pip e afte rthe elbow .

15 3



# VES01718 8A n investigatio n o f particl e dynamic s i n adilute phas e pneumati c conveyin g syste m 3 . Cross-sectional

characteristics of the solid

phase B y applyin g th

e extende d LD A technique , w e hav e investigate d particl e dynami c behaviou r o f three type s o f

glas s bead s whic h ar e selecte d t o simulate t

o simulat e th e pulverise d coa l an d biomas s pellets transporte d i n adilute pneumati c conveyin g system . Detaile d informatio n o n th e cross-sectiona l spatia l distribution s o f the axia l particl e velocit y an d particl e numbe rrat

e i s reported . (1 ) Annularcross-sectional flow pattern of

solid phase bv the axial

particle velocity. In a horizonta l pip e a

tthe minimu m ai rconveyin g velocit y lOm/s , th e experimental dat ao n a serie s o f

cross-section s clearl y illustrat e tha tth e axia l particl e velocit y distributio n ove ra horizonta l cross-sectio n i s annular , resemblin g tha to f the ai rphase , fo rparticle s with Stoke s numbe rles s than 16 . Fo rparticle s wit h aStoke s number s greate rtha n 16 , the characteristic s o f thi s annula rstructure becom e weak . (2 ) Stratified

cross-sectional

fluid pattern of

solid phase bv particle numberrate. In a horizonta l pip e a

tthe minimu m ai rconveyin g velocit y lOm/s , th e experimental contou ro f particl e numbe rrat

e (countin g i n on e second ) ove rahorizonta l cross-sectio n display s a stratifie d configuration , especiall y fo rglas s bead s with Stoke s numbe rles s than 16 . (3 ) Evolution of

the two cross-sectional fluid patterns. Thes e tw o type s o f cross-sectiona l flow patterns (fo rth e axia l particl e velocit y an d particl e numbe rrate ) ca n b e observe d a ta numbe ro f

position s alon g th e pip e axis , butthe positio n o f th e annula rcor e an d the value s o f iso-line s are dependento n particl e siz e an d var y alon g th e fluid direction . (4) Cross-sectional

characteristics of particle velocity in a vertical pipe downstream of a 90" bend. I n the vertica l pip e afte ran elbo w (R/D=1.3 , Rbein g th e ben d radiu s an d D th e pip e diameter) , ahorseshoe-shape d featur e ha s bee n observe d i n th e cross-sectiona l distribution s o f

th e dimensionles s axia l particl e velocit y fo ral l three type s o f glas s bead s (les s than 50pm ; 70-11 0 p m an d 180-30 0 um ) o n the sectio n 0 D clos e t o th e elbo w outlet. Furthe rdownstream , the horsesho e featur e i s graduall y distorte d unti l i tcompletel y disappear s an d th e axia l particl e velocit y i s fairl y uniform . Thi s degradatio n distanc e i s about 4 D fo rth e firs ttyp e o f glas s beads , 2 D fo rthe secon d typ e an d I D fo rthe third . (5 ) Cross-sectional

characteristics of particle numberrate in a vertical pipe downstream of a 90" bend. Th e cross-sectiona l distributio n o f th e dimensionles s particl e numbe rrat e o n the sectio n 0 D show s tha tth e rop e i s forme d a tthe pip e outerwal l wher e th e maximu m particl e numbe rrat

e occurs . O n the whole , the rop e forme d b y the firs ttyp e o f glas s bead s (les s than 50 u m diameter) ca n stil l b e observe d a tth e sectio n 6D . Fo rth e secon d typ e o f glas s bead s (70~110um) , it

s rop e i s re-distribute d acros s the pip e cross-sectio n from the sectio n 4 D accordin g to th

e similaritie s betwee n cross-sectiona l distribution s o f the dimensionles s axia l particl e velocit y an d the dimensionles s particl e numbe rrate . Overall , ropin g i s no tobviousl y

15 4



# VES01718 9

### Chapte r8-Conchision s show n i n th

e gas-soli d flow o f

th e thir d typ e o f

glas s beads (180-30 0 um ) downstream o f the sectio n OD . Thi s suggest s thatlarge rparticle s ar e les s pron e t

o for m rope s an d dissipat e mor e easil y whe n they do , perhap s du e t o the greaterinertia l influenc e o n thei rbehaviour . 4 . Visualization of

particle dynamics on a cross-section I n orde rt

o visualiz e particl e dynamic s o n across-section , avide o & imag e processin g syste m fo rmeasurin g particl e siz e an d analyzin g particl e spatial characteristic s ove ra horizonta l pip e cross-sectio n i n adilut e pneumati c conveyin g syste m was developed . A ligh t shee tproduce d fro m ahaloge n lam p bo x was use d t o illuminat e an d sectio n the gas-soli d flow ove rapip e cross-section . A hig h definitio n camcorde r(1900ixl008 i pixels , 2 5 frames pe rsecond ) was utilize d to recor d particl e behaviou rove rth e highlighte d region . (1 ) Decoding algorithms foruncompressed MPEG -2

videos. A se

to f vide o algorithm s was develope d t

o decod e th e compresse d MPEG- 2 video s int o AV I formatfo rfurthe rimag e processing . A n AV I video , lik e adatabase , consists o f aserie s o f

uncompresse d frames. Eac h pixe l o n each uncompresse d frame i s directl y mappe d t o aspatia l poin ti n the measuremen t regio n fo rfurthe rimag e processing . (2 ) Image processing algorithms formaking each colour frame binary. First , eac h colo r frame extracted from an uncompresse d AV I vide o i s converte d into the correspondin g gray-scal e pictur e accordin g t o th e particles ' luminanc e information . Secondly , thi s pictur e i s denoise d b y aWiene rfilter. Th e thir d ste p i s tha tabackgroun d imag e i s obtaine d throug h removin g th

e particl e image s i n th e denoise d pictur e usin g a25 x 2 5 Media n Filter . I n thi s way , the features o f

th e backgroun d environmen tca n b e preserved . Subsequently , whe n a separate d backgroun d imag e i s subtracte d from the denoise d image , the heterogeneou s backgroun d i s removed . Th e subtractio n resul to f agra y imag e i s then converte d into a binary imag e usin g Otsu' s method . (3 ) Extraction of

particle characteristics from a binary image. Th e features o f ever y particl e such a s shape , siz e an d spatia l positio n ca n the n b e extracte d b y applyin g th e Chai n Cod e Technique , whic h stores th e relativ e co-ordinate s betwee n consecutiv e pixels , an d record s th e shap e o f

aregio n b y analyzin g eac h poin to n the boundary i n sequenc e an d assign s acod e to denot e fh e spatial directio n betwee n tw o adjacentpoints . The n th e particl e siz e distributio n an d th e mean siz e ove rasectio n ca n b e calculate d from th e seto f Chai n Code . (4 ) Cross-sectional

characteristics of particle size distribution. Experimenta l results o f particl e siz e an d siz e distributio n o n each frame sugges tthatgas-soli d pip e flow i s alway s heterogeneous i n space an d unstead y i n time . Th e particl e mea n siz e b y mas s fluctuate s les s with tim e an d i s thus mor e suitabl e fo rstatistical description s o f the unsteady propertie s o f gas-soli d pipe . Bot h the contour s o f particl e numbe rrat e an d particl e time-average d

15 5



# VES01719 0A n investigatio n o f particl e dynamic s i n adilute phas e pneumati c conveyin g syste m concentratio n exhibi tth e stratifie d structure characteristi c o f particl e flo w i n ahorizonta l pip e cross-section . Thi s kin d o f stratifie d structure i s simila rt o the results reveale d b y Lase r Dopple rAnemometr y
5 . Discrepancies between experimental data and

numerical

results in respect of particle cross-sectional

distribution Base d o n experimental dat aan d th

e geometry o f

th e experimental rig, flo w patterns o n a serie s o f

pip e cross-section s an d thei rvertica l profile s alon g th e horizonta l pip e hav e been numericall y investigate d b y th e standard Discret e Phas e Mod e o f Fluen tan d Fluen tcouple d wit h EDE M t

o accoun tfo rth e effect s o f particle-particl e collision . Thre e conclusion s ca n b e deduce d fro m th

e compariso n o f

numerica l an d experimenta l data . (1 ) Region with a eood agreement

between the numerical results and

the experimental data. Th e annula rstructure o f th e particl e velocit y horizonta l componen tan d th e stratifie d structur e b y particl e numbe rca n b e predicte d b y bot h Fluen tDP M an d Fluen t& EDE M withi n acertai n distanc e o f th e inlet , whic h ca n b e estimate d b y th e produc tofparticl e mean velocity an d hal f

th e particl e free fallin g time . O n pip e cros s section s furthe rdownstream , the flo w patterns modelle d ar e distorte d unti l the annula rvelocity an d stratifie d particl e numbe rcharacteristic s completel y disappear . (2 ) Advantages of

considering particle-particle interaction in numerical simulations. Th e comparison s o f

numerica l an d experimenta l cross-sectiona l flow patterns o f soli d phas e sho w tha tther e i s reasonabl e agreementa tpip e cross-section s locate d a thorizonta l position s les s than hal f

th e produc to f

particl e mea n velocit y an d mea n fre e fal l tim e i n th e pip e from th e particl e inlet . Furthe rawa y from the inlet , the numerica l results sho w flo w pattern s whic h ar e increasingl y divergen tfrom th e experimental results alon g th e pip e i n th e directio n o f flow. Thi s discrepanc y indicate s thatparticles ' spatia l distributio n i n apip e i s no taccuratel y predicte d b y DP M o rFluen tcouple d with DEM . Thus , th e micro-mechanis m o f fin e particl e transpor ti n pipe s shoul d b e furthe rstudied . 

# 8.2 RECOMMENDATION S FO R FUTUR E WOR K

Th e finding s tha

taris e from thi s projec trelatin g t o th e experimental an d numerica l analysi s o f particl e behaviou rhav e explore d som e fundamenta l characteristic s o f particl e dynamic s i n a dilut e pneumati c conveyin g system . Du e t o the complexit y o f

th e phenomen ainvolved , research int o gas-soli d pip e flo w i s stil l an ongoin g are ao f interest , especiall y fo ramultiple-componen t soli d phases . Thre e possibl e extension s o f th e currentwor kshoul d b e carrie d ou ti n furthe r

15 6



# VES01719 1Chapte r8-Conclusion s studies . First , i n orde rt

o obtai n empirica l equation s fo rparticl e dynamic s i n pip e flow , especiall y i n a vertica l pip e downstream o f a90 ° bend , mor e experimental wor kusin g th e extende d techniqu e o f Lase rDopple rAnemometr y shoul d b e carrie d ou tt o determin e the behaviou ro f differen t granula rmaterial s unde rawid e rang e o f flui d conditions . Ou rcurren twor konl y focuse d o n lo w ai rconveyin g velocities . Second , the vide o & imag e processin g syste m develope d i n thi s wor kshoul d b e use d to measur e th e siz e an d spatial distributio n o f particle s mor e than 80(i m i n diamete rove rawhol e cross-sectio n o f

<|>75m m pipe . Thi s visualizatio n syste m ca n b e mad e suitabl e fo rfin e particl e measurement

s usin g asmalle rdiamete ro f pipelin e fo rexperiment . I n addition , usin g coloure d granula rmaterials , thi s syste m ca n b e develope d int o ameasurementtoo l fo rgas-soli d pip e flow wit h amulti-componen tsoli d phas e throug h addin g afunctio n capabl e o f discernin g particl e colour . Third , existin g model s o f particle-particl e interactio n an d particle-wal l collisio n shoul d b e investigate d i n detai l an d modifie d to explai n an d eliminate th e discrepancie s betwee n th e current numerica l results an d fh e experimenta l data . Fourth , statistical analysi s an d furthe rexperimentatio n shoul d b e undertake n t o quantif

y th e reliabilit y ofth e LD A result s an d t o estimat

e th e erro ri n th e fina l values . 

# 8. 3 PUBLICATION S ARISIN G FRO M TH E PROJEC T

L u Y. , Glas s H . D. , Easso n J . W. , (2009) . A n investigatio n o f particl e behaviou ri n gas-soli d horizonta l pip e flow b y a n extende d LD A Technique . Fuel . Accepte d (JFUE-D-08-00741) . L u Y , Glas s D . H. , Easso n W . J. , (2008a) . Investigatin g particle s behavio ri n gas-soli d horizonta l pip e flow b y an extende d Lase rDopple rAnemometr y Technique . In : Proceeding s o f 7t h Europea n Conferenc e o n Coa l Researc h an d it s Applications , Septembe r2 n d- 5 th , Cardiff, UK . L u Y , Glas s D . H. , Easso n W . J. , Crappe rM. , (2008b) . Investigatio n o f the Flo w Patterns o f Gas-soli d granula rflo w i n ahorizonta l pip e b y FLUEN T & EDEM . In : Proceeding s o f Particl e System s Analysi s 2008 , Septembe r1 s t- 3 rd , Stratford , UK . L u Y , Glas s D . H. , Easso n W . J. , (2007) . Investigatin g Flo w Propertie s o f Coa l Biomas s Blend s i n Pneumati c Conveyin g System s b y Computationa l Flui d Dynamics . In : Proceeding s o f 200 7 international conferenc e o n Coa l Scienc e an d Technology , Augus t28 lh - 31 lh , Nottingham , UK .

15 7

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turbulenc

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l Report : Th e economic

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