Proceedings of Short Term-Stay Program of Shizuoka University(Shizuoka University and Changwon National University)

From January 5, 2012 to January 11, 2012
Faculty of Engineering, Shizuoka University(Hamamatsu Campus)

Proceedings creator & Japanese-side student leader: Yasuyuki Nagami
1st-year master degree student, Saito Laboratory, Shizuoka University

Korean-side student leader: Jong-Min Kim
3rd-year Bachelor's degree student, Shin Laboratory, Changwon National University-0-Contents
1. Purposes of the Short Term-Stay Program of Shizuoka University
・・・・・・・・・・・・・・・・・・・・・・・・・2

2. Agenda of the Short Term-Stay at Shizuoka University
・・・・・・・・・・・・・・・・・・・・・・・・・ 3

3. List of Participants
・・・・・・・・・・・・・・・・・・・・・・・・・ 5

4. Report on Short Term-Stay Program of Shizuoka University
・・・・・・・・・・・・・・・・・・・・・・・・・ 7

5. Productive international exchange between Shizuoka University and Changwon National
University
・・・・・・・・・・・・・・・・・・・・・・・・・15

6. Proceedings of Japanese Students Technical Program
・・・・・・・・・・・・・・・・・・・・・・・・・17

7. Proceedings of Korean Students Presentation
・・・・・・・・・・・・・・・・・・・・・・・・・58

8. Acknowledgment・・・・・・・・・・・・・・・・・・・・・・・・・94-1-

1. Purposes of the Short Term-Stay Program of Shizuoka University

This project is promoted by Japan Student Services Organization (JSSO). The main
purpose is a student-based international exchange between a laboratory and a laboratory. In
order to achieve the productive international exchange for both sides’ students, the preparationand the progression managed by the students.

-2-2. Agenda of the Short Term-Stay at Shizuoka University
The project was held from January 5, 2012 to January 11, 2012. The detail agenda is asfollow.

5th January, DAY 1
Traveling:
Changwon → (Bus) → Busan → (Airplane) → Seoul Gimpo International Airport →(Airplane) → Tokyo Haneda International Airport → (Airport Limited Express) →Shinagawa Station → (Shinkansen) → Hamamatsu Station
Check into the hotel

6th January, DAY 2a.m.

Opening ceremony

Prof. Saito’s speech, Prof. Shin’s speechSelf-introduction

Presentation of Saito Laboratory
Tour in Saito Laboratory (Part 1, 4th floor)
Launchp.m.

Tour in Saito Laboratory (Part 2, 5th floor)
Presentation of Shizuoka University Motors (SUM)
Tour of Shizuoka University Motors (SUM)
Welcome Party (Japanese restaurant)

7th January, DAY 3a.m.

Fukuta Laboratory’s research presentation (1 student)
Sanada Laboratory’s research presentation (2 students)

Launchp.m.

Shin Laboratory’s research presentation (5 students)
Saito Laboratory’s research presentation (3 students)-3-

8th January, DAY 4a.m.

Saito Laboratory’s research presentation (5 students)

Launchp.m.

Saito Laboratory’s research presentation (2 students)
Korea side students’ report creating

9th January, DAY 5a.m.

Shopping at the huge shopping mall

Launchp.m.

Shopping at the huge shopping mall
Japan VS Korea bowling game
Farewell party (Korean-style grilled beef Restaurant)

10th January, DAY 6
Traveling:
Hamamatsu Station → (Shinkansen) → Shin-Osaka Station
Tour in Kyoto

11th January, DAY 7
Tour in Kajishima Laboratory (Graduate School of Engineering, Osaka University)
Traveling:
Kansai International Airport → (Airplane) → Busan → (Bus) → Changwon-4-

3. List of Participants

Guest: Shin Laboratory, Changwon National University, Korea
Name

StatusByeongrog Shin

Professor

Kyeongrock Jang

Department of
Mechanical Engineering

Jongmin Kim
Heesung Lee

Affiliation

3rd-year Bachelor's degree student

Changwon National
University

Chunggi Moon
Jeonghoon Song

Host: Saito Laboratory, Shizuoka University, Japan
Name

StatusAffiliation
Graduate School of

Takayuki Saito

Professor

Science and technology,
Shizuoka University

Rintarou Tachibana

2nd-year Master's degree student

Masahiko Toriu
Graduate School of
Yasuyuki Nagami
Engineering,
Yuki Mizushima

1st-year Master's degree student
Shizuoka University

Taikan Mori
Masahiro Yamada
Ryosuke Motoyoshi
Masanobu Tsukamoto
4th-year Bachelor's degree student
Yuta Nakamura

Faculty of Engineering,

Hajime Furuichi

Shizuoka University

Daisuke Shinohara
3rd-year Bachelor's degree student
Yuki Masumoto-5-Other Participants

Name:

Keisuke Noba

Affiliation: Fukuta Laboratory, Faculty of Engineering, Shizuoka University, Japan

Name:

Kazuhide Matsushita

Affiliation: Sanada Laboratory, Faculty of Engineering, Shizuoka University, Japan

Name:

Takuya Tanaka

Affiliation: Sanada Laboratory, Faculty of Engineering, Shizuoka University, Japan

Name:

Shintaro Hiragi

Affiliation: Shizuoka University Motors, Shizuoka University, Japan-6-

4. Report on Short Term-Stay Program of Shizuoka University

Opening ceremony: Prof. Saito’s speechOpening ceremony: Prof. Shin’s speech

Korean student self-introduction

Japanese student self-introduction

Tour in Saito Laboratory (4th floor)

Tour in Saito Laboratory (5th floor)

Tour of Shizuoka University Motors

Tour of Shizuoka University Motors-7-

Korean student presentation (Shin Lab.)

Korean student presentation (Shin Lab.)

Japanese student presentation (Sanada Lab.)

Japanese student presentation (Fukuta Lab.)

Japanese student presentation (Saito Lab.)

Japanese student presentation (Saito Lab.)

Japanese student presentation (Saito Lab.)

Japanese student presentation (Saito Lab.)-8-

Japanese student presentation (Saito Lab.)

Japanese student presentation (Saito Lab.)Free talks during coffee break

Korean student report creating

Japanese-Korean mixed bowling game

Japanese select team VS Korean select team

Farewell party(Korean-style grilled beef Restaurant)

Farewell party(Korean-style grilled beef Restaurant)-9-

Report 1
Date(D.M.Y) 8th Jan, 2012
Name

Jang Kyoungrock

Signature

University

Changwon National University

Country

Korea

I went to Shizuoka University in 5 January 2012. I was surprised at Japanese culture. Because
Shizuoka University`s student(Nagami) and professor(Saito) went early at Station.
And Nagami bring to our hotel. So i think to kind japanese.
Next day, we went to Shizuoka University with Nagami. And we reason about Saito lab.
We was very surprised to laboratory`s scale. For example, each student looked to specialist,
laboratory had expensive device(high speed video camera, HPTS ets) and very clean inuniversity. Saito`s lab researched about bubble motion and variety optical fiber probes (OFP).
It`s very interested in me. Because my lab research about fluid mechanics.
We went to hanabasi station for welcome party. We ate meat and Sake. It was similary to
Korea`s Soju. We broken up at PM. 8.
I thought similar theme but many element is different. So it`s a little diffcult that Shizuoka
university`s student say about bubble to me.
And our laboratoty`s student say about vertical and horizontal axis wind turbine and Magus
effect in presentation. Japanese student ask about our theme. It was very thanks.
This course is very beneficial to us. This course is Japan-Korea International Exchange
Program. We was good communicatation Though main language was English. Sometime
communication was hard. Because japaness used vocabulary is differnt in Korea.
I hope to get the more information about bubble. For example, how to make OFP, measuring
bubble`s velocity and motion. I know why Japanese education is high quality.
I`m pleased to make new friend. I want to get in touch with Shizuoka university`s student.
Thang you..

- 10 -

Report 2
Date(D.M.Y) 8th Jan, 2012Name

KIM JONGMIN

Signature

University

Changwon national University

Country

Korea

I write it classify by subject.

future development of the research : I think subject. beforehand we are plan ahead that'student exchange suppurt program' in detailed. of course, from this program, we are makepreparations arrangement. but we are only prepare that it. that is ppt, announcement data. thennext time, I hope that. that is actually experimentation accomplishment. of course this present
also very interest. in conclusion, if it is possible, that is a help to me.

understanding Japanese culture : In this time, learned to varios Japanese culture. ordinary
times, I'm very interested in Japanese culture. for instance, the first day in dining together,
new food culture come in contact. specially each pay a charge pay it. that is food charge. ofcourse I know little Japanese culture. and this part is originality. in conclusion, each contury
has merits and fauits, important point is comprehend it. that is diversity each culture.

importance foreign study : 'student exchange support program' on the way, Naver had I
realized my ignorance more keenly than at this time. I did not need foreign language in the
Korea. But That's needed immediately in this place. because to according to circumstances, I
must express my intention clearly. Result in, I know from learn by experience. that is'importance foreign study'

I would like to get in touch with between Changwon National University and Shizuoka
National University.

- 11 -

Report 3
Date(D.M.Y) 8th Jan, 2012
Name

LEE HEE SUNG

Signature

University

Changwon National University

Country

Korea

Thank you for invite Shizuoka university and i`m happy participate in Korea and Japan
exchanged program and cultural and scholarship exchange between Korea and Japan
I heard Shizuoka University is very excellent university and top level so i`m a glory
Our laboratory is computational fluid dynamic engineering
Our lab studied wind turbine the other side Saito` lab studied (I think) bubbles, optical fiber
probe then different subject between Shin lab and Saito lab thus scholarship exchange
between Shin lab and Saito lab is very important and helpful
Saito laboratory are studied very interesting but i`m felt a little difficult so i`m many learned
So Thank you for giving me a chance the listening the presentation the Saito laboratory
Saito lab has very expensive experiment equipment so we just laboratory tour time is very
interesting and exciting
Moreover we obtain English speech, listening ability during the get ready presentation
I think this era is international relationship is very important so Korea and Japan exchanged
program is very important thus I hope this program is maintenance
I am heard and watching just Japan culture from a television broadcast and comic books andmovie but this program through obtain directly experience so i`m delightful
Japan and Korea cultural have some similarity also foodI am hope the this program is more extension and we would like to get in touch with between
Changwon National University and Shizuoka National University .

- 12 -

Report 4
Date(D.M.Y) 8th Jan, 2012
Name

Moon Chung Gi

Signature

University

Changwon National University

Country

Korea

Thank you for invite me in Shizuoka university.
I travel Japan in first my life. I saw many different culture, food, house, shop....
I impress the food because Korea food similar. And Japan is very clean street, toilet…
This program is studied good culture in Japan.
We get through discussion in Shizuoka University of professor saito laboratory student.
They present subject in make use of Bubble. I know that Bubble is development possibility.
And I realize that basic theory fluid dynamics. And I see vary experiment equip in professor
Saito laboratory.This equip is interested and novelty. Specially pipe cut equip is best Smallpipe see through telescope and the combination two pipe is very delicacy.
My English ability is nice the better friendship in Shizuoka University students.It leaves has
something to be desired because communication is not very well.
And thank you for giving me a chance the listening the presentation the professor Saito
Laboratory.
If my Return to korea very hard study English. I hope japans friend better than friendship.
Get in touch with between Cangwon National University and Shizuoka University
I hope see we again.
Thank you.

- 13 -

Report 5Date(D.M.Y) 8th Jan, 2012
Name

Song Jeong Hoon

Signature

University

Changwon National University

Country

Korea

first of all , thank you for granting me Shizuoka university .
I am very interesting in Jappanese culture. During the 5days , I am very impressed by
Japanese students research and citizen`s ceremony. For examples , a city is very clear andpeople is kindhearted. Specially Saito`s lab people is very kind and enthusiastic.
Their research is professional. Such as s-top , t-top is rare information . I have not seen ever
korea. This opportunity is very important experience. Also I realize necessity about
importance of foreign study. This opportunity is very rare, but I realize that Culturalinterchange between korea and Japan is very important. After this cultural interchange,if weenlarge cultural interchange between Korea and Japan , So many advantage is existed.
Their experiment equipment is very expensive I have not seen that in Korea.
I will tell Korean that these sensation , Japanese culture , fluid dynamics study, and manyothers. In order to development in Korea.
Thank you for valuable experience for us. Taking this opportunity ,We would like to get intouch with between Changwon National University and Shizuoka Natiouniversity.
In order to each other `s development,I think that each other`s continuous relationship is very
important. So ,after this chance ,we must get in touch with each other.
And I feel that my a basic knowledge about fluid dynamics is very insufficient.
So I am encouraging , I would like to study hard after return the Korea. I am put feelinconvenience about Japanese separation.
Thank you.

- 14 -

5. Future Framework International Exchange between Shizuoka University andChangwon National University

Host teacher’s report on Short Term-Stay Program in Shizuoka University

Takayuki Saito, Prof. and Dr. Eng.
Graduate School of Science and Technology
Shizuoka University

The Short-term Stay Program in Shizuoka University, that is a student program between
Saito’s laboratory of Shizuoka University and Shin’s laboratory of Changwon National
University (Korea), promoted by Japan Student Service Organization (JASSO) was
successfully performed. The students who participated in this program have exchanged theirfriendships and built a new relationship between the two countries. Furthermore, for thesethree months from October to December, by themselves, they discussed how to carry out thisstudent program, through a lot of e-mail in English, and prepared meetings that should be heldat Hamamatsu campus. Prof. Shin and me gave them only aims of the program and did not
direct the details. In spite of the first experience for them, they perfectly prepared it andsuccessfully performed it.
They now know that “open mind” is essential to build friendship and to understand eachother. This is the great success which is impossible to describe in a thin report.
I thank Prof. Shin heartily for his acceptance to my proposal regarding this student programand his visit to Shizuoka University.

- 15 -

6. Proceedings of Japanese Students Technical Program
In order to achieve meaningful discussions about presentations with Korean students,
under Prof. Saito’s supervision, Japanese students made the proceedings of the researchcontent.

- 16 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Relation between Wake and Zigzag Motion of a Single Bubble
Rintarou Tachibana
Graduate school of Engineering,
Shizuoka University
3-5-1 Johoku, Naka-ku, Hamamatsu,
Shizuoka, Japan

Takayuki Saito
Graduate school of Science and Technology,
Shizuoka University
3-5-1 Johoku, Naka-ku, Hamamatsu,
Shizuoka, Japan

Keywords: Zigzag motion, Wake, Lift force, Shape deformation
Abstract: In the present study, a transition mechanism to explain the change in the motion of a single ascending bubbl
e from linear to zigzag was investigated experimentally. We focused on the relationship between bubble motion (gravity-center motion and shape deformation) and hairpin-like vortex motion. First, these motions were visualized using the inf
rared shadow technique (IST) and the laser induced fluorescence using HPTS (LIF/HPTS) method. Based on the visuali
zation, the relationship was discussed qualitatively. Second time-series fluctuations of the bubble motion and the vortex
motion were quantified. Furthermore, the lift force acting on the bubble was calculated from the displacement of the gr
avity-center. Finally, the close relation between the wake, the lift force and the shape deformation was discussed quantit
atively. We concluded that the wake instability induced by the initial shape deformation observed just after the launch
was the dominant factor for the zigzag motion.

1. Introduction
Bubbles are frequently employed in a great variety ofindustrial process such as CO2 dissolution process in theenvironmental plant (Saito et al., 2001), transportation of oil
by employing bubble buoyancy driven flows, oxygen supply
in the bio reactor and so on. For the safe and efficient
operation of the plants, the accurate and adequate modeling of
the bubbly flow is essential. To clarify the bubbly flow
structure (coherent structure), a lot of researches have been
conducted both experimentally and numerically (Mudde,2005; Darmana et al., 2009). A step-by-step understanding of
the bubbly flows is important because there are mutual
correlations between the hierarchical structures (Higuchi and
Saito, 2010). The size of a single bubble has a great effect on
the motion or formation of the bubbly flow (Azbel, 1981).
However, even if the knowledge of a single bubble, thesmallest unit in the bubbly flow, such as a motion mechanism
and its relations with mass transfer have not been yet
completely understood. It is well known that the bubble size isa dominant factor for characterizing the bubble motion (Cliftet al., 1978). In particular, bubbles with 1.3 – 4.2 mm
diameter have interesting characteristics such as zigzag/spiralmotion in a rest water column (Magnaudet and Eames, 2000),
wake structure so called hairpin-like vortex (Lunde andPerkins, 1997) and the unsymmetrical shape deformation(Saito et al., 2010) and so on. Because of their deep
correlation with the mass transfer, researches bases on a
discussion with their relationship have been spiritedly
conducted (Fan and Tsuchiya, 1990; Koynov et al., 2005).
Intriguingly the bubble in the range takes the highest masstransfer coefficient κL (Motarjemi and Jameson, 1978).
Many researchers have been investigating the motion
mechanism of the bubble by employing various experimental
methods and reported some noteworthy results. For an
instance, a bubble wake structure is closely related to bubble
shape deformation (Sanada et al., 2007; Brücher, 1999).
Sanada first visualized the standing eddy on the bubble rearsurface by using photochromic dye. Brücher visualized
pseudo wake structure by employing DPIV. They consistently
concluded the bubble shape deformation is closely related tothe structure or shedding of the hairpin like vortex. However,to obtain or clarify the more precise relationship between
them, the detailed description of the bubble shape is required.
In fact the bubble surface deformations can not be perfectly
described by the fluctuation of the aspect ratio (Miyamoto andSaito, 2005). Furthermore a relationship between the wakeinstability and the path instability was reported (De Vries etal., 2002; Zenit and Magnaudet, 2009). De Vries et al.
visualized the wake by employing schlieren method withslight temperature gradient. They concluded the zigzag
motion is triggered by periodical replacement of two
streamwise vortices. Zenit and Magnaudet employed
2-dimensional PIV measurement for the purpose of
calculating force acting on the bubble from circulation in thewake. They experimentally identified that the existence of thetwo vortices took a significant role in the path instability,
namely the wake generates the lift force on the bubble.
Researches based on DNS have been devoted to the goodunderstanding of the zigzagging motion (Magnaudet andMougin, 2007; Gaudlitzs and Adams, 2009). Magnaudet andMougin investigated the difference between the stable pathand unstable path in terms of the relationship between the
bubble shape deformation (aspect ratio) and the wakeinstability. They concluded the wake instability induces thelift force on the bubble; therefore, the bubble path oscillates.
Gaudlitzs reported the existence of two surface waves on the
bubble surface leads to the periodical deformation of bubble
shape. Also, he suggested the relationship between the bubble
shape and the shedding of a horse-shoe-like vortex.
As mentioned above, a lot of researchers focused on the
representative three factors, namely, the bubble surface
deformation, the wake instability and the Lift force. However
the answer for the open question, which is the dominant factor
for the motion mechanism so called “egg or chicken”, is still
unspecific.

- 17 -

The purpose of the present study is to experimentally
clarify a transition mechanism of a single bubble motion interms of a close relationship among the bubble motion(gravity center motion and the lift), the bubble deformation(not aspect ratio but left-right asymmetry at the bubble edge)
and the bubble wake motion. We simultaneously visualized
the bubble shape and the bubble wake by employing the Laser
induced Fluorescence using HPTS (LIF/HPTS) combinedwith Infrared Shadow Technique (IST). First we qualitatively
discuss a relationship between the bubble motion and thewake motion (PPHVL, Position of the point of the hairpin-likevortex leg). Second the quantitative relationship between themis discussed. Based on the results we discuss a mechanism of
the bubble zigzagging motion. Finally we tentatively
concluded that the bubble zigzag motion was triggered andmaintained by the wake instability which was induced by theunsymmetrical liquid motion near the bubble surface.

2. Experimental setup
Figure 1 shows a schematic diagram of an experimental
setup employed in the laser induced fluorescence using HPTS
(LIF/HPTS) combined with infrared shadow technique (IST)
method. By employing LIF/HPTS method, the dynamicaldissolution process and the structure of the part of the bubble
wake can be visualized (Hanyu and Saito, 2010). Also the IST
method was employed for the clear visualization of the bubble
shape; e.g. the interface between the bubble and its
surrounding liquid (Tokuhiro et al., 1998).
An acrylic water vessel (a) (100 × 100 × 300 mm3) was
filled with degassed clean water (produced with a Millipore
system, specific water resistance was 18.2 MΩ cm andorganic particles were less than 5 p.p.b.), and a very small
amount of HPTS (0.0001 [mol/l]) was dissolved into the water(b). The temperature of the water during all experiments was
25 ± 0.5 °C. An argon ion laser (Innova 70C-3, COHERENT)(c) was used to excite the HPTS. The laser beam was sheetedby a rod lens (d). The thickness of the laser sheet was 1 mm.
CO2

z
x

(a)
(k)

(b)
(k)

y
(d)

(i)

(c)

(i)

(g)

(f)

(h)

(e)

(j)

(a) Water Vessel, (b) Clean water & HPTS, (c) Ar ion laser,(d) Rod lens, (e) Bubble-launch device, (f) Hypodermic needle,(g) High-speed video Camera A, (h) High-speed video Camera B(i) Sharp cut filter, (j) Function generator, (k) Red LED (633 nm)

FIGURE 1. Schematic of Experimental setup used in
LIF/HPTS combined with IST method.

To obtain a high reproducibility of the bubble condition andthe perfect 2-D zigzag trajectory, a special-madebubble-launch device (e) (Saito et al., 2010) with hypodermic
needle (f) was employed. High-speed video cameras(Photoron, Fastcam) (g), (h) were mounted on 6 axes opticalstages for the precise adjustment (the smallest unit of theregulation was 1.0 µm for x, y, z and 0.01 deg for α, β, θ ).
The camera A was for the visualization in x-z plane; i.e.
zigzag plane. The camera B was for the confirmation of thelinear trajectory in the y-z plane and the positional relation
ship between the laser sheet and the bubble. Horizontaltransition of the bubble for the y-z plane was 0.1 mm. On theother hand, the transition for the x-z was 10 mm; therefore thebubble infallibly shows perfect 2-D motion in the x-z plane.
All bubbles launched from the device were inevitably within
the same plane; i.e. the bubbles passed the same position in
the laser sheet. The uncertainty for the average value of the
bubble gravity-center was within 2 %. These cameras were
equipped with a zoom lens (f=105mm: Nikon) and bellows(Bellows Focusing attachment pb-6: Nikon) to obtain highspatial resolution: 12 [µm/pixel]. The uncertainty of the
bubble shape mainly due to pixel error was within ± 1 %. A
sharp-cut filter (512 high-pass, SIGMA KOKI) (i) inserted
between the lens and the vessel cuts scattering light from the
bubble surface. The bubble launch-device and the high-speed
video camera were synchronized through a function generator(SG-4105, IWATSU) (j). The single bubbles were filmed at
any given location and at any given timing. In order to obtainclear images of the bubble shape (contour), IST method using
a red LED lights (wave length of 630 nm, LDR-140, NISSIN
ELECTRONIC) (k) was employed. Hence, the simultaneous
measurements of both IST images and LIF images were
performed.

3. Results and discussion
3.1 Bubble motion
A bubble with critical Weber number ranging from 3 to 3.5
shows zigzag trajectory (Hartunian and Sears, 1957; Moore,1965). More recently, some researchers focused on not only
Reynolds number and Weber number but also aspect ratio
because the detailed description of the bubble shape isessential for a good understanding of the zigzag motion
mechanism (Ellingsen & Risso, 2001; Magnaudet andMougin, 2007; Zenit and Magnaudet, 2008). Furthermore, thebubble oscillates in its own surface at mode 2,0 or mode 2,2(Lunde and Perkins,1998; Pozrikidis, 2004).
The properties of our examined bubble were Deq= (a2·b)
1/3=2.8 mm, ReB = 849, We = 3.4, Mo = 2.6×10-11 and Eo =1.2 respectively. All dimensionless numbers were calculatedbase on the bubble just after its launch where the shape can beassumed oblate ellipsoid. The error for the calculation of theDeq was within 1% (Miyamoto and Saito, 2005 for acomprehensive review).
In the image analysis for the bubble motion, we calculated
the coordinates of bubble contours from the bubble images
processed by binarization and a Sobel filter, and also thecoordinates of the bubble gravity centers were obtained.
Furthermore, the coordinates were transformed topolar-coordinate system (r, θ) with its origin at the gravity- 18 -

center (See Fig. 3). The bubble contours were expressed asfollows (Duineveld, 1995);Nr (θ ) = A0 + ∑ ( An cos nθ + Bn sin nθ ) ,n =1

where An and Bn were calculated by FFT with mode order N of
8. The major axis D1 of the bubble image was calculated as the
maximum value (i.e. D1∣θ = θ1), and the minor axis D2 was
calculated as r (θ1 + π/2) + r (θ1 + 3π/2). The aspect ratio was
calculated by D1/D2. The ratio has been used in many former
researchers (Ellingsen and Risso, 2001); however it isinsufficient for the purpose of discussing left-right asymmetryof the bubble shape. Therefore we introduce right and leftedge curvatures, κR(θ )∣ θ = θ1 at the right edge and κL(θ )∣θ = θ1+π at the left edge in order to quantitatively discuss thetime-series shape asymmetry (Saito et al., 2010; Miyamotoand Saito, 2005). They are calculated byκ=| r 2 + 2(dr / dθ ) − r (d 2r / dθ 2 ) |[r 2 + (dr / dθ ) 2 ]2 / 3,

here, θ = θ 1 for κR, θ = θ 1 + π for κL.
Figures 2 show the bubble zigzag trajectory with bubble
shape (left figure) and the dimensionless curvatures of theedge (center and right figure), respectively. The dominantfrequency, wavelength and amplitude of the zigzag motion
were 7 Hz, 39.6 mm and 3.0 mm, respectively. The dominantfrequencies of the edge dimensionless curvatures were 70.0
Hz. At first, a single bubble ascents linearly, and then the
bubble shape was axisymmetric [t = 0 [s] - t = 0.075 [s]]. Near
the first inversion point, the symmetric property collapsed; e.g.
the magnitude of the shape deformation at the right edge (κR)
was larger than that of the left edge (κL). However, after the
middle point between the inversion points (0.12[s]), thetendency collapsed: i.e. magnitude of the shape oscillation of
the left edge gradually increased, while that of the right edge
decreased. Near the second inversion point, the κL took
maximum value. After the point, the magnitude of the shape

Elapsed time [s]0.4

deformation at right edge increased again and took maximum
value near the third inversion point. These asymmetrical andperiodical deformations of the bubble edge characterize thezigzag motion. The zigzag motion is closely related to the
bubble shape (surface) deformation.

3.2 Wake structure and its motion
The wakes behind a hard sphere or bubble are one of the
fascinating phenomena in the fluid mechanics field. The
formation and shedding frequency of vortices from a spherehighly depends on the Reynolds number (Sakamoto andHaniu, 1994). In terms of the bubble wake, the key factors
which describe the wake are not only the Reynolds number
but also the bubble shape because millimeter size bubble
oscillates its own surface periodically (Lunde and Perkins,
1998). Some researchers tightly focused on the wakeinstability, because the transition of the bubble gravity centerfor horizontal direction coincides with the stability of thewake (Magnaudet and Mougin, 2007).
Figure 3 shows time-series growth process of the wakebehind a single zigzag bubble near the first inversion point. A
standing vortex developed from the center of the bubble rearis observed in Fig. 3 (a), and during this section the bubble
rose vertically. Furthermore, the bubble shape is axisymmetricand the major axis of the bubble is horizontal. The symmetricproperty is gradually collapsing with the bubble ascent andthe major axis is gradually leaning to the left. Just before thefirst inversion point, at (b), the hairpin-like vortex is shed.
The bubble changes its orientation and the direction of the
motion. After this, the vortex is periodically shed from the
bubble rear (c)-(d), and each time the bubble changes its
direction of the motion. As marked by a black allows in Fig. 3,
a position of the point of the hairpin-like vortex leg (PPHVL)
fluctuates at the rear of the bubble. Before the first inversion
point, Fig. 3 (a), PPHVL was positioned just at the minor axisof the bubble. At this time, the fluctuations of curvature were
gentle. However, when the curvature changed its balance (i.e.
the magnitude of the curvature fluctuation at right edge
increased), PPHVL shifted toward the right edge [(b)-(c)].
When the bubble shape became axisymmetric again, PPHVL
shifted toward the center [(c)-(d)]. The deep correlation
between the bubble shape and the wake motion emerges.

0.3

0.2

0.1

0
-15 -10 -5

x [mm]

0

0.5

1

1.5

κL [1/mm]

0.51(a) t=t0 [ms] (b) t0+20 [ms] (c) t0+30 [ms] (d) t0+40 [ms]
κL ≒ κR
κL > κR
κL > κRκL ≒ κR

1.5

κR [1/mm]

FIGURE 3. Wake behind a single zigzag bubble aroundthe first inversion point.
FIGURE 2. A relation between trajectory and bubble shape.

- 19 -

3.3 Relation between the bubble motion and thewake motion
3.3.1. Shape deformation and the wake
A lot of researchers focused on the relationship between
the wake and the bubble shape deformation (Brücker, 1999;
Magnaudet and Mougin, 2007; Gaudlitz and Adams, 2009).
Their researches are very interesting and valuable tounderstand the motion mechanism of the zigzag bubble,
however, to deeply understand the mechanism, more detailed
discussions based on the micro phenomena are essential. As
discussed in the 3.2, the wake legs shift its attaching positionat the bubble rear. To quantitatively discuss the relationship,
we defined the leg position (Figure 4).
Major axis
Minor axis
Gravity CenterαHorizontallineθκR/κL. After the first inversion point (0.075[s] ~), the lag was
π [rad]. The shape deformation was accompanied by thewake instability. This quantitatively means the wake motion
dominates the bubble zigzag motion.

3.3.2 Lift force and the wakeSome researchers reported that the wake motion is closely
related to lift force acting on the bubble (de Vries et al., 2003;
Mougin and Magnaudet, 2006; Zenit and Magnaudet, 2009).
They reported that the path instability of the zigzagging
bubble was triggered by the instability of the bubble wake.
In this study we estimated the lift from the x-direction
displacement of the gravity-center of the bubble, Fx=
ρVd2x/dt2. This estimation was adequate according to aprevious study (Zenit and Magnaudet, 2009).
Figure 6 shows the time-series fluctuation of the lift. The
dominant frequency of the lift force fluctuation was 70 Hz.
This value is almost as same as that of the wake motion andthe shape deformation of the bubble. The lag between θ andFx was π/4 [rad.]. This implies the wake instability induced
the lift force acting on the bubble. On the other hand, the lag
between Fx and κR/κL was also π/4 [rad.]. It is considered thatbubble gravity-center transition toward horizontal direction
increases the asymmetry property between the bubble and theliquid; therefore the bubble shape became axisymmetric.
0.08

Elapsed time [s]Position of the Point of the
Hairpin like Vortex Leg

FIGURE 4. Definition of PPHVL,  and .
Figure 5 shows the time-series fluctuation of thegravity-center, the shape deformation and the wake leg
position. Obviously wave form of each profile was very
similar. The dominant frequency for the θ was 70 Hz. Whenthe bubble ascents linearly (0.02 [s] ~ 0.05 [s]), no time lags
are observed between each fluctuation. However thefluctuation of the θ became slightly faster than that of the

0.06

0.04

0.02
-3 -2 -1 0x [mm]-1 0
Fx

1[10-3 N]FIGURE 6. Time-series fluctuation of the lift force acting
on the bubble.

0.08

Elapsed time [s]3.4 Primary cause of the wake instability
0.06

0.04

0.02
-3 -2 -1 0

0.8 1 1.23040x [mm]

κR /κL [-]θ [deg]

FIGURE 5. Time-series fluctuation of x position, curvatureand the vortex leg position.

Initial shape deformation just after launch characterizes the
motion of the bubble (Tomiyama et al., 2002). In the present
study we control the drift angle of the bubble trajectory by
employing an unsymmetrical-shape hypodermic needle.
Furthermore the reproducibility of the bubble was so high thatthe initial shape deformation will be always the same.
Therefore the trajectory will also be the same. Figure 6 shows
the visualization results of the interface deformation just after
bubble was launched from the needle. As marked gray broken
line in the figure, a ripple with high curvature propagates the
bubble surface in the counterclockwise direction. On the other
hand, no noticeable deformation was observed at the left edge.
Because of this left-right symmetry, the production amount of
the vortex at each edge (right and left) should not be the same

- 20 -

as reported by the numerical study (Magnaudet and Mougin,2007). Therefore the stagnation points at the front and the rear
were differing from that of the linear trajectory (Saffman,
1956). In our characteristic however reliable experimental
setup, the trigger for the zigzag motion was the initial shapedeformation which induces the asymmetric properties for thesurrounding liquid, namely, wake instability. The detailed
discussion on the primary instability is the most important
future work.

ripplet=0.0 [ms]t=1.0 [ms]t=3.0 [ms]t=5.0 [ms]FIGURE 7. Bubble surface deformation observed justafter the bubble launch.

4. Concluding remarks
In the present study, a transition mechanism to explain thechange in the motion of a single ascending bubble from linear
to zigzag was investigated experimentally. The following
conclusions were obtained:• Fluctuation of the wake motion (vortex leg motion), the Lift
force and the shape deformation showed same tendency; i.e.
the dominant frequencies of the each fluctuation were thesame.
• The wake motion was the dominant factor for the bubble
zigzag motion.
• The shape deformation observed just after bubble launch
have a great effect on the zigzag trajectory (drift angle) andthe wake instability.

5. Acknowledgements
The present study was promoted and financially supported
by Category "A" of the Grants-in-Aid for Scientific Research,
Japan Society for the Promotion of Science. We thank JSPS
for its help in the financial support.

6. Reference
Azbel, D. 1981 Two-phase flows in chemical engineering,
Cambridge.
Brücker, C. 1999 Structure and dynamics of the wake of
bubbles and its relevance for bubble interaction. Phys.
Fluids 11, pp. 1781-1796.
Clift, R., Grace, J.R. & Weber, M.E. 1978 Bubbles, Drops andParticles, New York: Academic.
Darmana, D., Deen, N. G., Kuipers, J. A. M., Harteveld, W. K.
& Mudde, R. F. 2009 Numerical study of homogeneous
bubbly flow: Influence of the inlet conditions to thehydrodynamic behavior, Int. J. Multiphase. Flow 35, pp.
1077-1099
De Vries, A.W.G., Biesheuvel, A. & Van Wijngaarden, L.
2002 Notes on the path and wake of a gas bubble rising inpure water, Int. J. Multiphase. Flow 28, pp. 1823–1835.
Duineveld, P. C. 1995 The rise velocity and shape of bubbles
in pure water at high Reynolds number. J. Fluid Mech.
292, pp. 325-332.
Ellingsen, K. & Risso, F. 2001 On the rise of an ellipsoidal
bubble in water: oscillatory paths and liquid-induced
velocity. J. Fluid Mech. 440, pp. 235-268.
Fan, L.S. & Tsuchiya, K. 1990 Bubble wake dynamics inliquids
andliquid-solid
suspensions,
Butterworth-Heinemann Series in Chemical Engineering.
Gaudlitz, D. & Adams, Nikolaus A. 2009 Numericalinvestigation of rising bubble wake and shape variations.
Phys. Fluids 21, pp. 122102.
Hartunian, R. A. & Sears, W. R. 1957 On the stability of smallgas bubbles moving uniformly in various liquids. J. Fluid
Mech. 3, pp. 27-47.
Higuchi, M. & Saito, T. 2010 Quantitative characterizationsof long-period fluctuations in a large-diameter bubble
column based on point-wise void fraction measurements.
Chem. Eng. J. 160, pp. 284-292.
Hanyu, K. & Saito, T. 2010 Dynamical mass-transfer processof a CO2 bubble measured by using LIF/HPTS
visualization and photoelectric probing. Can. J. Chem.
Eng. 88, pp. 551-560.
Koynov, A., Khinast, J. & Tryggvason, G. 2005 Mass
Transfer and Chemical Reactions in Bubble Swarms with
Dynamic Interfaces, AIChE J. 51, pp. 2786-2800.
Lunde, K. & Perkins, R.J. 1997 Observations on wakes
behind spheroidal bubbles and particles. ASME Fluids
Engineering Division Summer Meeting, paper 3530.
Lunde, K. & Perkins, R.J. 1998 Shape Oscillation of RisingBubbles. Appl. Scientific Research 58, pp. 387-408.
Magnaudet, J. & Eames, J. 2000 The motion ofhigh-Reynolds-number bubbles in inhomogeneous flows.
Annu. Rev, Fluid Mech. 32, pp. 659-708.
Magnaudet, J. & Mougin, G. 2007 Wake instability of a fixed
spheroidal bubble. J. Fluid Mech. Vol. 572, pp. 311-337.
Miyamoto, Y. & Saito, T. 2005 Relationship between interface
motion of an isolated bubble and its zigzagging motion of
the center of gravity. Transaction of Japan Society of
Mechanical Engineers Series B 71, pp. 1307-1313.
Moore, D. W. 1965 The velocity of distorted gas bubbles in aliquid of small viscosity. J. Fluid Mech. 23, pp. 749-766.

- 21 -

Motarjemi, M. & Jameson, G.J. 1978 Mass transfer from verysmall bubble -The optimum bubble size for aeration-.
Chem. Eng. Science 33, pp. 1415-1423.
Mougin, G. & Magnaudet, J. 2006 Wake-induced forces andtorques on a zigzagging/spiraling bubble. J. Fluid Mech.
567, pp. 185-194.
Mudde, R.F. 2005 GRAVITY-DRIVEN BUBBLY FLOWS.
Annu. Rev, Fluid Mech. 37, pp. 394-423.
Pozrikidis, C. 2004 Three-dimensional oscillations of risingbubbles. Engineering Analysis with Boundary Elements 28,
pp. 315-323.
Saffman, P. G. 1956 On the rise of small air bubble in water. J.
Fluid Mech. 1, pp. 249-275.
Saito, T., Kosugi, S., Kajishima, T. & Tsuchiya, K. 2001
Characteristics and Performance of a Deep-Ocean
Disposal System for Low-Purity CO2 Gas via Gas Lift
Effect. Energy & Fuels 15, pp. 285-292.
Saito, T., Sakakibara, K., Miyamoto & Y., Yamada, M. 2010 A
study of surfactant effects on the liquid-phase motion
around a zigzagging-ascent bubble using a recursive
cross-correlation PIV. Chem. Eng. J. 158, pp. 39-50.

Sakamoto, H., Haniu, H. 1994 the formation mechanism andshedding frequency of vortices from a sphere in uniform
shear flow. J. Fluid Mech. 287, pp. 151-171.
Sanada, T., Shirota & M., Watanabe, M. 2007 Bubble wakevisualization by using photochromic dye. Chem. Eng.
Science 62, pp. 7264-7273.
Tokuhiro, A., Maekawa, M., Iizuka, K., Hishida, K. & Maeda,
M. 1998 Turbulent flow past a bubble and an ellipsoidusing shadow-image and PIV techniques. Int. J.
Multiphase Flow 24, pp. 1383-1406.
Tomiyama, A., Celeta, G.P., Hosokawa, S., Yoshida, S. 2002
Terminal velocity of a single bubbles in surface tension
force dominant regime, Int. J. Multiphase Flow 28, pp.
1497-1519
Zenit, R. & Magnaudet, J. 2008 Path instability of risingbubbles: A shape-controlled process. Phys. Fluids 20, pp.
061702.
Zenit, R. & Magnaudet, J. 2009 Measurement of thestreamwise vorticity in the wake of an oscillating bubble.
Int. J. Multiphase Flow 35, pp. 195-203.

- 22 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

An effect of zigzag and surface motions of a CO2 bubble
on the mass transfer from the bubble to the surrounding
Masahiko Toriu
Graduate School of Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: CO2, mass transfer coefficient; zigzag motion.
Abstract: A bubbly flow is very useful for aeration, agitation and an enhancement of chemical reaction, etc. in industrial
processes. In order to improve the efficiency of the industrial plants, we should acquire the knowledge of a bubbly flow: e.g.
bubble motion, mass transfer and surrounding liquid motion. Using a single CO2 bubble well-controlled in its zigzag motion andsurface oscillation, we discuss a relation between the bubble motion and the mass transfer. For this particular purpose, we
precisely measured the bubble volume and the surface area, using two high-speed cameras and mirrors. By image processing, a
3D-bubble shape was reconstructed based on the projected bubble images. We regarded the volume/surface area of 3D-model as
the volume/surface area of the examined bubble. In addition, instantaneous mass-transfer coefficients were calculated from theseresults. The mass transfer of the bubble was enhanced when the bubble trajectory shifted from the linear mode to the zigzag mode.

1. Introduction

2. Experimental setup
Fig. 1 shows a schematic diagram of experiment setup. An
acrylic water vessel (c) was filled with ion-exchanged anddegassed water. An Ar ion laser system (a) was used as
backlights. The laser beams were split by a half mirror, andthe beams were expanded/collimated by a beam expander andilluminated an observed area. A highly-reproducible bubble
was launched from a bubble generator (e); the device consistsof a hypodermic needle(d), an audio speaker and two precisepressure controllers, and controls the zigzag motion, size,
surface oscillations, position and orientation (Saito et al,2010). The bubble generator and high-speed cameras(exposure time 10µs, resolution 1024×1024 pixels, and spatial
resolution 6.01µm/pixel) were synchronized with a function
generator; i.e. launching and filming the single bubbles at the

(c)

(a)

Bubbles of 2-3 mm diameter take the highest mass transfer
coefficient KL(Motarjemi & Jameson, 1978). The physicalphenomena of those bubbles are far more complex than thoseof the small spherical bubbles due to the following reasons;they can be approximated as a oblate ellipsoid with surface
oscillation (Miyamoto & Saito, 2005, Saito, et al., 2010); theyrise zigzagging or spiraling in a rest water column; in addition
it is known that the zigzagging bubbles shed a characteristic
wake (i.e. horse-shoe-like vortex). The effects of the vortex
shedding on the mass transfer and the relation between the
bubble motion and the mass transfer are still unknown. In thispaper, we discuss a relation between the instantaneous masstransfer and the bubble motions, based on the highly precise
measurement of the bubble volume. For this particularpurpose, we visualized the zigzagging motion and the surface
oscillation 3-dimensionally and simultaneously, using two
high-speed cameras and mirrors. Finally, we discuss dominantfactors that affect the mass transfer from the bubble to theambient liquid by comparison of the instantaneous masstransfer, the bubble motions and the bubble dynamics.

(g)
(b)
(f)
(d)

(g)

(e)

(a)Ar+ laser, (b)Half mirror, (c)Water vessel,(d)Hypodermic needle, (e)Bubble-launch device,(f)Function generator, (g)High-speed cameras
FIGURE 1. Schematic of experimental setup.
same timing were realized. As a result, the zigzag motion of
the bubble and the bubble surface oscillation were visualized
from two directions simultaneously. Moreover, for theverification of bubble shape, the projected bubble geometry
was visualized from vertical direction by using a high speed
camera (exposure time 10µs, resolution 1024×1024 pixels,
and spatial resolution 8.46µm/pixel) and mirrors.

3. Calculation of the bubble volume
3.1. Bubble shape
In preparation for the bubble-volume calculation, we
verified the shape of a bubble with the zigzag motion andperiodical surface oscillations. The projected bubble image
was visualized from two directions intersecting at right angles- 23 -

z

y

y

z

(a) frontxx(b) sideyz(c) topx

FIGURE 2. Bubble geometry on each plane.

3.2. Algorithm for reconstruction of a 3D-bubble
from the projected bubble images
We propose a method for accurate calculation of a bubble
volume and surface area by image processing. The bubble
volume was calculated from the projected bubble images fromtwo directions and the geometric assumptions described above.
This calculation composed of three processes as described
below: (1) the extraction of bubble geometry on the front/side,(2) the construction of 3D-bubble model (Fig. 3), (3) the
calculation of volume and surface area of the 3D-bubble
model.
(1) The extraction of bubble geometry.
The bubble geometries were extracted by the edge
extraction by zero-crossing method and the binary process. In
addition, the position of bubble centroid and major/minor axis,
etc. are calculated from the bubble image.
(2) The formation of rough bubble shape.
Fig. 3 shows the algorithm for the construction of
3D-bubble model. First, we define a cubic model which islarger than bubble and composed of a lot of micro cubes
6.01µm on a side. This size of micro cube is determined fromthe spatial resolution of the bubble image. We construct a
3D-bubble model from the cubic model. At first, the cubicmodel is cut away some fat that don’t fit the bubble image on
the front/side by checking a model shape from the bubble
geometries on the front/side. Next, we apply the above
presumptions of bubble-shape characteristics to the bubble
model for the construction in minute detail of 3D-bubble
model. The presumptions which are No.1 and No.2 shave theextra part of bubble model on the each layer which is parallelto the major axis on front/side and perpendicular to theminor-axis of bubble.
(3) The calculation of volume and surface area.
To begin with, we calculate the bubble volume. We obtaina number of layer-by-layer micro cubes by counting micro

cubes at each layer of the bubble model and multiply amicro-cube volume. Then, we integrate numerically all
layer-by-layer volume by Simpson’s rule. Next, we calculate
the bubble surface area. It is counted the faces, which
compose the gas-liquid interface, of a micro cube. And then,we obtain the bubble surface area by multiplying the total
number of face by the lateral area of micro cube.

3.3. Evaluation of the bubble volume calculation
Fig. 4 shows the air-bubble volume of both the calculation
by image processing and the actual measurement. The bubble
image was taken in the section which is from the tip divisionof hypodermic needle to above the needle (i.e. z=0-3[mm]). Ina section from z=2[mm] to 3[mm], the bubble shape isassumed oblate ellipsoid from the bubble geometries onfront/side. It was verified that the difference between
air-bubble volume of actual measurement and calculation by
image processing is within ± 0.4[%]. In a section from z=0 to2[mm], It was verified that the difference between air-bubble
volume of actual measurement and calculation by image
processing is up to 1.4[%]. Why the difference in a section in
z=0-2[mm] is larger than in z=2-3[mm], the bubble
deformation is excited when the bubble is away fromhypodermic needle. So, the bubble shape doesn’t match withthe presumptions of bubble-shape characteristics. Also, in
other section, there are the differences by the discriminative
bubble deformation. So, we need to correct for the influenceof bubble deformation against calculation result. For therevision of bubble-volume values, we accurately measured
the air/CO2 bubble volume at the same position and timing.
We decided that the volume change of the air bubble is due tothe influence of bubble deformation, because the Air bubble
is least soluble compared to the CO2 bubble. So, we corrected
for the differences by the bubble deformation, based on a
result of air-bubble volume measurement.

- 24 -

(a)
z

(c)

(b)
z

y

y

x
(d)

z

z

y

x

x
(e)

y
x

FIGURE 3. Algorithm for the construction of
3D-bubble model.
11
volume [mm3]each other (the x-z plane is called “front”; the y-z plane iscalled “side”). The bubble showed the perfect 2-D zigzag
motion on the front and the linear ascent motion on the side.
Fig. 2 shows the projected bubble geometry. The projectedbubble geometry was a symmetrical about a minor axis on thefront and symmetrical about zigzag-motion plane on theside/top. From these characteristic bubble geometries, wemade the following assumptions; 1) the projected bubble
geometry on a top is fairly circle or ellipse, 2) the bubble
geometry is nearly circle or ellipse in each cross-section
which is parallel to the major axis on front/side andperpendicular to the minor-axis of the bubble.

calculation
actual measurement

10.5
10
9.5

0

1

2

3

z [mm]FIGURE 4. Actual measurement/calculation valuesof the air-bubble volume.

4. Results and discussion

5. Conclusion

Figures 5 show (a) a bubble trajectory, (b) a bubble volume,(c) a bubble surface area, (d) an instantaneous mass-transfer
coefficient, and (e) a bubble rise velocity during the bubble
ascent motion from the tip of the hypodermic needle to thesecond-inversion point, respectively. We calculated theinstantaneous mass-transfer coefficient kL by the following
formula,In this study, we discussed a relation between the
instantaneous mass transfer and the bubble motion. For
this particular purpose, we obtained the instantaneous
mass-transfer coefficient, based on the accurate and precise
bubble volume measurement.

k L = ∆V (S ⋅ ∆t ) ,As a result, kL clearly increased at the sections near the
bubble launch and the second inversion point. In these
sections, the bubble made the increase in a relative velocity,
the induction of shedding vortices, and the strong upward
flow behind the bubble. Hence, the concentration gradient in
the interface was increased by the high renewal speed ofliquid on the interface and the enhancement of mass transportand diffusion. Consequently the mass transfer from bubble toliquid is enhanced. We conclude that the characteristic bubble
motion affects the mass transfer from bubble to liquid.

(1)

where ∆V is the value of volume shrinkage in ∆t seconds,
S is the averaged surface area in ∆t . kL clearly increases atthe sections of 0 mm < z < 15 mm (just after the bubble
launch) and 35 mm < z < 50 mm (around the second-inversion
point of zigzag trajectory). At the section of 0 mm < z < 15mm, the bubble was accelerated rapidly (Fig. 5 (e)); i.e. therelative velocity of the surrounding liquid became highrapidly. The surrounding liquid on the bubble surface wasquickly renewed, and hence the mass transfer from the bubble
to liquid is enhanced by the effect of a heightened
concentration gradient in the interface. On the other hand, atthe section of 35 mm < z < 50 mm, the bubble reached its
terminal velocity and moved at a constant velocity (Fig. 5 (e)).
Therefore, there is no effect of the increase in a renewal speed
on enhancement of the mass transfer. However, in this section,
shedding hairpin vortices are induced, and the vortices aretransported and defused by a strong upward flow behind the
bubble. These promote the mass transport from the bubble tothe surrounding liquid.

6. References
Motarjemi, M. & Jameson, 1978, G. J. Mass Transfer from
Very Small Bubbles-The Optimum Bubble Size for
Aeration, Chem. Eng. Sci., 33, 1415-1423.
Miyamoto, Y. & Saito, T., 2005, Relationship between
Interface Motion of an Isolated Bubble and its
Zigzagging Motion of the Center of Gravity., J. Soc.
Mech. Eng., B71-705, 1307-1313.
Saito, T, et al. 2010, A study of surfactant effects on theliquid-phase motion around a zigzagging-ascent bubble
using a recursive cross-correlation PIV, Chem. Eng. J.,
158, 39-50.

5040z [mm]

30

20

10

0
-5

0

5 10
x
[mm]
(a)

13

14
V
[mm3]
(b)

45
S
[mm2]
(c)

- 25 -

46

0.6

1
1.4 200
300
kL×10-4(vx2+vy2)2[m/s][mm/s](d)(e)

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

An Experimental Study of Gas-liquid Interaction in Decaying Turbulence
Formed in a Water Vessel Equipped with an Oscillating-gridYasuyuki Nagami
Graduate School of Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: Gas-liquid two-phase flow, Gas-liquid interaction, Oscillating-grid decaying turbulence, Bubble.
Abstract: Gas-liquid interaction is essential to deeply understand the complicated mechanism and structures of a gas-liquid
two-phase flow. The purpose of the present study is to clearly extract modulation of the bubble-liquid interaction and to discuss
the relations between the bubble and liquid-phase motions through experiments. We employed a completely controlled bubble(with high reproducibility of size, a trajectory and a surface oscillation) and oscillating-grid decaying turbulence (grid frequency:
4 Hz, grid stroke: 40 mm). We found out that the transition of the 2D zigzagging motion to the 3D motion was enhanced in theoscillating-grid decaying turbulence. In the area of the transition start, we measured liquid-phase motion with PIV/LIF andsimultaneously filmed bubble images with infrared shadow bubble technique (IST). We discussed the modulation of the bubble
motion and ambient liquid-phase motion and considered the dominant factor for the transition of the bubble motion from 2D to
3D.

1. Introduction
The interaction between the gas and liquid-phase plays asignificant role in gas-liquid two-phase flows (e.g. Boden et al.
2008, Vlasogiannis et al. 2002, Saito et al. 1999, 2010).
Quantitative discussion of the gas-liquid interaction isimportant to understand their complicated structures andmechanisms. The objective of this paper is to discuss the
bubble-liquid interaction in the gas-liquid two-phase flows
through experiments.
Although many researches about the bubble motion,liquid-phase motion, and the interaction between the bubble
and liquid-phase motion numerically and/or experimentally, aknowledge of the interaction is still insufficient in particular
for bubbly flows. The bubble examined in the present study
was an oblate ellipsoid of 2.9 mm in equivalent diameter; thebubbles ascend zigzag or spirally (Clift et al. 1978)
accompanying with the drift motion (Brücker 1999) andsurface oscillation (Fan & Tsuchiya 1990). Thompson &Turner (1975) quantified oscillating-grid turbulence in a rest
water column. Hopfinger et al. (1982) applied an
oscillating-grid to a rotating tank experiment, and discussed
an interaction between the homogeneous isotropic turbulence
and the vortex produced by the rotation. Bröder &Sommerfeld (2003) described a measurement system toacquire bubble sizes, bubble velocities and liquid velocities
the decaying turbulence, resulted in the enhancement of thetransition of the bubble motion from 2D motion to 3D motion.

2. Experimental setup
2.1. Oscillating-grid decaying turbulence
The schematic view of the employed experimental setup is
illustrated in Fig. 1. The oscillating-grid decaying turbulence
was formed in an acrylic cylindrical vessel (diameter: 149 mm,height: 600 mm) covered with a square-section acrylic water
jacket to remove refraction and a deformation of a bubble

allowed in a bubbly two-phase flow by combining images
obtained via PIV and PTV. Zenit & Magnaudet (2009)
measured the steamwise vorticity in the wake of a bubble withoscillating motion and reported the bubble wake motion
becomes unstable when the bubble aspect ratio exceeds a
critical value.
Morikawa & Saito (2008) described a turbulence
modulation induced by an interaction between flow producedby bubble swarms and liquid-phase ambient isotropic
turbulence, by using a LDA system. Imaizumi & Saito (2010)
advanced that standard deviation of liquid-phase motion wasincreased by a bubble swarm. In order to more deeply
understand the relation between the bubble motion and theliquid-phase motion, we employed IST (Infrared Shadow
Technique) for capturing the bubble motion, and PIV/LIF for
obtaining the liquid-phase motion. Furthermore, we visualized
the bubble-wake motion with LIF/HPTS in order to discuss
the relation between the bubble motion and the bubble-wakemotion. We found out the transition of the bubble motion
from 2D zigzagging motion to 3D motion was enhanced in
the oscillating-grid decaying turbulence. The initial bubble
motion was not influenced by the surrounding decaying
turbulence. The asymmetry of the standard deviation of theliquid-phase velocity and the irregular fluctuation of the
bubble wake motion, which were influenced byimage. The origin of the coordinate system (x, y, z) was set atthe center of the vessel bottom. The vessel was filled withpurified water (ion-exchanged and degassed tap water). The
grid (mesh size: 18 mm, bar thickness: 4 mm) was driven bycomputer-controlled servomotor (frequency: 4 Hz, stroke: 40mm). The neutral position of the grid oscillation was
positioned at z = 392 mm. The oscillating-grid was stopped
after worked for 60 seconds. The decaying turbulence wasformed after stopping the oscillating grid. The measurements
were performed under two experimental conditions; the first- 26 -

one was the bubble launched into the stagnant water(Condition-B), the second one was the bubble launched into
the oscillating-grid decaying turbulence (Condition-OB).

rleft

Minor axis
Major axis

(e)
(d)

(c)

(a)
z (w)

rrightSignalAir(j)

Deq = 3 Major 2 ⋅ Minorκ R ,L = Deq 2rR ,LGravity-centers

FIGURE 2. The valuation method of the bubble motion.

x (u)
(g)

y (v)

3. Results and discussions

(o)
(h)

(q)

3.1. Bubble motion

(f)

(i)
(b)

Condition-B

Condition-OB

115
(l)
(p)

(m)

(k)

110
z [mm](n)(a) Cylindrical vessel, (b) Water jacket, (c) Grid, (d)Controller, (e) Servomotor, (f) YAG Laser, (g) Rod lens,(h) High-speed video camera, (i) Sharp cut filter, (j)LED, (k) Cylinder of pure air, (l) Pressure controller 1,(m) Pressure controller 2, (n) Function generator, (o)Power amplifier, (p) Audio speakers, (q) Hypodermic
needle105100
0 5 10 1 2 3 1 2 3 -5 0 5 1 2 3 1 2 3xyκR_x-z κL_x-z
κR_y-z κL_y-z
[mm]
[-]
[-]
[mm]
[-]
[-]

FIGURE 1. Schematic diagram of experimental setup.

FIGURE 3. The gravity-center motion andthe surface oscillation.

2.2. Bubble launch device
The bubble was launched via the in-house specially-madebubble launch device equipped with a hypodermic needle;
hence uniform bubble was repeatedly formed and launched atcontrollable launch timing (Saito et al. 2010). Pure air from acylinder was adjusted by two pressure controllers forcoarse-range adjustment and precise-range adjustment, andwas inputted to the narrow space between the audio speakerand pressure vessel. The audio signals were sent to the
speaker from a function generator through a power amplifier.
The bubble launch interval was arbitrarily controlled by thefunction generator. The bubble was launched into the water
through the hypodermic needle (outer diameter: 0.65 mm,
inner diameter: 0.40 mm) which set at the bottom and centerof the vessel. The edge of hypodermic needle was set towardx-direction. The needle was able to repeatedly release thebubble of the same initial shape. In addition, the trajectory
was also highly controlled (Saito et al. 2010). We visualized
the bubble motion via IST (Infrared Shadow Technique with ahigh-speed video camera). In order to extract a clear contourof the bubble, a ring-shaped continuous red-LED array(wavelength: 660 nm) was placed at the opposite side of thecamera and a sharp cut filter (wavelength 560 nm) was set infront of high-speed camera in order to remove scattering noisefrom the bubble surface. The spatial resolution was 1024 ×
1024 pixel2 (19.1 µm/pixel), and the frame rate was 1000 fps.
The valuation method of the bubble motions were shown in
the Fig. 2.

In the past study, we already meticulously confirmed theinitial condition of the bubble motions (gravity-center motion
and surface oscillation) were not influenced by the ambient
decaying turbulence (Nagami & Saito 2011). The trajectoriesof the gravity-center and the surface oscillation in z = 95 –115 mm are plotted in Fig. 3. This is the area where thebubble reached to the first inversion point from the rectilinear
rise. Considering these results, under Condition-B, thetrajectory was rectilinear on the y-z plane. The bubble motionin the stagnant water was 2D motion in the examined area. On
the other hand, the difference in the trajectory under
Condition-OB appeared obviously in the area near z = 95 mm.
This indicates the point at which the transition from 2D
motion to 3D motion started. Comparing the bubble
gravity-center motion with the bubble surface motion, theregion at which the former motion was modulated wellcorresponded with the region at which the phase difference ofthe curvature fluctuation occurred. In this area, the amplitudeof right-side and left-side curvature fluctuations is almost thesame under Condition-B and Condition-OB. However, in aheight near to z = 105 mm under y-z plane, the largest
difference of the right-side and left-side curvature wasappeared. This result corresponded to the standard deviationof liquid-phase deviation which described in the next section.

- 27 -

3.2. Liquid-phase motion

3.3. Bubble wake motion

An Nd: YAG laser (wavelength: 532 nm), and laser
fluorescence particles (average diameter: 8 µm, excitation
wavelength: 532 nm, emission wavelength: 570 nm)
completely dispersed in the water were used. Theinterrogation area was illuminated with the laser sheet througha rod lens. We calculated the standard deviation ofliquid-phase motion from the original PIV images. Because
the condition of the decaying turbulence is inability to predictin each time, we separately compared the experimental resultin each time, based on the spatial and time average results
calculated from all of data sets. The contour maps of thehorizontal and vertical standard deviation of liquid-phasevelocity components calculated from one data set are shownin Fig. 4.

In the present study, we employed LIF/HPTS(8-hydroxypyrene-1, 3, 6-trisulfonic acid) method in order tovisualize the CO2 transportation from the bubble surface tothe oscillating-grid decaying turbulence. An argon-ion laser
system (wavelength: 488 nm) was used to excite the HPTS
(excite wavelength: 488 nm, emission wavelength: 532 nm).
HPTS changes its emission intensity depending on pH of thesolvent. A CO2 gas (CO2: 99.9%, N2: 0.9ppm, O2: 0.9ppm)
was supplied from a gas cylinder through the bubble launchdevice. During the ascent of the CO2 bubble in HPTS solution,
the emission intensity decreases in the regions in which theCO2 included in the bubble is dissolved. The CO2-rich regions
are easily distinguished from the other regions of no
dissolution of CO2 due to the brightness differences. A set of
typical original images is shown in Fig. 5.

FIGURE 5. A set of typical image of the bubble wake motion.

FIGURE 4. A set of typical contour figures standard deviationof liquid-phase velocity components on the y-z plane.
Yoshimoto & Saito (2010) measured a single bubble
motion (shape oscillation and zigzag motion) and thesurrounding liquid motion around the bubble by using
Stereo-PIV method near the first inversion point. They
considered that the asymmetry of shape oscillation resulted in
the velocity difference between left-side and right-side of the
bubble. In the Fig. 4, the areas of the negative standard
deviation under Condition-B were reduced or disappeared
under Condition-OB. The asymmetry and imbalance of thestandard deviation of liquid-phase velocity was influenced by
the decaying turbulence and the bubble surface oscillation.
Based on these result, we consider that the bubble surface
motion is related to the enhancement of the transition of
bubble motion from 2D motion to 3D motion. In fact, theamplitudes of the curvature fluctuations observed in the y-z
plane modulated in the decaying turbulence as shown in Fig.
3.

Tachibana & Saito (2011) experimentally investigated asingle bubble motion translated from linear motion to zigzag
motion induced by the fluctuations of the position of the pointof the hairpin like vortex leg on the bubble rear surface. In
this paper, because the measurement area is where the bubble
motion started to translate from 2D motion to 3D motion, thegrowth process of the dynamic vortexes and the position of
the point of the hairpin-like vortex leg were considered tohave been influenced by the ambient decaying turbulence. As
a result, the gauge of the bubble wake under Condition-OB
was thinner than that under Condition-B. Influenced by theambient decaying turbulence, the irregular fluctuation of the
bubble wake motion is another significant factor for theenhancement of the transition of the bubble motion from 2D
motion to 3D motion.

4. Conclusions
In the present study, we employed oscillating-griddecaying turbulence and an in-house specially-made bubble
launch device in order to systematically and experimentallyinvestigate the interaction between the bubble motion and theambient liquid-phase motion. The modulations of the bubble
gravity-center motion, bubble surface oscillation, the standard
deviation of the liquid-phase velocity and the bubble wake- 28 -

motion were discussed by comparing those in the decaying
turbulence with those in the rest water. By combining theseresults, we pinpointed the area where the transition of the
bubble motion from 2D to 3D was enhanced in the decaying
turbulence compared with that in the rest water. In the y-z
plane, the asymmetry and imbalance of the standard deviationof liquid-phase velocity was influenced by the decaying
turbulence and the bubble surface oscillation. We considered
the two-way interaction is one of the dominant factors in theenhancement of the transition of the bubble motion from 2D
motion to 3D motion. In addition, we successfully captured
the bubble wake motion in the decaying turbulence. We
considered the irregular fluctuation of the bubble wake motion
influenced by the ambient decaying turbulence is anothersignificant factor for the enhancement of the transition of the
bubble motion from 2D motion to 3D motion.

5. References
Boden, S., Bieberle, M. & Hampel, U. 2008 Quantitative
measurement of gas hold-up distribution in a stirred
chemical reactor using X-ray cone-beam computed
tomographay. Chem. Eng. J. 139, pp 351-362.
Bröder, D. & Sommerfeld, M. 2003 Combined
PIV/PTV-measurement for the analysis of bubble
interactions and coalescence in a turbulent flow. The
Canadian Journal of Chemical Engineering, Vol. 81, pp.
756-763.
Brücker, C. 1999 Structure and dynamics of the wake of
bubbles and its relevance for bubble interaction. Physics
of Fluids Vol. 11(7), pp 1781-1796.
Clift, R., Grace, J. R. & Weber, M. E. 1978 Bubbles, Drops
and Particles New York: Academic.
Fan, L. S. & Tsuchiya, K. 1990 Bubble wake dynamics inliquids
andliquid-solid
suspensions.
Butterworth-Heinemann Series in Chemical Engineering.
Hopfinger, E. J., Brow, F. K. & Gagen, Y. 1982 Turbulence
and waves in a rotating tank. Journal of Fluid Mechanics,
Vol. 125, pp. 505-535.
Imaizumi, R. & Saito, T. 2010 Bubble and liquid-phasemotion in a decaying turbulence field of oscillating-gridturbulence. 7th ICMF, in usb.

Morikawa, K., Urano, S., Sanada, T. & Saito, T. 2008
Turbulence modulation induced by bubble swarm inoscillating-grid turbulence. Journal of Power and Energy
Systems, Vol. 2(1), pp. 330-339.
Nagami, Y and Saito, T 2011 The motion of a bubble swarm
in decaying oscillating-grid turbulence and themodulationoftheliquid-phasemotion.
ASME-JSME-KSME
Joint
FluidsEngineering
Conference 2011
Saito, T., Sakakibara, K., Miyamoto, Y. & Yamada, M. 2010
A study of surfactant effects on the liquid-phase motion
around a zigzagging-ascent bubble using a recursive
cross-correlation PIV. Chemical Engineering Journal,
Vol. 158, pp. 39-50.
Saito, T., Kajishima, T. & Tsuchiya, K. 2010 Deep ocean CO2
sequestrationvia
GLAD(Gas-Lift
Advanced
Dissolution) system. J. of Environment and Engineering,Vol. 6(2), pp. 412-415.
Tachibana, R. & Saito, T. 2011 A relation between the wakeand zigzag Motion of a single bubble. Transactions of theJapan Society of Mechanical Engineers series B,
accepted, in Japanese.
Thompson, S. M. & Turner, J. S. 1975 Mixing across aninterface due to turbulence generated by an oscillating
grid. Journal of Fluid Mechanics, Vol. 67, pp. 349-368.
Tomiyama, A., Celata, G. P., Hosokawa, S. & Yoshida, S.
2002 Terminal velocity of single bubbles in surface
tension force dominant regime. International Journal of
Mulutiphase Flow, Vol. 28, pp. 1497–1519.
Vlasogiannis, P., Karagiannis, G., Argyropoulos, P. &Bontozoglou, V. 2002 Air-water two-phase flow and heattransfer in a plate heat exchanger, Int. J. Mult. Flow Vol.
28, pp. 757-772.
Yamamoto, M., Masato Y., Koichi M. & Saito, T. 2008
Coupling mechanism between liquid phase motion andmass transfer around single rising bubbles by using
PIV/LIF. In 14th Int Symp on Applications of Laser
Techniques to Fluid Mechanics.
Zenit, R. & Magnaudet, J. 2009 Measurements of thestreamwise vorticity in the wake of an oscillating bubble.
International Journal of Multiphase Flow, Vol. 35, pp.
195-203.

- 29 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

A simple yet powerful technique to detect the pierced position
by using a pre-signal in bubble measurementwith a Single-Tip Optical fiber Probe
Yuki Mizushima
Graduate School of Engineering,
Shizuoka University, 3-5-1 Johoku, Hamamatsu,
Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology,
Shizuoka University, 3-5-1 Johoku, Hamamatsu,
Shizuoka, Japan

Keywords: Single-Tip Optical fiber Probe, Bubbly flow, Measurement accuracy, Pre-signal.
Abstract: The Optical Fiber Probe (OFP) measurement is generally used for gas-liquid two phase flow measurements. The OFP
enables researchers to measure the diameters and the velocities of the bubbles/droplets simultaneously, in real time. One of theauthors originally developed a Single-Tip Optical fiber Probe (S-TOP) with a wedge-shape tip. The S-TOP can measure theproperties of the bubbles/droplets with only the single-tip. Due to the simple but smart structure, the S-TOP is specialized formeasurement of a sub-mm or µm order bubble/droplet. However, this advantage of the single-tip inevitably brings a bottleneckproblem: i.e. an unknown factor of a touch position between the S-TOP and the bubble/droplet. The bubble diameter is calculatedwith the S-TOP’s piercing chord length. Hence, the chord length greatly depends on the touch position; however, the touch
positions are different in every bubble. As a result, the bubble diameter obtained by the S-TOP has uncertainty. This uncertainty isdifficult to be quantified and removed. The purpose of this study is improving the accuracy of the S-TOP bubble measurement. To
realize this, we overcome the bottleneck with a pre-signal. The pre-signal appears when the OFP tip shapes wedge, and just before
the tip pierces the bubble. Its amplitude is the largest of all touch-conditions, when the S-TOP touches the center of the bubble,
perpendicularly: this is the best touch-condition that the S-TOP can measure the properties of the bubbles with high degree of
accuracy. Utilizing this phenomenon, we propose a pre-signal threshold method. By using this, we can easily discriminate whether
the touch-condition is needed, or is not. In this paper, we have demonstrated the effectiveness of the method, empirically.
Consequently, as for the bubble chord length measurement, the difference of the results between the visualization and the S-TOP
is remarkably improved from -42% to -21%.

1. Introduction
Gas-liquid two phase flows widely appear in the industrial
processing, such as the bioreactor, the chemical plants, and soon. However, the flow structure is very complicated; hence,the description for the bubbly flow is still non-committal. It isbecause that there are no reasonable measurement techniques
for the two phase flows. The visualization, PIV (Particle
Image Velocimetry) (Brücker, 1999), PTV (Particle Tracking
Velocimetry) (Ortiz-Villafuerte et al, 2000), and so on, isuseful measurement method; however, visualizing bubbles
quantitatively and individually is impossible. It causes that weseem to overlook the important facts, the bubble
diameters/velocities and the local void fraction. As a result,the measurement results from the visualization stay rough.
The optical fiber probe (OFP) (Miller et al, 1970, Abuaf et al,
1978, Cartellier, 1990, Mudde and Saito, 2001, Higuchi and
Saito, 2010) is one of the novel measurement techniques forthe two phase flows. The OFP directly measures the diameters
and the velocities of the bubbles/droplets intrusively but
successfully, even though in a high number of density. One of
the authors newly developed a Single-Tip Optical fiber Probe(S-TOP) (Saito, 2000, Matsuda et al, 2009, Ozawa et al, 2009,
Saito et al, 2010). The S-TOP can measure the diameters andthe velocities of bubbles/droplets with its single wedge-shapetip.
In this study, we aim at establishing a correction method
for the S-TOP measurement. The S-TOP measurement is thepoint-wise measurement; therefore, the piercing position on

the bubble is quietly important. When the S-TOP detects the
bubble, a chord length of piercing is obtained. The length isequal to the minor axis of the bubble, when the S-TOP pierces
the center of the bubble vertically. In this case, the S-TOP
measurement is accurate; however, this is the rare case. The
bubbles in the bubbly flow move with various orientations.
The S-TOP often pierces the bubbles imperfectly. The S-TOP
grazes the bubbles, pierces the edge of the bubbles, or so on.
As a result, the results from the S-TOP have uncertainty. N. N.
Clark et al have attempted to quantify this uncertainty fromthe numerical approach (Clark and Turton, 1988, Liu and
Clark, 1998); however, it has never been a radial solution.
Consequently, this problem always follows the OFP
measurement, and is considered as two sides of the coin.
To break out this problem, using a pre-signal is very
effective (Mizushima and Saito 2011). The pre-signal appears
when the tip shapes wedge. It occurs just before the S-TOP’s
touching on the bubble, and intensively when the S-TOP ispositioned at the center region of the bubble, vertically. In thispaper, we propose a newly developed correction method, apre-signal threshold method for the S-TOP bubble
measurement. Then, we demonstrate the effectiveness of themethod empirically.

2. Single-Tip Optical fiber Probe (S-TOP)
2.1 Optics
The optics employed in this study is illustrated in Fig. 1. A
Laser diode (1) (wavelength 635 nm) is- 30 -

used for the light source of the S-TOP. The laser beams passlens (3). The focused laser beams enter an optical fiber, andreach the S-TOP sensing tip (4). The laser beams reaching thetip surface are returned/emitted at/from the tip, depending on
the Snell's law. The returned beams enter a photomultiplier (6)through a polarizer (5). Hence, we obtain electrical signals
outputted from the photomultiplier. In succession, we
analyzed the raw signals, and simultaneously obtained thevelocities, diameters and the number density of the bubbles.
(6)

(7)

(8)

through a beam splitter (2) and are focused by an objective
As a result, the bubble diameter is calculated from Eq. (3),Lb = U b ⋅ (t e − t s )(3)where (te – ts) is the residence time of the S-TOP tip
covered completely with the bubble. The event time, ts (start
time of S-TOP tip touching the bubble frontal surface) and te(end time of the S-TOP tip departures from the bubble at the
bubble rear surface), is detected by using the thresholds,
VLiquid, and VGas.
(1)

(3)

Output voltage [V]

(2)

(4)

(1)Laser diode, (2) Beam splitter, (3) Objective lens,(4) S-TOP, (5) Polarizer, (6) Photo multiplier,(7) Amplifier, (8) Digital oscilloscope.

FIGURE 1 Optics.

3

P2

2

Vthh

P1
ts

1
0

Vthl

VPmax
VLiquid

0

5

10

15

time [ms]The schematic of the S-TOP employed in this study isshown in Fig. 2. The S-TOP is made from the optical fiber(synthetic quartz; step index type; the core diameter: 190µm;
the clad thickness: 5µm). The sensing tip is smoothly groundinto a wedge-shape with an angle of 35 degrees. The fiber isfixed by the stainless capillary and the stainless tube

1.0 mm
(1)

(2)

(3)

Stainless capillary

FIGURE 3 Signal processing of the S-TOP.

3. Pre-signal Threshold Method
3.1 Properties of the pre-signal

35゜
Stainless tube

FIGURE 2 S-TOP configuration.

2.3 Signal processing of the S-TOP
Typical output signal delivered from the S-TOP in the
single-bubble measurement (main signal) is shown in Fig. 3.
First, the output signals are smoothed by 25-points moving
average.
Second, VGas (gas-phase output level) and VLiquid(liquid-phase output level) are obtained using thehistogram-method (Sakamoto and Saito, 2006).
Third, the high threshold level Vthh and the low
threshold level Vthl are determined from the VGas and VLiquid.
Finally, we obtain grd as the line of intersection of P1 andP2,
1 dV 
grd =  dt  (VGas − VLiquid )A temporal peak occurs just before the main signal. We
call this “a pre-signal”. The pre-signal is caused by thesurface reflection on the bubble; the discharged beams fromthe S-TOP are reflected at the bubble frontal surface. It
appears intensively, only when the tip shapes wedge. Its
intensity is the largest of all conditions, when the S-TOP
touches the center region of the bubble. This is attributed tothe touch-angle (φ [degree]) between the S-TOP and the
bubble surface (Fig. 4).

S-TOP

φ

(2)

normal ninterface(1)

grd is proportional to the gas-liquid interface velocity. By
using the α, a coefficient of the proportionality between theinterface velocity and grd, Ub, the bubble velocity, is calculated
from Eq. (2),U b = α ⋅ g rd

VGas

grd

2.2 Structure of the S-TOP

5mm

(3)
te

Pre-signal

(5)

(1)

(2)

FIGURE 4 Touch-angle between the S-TOP and the
bubble.
When the S-TOP touches the center region of the bubble,
the φ is small, and the reflected beams at the bubble surface
re-enter the S-TOP tip: the pre-signal appears strongly. On theother hand, when the S-TOP touches the outer edge of the- 31 -

bubble, the φ is large, and the reflected beams are head to theother direction of the S-TOP axis: the pre-signal becomes very
feeble. Fig. 5 clearly indicates this tendency.
1mm

region of the bubble perpendicularly, when the VP is larger
than 0.15”.
Based on this, we propose a pre-signal threshold method.
The schematic view is illustrated in Fig. 7.
First, all signals delivered from the S-TOP is obtained.
Second, we extract main signals when VP exceeds 0.15.
At last, we bring out the velocity and the diameter of the
bubble, only by using the extracted signals.
(2)

(1)

(3)

Output voltage [V]4(a) The S-TOP pierces the outer edge of the bubble.

3
2
1
0

0

10

20

30

time [ms](a) Examples of signals delivered from the S-TOP.
(b) The S-TOP pierces the center of the bubble.

3.2 Pre-signal threshold method
Fig. 6 is some of the results, the relationship between thetouch position/angle and the pre-signal intensity, VP.

Output voltage [V]4

FIGURE 5 Visualization of the discharged beams
from the S-TOP tip (pseudo-colored images: the redcolor means bright, the blue color means dark).

3
VGas

2
1
0

1

2

3

500µm

4

5

6

VLiquid

7

time [ms]

0.2

4

0.1

0

Output voltage [V]VP [ - ](b) Signal 1 (Pre-signal does not occur).

-40
-20
0
20
40
Touch position of the S-TOP [%](a) The S-TOP pierces the bubble, vertically.

VGas

3
2
1

VPmax

0
11
500µm

12

13

15

16

17

(c) Signal 2, VP =0.13 (<0.15) (VGas =3.70 [V], VLiquid=0.10 [V], VPmax =0.60 [V])

0.1

-40

-20

0

20

Output voltage [V]40

VLiquidtime [ms]0.2

VP [ - ]14

40

Touch position of the S-TOP [%](b) The S-TOP pierces the bubble, tilting by 15
degrees.
FIGURE 6. Comparison of output voltage of the
pre-signal

VGas

3
2
1
0

VPmax

22

23

24

25

26

27

VLiquidtime [ms]The touch position is defined L/Lm, where L is the distancefrom the minor axis of the bubble, Lm is the length of the
major axis.
We already quantified the relationship in many touchconditions, and concluded that “the S-TOP touches the center- 32 -(d) Signal 3, VP =0.21 (>0.15) (VGas =3.85 [V], VLiquid=0.10 [V], VPmax =0.9 [V])FIGURE 7 Schematic of the pre-signal thresholdmethod.

4. Experiment
We examine the bubbles in a bubbly flow by using the
S-TOP. The experimental setup is illustrated in Fig. 8. The
vessel is made of an acrylic pipe (149 mm in inner diameterand 600 mm in height) covered with a rectangular acrylic
water jacket to remove refraction and deformation of theimage. The bubble swarms are grown and launched fromhypodermic needles (0.40 mm in inner diameter); using abubble launch device (Saito et al, 2010) that forms repeatedly
uniform bubbles at controllable launch timing. The device
consists of a function generator and audio speakers. The
bubble launch interval is arbitrarily controlled by function
generator. The high-speed video camera is settled at the frontof the vessel, and visualizes the bubbles. The S-TOP is placed
above the needles.
Thus, we make the uniform-size bubbles touch the S-TOP
with various orientations. We calculate the bubble properties
from the results of the visualization, the S-TOP raw data, andthe S-TOP data processed by the pre-signal method. And then,the results are compared with each other.

5. Results and Discussion
5.1 Velocity measurement result
The results of the velocity measurements are shown in Fig.
9. These figures evince the effectiveness of the pre-signal
method. In Fig. 9, the white bar indicates P.D.F obtained fromthe visualization. The dashed lines are the results from the
S-TOP (unprocessed by the pre-signal method). The
measurement results are summarized in Table 1. The P.D.F ofthe visualization takes a peak only at 300 mm/s, while that of
the S-TOP (unprocessed) is broad. The average velocity fromthe visualization is 295 mm/s, while that of the S-TOP(unprocessed) is 258 mm/s. The difference in the averagevelocities is about -13 %. These are caused by counting
signals of incomplete piercing of the S-TOP; i.e. the S-TOP
touches the edge area of the bubbles and the S-TOP scratches
the bubbles; however, it is very difficult to distinguish thesituation of the S-TOP touching a bubble; hence, usual signal
processing cannot eliminate the unpleasant signals. As a result,the values of the S-TOP (unprocessed) have a widespread
distribution.
In order to solve this serious problem in data processing,
we employed the newly developed pre-signal method forprocessing of the raw S-TOP signals. The solid line, in Fig. 8,
represents P.D.F of the velocity obtained from the S-TOP(processed by the pre-signal method).
Obviously, the degree of precision of the S-TOP issignificantly improved. Further, the average velocity is 319
mm/s; hence, the difference between the visualization and the
S-TOP result is also reduced to 8 %.
0.6

Visualization
S-TOP(before processing)

0.5

S-TOP
(processed)

0.4
P.D.F [-]

According to this, we can clearly identify the
S-TOP-bubble interaction.
In Fig. 7 (b), signal 1 is obtained when the S-TOP pierces
the outer region of the bubble: the pre-signal does not appear.
Due to the incomplete penetration of the S-TOP tip into the
bubble, Vgas becomes instable. As a matter of course, thissignal is not suit to the S-TOP measurement.
In Fig. 7 (c), signal 2 is obtained when the S-TOP touches
the halfway region of the bubble with some touch-angles: thefeeble pre-signal appears. The piercing seems to be complete
and successful; however, signal 2 is an inappropriate to the
S-TOP measurement. VP in signal 2 is about 0.13. From Fig. 6,
it indicates that the S-TOP has touched the bubble within 20%
to 40%.
These signals incur miscalculations of the bubble
properties; hence, we shall remove them.
In Fig. 7 (d), signal 3 is obtained when the S-TOP touches
the center region of the bubble, vertically: the intensive
pre-signal comes out, whose VP is about 0.21. This is what wehave to extract.
Thus, we can choose only the desirable signals by using
pre-signal. The effectiveness of the pre-signal method is
discussed bellow.

0.3
0.2
0.1
0
0

50

100 150 200 250 300 350 400 450
Velocity [mm/s]

FIGURE 9. Velocity measurement results.
TABLE 1. Velocity measurement results(a)(a) Visualization vs. S-TOP (unprocessed)
(b)

(e)

(c)
(d)
(j)

(f)
(h)

(i)

(a) Optics(b) S-TOP(c) Cylindrical vessel(d) Rectangular water jacket(e) Recorder(f) Halogen light source(g) Bubble launch device(h) Needles(i) High-speed video camera(j) PCVisualization[mm/s]
295

S-TOP(unprocessed)[mm/s]
258

Difference[%]-13(b) Visualization vs. S-TOP (processed)
Visualization[mm/s](g)

295

FIGURE 8. Experimental setup.

- 33 -

S-TOP(processed)[mm/s]
319

Difference[%]85.2 Chord length measurement result
Fig. 10 shows the differences of the chord length between
the visualization and the S-TOP (unprocessed/processed).
Each average value is listed in Table 2. The pre-signal method
remarkably improved the accuracy of the chord length
measurement, because the method successfully removed theneedless signals. The difference in the results of thevisualization and S-TOP was significantly decreased from
-42% to -21%.
In particular, it is obvious that the P.D.F of thevisualization and that of the S-TOP (processed) are very
similar. That is, the precision of the S-TOP measurement isgreatly improved. Previously, the OFP measurement is only
able to measure whole bubbles “statistically”, due to the
problem of the measurement uncertainty.
By contrast, our OFP technique is able to probe thebubbles “individually”. Although the difference between the
S-TOP results and the visualization results remains, these arebias errors.
Visualization
S-TOP(before processing)

0.6

S-TOP
(processed)

0.5
P.D.F [-]

0.4
0.3
0.2
0.1
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

FIGURE 10. Chord length measurement results.
TABLE 2. Chord length measurement results.
(a) Visualization vs. S-TOP (unprocessed).
S-TOP(unprocessed)[mm]

Difference
[%]

1.59

0.93

-42

(b) Visualization vs. S-TOP (processed).
Visualization
[mm]
1.59

S-TOP
(processed)[mm/s]
1.25

7. Nomenclature
grd
Ub
Lb
L

= gradient from water to air in the signals (/s)= bubble velocity (m/s)= piercing chord length of the bubbles (m)= distance between the bubble center and the S-TOP(m)
Lm= half length of the bubble major axis (m)ts= time which the S-TOP starts touching the bubbles (s)te= time which the S-TOP’s contact ends (s)VPmax = largest value in each pre-signal (V)VP= normalized value of the pre-signal (-)
Vgas, Vliquid = voltage which indicates that S-TOP tip is in the
bubble and water (V)= voltage as a threshold (V)Vthh, Vthl
Greek lettersα= coefficient of the proportionality between theinterface velocity and grd (m)φ= touch-angle between the S-TOP and the bubble
surface (degree)

8. Reference

Chord length [mm]Visualization[mm]

tip shape of the OFP, the wedge-shape tip. The S-TOP withwedge-shape tip has latency, to proofread its measurement
accuracy. That is the pre-signal. It peaks when the S-TOP
touches the center of the bubble. By using this phenomenon,
we establish the pre-signal threshold method. Finally, it isfound that this method greatly improve the measurement
accuracy of the S-TOP. As for the bubble chord length
measurement, the difference of the results between thevisualization and the S-TOP is remarkably improved from
-42% to -21%. The pre-signal method is not only simple but
also powerful to process the OFP signals.

Difference[%]-21

6. Conclusions
The OFP measurements, particularly the S-TOP, include
the inevitable problem; the touch positions between the OFP
and the bubbles. This problem causes that the accuracy of the
OFP measurement declines, and is a longtime issue for the
OFP researchers. To overcome this difficulty, we focus on the

Brücker, C. 1999 “Structure and dynamics of the wake of
bubbles and its relevance for bubble injection” Physics of
fluids, Vol. 11, pp. 1781-1796.
Ortiz-Villafuerte, J. , Schmidl, W. D., Hassan, Y. A. 2000
“Three-dimensional PTV study of the surrounding flow
and wake of a bubble rising in a stagnant liquid”
Experiments in fluids, Vol. 29, Supplement 1, S202-S210.
Miller, N. & Mitchie, R. E. 1970 “Measurement of local
voidage in liquid/gas 2-phase flow systems using auniversal probe” J. Brit. Nucl. Energy Soc., Vol. 2, pp.
94-100.
Abuaf, N., Jones, O. C. Jr., Zimmer, A. 1978 “Optical probe
for local void fraction and interface velocity
measurements” Rev. Sci. Instrum., Vol. 49, pp.
1090-1094.
Cartellier, A. 1990 “Optical probes for local void fraction
measurements; characterization of performance” Rev. Sci.
Instrum., Vol. 61, pp. 874-886.
Mudde, R. F. & Saito, T. 2001 “Similarities between bubble
column and pipe flow” J. Fluid Mech., Vol. 437, pp.
203-228.
Higuchi, M., & Saito, T. 2010 “Quantitative characterizationsof long-period fluctuations in a large-diameter bubble
column based on point-wise void fraction measurements”
Chem. Eng. J., Vol. 160, pp. 284-292.
Saito T. 2000 Japanese patent, No. 3018178.

- 34 -

Matsuda, K., Ozawa, Y., Oishi, S., Aoshima, S., Saito, T. 2009
“Measurement of surface tension using a Single-Tip
Optical fiber Probe (S-TOP)” The review of laser
engineering, Vol. 37, pp. 528-534.
Ozawa, Y., Sanada, T., Oishi, S., Aoshima, S., Saito, T. 2009
“Measurement technique of micro-droplets using an
Optical Fiber Probe” The review of laser engineering, Vol.
37, pp. 535-539.
Saito, T., Matsuda, K., Ozawa, Y., Oishi, S., Aoshima, S. 2009
“Measurement of micro-droplets using a newly developed
opticalfibre
probe
microfabricatedby femtosecond pulse laser” Measure. Sci. Tech., Vol. 20,
pp. 114002.

Clark, N. N. & Turton, R. 1988 “Chord length distributions
related to bubble size distributions in multiphase flows”
Int. J. Multiphase Flow, Vol. 14, pp. 413-424.
Liu, W. & Clark, N. N. 1998 “Relationship between Bubble
Size Distributions and Chord Length Distribution in
Heterogeneously Bubbling Systems” Chem. Eng. Sci.,
Vol. 53, pp. 1267-1276.
Mizushima Y. & Saito T. 2011 “A Discrimination Method ofTouched Positions by Using A Pre-Signal in Bubble
Measurement with An Optical Fiber Probe”. The review
of laser engineering, Vol. 39, pp. 528-534.
Saito, T. Sakakibara, K., Miyamoto, Y., Yamada, M. 2010 “A
study of surfactant effects on the liquid-phase motion
around a zigzagging-ascent bubble using a recursive
cross correlation PIV” Chem. Eng., J., Vol. 158, pp.
39-50.

- 35 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Compartmentalization of forces at an acoustic cavitation bubble
by numerical simulation and by visualization of sonoluminescence
Taikan Mori
Graduate School of Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: Acoustic cavitation, Sonoluminescence, Bjerknes force
Abstract: Forces (gravity force, buoyancy force, drag force, added mass force, history force, primary bjerknes force, secondary bjerknes force) at an acoustic cavitation bubble are compartmentalized by numerical simulation and by visualiza
tion of sonoluminescence. Numerical simulation is employed Runge-Kutta-Fehlberg method and bubble velocity and theforces are calculated. In contrast, sonoluminescence is visualized by I.I.unit (ICCD). In this study, in order to compartm
entalize the 7 forces, the bubble rising velocity is calculated by numerical simulation and by image analysis. On the nu
merical simulation, a bubble terminal velocity in static fluid is 1.2 mm/s. In contrast, a bubble velocity calculated by vi
sualization of sonoluminescence is faster than the velocity. Then, the dominant of force at an acoustic cavitation bubble
is acoustic radiation force (primary bjerknes force and secondary bjerknes force). In the future study, we will compartmentalize the forces by relating with the results of numerical simulation and image analysis.

1. Introduction
Cavitation is phenomenon of phase transition from liquid
phase to gas phase. Cavitation generates on a surface on pumps
and screws and it is disputed as erosion at the impeller.
However, processing and cleaning techniques applied
cavitation are developed in industry. Especially, cavitation
which generated by radiating acoustic in liquid is applied incleaning and chemical fields.
Acoustic cavitation bubbles which generated by acoustic
expand and contract in synchronization with period of acoustic.
Furthermore, the bubble is collapsed by rapid compression. At
this time, the bubble radiates faint light and this phenomenon
is called sonoluminescence. In the past study, it is reported thata profile of acoustic cavitation bubbles correlates strongly witha profile of sonoluminescence.
The acoustic cavitation bubble motion is forced on 7 forces(gravity force, buoyancy force, drag force, added mass forces,
history force, primary bjerknes force, and secondary bjerknes
force). Primary and secondary bjerknes force is force by
acoustic radiation pressure. In this study, forces at an acoustic
cavitation bubble are compartmentalized by numericalsimulation and by image analysis. Numerical simulation
employs Runge-Kutta-Fehlberg method. In contrast, thegenesis location of sonoluminescence is assumed the genesis
location of acoustic cavitation bubble, and multi-bubble
sonoluminescence (MBSL) is visualized. The primary bjerknes
force is calculated by analyzing the image.

is applied in experiment is ultrapure water made by ultrapure
water production equipment (Millipore). Sonoluminescence isvisualized by Image Intensifier unit (C9546, Hamamatsu
Photonics K.K.). Furthermore, the signal from I.I.unit isrecorded in PC through camera adaptor. To calculate bubble
rising velocity by image analysis, the vertical sectional imageof sonoluminescence is visualized by I.I.unit. Fig. 2 shows thevertical sectional image of MBSL visualized by I.I.unit. The
white part is sonoluminescence visualized by I.I. unit.

2. Experimental setup
Fig. 1 shows a schematic diagram of an experimental
setup to visualize MBSL. Acoustic is generated bybolt-clamped Langevin type transducer. The transducer isdriven by the output voltage signal from function generator
amplified by high output amplifier. The experimental
parameters are listed in Tab. 1. To visualize with a highaccuracy, an acrylic vessel, outer wall is right octagon andinner wall is round, is applied in experiment. The liquid which- 36 -

(g)
(e)

(f)

(a)

(d)

(c)
(b)

(a)Function generator, (b)Power amplifier, (c)BLT,(d)Water Vessel, (e)Image Intensifier unit,(f)Camera adaptor, (g)PC
FIGURE 1. Schematic diagram of experimental setup.
TABLE 1. Experimental parameters.
Voltage[mV]
630

Frequency[kHz]
20

Exposure time
[ms]
16.7

Resolution[ µm/pixel]
75.2

Volume[ml]200

3. Numerical simulation
We will consider the motion equation of acoustic bubble asfollows:mb

dub= FG + FB + FD + FAM + FH + FPBF + FSBF (1)dtwhere mb is the mass of a bubble, ub the rising velocity of abubble, FG the gravity force, FB the buoyancy force, FD thedrag force, FAM the added mass force, FH the history force,
FPBF the primary bjerknes force, FSBF the secondary bjerknes
force. In this study, the primary bjerknes force and thesecondary bjerknes force aren’t considered. The rising velocityof spherical bubble in static fluid is calculated.
Runge-Kutta-Fehlberg method is applied to numericalsimulation. The parameters of the numerical simulation arelisted in Tab. 2.

The bubble rising velocities calculated by visualization ofsonoluminescence is 4~500 mm/s. This is because theprimary/secondary bjerkness force forces on a bubble. The
primary bjerknes force depends on the pressure gradient. In
addition, the pressure P depends on position in the standing
wave. Hence, in the case of one dimension, pressure isexpressed as P(z) and the primary bjerknes force is expressed
as FPBF(z). Furthermore, a bubble position in the standing
wave z depends on time. Then, a bubble position in thestanding wave is expressed as z(t). In the future study, we willmodel z(t) and calculate the primary bjerknes force bynumerical simulation.

5mm

TABLE 2 Parameters of numerical simulation.
Bubblediameter[µm]
57.3

Kinetic
viscosity[m2/s]
1.307×10-6

Density ofwater[kg/m3]999.69z

4. Image analysis
Fig. 3 shows the algorithm for image analysis. We consider
the motion of MBSL in one dimension. The brightness wave isformed by the fluctuation of brightness in one dimension. The
rising velocity of sonoluminescence is calculated by analyzing
the time series waves. This velocity assumes the rising velocityof an acoustic cavitation bubble.

5. Results and discussion

FIGURE 2. MBSL image visualized by I.I. unit.

100
100

000
0

(3)

where ρ w is density of water ,d is distance between two
bubbles. This force is generated by acoustic wave generated
from two oscillating bubbles. This force depends on the
distance between two bubbles. Hence, if the distance is shorter,
the secondary bjerknes force increases and the bubble velocity
is faster.

- 37 -

44

66

100
100

000
0

8
8

2
2

4
4

66

88

position [mm] (z axis)(a) t

Brightness [-]ρ w dV1 dV2
4πd 2 dt dt

22

200
200

position [mm] (z axis)

where V is a bubble volume,∇P is a pressure gradient and thebracket <> indicates the average over a cycle. In contrast, thesecondary bjerknes force on the bubble is expressed below.

FSBF = −Brightness [-]

(2)

200
200

Brightness [-]FPBF = − < V∇P >zBrightness [-]Fig. 4 shows the results of numerical simulation and ima
ge analysis. The terminal velocity calculated by numericalsimulation is 1.2 mm/s. In contrast, the velocity calculate
d by image analysis is faster than the terminal velocity. T
hen, an acoustic cavitation bubble is strongly forced on bj
erknes forces (primary bjerknes force and secondary bjerk
nes force). The primary bjerknes force on the bubble is e
xpressed below.

200
200

100
100

000
0

2
2

44

6
6

88

200
200

100
100

000
0

position [mm] (z axis)

2

2

4
4

6

6

position [mm] (z axis)(b) t +⊿⊿t

FIGURE 3. The algorithm for image analysis.

88

7. References

100

W. Lauterborn et al, 2007, “Acoustic cavitation, bubble
dynamics and sonoluminescence“ Ultraso. Sonochem.,
Vol. 14, 484-491.
T. Saito, T. Kajishima, F.Kiyono & T. Usami, 1993, “Particle
Velocity in the Main Stream Direction of Solid-Liquid
Two-Phase Flows in a Swaying Pipe“ Trans. Jpn. Soc.
Mech. Eng. (B), Vol. 59, Issue 563, pp. 29-34.
Sueung-Man Yang & L .G. Leal, 1991, “A note on
memory-integral contributions to the force on an
accelerating spherical drop at low Reynolds
number“ Phys. Fluids, Vol. 3, pp. 1822-1824.
R. Mei, 1994, “A note on the history force on a spherical
bubble at finite Reynolds number“ Phys. Fluids, Vol. 6,
pp. 418-420.
H.
Mitome,2001,“MicroBubbleand
Sonoluminescence“ Jpn. J. Appl. Phys., Vol. 40, pp.
3484-3487.

experimental value

Log10 ub [m/s](in standing wave)

10-1

simulation(in static fluid )

10-2

10-3
0

0.005

0.01
z [m]

0.015

FIGURE 4. The rising velocity of a bubble calculated
by numerical simulation and by image analysis

6. Conclusions
In this study, forces at an acoustic cavitation bubble arecompartmentalized by numerical simulation and by
visualization of sonoluminescence. The bubble rising velocity
calculated by image analysis is faster than the terminal velocity
in static fluid. This is because the bubble is forced by acoustic
radiation forces (primary bjerknes force and secondary
bjerknes force). In the future study, we will compartmentalize
the forces by relating with the results of numerical simulationand image analysis.

- 38 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Relations of Void Fractions and Liquid Motions to Dissolved Gas Concentrations
in a Large-Diameter Bubble Column
Masahiro Yamada
Graduate school of Engineering, Shizuoka
University,
3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka,
Japan

Takayuki Saito
Graduate school of Science and Technology,
Shizuoka University,
3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka,
Japan

Keywords: Photoelectric optical fiber probe, LDV, Mass transfer, Flow structure.
Abstract: We investigated correlations between the CO2 concentration transportation and the large-scale flow structure by using
a newly developed photoelectric optical fiber probe (POFP) and LDV. The POFP simultaneously measures the bubble
characteristics and the CO2 concentration. Based on the fluctuation characteristics of the void fractions, the flow field in the
bubble column was divided into three zones by height. We focused on the spatial cross-correlation coefficient and a thinking ofintegral length scale in each zone. The integral-length-like scale of the liquid phase motions indicated few change against theheight. On the other hand, the similar length scale of the void fraction becomes small toward the upper zone. The similar lengthscale of the CO2 concentration exists up to the height of the middle zone. Based on these results, we discuss the relations ofspatial-scale of the void fraction and the liquid motion to the CO2 concentration.

1. Introduction
Gas-liquid two-phase flows are encountered in various
industrial plants, such as chemical reactors, bioreactors, andso on. For the purpose of saving energy and improving
operation security, the high efficiency of the gas absorption
has been strongly demanded in various fields. Hence, we needto clarify the relations between mass transfer mechanism(Komori et al., 1990) and structure of the bubbly flow (Muddeand Saito, 2001). In the past research, Akita and Yoshidaindicated the effects of the liquid properties on the gas holdup
and the volumetric coefficient for liquid phase mass transfer(Akita and Yoshida, 1973). However, a relationship of thelocal fluctuation of the liquid-phase motion and thevoid-fraction to the CO2 concentration transportation has notbeen discussed. As the major problem, although there aresome devices for detecting the concentration (Maceiras et al.,2008) or bubble characteristics (Mudde and Saito, 2001),
there was no instrument to enable the simultaneous
measurement.
Thus, we newly developed a photoelectric optical fiber
probe (POFP) in order to solve this difficult problem (Hanyu
and Saito, 2010). The POFP has two functions of an opticalfiber probe and an electric sensor. The optical fiber probe andthe electric sensor measures bubble characteristics andconcentration, respectively; i.e. we are able to simultaneously
obtain the bubble diameter, velocity, time-series void fraction
and the CO2 concentration dissolved in the liquid around the
bubbles. Therefore, the new photoelectric optical fiber probe
enables researchers to simultaneously measure both masstransfer and the flow structure at the same point in the bubble
column. Moreover, we measured the velocities of the liquid
phase at the same point by using the laser Doppler
velocimetry (LDV).
In the present study, we discuss the relations ofspatial-scale of the void fraction and the liquid motion to theCO2 concentration. Therefore, we introduced the thinking of
the integral length scale to extract a spatial-scale which has

the similar characteristics. Firstly we calculated theintegral-length-like scale for extracting a size of a fluid body.
Secondly we adopted a similar way of thinking into aconsideration of the length scale to the void fraction and CO2
concentration in order to evaluate spatial-scale. Finally we
discuss the relations of spatial-scale of the void fraction andthe liquid motion to the CO2 concentration from these results.

2. Experimental
2.1 Bubble column- 39 -A schematic diagram of the experimental setup employed
(h)

(h)
(j)

(f)

(j)

(g)

(b)

(n)
(m)

(l)

(a)

(o)
(e)
(d) (k)

(j)

(i)

(c)
(h)

(j)

(a) Bubble column, (b) Water jacket, (c) Air chamber, (d)Perforated plate, (e) Photoelectric Optical Fiber Probe, (f)Differential amplifier circuit, (g) Optical system, (h) PC, (i)Air compressor, (j) CO2 gas cylinder, (k)Gas mixer, (l)Mass flow controller, (m) LDV probe, (n) Argon ion laser,(o) LDV measurement unit
FIGURE 1. Experimental setup.

in the present study is shown in Fig. 1. An acrylic bubble
column of 380 mm in inner diameter and 1500 mm in height
was employed. The bubble column is covered with an acrylic
water jacket of 440 mm × 440 mm in square cross section and1605 mm in height. Both the bubble column and the water
jacket were filled with the ion-exchanged water and thedegassed tap water, respectively. An air chamber (380 mm indiameter and 200 mm in height) and a perforated plate(diameter of pores: 1.0 mm; equilateral triangular pitch: 10mm; the number of pores: 1240) were installed at the bottomof the bubble column. A mixture gas of CO2 and pure air was
pumped into the bubble column through them. We adjusted
the composition of the mixture gas (1.8×10-5 kg/s of CO2 and9.7×10-4 kg/s of pure air) by using two mass flow controllers.
A LDV measurement unit and LDV probe was used formeasurement of the liquid motion.

beams from a laser diode go straight through a beam splitter,and are focused on the incident tip of the optical fiber throughan objective lens. Some of the beams reaching thewedge-shape tip are reflected at the tip surface, andsubsequently return into the same fiber. Some of the returned
beams input into a photomultiplier through a beam splitterand a polarizer. The output signal obtained from thephotomultiplier is recorded at a PC via an A/D converter.
When the tip of the optical sensor is positioned in a gas
phase, the amount of the returned beams is larger than that ina liquid phase. As a result, the output voltage becomes highlevel. On the other hand, when the POFP is positioned in aliquid phase, most of the beams are emitted into the liquid
phase. Hence the output voltage becomes low level. We caneasily distinguish a change in gas/liquid phases by thedifference of the recorded output voltage.

In this study, we discuss the relations of spatial-scale of thevoid fraction and the liquid motion to the CO2 concentration.
We focused on the spatial-scale of radial direction at threezones (z = 300mm, 700mm, 1200mm). Hence, we
simultaneously measured the center of the horizontal sectionof the bubble column as well as the mobile point to radial
direction at each zone.

(e)

(a)

(d)
(c)
(b)
(a) Laser diode, (b) Beam splitter, (c) Objective
lens, (d) Optical Fiber Probe, (e) Polarizer, (f)Photomultiplier, (g) A/D converter, (h) Recorder

2.3 Photoelectric optical fiber probe (POFP)
We have newly developed a Photoelectric Optical Fiber
Probe (POFP). The POFP has two functions of aconcentration measurement by an electric probe (Maceiras,
2007) and a bubble measurement by an optical fiber probe(Mudde and Saito, 2001) (Saito et al., 2009); i.e. we are able
to measure the mass transfer and the void fraction
simultaneously by a pair of the POFPs. The structure of the
POFP is illustrated in Fig. 2. It is made of a quartz opticalfiber (external diameter: 230 µm, core diameter: 190 µm, clad
thickness: 5 µm, jacket thickness: 15 µm) plated with nickel(SEK-797, Japan Kanigen Co., Ltd.) and platinum. The
plating thickness of nickel and platinum are 130 µm and 5 µm,
respectively. The plated area of the POFP is an electric sensor,
and the tips are an optical fiber probe. A micrograph of thissensor is shown in Fig. 3. The external diameter of the POFP
is 500 µm. The axial distance LP and the clearance RP between
the probes are 1.2 mm and 500 µm, respectively. The tips of
the POFP are wedge shaped, with a 35 degree wedge angle.
Nonelectrolytic
Platinum plating nickel plating

Electroforming nickel plating

FIGURE 2. Structure of the
POFP.

FIGURE 4. Optical system of the optical fiber probe.

2.5 Principle of the electric sensor, and calibration
By using the function of the electric sensor, we are able tomeasure local CO2 concentration indirectly. This
concentration measurement utilizes electric conductivity
depending on the amount of CO2 dissolution. An electricdifferential amplifier circuit was employed to detect theelectric conductivity as an output voltage which depends on
the amount of dissolved CO2. To obtain the CO2
(e)
(d)

(j)
(l)

(b)

LP

(i)

(c)
(k)

(g)

RP

Clad
Core

Bottom Probe

(h)

(g)

(f)

2.2 Measurement points

CΟ2

Top Probe(f)(h)(a) Flask, (b) Syringe, (c) Photoelectric Optical Fiber Probe,(d) Differential amplifier circuit, (e) Recorder, (f) CO2
cylinder, (g) Cylinder, (h) Beaker, (i) Check valve, (j)Three-way valve, (k) Syringe, (l) Two-way valve
(a)

500µm

FIGURE 3. Micrograph of
the POFP.

2.4 Principle of the optical fiber probe
The optical fiber probe of the POFP utilizes the differencesin refractive indexes of gas/liquid phases and optical fiber.
The system for the optical sensor is shown in Fig. 4. The laser- 40 -FIGURE 5. Schematic diagram for calibration of theelectric probe.

concentration from the output voltage, we preliminarily
obtained the relationships between output voltage and CO2
concentration at some solution temperatures. For this specificpurpose, we conducted an experiment for making calibration
curves between the CO2 concentration and the output voltage.
The CO2 solubility depends strongly on the liquid temperature.
Therefore, we made the calibration curves with great attention
paid to the liquid temperature. Some calibration curves against
several temperatures were obtained. The schematic diagram tomake the calibration curves is illustrated in Fig. 5. First, aflask (a) was fully filled with ion-exchanged and degassed
water. Second, CO2 gas collected in a cylinder (g) placed in a
vessel filled with ion-exchanged and degassed water by
downward displacement of the water was suctioned into a
precision syringe (k). The CO2 gas was dissolved in theion-exchanged water in the flask (a) by mixing with a stirrer
chip. During this process, a pressure inside the flask is kept
equal to the atmospheric pressure by a syringe (b). Finally,
after 5 minutes mixing, the CO2 gas undissolved in the water
was pumped out by using the syringe (k). Then, we calculated
the amount of CO2 dissolution from the relationship between
injected amount and recovered amount. We obtained thecalibration curves from both the amount of the dissolved CO2
and the output voltage.

A raw signal of the electric probe is very noisy as shown in
Fig. 7 (a). In order to obtain a time-series local CO2
concentration, we need to remove the noises from the raw
signals.
First, we processed the raw signal with FFT, and decided
cutoff frequencies in order to remove applied AC component.
Second, filtering the raw signal by a low-pass filter andtransforming the processed signal by IFFT, we obtained thefirst-processed data (Fig. 7 (b)). Finally, we removed the
bubble noises from the data by a median filter [6] (Fig.7 (c)).
Before injection of the CO2-mixture gas into the bubble
column, the indicated value of the initial CO2 concentration in
the bubble column experiments is slightly different from that

3. Signal analysis
3.1 Processing of the optical fiber probe signals
We employed a method to extract the long-period
fluctuations formed in a bubble column from time-series
point-wise void fractions (Higuchi and Saito, 2010). Fig.6
shows an outline of the time-series raw data obtained from theoptical fiber probe. We analyzed a time-average void fraction
at the same time interval TL. The local time-series void
fraction α(t) was calculated by the following equation;α (t ) =1 N∑t j
Ti j =1(i = 0,1,2,...n)(1)

ti is the interval of time that the tip of the top probe existed
in the gas phase.
t2

t3

t4

t5

Output voltage [V]t1

T1

FIGURE 7. Processing of the electric sensor.
of the preliminary calibration (0 mol/m3). The difference of
supplied water causes the above; ion-exchanged and degassed
water was used in the calibration, while tap water was used in
the bubble column experiments. Since the difference in theamount of initial dissolved ions resulted in the difference in
the indicated value, we removed the difference as biased
error.

3.3 Processing of the LDV data
In this study, we applied LDV to gas-liquid two-phaseflows. Hence, we removed laser beam scattered from the
bubble surfaces from the raw data by the following procedure(Higuchi and Saito, 2010). The mean µ and standard
deviation σ are calculated from the raw data. The raw data
was processed by applying µ ± 3σ, and almost the
bubble-scattered noises were removed from the raw data.
Since the processed data was intermittent, the velocity defects
were interpolated by a liner interpolation method.

3.4 Integral-length-like scale

T2

The integral length scale is usually employed for theevaluation of eddy scale in investigations of single-phaseturbulent flows (H. Belmabrouk, M. Michard, 1998). The
integral length scale is defined by the following equation;

Time [s]FIGURE 6. A typical signal of the optical fiber probe.

3.2 Processing of the electric sensor signals
The output signals from the electric probe of the POFP
include three-type signals as shown in Fig. 7 (a). The first one
is signals of the local CO2 concentration, the second one isnoises of the applied AC voltage, and the third is bubble
noises. The bubble noises are sharp increases in the output
signals owing to the sudden decreases of electric conductivity.

∞

L ( x) = ∫ R (∆x ) dx

(2)0R(∆x) is the correlation coefficient and given by thefollowing equation;- 41 -

R ( ∆x ) =[ f ( A) − f ave ( A)・] [ f ( A + ∆x) − f ave (a + ∆x)]1∑
N
f rms ( A・
) f rms ( A + ∆x )Based on the fluctuation characteristics of the void fractions,the flow field in the bubble column was divided into threezones by height (Higuchi and Saito, 2010). Hence, weinvestigated the integral-length-like scale at three different
height (z=300mm, 700mm, 1200mm). Fig.8 (a) shows the
cross-correlation coefficient of the liquid-phase motion. The
horizontal section) and the mobile point in the radial direction.
The results of spatial-scale are summarized in Table 1. Few
changes in the integral-length-like scale of the liquid-phasemotion were observed against the height. The results indicate
the liquid-phase flow has almost the same size body in thewhole of the bubble column.

(3)∆x is a distance between the fixed measurement point in
the center of the horizontal section of the bubble column andthe mobile point in the radial direction.
In this study, we introduced the thinking of the integral
length scale to extract a spatial-scale which has the similar
characteristics. We investigate spatial-scale of a liquid-phasemotion, the void fraction and CO2 concentration transportation
by introducing the similar way. Firstly, we calculated theintegral-length-like scale for extracting a size of a fluid body.
Secondly, we calculated a similar length scale in order toevaluate spatial-scale of the bubble swarm and CO2
concentration transportation.

4.2 A similar length scale of the void fraction
Figure 8 (b) shows the results of the void fraction. The
similar length scale of the void fraction decreases in theheight direction. At the height of z = 1200mm, it was not
calculated. In the bottom zone of the bubble column, thebubble swarms which have the similar characteristics of

4. Results and Discussion
4.1 Integral-length-like scale of the liquid-phasemotion1

11

z = 1200mm

0.5

0

0.5

50

∆ x [mm]

100

150

0

50

∆ x [mm]

100

-1
0

150

1

1

50

1

∆ x [mm]

R (∆ x)[-]R (∆ x)[-]

0.5

100

150

z = 700mm

z = 700mm

z = 700mm
R (∆ x)[-]

0

0
0

0.5

0

0

0
0

50

1

∆ x [mm]

100

0

150

50

1

∆ x [mm]z = 300mm

100

-1
0

150

50

1

∆ x [mm]

R (∆ x)[-]

0.5

100

150

z = 300mm

z = 300mm
R (∆ x)[-]R (∆ x)[-]z = 1200mm
R (∆ x)[-]R (∆ x)[-]R (∆ x)[-]z = 1200mm

0.5

0

0

0
0

50

∆ x [mm]

100

0

150

(a) Liquid-phase motion

50∆ x [mm]

100

150

-1
0

50

∆ x [mm]100(c) CO2 concentration(b)Void fraction
FIGURE 8. Cross-correlation coefficient.
TABLE 1. Integral-length-like scale.

Liquid-phase motion

Void fraction

CO2 concentration

z=1200mm

37.3

23.8

21.5

z=700mm

36.7

7.6

28.8

z=300mm

38.1

-

-

- 42 -

150

relatively large size are formed. However, the bubble swarms
become smaller in the height direction.

4.3 A similar length scale of the CO2 concentrationtransportation
Figure 9 (c) shows the results of the CO2 concentrationtransportation. The similar length scale was not calculated at z
= 1200mm. However, we consider that CO2 concentrationtransportation has a relationship with the size ofcharacteristics liquid-phase flow up to the middle zone (z =700mm).
From these results, in the bottom zone of the bubble
column, the bubble swarms which have the similar
characteristics are formed, and the bubble swarms are
relatively large size. Hence, CO2 concentration is transported
by liquid-phase motion around the bubble swarm. In the
middle zone, the bubble swarms become smaller than thebottom zone. However, CO2 concentration is transported by
the characteristics liquid-phase flow. On the other hand, in theupper zone of the bubble column, the bubbles are dispersed.
The dissolved CO2 gas is diffused by liquid-phase motion.
However, CO2 concentration is not transported by thecharacteristics liquid-phase flow.

5. Conclusions
The relations of spatial-scale of the liquid-phase motion
and the void fraction to the CO2 concentration transportation
were discussed. First, the liquid-phase flow has almost thesame size body in the whole of the bubble column. Second,
the bubble swarms become smaller in the height direction.
CO2 concentration was transported by the characteristics
liquid-phase flow up to the middle zone of the bubble column.

6. References
Higuchi, M. & Saito, T. 2010 Quantitative characterizationsof long-period fluctuations in a large-diameter bubble
column based on point-wise void fraction measurements,
Chem. Eng. J., Vol.160, pp. 284-292.
Komori, S. et al. 1990 Mass Transfer into a Turbulent Liquid
Across the Zero-Shear Gas-Liquid Interface, AIChE. J.,
Vol. 36, pp. 957-960.
Mudde, R. F., & Saito, T. 2001 Hydrodynamical similarities
between bubble column and bubbly pipe flow, J. Fluid
Mech., Vol. 637, pp. 203-228.
Akita, K., & Yoshida, F. 1973 Gas Holdup and Volumetric
Mass Transfer Coefficient in Bubble Column, Ind. Eng.
Process Des. Develop., Vol. 12, pp. 76-80.
Rocio, M. et al. 2008 Effect of bubble contamination on
gas-liquid mass transfer coefficient on CO2 absorption inamine solutions, Chem. Eng. J., Vol. 137, pp. 422-427.
Hanyu, K., & Saito, T. 2010 Dynamical Mass-Transfer
Process of A CO2 Bubble Measured by Using LIF/HPTS
Visualization and Photoelectric Probing, Can. J. Chem.
Eng., Vol. 88, pp. 551-560.
Maceiras, R. et al. 2004 Local mass transfer measurements ina bubble column using an electrochemical technique,Chem. Eng. Process., Vol. 43, pp. 987-995.
Saito, T. et al. 2009 Measurement of tiny droplets using a
newly developed optical fiber probe micro-fabricated bya femtosecond pulse laser, Meas. Sci. Technol., Vol. 20,
pp. 1-12.
Belmabrouk, H., & Michard, M. 1998 Taylor length scalemeasurement by laser Doppler velocimetry, Experiments
in Fluids, Vol. 25, pp. 69-76.

- 43 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Quantification of the measurement accuracy and structure optimization
for a Two-Tip Optical fiber Probe in the bubble measurement
Ryosuke Motoyoshi
Graduate School of Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and technology,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: Two-Tip Optical fiber Probe, bubble measurement, measurement accuracy, bubble deformation
Abstract: An optical fiber probe has been frequently employed to measure bubble diameters and velocities in gas-liquid
two-phase systems. One of the common types for the bubble measurement is a Two-Tip Optical fiber Probe (T-TOP).
However, due to its intruding, the affected motion of the bubbles inevitably declines the measurement accuracy. The
magnitude of the bubble motion considerably depends on the T-TOP structure. Hence, the optimization for the T-TOP structure is needed for an accurate measurement. In this study, we arranged some types of the T-TOP size (Lp and Rp)
and demonstrated which T-TOP sizes satisfy the bubble measurement with a high degree of accuracy. First, the bubbles
deformation quantified in each condition by using the visualization. Second, we compared results of the visualization to that of the T-TOP for confirming the measurement accuracy of the T-TOP. Finally, optimal the T-TOP structure forthe bubble measurement is defined.

Gas-liquid two-phase flows are frequently encountered in
the industrial plants such as electrical generating plants,
chemical plants and so on. In order to realize higher efficiency
and safer operation of these plants, it is essential to measure
the characterization of bubbles accurately. One of thecommon tools for the gas-liquid two-phase flow measurement
is an optical fiber probe (OFP). This method successfullymeasures the velocity, the chord length of the bubble, and the
local void fraction even though in a high density of bubbles;
however, due to its intruding, the bubbles largely deformwhen the OFP touches them. The affected motion of the
bubbles inevitably reduces the OFP measurement accuracy. In
this study, we improve the measurement accuracy of a
Two-Tip Optical fiber Probe (T-TOP) in the bubble
measurement. The optimization for the T-TOP structure isconducted. Finally, it is found that the optimized T-TOP
structure minimizes the influence of touching the bubble, andmeasures the bubbles with a high degree of accuracy.

T-TOP that is obtained by the recorder (p). The interaction of
the T-TOP with a bubble rising in the stagnant water isvisualized by two high-speed video cameras (d), (e).

Top Probe (TP) Stainless capillary
Rp

1. Introduction

Lp

BottomProbe (BP) Stainless tube

FIGURE 1. Structure of the T-TOP.
(k)

(j)

(l)
(m)
(f)
(a)

(n)

(p)

(o)

2. T-TOPA schematic diagram of the T-TOP is shown in Fig. 1. The
T-TOP is composed by silica glass (Diameter of a wire:
230µm, Diameter of core: 190µm, Thickness of clad: 5µm,
Thickness of Jacket: 15µm). The T-TOP consists of two fibers
whose tips shape wedge (the wedge angle is 35 degrees), andits structure is controlled by two parameters, Rp and Lp(T-TOP size). We arranged some types of the T-TOP size interms of Lp, and demonstrated which T-TOP sizes satisfy the
bubble measurement.

3. Experimental setup
A schematic diagram of the experimental setup is shown in
Fig. 2. The vessel (f) is filled with the ion-exchanged water.
Each bubble is injected from the hypodermic needle (g)(equivalent particle diameter =2.99 mm). The T-TOP (a) is set
on the 3-axis unit. The optical signal delivered from the- 44 -

(i)
(c)

(b)
(e)
(h)

(g)
(d)
(q)

(r)

(a) T-TOP, (b) Halogen light source 1, (c) Halogen lightsource 2, (d) High-speed video camera 1, (e) High-speed
video camera 2, (f) Acrylic water vessel, (g) Needle, (h)PC 1, (i) PC 2, (j) LD, (k) Objective lens, (l) Beamsplitter, (m) Polarizer, (n) Photo multiplier, (o)Amplifier, (p) Recorder, (q) Flow meter, (r) Air tank.
FIGURE 2. Experimental setup.

4. Signal process of the T-TOP
A typical output signal of the T-TOP is illustrated in Fig. 3.
When the optical fiber is covered with gas, the propagatedbeams are reflected and return at the tip, because of thedifference for the refractive indices between the fiber and gas;
hence, the signal of the TP (BP) increases at t1 (t2). On theother hand, when the optical fiber is covered with water, thepropagated beams pass through into the water, because therefractive indices of the fiber is nearly equal to that of water;
hence, the signal of the TP (BP) decreases at t3 (t4). By using
the ON/OFF signal, the bubble velocity (=Ub) is calculated
from the difference between t2 and t1 (∆t1= t2-t1), and Lp. Then,the bubble velocity is defined as following equation.

The difference is the smallest of all conditions, when “Lp=1.03mm”, and the difference is 10% below. From thevisualization result, in this case, the surface deformation
recovers, when the BP touches the bubble; hence, the Ub isexactly calculated as the gravity-center velocity of the bubble.
If Lp is longer than 1.03mm, the bubble-interface
oscillation becomes dominant; hence, the difference of theresults between visualization and T-TOP increases when “Lp=1.40mm”.
Summarizing these results, we can determine theoptimized T-TOP size, that is, “Lp =1.03mm, Rp =0.5mm”.
The difference for the results of visualization and T-TOP is
10% below, and this value is a bias error.
TABLE.1 Comparison of velocity fromvisualization and T-TOP.

(1)

U b = L p / ∆t 1

The bubble chord length (=Lb) is obtained from the Ub andthe residence time of the TP (∆t2=t3-t1). The bubble chord
length is calculated,

t1

Output voltage [V]

t2

0.18
0.67
1.03
1.40

(2)

Lb = U b ⋅ ∆ t 2
5

Lp

t3

t4
Vtop-gas

4

∆t1
∆t2

TP
BP

2

Lp

1
0

0.18
0.67
1.03
1.40

Vtop-liquid
Vbottom-liquid
0510Time [ms]Difference[%]
397.74-17.95-2.98-14.28TABLE 2 Comparison of chord length fromvisualization and T-TOP.

Vbottom-gas

3

Velocity [mm/s]
Visualization T-TOP
299.441478.1296.96
243.67295.25286.46277.28237.6815

Chord length [mm] Difference[%]
Visualization T-TOP
1.67
8.23
393.571.76
1.49-15.22
1.72
1.59
-7.85
1.92
1.67
-12.85

6. Vision
2 mm

t1

t2

t3

t4

FIGURE .3 Typical signal of the T-TOP.

5. Result and discussion
In this research, four types of the T-TOP were employed
for the bubble measurement to quantify the relationshipbetween the T-TOP structure and the measurement accuracy.
Note that Rp is constant, 0.5mm. The results of thevisualization and T-TOP are presented in Tab. 1 and Tab. 2.
The difference between visualization and T-TOP is larger
when “Lp =0.18mm”, in comparison to the other conditions. It
is due to the effect of the interface deformation of the bubble;
just before the BP touches the upper surface, the surface
deformation spread around the bubble. This deformation
causes the error of the detecting t2. Consequently, thecalculation of Ub and Lb is largely affected, when “Lp=0.18mm”.

We confirmed the accuracy and influence for bubble
measurements by using four types of the T-TOP and thevisualization. The bubble motions are significantly differ ineach T-TOP. Especially when “Lp =1.03mm, Rp =0.5mm”, the
T-TOP minimizes the influence of touching the bubble, andmeasures the bubbles with a high degree of accuracy. As aresult, we defined this condition as the optimum T-TOP size.
In future study, we focus on the signals from the T-TOP to
improve the measurement accuracy.

7. Reference
Saito, T. & Kazishima, T. 2002 JSME-B, Vol. 68, No. 674,
pp. 2719-2716.
Saito, T. & Matsuda, K. & Ozawa, Y. & Oishi, S. & Aoshima,
S. 2009 Measurement of tiny droplets using a newly
developed optical fibre probe micro-fabricated by afemtosecond pulse laser, Measure. Sci. and Tech. Vol. 20,
No. 11, pp. 114002.
Sato, Y. 2010 Graduation thesis, Graduate School ofEngineering, Shizuoka University, Saito Sanada
Laboratory.

- 45 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Dynamical Mass Transfer Process of a CO2 Bubble
Measured by using LIF/HPTS Visualization and Photoelectric Probing
Masanobu Tsukamoto
Department of Mechanical Engineering
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: CO2 bubble, mass transfer, LIF, photoelectric optical fiber probe, PIV
Abstract: We directly visualized the dynamical mass transfer process from a zigzagging rising CO2 bubble to its surrounding
liquid by using LIF/HPTS. We measured the surrounding liquid motion induced by bubble buoyancy using PIV. Further, the CO2
concentration profile inside the bubble wake was measured directly by using a newly developed photoelectric optical fiber probe.
Making the best and mutually complementary use of these three measurement techniques, we discuss the relationship between themass transfer process and the flow structure. We succeeded in clearly visualizing CO2-rich regions corresponding with the
dynamical mass-transfer process from the bubble to the wake and the surrounding liquid. We also obtained a CO2 concentration
profile in the bubble wake. It was found that the CO2-rich regions were formed into horseshoe-like vortices. In addition, we
discuss the performance and characteristics of the newly developed photoelectric optical fiber probe.

1. Introduction
Gas-liquid two-phase flows are widely used in various
industrial plants: chemical reactors, bioreactors, heatexchangers, and so on. The high efficiency of the gas
absorption and the operation safety has been requested for the
purpose of saving the energy and improving the economical
performance. Hence, understanding of the relation between
the mass transfer mechanism and the structure of the bubbly
flow is essential.
In this paper, the first objective is to discuss the dynamical
processes of the mass transfer from a zigzagging rising CO2
bubble of 2.9 mm in equivalent diameter by using threemeasurement methods (i.e., LIF/HPTS, PIV and a newly
developed photoelectric optical fiber probe). The second
objective is to consider the characteristics of the new method(photoelectric optical fiber probe: POFP) to measure thepoint-wise concentration in the bubble wake as well as the
bubble diameter and velocity, and to demonstrate its
performance.

(e)

The POFP was inserted into the side wall of the water
vessel to measure the CO2 concentration in the bubble wake.
Fig. 1 shows a schematic diagram of an experimental setup
employed in POFP measurement. An acrylic water vessel(100 mm × 100 mm × 400 mm) was filled with ion-exchanged
and degassed tap water (29°C) to a depth of 380 mm. A
specific bubble launch device composed of an acrylicchamber, an audio speaker, a precise pressure controller andcheck valves was used for launching single bubbles under thecomplete control of diameter, initial orientation, initial shapeand launching interval (Sanada et al., 2006). The single
bubbles were launched from a hypodermic needle (innerdiameter: 0.40) fixed to the acrylic water vessel at the desired
time interval. The red LED light and halogen light sourceswere used as back lights to clearly extract the bubble

(a)

(j)
(h)

(g)
(d)
(b)

(a)

(c)

(a) High-speed video camera, (b) Bubble generator, (c)Function generator, (d) Needle, (e) Water vessel, (f) Halogen
light source, (g) Photoelectric fiber probe, (h) Acrylic plate,(i) 3-axis unit, (j) Continuous red LED
FIGURE 1. Experimental setup of the photoelectric
fiber probe measurement.

2. Experiment
2.1 Experimental setup for photoelectric optical fiber
probe

(f)

(i)

2.2 Structure of the photoelectric optical fiber probe
A photoelectric optical fiber probe (POFP) was newly
developed. The clearance L P between the probes is 500 µm.
The POFP has two functions of the concentration
measurement by an electric sensor and the bubble
measurement by an optical sensor. The optical sensor of the
POFP utilizes the differences in refractive indexes ofgas/liquid phases and optical fiber. On the other hand, themeasurement of the concentration utilizes the difference ofelectric conductivity depending on the amount of CO2
dissolution. To obtain the CO2 concentration from the output
voltage, we preliminarily obtained the calibration curves.

- 46 -

Bubble3. RESULTS AND DISCUSSIONS
3.1 Formation of the horseshoe-like vortices
Just after the launch of the bubble from the needle, clear
horseshoe-like vortices (in a strict sense, a part of thehorseshoe-like vortices) were observed. We visualized
vortices simultaneously included both the wake structure andthe mass transfer from the bubble to liquid phase across the
bubble interface. The high-CO2-concentration thin layer
around the bubble was continuously flushed away andaccumulated into the horse-shoe-like vortices. The vortices(i.e., bundles of CO2-rich solution) were intermittently shedfrom the bubble in association with both the zigzagging
motion and the surface oscillation; in succession the wreckageof the wake (i.e., small bodies of CO2-rich solution) wastransported widely into the surrounding liquid by thebuoyancy driven flows. The surface oscillation plays a keyrole in turbulence characteristics (in a strict sense, velocity
fluctuation) of the surrounding liquid(a) 0 msec(b) 32 msec later

Trajectory of
the bubble

3.2 Flow structure of the CO2-rich regions
The panels in Fig. 2 show a typical time evolution of theadvective liquid-phase flows detected by PIV, and theircorresponding dynamical mass transfer process induced by theflows. The measurement cross-sectional areas are indicated in
Figure 2. Figure 3 shows the original snapshots of thecross-sectional bubble wake at each measurement time (0msec: just after the bubble passing; 32 msec later; and 64
msec later). Fig. 4 presents the vorticity contour map obtained
from PIV, and Figure 5 the velocity contour map.
In Fig. 2 - (a), a pair of cross-sectional bubble wakes,
which are the same size and axisymmetric, is observed. In Fig.
3 – (b), the pair moves upward. Below the pair, a pair ofcross-sectional bubble wakes, which are the same size andaxisymmetric, is observed. Similarly, a pair of cross-sectional
bubble wakes is observed further below. The interval between
the pair wakes increases with time. The bubble wakes are
diffused. Just before the vortex shedding, it is clearly observedthat the pair wakes rotate in the opposite direction (Fig. 3 –(c)).
As shown in Fig. 4 – (a), positive/negative vorticity regions
are formed between the pair wakes. The upward flows occur
between the pair wakes as shown in Fig. 5 – (a). The CO2-richregions (the wreckage of the wake) are transported and spread
upward by this strong upward flow (Fig. 5 – (b) & (c)). The
velocities of the liquid phase gradually decrease, and theCO2-rich regions spread slowly. These results indicate that the
wreckage of the horseshoe-like vortices is transported over awide range by this strong upward flow.

(c) 64 msec later

Bubble wake
Visualization planezyx

FIGURE 2. Visualization planes of the cross-sectional
bubble wake.
Trajectory of the bubble
PIV particle
gravity center
RotateBubblewakezy(a) 0 msec (b) 32 msec later (c) 64 msec later

FIGURE 3. Snapshots of the cross-sectional
bubble wake at each measurement time
Trajectory of the bubble gravity center(a) 0 msec(a) 0 msec(b) 32 msec later(b) 32 msec later

TABLE 1. Properties of the bubbles
Equivalent diameter [mm]2.9Terminal velocity [m/s]0.28

Reynolds number [-]849

Weber number [-]3.4

Schmidt number [-]529

Sherwood number [-]687

Morton number [-]2.6×10zy

3 mm(c) 64 msec later
Scale for vorticity contour-20

0
20 [1/s]
FIGURE 4
The vorticity contour map.

-11

- 47 -

3 mm(c) 64 msec later
Scale for velocity contour
30

115
200 [mm/s]
FIGURE 5.
The velocity contour map.

3.3 Results of measurements
3.3.1 CO2 concentration measurement of the bubble wake
via POFP. The lower probe of POFP pierces the bubble, andthen it is completely covered with the bubble (gas phase). At
this time, the output voltages of both the OFP and electricprobe (EP) take the maximum. Next, since the space between
two sensors of the EP is filled with the CO2 solution of thethin concentration layer, the output voltage of the EP
decreases.
Fig. 6 shows the profile of the CO2 concentration
measured in the wake near the bubble rear via the POFP.
We succeeded in clarifying the profile of the CO2
concentration inside the bubble wake, which is difficult toobtain from only the LIF/HPTS method. From this result, theCO2 concentration takes the maximum at the center region of
the bubble wake and sharply decreases toward the outer edgeof the bubble wake.
1 mm

4. CONCLUSIONSIn this research, the dynamical mass transfer process of
single bubble and surrounding liquid motion induced bybubble buoyancy were visualized via PIV and LIF/HPTS. In
addition, we newly developed a photoelectric optical fiber
probe to measure the CO2 concentration inside the bubble
wake directly.
We demonstrated that the mutually-complementary use of
three measurement methods (i.e.,LIF/HPTS,PIV and a newly
developed photoelectric optical fiber probe) is very effective
to experimentally examine the dynamical processes of themass transfer from a zigzag rising CO2 bubble.

5. REFEERENCES
Saito, T., Sakakibara, K., Miyamoto, Y., Yamada, M. 2010 A
study of Surfactant Effects on the Liquid-Phase Motion
Around a Zigzag-Ascent Bubble Using A Recursive
Cross-Correlation PIV. Chemical Engineering Journal,
Vol. 158, pp 39-50.
Sanada, T., Watanabe T. & Fukuno T. 2006 Interaction andCoalescence of Bubbles in-Stagnant-Liquid. Multi
Science Technology, Vol. 2, pp 155-174.
Boden, S., M. Bieberla & U. Hampel. 2008 Quantitative
Measurement of Gas-Hold-up Distribution in a Stirred
Chemical Reactor Using X-Ray Cone-Beam Computed
Tomography. Chemical Engineering Journal , Vol. 139,
pp 351-362.

CCO2/Cmax

Center of the bubble
1.0
0.8
0.6
0.4
0.2
0

Bruker, C. 1999 Structure and Dynamics of the Wake of
Bubbles and its Relevance for Bubbles Interaction.
Physics Fluids, Vol. 11, pp 781 – 1796.

-40 -200

Clift, R., J. R. Grace & M. E. Weber. 1978 Bubbles,
and Particles. Academic Press, New York.

20 40

Measurement point [%]FIGURE 6. Normalized CO2 concentration of the bubble
wake.
3.3.2 Measurement of the bubble diameter and velocity.
The measurement results of the bubble velocity and length via
the POFP calculated from data which the POFP contacts thecenter of the bubble were compared with those of thevisualization. Tab. 1 shows the comparison of thosemeasurement results. The difference in the average chord
length between the two methods was less than 15%. The
results obtained from the POFP were larger than those fromthe visualization; this was due to the bubble-POFP contact.
Hence, the pierced chord length was measured as being longer
than the original chord length.
TABLE 2. Difference between the photoelectric fiber
probe and visualization result.
Visualization

Photoelectric fiber
probe

Difference [%]Bubble diameter [mm]

1.65

1.85

12.0

Bubble velocity[mm/s]

248.8

206.8

-16.9

Drops

De Vrise, A. W. G., A. Biesheuvel & L. Van Wijngaarden.
2002 Notes on the Path and Wake of a Gas Bubble
Rising in Pure Water. International Journal ofMultiphase Flow, Vol. 28, pp 1823 – 1835.
Madhavi, T., A. K. Golder, A. N. Samanta & S. Ray. 1996
Studies of Bubble Dynamics With Mass Transfer.
Chemical Engineering Journal, Vol. 128, pp 95 – 104.
Motarjemi, M. & G. J. 1978 Mass Transfer From Very Small
Bubbles – The Optimum Bubble Size for Aeration.
Jamesone, Chemical Engineering Science, Vol. 33. pp1415 – 1423.
Vlasogiannis, P., G. Karagiannis, P. Argyropoulos & V. 2002
Air-Water Two-Phase Flow and Heat Transfer in a Plate
Heat Exchanger. Bontzoglou, International Journal ofMultiphase Flow, Vol. 28, pp 757 – 772.

Proceedings of Japan-Korea International Exchange Program- 48 -

Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Particle motion in a kHz-order-ultrasound-irradiated water(The relation between the particle motion and an acoustic cavitation bubble)
Yuta Nakamura
Faculty of Mechanical Engineering,
Shizuoka University,
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and technology,
Shizuoka University,
Hamamatsu, Shizuoka, Japan

Keywords: Cavitation bubble, Particle aggregation, kHz-order ultrasoundAbstract: We investigated a new solid-liquid separation technique using kHz-order ultrasound. This method is able toaggregate particles dispersed in a water by contactless operation. Few studies were reported about the particle-aggregatin
g technique by ultrasound of kHz-order frequency. Moreover the mechanism of the particle aggregation in such a condition is still unclear. In the present study, in order to clarify the mechanism of the particle aggregation in a water irradi
ated by kHz-order ultrasound, we investigated the relation between the particle motion and the acoustic cavitation bubbl
e motion. We have found out that the acoustic cavitation bubble adhering to the particle contributes significantly to agg
regation of the particles. Based on the time-resolved visualization of the bubble motion on the particle and the 3D str
ucture of bubble clouds obtained from sonoluminescence distribution, we discuss the particle aggregation quantitatively.

1. Introduction
The ultrasound techniques are encountered in a lot ofindustrial apparatuses such as ultrasonic cleaning, particle
manipulation and ultrasonic atomization. These techniques
have an useful characteristic that non-contact operation isavailable. The ultrasound techniques are also available forsolid-liquid separation. This separation method has almost noenvironmental load, because this method does not needmaintenance, and does not need chemicals such as
aggregating agent. We focused attention on solid-liquid
separation by using ultrasound of kHz order.
In the past studies, MHz-order ultrasound has been mostly
employed in the ultrasound separation techniques. It wasreported that the acoustic radiation force dominantly acts on
aggregation of particles. This force is caused by pressure
gradient generated in liquid phase by the sonic waves.
However, the studies on kHz-order ultrasound had almost notbeen reported before. Therefore, the mechanism of particles
aggregation is not clear yet.
We conducted the present study in order to reveal themechanism of particle aggregation under irradiation of
kHz-order ultrasonic in water. We quantitatively discuss theparticle motion and the acoustic cavitation bubble motion
based on time-resolved visualization. Furthermore weevaluated the acoustic force quantitatively.

2. Experimental setup
The experimental setup consisted of an ultrasound driving
system and a camera system. In the former system, a sine
wave voltage signal (frequency: 20.3 kHz, output voltage:
1.00 V) was supplied into a BLT transducer through a power
amplifier. The ultrasound was irradiated vertically from thebottom of an acrylic water vessel (diameter: 50 mm, height:
110 mm). A standing wave field was formed by the incident
waves from the BLT transducer and the reflected waves fromthe surface of the water. The vessel was filled with two typesof 150 ml ultrapure water: ultrapure water degassed andincluding air. In the camera system, the conditions of Case 1
and Case 2 are described below in detail.

2.1 Case 1 : Position of the particle aggregation
First, we investigated the particle motion with respect toparticle diameters. The examined particles were 300, 400, 600,
1000 µm in diameter. The density of each particle was 1.05
g/cm3. The images were captured by CCD camera. In order tocapture the whole vessel, the spatial resolution was
1024×1024 pixel2 (64.5 µm/pixel), and the frame rate was 30
fps.

2.2 Case 2 : Particle motion and acoustic cavitation
bubble motion
Second, we investigated the interaction between the
300-µm-diameter particle and the acoustic cavitation bubble.
The images were captured by high speed camera. The spatial
resolution was 512 × 512 pixel2 (3.85 µm/pixel), and theframe rate was 20,000 fps. The interrogation area waspositioned just under the pressure antinode (height from thebottom of the vessel: approximately 20 mm) in the standingwave.

3. Results
Fig. 1 shows the relation between the particle
concentration and the position of the aggregated particles
against the particle diameter. The particle aggregations stayednear the pressure node or antinode in the standing wave field,
depending on the particle diameter. The acoustic cavitation
bubble also gathered near the pressure node and the antinode.
Therefore, the particle motion qualitatively conforms to thatof the acoustic cavitation bubble. Furthermore, when there
was no acoustic cavitation bubbles in the water (degassed
ultrapure water), particles did not aggregate. Therefore, theacoustic cavitation bubble significantly contributes to theaggregation of particles.
Fig. 2 shows time-series images of a particle and an
acoustic cavitation bubble adhering to the particle surface,and- 49 -

the definitions of θv and θ b. We successfully captured an
acoustic cavitation bubble adhering to the particle, that
expanded and contracted in synchronization with the soundpressure. It is confirmed that a particle moved toward upper
left of the image and the acoustic cavitation bubble wasadhering at the traveling direction of the particle. We definedthat θv was the angle formed between x axis and particle
velocity vector, θb was the angle formed between x axis andthe adhered bubble position, as shown Fig. 2. Then, θd wasangular difference between θv and θ b.
Fig. 3 shows the relation between the particle velocity Vand θd. The particle velocity was constant until 1.5 ms when
θd was relatively-large. However, the particle velocity
increased since 1.5 ms when θd was approximately 0.
Therefore, we considered that particles were towed by theadhered acoustic cavitation bubbles, then the acoustic
cavitation bubble lies between aggregated particles.

150

45
0

100
Particle velocity Vθd [deg]

Particle velocity V [mm/s]

90

-45

θd

50

-90
50
100
150
7.5
2.5
5.0
Elapsed time [ms]FIGURE. 3 The relation between the particle velocity V and θddepending on the elapsed time.

00

The position of the trapped
particle aggregation [mm]4. Conclusions
60
Antinodes
Nodes
φ300 µm
φ400 µm
φ600 µm
φ1000 µm

40
20
00
0

11
22
33
44
Particle concentration [g/L]*Particle diameter

FIGURE. 1 The position of the trapped particle aggregation.

In the present study, we have revealed the mechanism of
the particle aggregation in water under irradiation of
kHz-order ultrasound. The positions of the aggregatedparticles were discussed by comparing the position that the
acoustic cavitation bubble gathered. Furthermore, we
evaluated the relation between the particle motion and theacoustic cavitation bubble motion quantitatively. The acoustic
cavitation bubble significantly contributes to aggregation ofparticles. In detail, the acoustic cavitation bubble adhered tothe particle surface, then the particle was towed by the
acoustic cavitation bubble. In the future study, we will clarify
the mechanism that the acoustic cavitation bubble adheres tothe particle surface.

5. Nomenclature
t
V

θ
500µ
µm

t=0 msSubscriptsbbubblevvelocity vectorddifference

Particle

BubbleBubblet=0.05 ms

θb

x

θv
Particle
t=2.5 mst=7.5 ms
FIGURE. 2 Images of a particle and acoustic
cavitation bubbles.

Elapsed time, ms
Particle velocity, mm/s
Angle, deg

6. References
Yamakoshi,
K.
1996,“Erythrocytes
concentrated
non-destructively by acoustic radiation force” Technicalreport of IEICE, US96-71
Steven, M. W. 1997, “Measurement of Ultrasonic force forparticle-liquid separation” AIChE Journal, Vol. 43, No.
7
Mitome, H. 2001, “Micro bubble and sonoluminescence” Jpn.
J. Appl. Phy., Vol. 40, 3484-3487.

- 50 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

3D Simulations of a Bubble/Droplet Measurement
via a Single-Tip Optical fiber Probe
Hajime Furuichi
Faculty of Mechanical Engineering,
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate school of Science and Technology,
Hamamatsu, Shizuoka, Japan

Keywords: Ray tracing method, Optical fiber probe, bubble/droplet measurement
Abstract: An optical fiber probe (OFP) method is one of very available techniques for gas-liquid two-phase flows, to measure avelocity and size of a bubble/droplet. To improve its measurement accuracy, the output signals from the OFP must be considered
deeply. However, previous studies on the OFP seem to lack quantitative analysis of the signals. For the practical purpose to extract
meaningful signals, we have developed the numerical simulation code via 3D-ray-tracing method. In this study, firstly, we
verified appropriateness and accuracy of the developed code, comparing with some experiments. Second, output signals from the
bubble measurement were observed and it was described that some noises occurred. We also clarified the mechanism of thesignals from the numerically reconstruction. Furthermore, to extract signal potentials, we focused on that the output value depends
on contact conditions between a bubble and the OFP. Finally the measurement accuracy was successfully advanced.

1. Introduction
An optical fiber probe method (Hanyu & Saito, 2010,
Sakamoto & Saito 2011) is one of the common techniques
employed to the gas-liquid two-phase flows. Recently, one ofauthors uniquely developed a Single-Tip Optical fiber Probe(S-TOP) (Saito, T. et al, 2009). By using the S-TOP
measurement, the ascending velocity and the chord length of abubble successfully measured only with a wedge-shaped tip ofa single probe. However to bring out its hidden potential wehave to deeply consider the optical signals from the probe andprecisely analyze them. Many past studies on the probing
showed successful results, however they seem to lackquantitative analysis of the optical signals. The optical fiber
probing utilizes optical interaction between the laser beams
emitted from the optical fiber and the bubble/droplet.
Although the probing system (an LD, a photo detector and adigital recorder) and measurement principle (detection ofchange of refraction indexes) are simple, the optical signals
are very difficult to analyze due to the complicated interaction
between the laser beams and gas-liquid interface. For thepractical purpose of extracting the meaningful signals, wehave developed the numerical simulation code of
3D-ray-tracing and conducted precise experiments to consider
the interaction.

sin 2 (θ i − θ t )sin 2 (θ i + θ t )(2)

S PolarizationT=sin 2θ i sin 2θ t
sin 2 (θ i + θ t )where θi and θt are the incidence and refraction angles of rays
transmitting a surface, based on the Snell’s law. According to
the described algorisms, we model the S-TOP measurement(including the S-TOP, lights, and a bubble) in the spatial
coordinate, as demonstrated in Fig. 1.

Rays

S-TOP

FIGURE 1. A demonstration of the ray-trace simulation.

3. Experiments for the validationtan 2 (θ i − θ t )tan 2 (θ i + θ t )T=

sin 2θ i sin 2θ t
sin 2 (θ i + θ t ) cos 2 (θ i − θ t )(1)

3.1 S-TOP
Fig. 2 shows that a micrograph of the S-TOP employed inthis study. The tip is 200µm of diameter, and ispolishing-processed to 35 degrees of a wedge angle.

200µm

A ray tracing method (Koshiba, M. et al., 1992) isappropriate for our purposes. The light waves are assumed to
be ray segments and the diffraction is ignorable in this method.
These assumptions enable us to determine ray trajectories.
Thus, the reflection and refraction of the incident laser beams
are numerically calculated in accordance with the Snell’s law.
Our new code takes each beam 3D trajectory, each beamenergy and each beam polarization into account. The
reflectivity R and the transmissivity T are defined as follows:35
゜

2. Algorisms

R=

R=

FIGURE 2. A micrograph of the S-TOP.
In practical measurement, the S-TOP has some advantages:
simple system and high adaptation for a small bubble/droplet.

P Polarization- 51 -

In particular, the single tip optical fiber probe with awedge-shaped tip enables us to simultaneously measure
diameters, velocities and number density of bubbles/droplets.
The problem is that a position pierced by the S-TOP is notdetected. We have found out how to detect the position byusing “pre-signal”. The pre-signal was considered to be noisein the past investigations; however it includes very important
information. We consider the mechanism of the pre-signal,and the method to detect the pierced position via thepre-signal, numerically and experimentally.

In water

3.2 Results of the validation

In air(a)

Numerical simulation
S-TOP

400µm

400µm

400µm

400µm

(b)

(a)

(b)

Experiment
S-TOP

FIGURE 4. A comparison of discharged lights.

4. Output signals in a bubble measurement(g)

4.1 Measurement principle of the S-TOP
(f)

(f)
(j)
(j)

(d)
(d)
(e)
(e)

(a) YAG laser(b) S-TOP(c) Film with a fluorescent dye(d) CCD camera(e) Computer(f) Sharp cut filter(g) Acrylic vessel

FIGURE 3. Experimental setup.
We verified appropriateness and accuracy of our numericalsimulation code by comparison with experimental results. Fig.
3. shows that the experimental setup. The laser beams(wavelength: 570nm) emitted from the probe tip into water
were visualized by using a fluorescent dye (Rhodamine B:
excitation wavelength of 535nm). The beams emitted from the
tip into air were also visualized by using a thin film uniformlyinterpenetrated by the same dye. Thus, we employed asharp-cut filter that only passes above 550nm, and YAG-laser
as the light source, so then images of the emitted lights werefilmed by CCD camera. On the other hands, the developed
code constructed the S-TOP and rays transmitting as alreadyshown in the Fig. 1. They were converted to a 3D spatial mapof the ray energy, to specifically compare with theexperiments.
Fig .4 shows a comparison between the numericallysimulated results of the emitted laser beams from the S-TOP
tip and the experiment ones. The beam distributions in thewater phase and the gas phase obtained numerically agree
well with the experimental ones. The energy density
distributions from the numerical simulation also agree withthe experimental ones. Therefore, the appropriateness andaccuracy of our code are demonstrated.

A typical output signal of the S-TOP is plotted in Fig. 5.
When the wedge-shaped tip of the S-TOP is completely
positioned in the water phase (Fig. 5.(1)), the output intensity
is low. Just before the tip touches the bubble frontal surface, asharp peak signal (pre-signal) is observed. The wedge-shaped
tip is gradually covered with the gas phase, and the output
signal gradually increases. When the tip is completely
positioned in the bubble (Fig. 5.(2)), the output signal takes
almost a constant value. When the tip goes through the bubble
rear surface, the output signal rapidly decreases. An intensive
and clear pre-signal occurs only when the tip penetrates abubble frontal surface at the center region. Using thischaracteristic of the pre-signal, we are able to detect theposition pierced by the S-TOP. In other words, we are able toextract burst signals that the S-TOP pierced bubbles at theircenter region. As illustrated in Fig. 6., when the S-TOP
penetrates a bubble at the center region, correct measurementof the diameter and velocity are achieved.

Output value [-]

(c)

1.2
1

(1)

Pierced time

(2)

(3)

0.8
0.6
0.4
0.2
0

0

2

4

6

8

10 12 14

Time [ms]
S-TOP

1 mm

(1)

(2)

(3)

FIGURE 5. An output signal of the bubble measurement.

- 52 -

5. Summary
In order to develop a new method to detect a position
pierced by the S-TOP, we conducted the numerical simulationof 3D-ray-tracing and considered the mechanism of the
pre-signal. As a result from a new signal analysis via thesimulation, pre-signal occurred. The intensity of the
pre-signal depends on positional relation between the tip andbubble surface. Using the numerical simulation of
3D-ray-tracing, we understood the mechanism of the
pre-signal and established Pre-signal threshold method.
Further, we improved the accuracy of the S-TOP
measurement.

Bubble(True length)(Undesirable length)

S-TOP

FIGURE 6. Chord length measurement by the S-TOP.

4.2 The numerically analysis
Fig. 7. shows a numerical result. The laser beams emitted
from the S-TOP are reflected at the bubble frontal surface, andsome of them re-enter into the S-TOP. According to the result,the signal was separated into the three signal patterns. They
enable us to discuss the mechanism of the pre-signal in theempirical S-TOP signal. Moreover, such the peak (pre-signal)
appears in the specific case as shown in the Fig. 6. Based on
this meaningful information, we established a new method todecay the random error in the S-TOP measurement (Pre-signal
threshold method (Mizushima & Saito, 2011)), andsuccessfully improved its accuracy.
Pierced time

Output value [-]1.2

A (a) + (b) + (c)

1
0.8
0.6
(c)

0.4
0.2
0

(a) Probe tip(b) Bubble front

(a)

(b)
0

2

4

6

8

10 12 14(c) Bubble rear

6. References
Hanyu, K. & Saito, T., 2010 Dynamical Mass Transfer
Process of a CO2 Bubble Measured by using LIF/HPTS
Visualization and Photoelectric Probing. Can. J. Chem.
Eng., Vol. 88, 551-560.
Sakamoto, A. & Saito, T., 2011, Robust algorithms forquantifying noisy signals of optical fiber probes
employed in industrial-scale practical bubbly flows
International Journal of Multiphase Flow, Under
Review.
Saito, T. et al, 2009 Measurement of tiny-droplets using a
newly developed optical fiber probe microfabricated byfemtosecond pulse laser. Meas. Sci. Technol., Vol. 20,
114002.
Koshiba, M. et al., 1992 Simple scalar finite element
approach to optical rib waveguides. IEE Proc. J., Vol.
139, 166-171.
Mizushima, Y.. & Saito, T., 2011 Detection method ofpiercing positions for the bubble measurement by aSingle-Tip Optical fibre Probe. Meas. Sci. Technol.,
Under Review.

Time [ms]FIGURE 7. An analysis of the signal patterns.

- 53 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Measurement of ozone bubbles using optical fiber probe
in wastewater treatment system
Daisuke Shinohara
Department of Mechanical Engineering,
Shizuoka University
3-5-1 Johoku, Nakaku, Hamamatsu,
Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology
Shizuoka University
3-5-1 Johoku, Nakaku, Hamamatsu,
Shizuoka, Japan

Keywords: S-TOP, Ozone bubble, Wastewater treatment
Abstract: Wastewater from a dairy farm, which contains milk fatty acids and proteins, is very difficult to treat by commonplacewastewater processing. Recently, these contaminations and the visual pollution is a major concern for the dairy farmers. In orderto overcome these problems, we study the wastewater treatment system with ozone. This system is easy to introduce for small andmedium-scale dairy farmer because the structure of the ozone treatment system is compact and simple. However, we have notinterpreted the flow regime in the system enough. The purpose of this study is to clarify the flow dynamics of ozone bubbles in thesystem with a Single-Tip Optical fiber Probe (S-TOP). Using this measurement, we can measure the ozone bubble velocity andthe pierced chord length. Based on these feature of ozone bubbles, the flow structure in the wastewater treatment system wasdiscussed. Finally, we clarified what contributes to the effectiveness of the system.

Wastewater from a dairy farm, which contains milk fatty
acids and proteins, is very difficult to treat by commonplacewastewater processing. Recently, these contaminations and thevisual pollution is a major concern for the dairy farmers.
Wastewater treatment with ozone is the way which resolves
organic substances with injecting ozone bubbles into thewastewater. The system is easy to introduce for small andmedium-scale dairy farmer because the structure of the ozone
treatment system is compact and simple. Saito laboratory
and Shizuoka Prefectural Research Institute of AnimalIndustry research the ozone treatment of the wastewatercontaining milk to demonstrate and improve the efficiency ofthe system.
The purpose in this study is to clarify the flow dynamics ofozone bubbles in the system with a Single-Tip Optical Fiber
Probe (S-TOP).

where ts is start time of touching the bubble and te is thetime departing from the bubble.
(1)

5
O utput voltage [V]

1. Introduction

(2)

(3)

te
VGas

4
3

Vthh

grd

Vthl

2
1

ts

VLiquid

50time [ms]

10

1 mm

2. Measurement method
experimental setup

of

S-TOP

and

(1)

2.1 The bubble measurement of the S-TOP

(2)

(3)

FIGURE 1. Typical output signal of S-TOP

Typical output signal of the S-TOP is depicted in Fig. 1.
When the S-TOP positions in the water phase, the output
voltage is low. On the other hand, when the S-TOP detects
bubbles, the output voltage increases. Due to the wedge shapeof the S-TOP, The gradient of the steep surge in the signal is
proportional to the bubble interface velocity; hence, The
bubble velocity UB is easily obtained from the following
equation :(1)
U B = α × g rd
where grd is the gradient of the steep surge in the output
signal and α is a proportional coefficient.
The pierced chord length, LB is obtained from the following
equation:
LB = U B × (t e − t s )(2)

2.2 The experimental setup
Fig. 2 shows an outline of the experimental equipment. A
tank (a) (900mm in height and 565mm in diameter) is filledwith the water included fatty milk about 160L. The ozone is
generated from an ozone generator (e) and injected into thetank through a pipe (f) (267mm in diameter). In order tomeasure the ozone bubbles, the S-TOP (b) is fixed nearby thepipe exit. The S-TOP signals are obtained with the opticalsystem (c) and the digital oscilloscope (d). The measurement
is conducted at 9 points (H = 209, 329, 449mm and r = 49, 71,
94mm, in Fig, 3). Each measurement time is 3 min. The flowrate of ozone bubble is constantly kept in 9.5 L/min during
the measurement.

- 54 -

Consequently, the measurement results are different ineach height. We consider that it is caused by the difference ofthe dominant phenomena in respective heights. The freshozone bubbles react to the wastewater at the lower region in
the system, however, the descent flow and mixing occur near
the water surface.
In future study, we deeply examine the effective flow
pattern for the ozonization. We will focus on the initialcondition of the ozone bubble, “a measurement at the outletof the ejector”. Then we will improve the reaction between
ozone and wastewater from a flow dynamic and chemical
point of view.

(e)

(c)
(d)
(b)

(a)

(a) water tank, (b) optical system, (c) digital
oscilloscope, (d) optical fiber probe, (e) ozone
generator

400

Velocity [mm/s]

r = 49 mm
r = 71 mm
r = 94 mm

FIGURE 2. Experimental setup
r

350

300

250
200

300

H [mm]

400

500

FIGURE 4. Result of bubble velocity

～
～

Water
surface

Chord length [mm]

2.5

H

～
～

2

r = 49 mm
r = 71 mm
r = 94 mm

1.5

1
200

300

400

500

H [mm]FIGURE 5. Result of bubble chord length
FIGURE 3. Experimental condition

5. References
3. Results and discussion
Fig. 3 describes the relationship between the measurement
point and the bubble velocity. In Fig. 3, the bubble velocity
increases from 209 to 329mm in height (lower region)
especially at 49mm in radius. However, all the velocity
decreases from 329 to 449mm in height (upper region).
Fig. 4 describes the relationship between the measurement
point and the chord length of the bubble. In Fig. 4, the chord
length decreases at the lower region, however, it increases at
upper region.
We consider these results as follows: depending on theheight, the dominant phenomena are different. Namely, at thelower region, the chemical reaction (i.e. ozone dissolving in
wastewater) is dominant; hence, the bubble size is small. By
contract, at the upper region, the dynamics of fluid isdominant; hence, the coalescence enlarges the bubble sizes,
and the descent flow decelerates the bubble ascending.
Consequently, the measurement results are different in eachheight.

Sato, K. & Saito, T. 2011 Capture/separation of fatty acids
and proteins from wastewater containing milk by ozone
treatment. The 9th International Conference on
Separation Science and Technology
Mizushima, Y & Saito, T.2011 A newly developed techniquefor detection of a contact position in bubble
measurements by a single- tip optical fiber probe.
ASME- JSME- KSME Joint Fluids Engineering
Conference 2011

4. Conclusion
In this study, we clarify the flow dynamics of ozone
bubbles in the wastewater treatment system with the S-TOP.

- 55 -

Proceedings of Japan-Korea International Exchange Program
Jan. 5-11, 2012, Shizuoka University, JAPAN
Saito Laboratory and Shin Laboratory

Elucidation of a large-scale structure of a bubbly flow in a bubble column
by using a Four-Tip Optical Fiber Probe
Yuki Masumoto
Department of Mechanical Engineering,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Takayuki Saito
Graduate School of Science and Technology,
Shizuoka University
Hamamatsu, Shizuoka, Japan

Keywords: Bubbly flow structure, Optical fiber probe, Void fraction
Abstract: The large-scale flow structure in a bubble column has a strong relation to the mass transfer mechanism. Hence,elucidating of the flow structure is important in order to improve the efficiency of the gas absorption. In the present study, thelarge-diameter bubble column of 380 mm in inner diameter and 1500 mm in height was employed. We measured bubble
diameters, velocities and void fraction, by a Four-Tip Optical Fiber Probe (F-TOP). We obtained the histogram of bubble
diameters and velocities and the fluctuation of the void fraction. The large-scale fluctuation of the void fractions faded out toward
the upper zone of the bubble column. From these results, a flow structure in a bubble column was divided into three zones which
are the bottom, middle and upper zone.

1. Introduction
Bubble column reactors are widely used in various
industries such as chemical industry because of their simple
structure and high-mass-transfer performance. However, it isessential to clarify the details of the flow structure in a bubble
column in order to improve the efficiency of chemical
reactions and gas absorption.
In the present study, we measure a bubble diameter,velocity and time-series void fractions by using a Four-Tip
Optical fiber Probe (F-TOP). From these results, we discuss alarge-scale structure of a bubbly flow in the bubble column.

recorded at a PC via an A/D converter. From the output signal,
we calculate bubble diameters/velocities and time-series void
fractions in a bubble column.

(5)
(11)

(12)
(13)
(14)
(3)

(15)

2. Experimental setup and measurement method(10)

2.1 Experimental setup
Fig. 1 shows a schematic diagram of experimental setup.
We used an acrylic bubble column of 380 mm in innerdiameter and 1500 mm in height and covered with an acrylic
water jacket (1605 mm × 440 mm × 440 mm) to reduce a
distortion due to the refractive indices. A perforated plate(diameter of pores: 1.0 mm; equilateral triangular pitch: 10mm; the number of pores: 1240) was installed at the bottom of
the bubble column. Tap water (temperature 290.5 – 296 K) is
supplied into the bubble column through a water inlet. In
addition, compressed air (temperature 295 – 296 K) adjusted
to 67 NL/min by using a mass flow controller was pumped
into the bubble column.

(9)

x

(1)

(6)

(4)

(7)

(8)

FIGURE 1. Experimental setup of bubble column.

(1)

(5)

(6)

(7)

(8)

(2)

2.2 Four-Tip Optical fiber Probe (F-TOP)- 56 -

y

(2)

(3 )

We used the F-TOP measurement system to measure
bubble characteristics. An optical fiber probe is the phasedetecting method which utilizes differences in the refractive
indices of gas/liquid phase and optical fiber. The system of an
optical fiber is shown in Fig. 2. Some of the laser beam from alaser diode reaches the tip of the optical fiber probe. When the
tip of the optical fiber is positioned in a gas phase, the laser
beam is reflected at the tip surface and returns into the same
fiber. The output signal obtained from a photomultiplier isz(1) Bubble column(2) Water inlet(3) Water jacket(4) Perforated plate(5) Water reservoir(6) Compressor(7) Mass-flow meter(8) Air chamber(9) Resistance material(10) F-TOP(11) Laser-diode(12) Beam splitter(13) Photo multiplier(14) A/D converter(15) PC

(4)

(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)

Laser diodeBeam splitter
Objective lens
Optical-fiber probe
Polarizer
Photo multiplier
A/D converter
PC

FIGURE 2. F-TOP measurement system.

3.1 Bubble diameter and velocity
Fig. 3 shows histograms of bubble diameters and velocities
in a bubble column. The distribution patterns of the bubble
diameter at z = 100 mm and z = 700 mm are almost the same,and the distribution range is 2.0 ~ 9.0 mm. On the other hand,in the case of z = 1300 mm, the distribution range changes
into 2.0 ~ 7.0 mm. However, the peak-value of bubble
diameters shows approximately 4 mm regardless of z which isheight from the bottom of the bubble column. The bubble
velocities shift to a lower value along with an increase inheight from the bottom.

region of the cross-section surface. This spatially non-uniform
distribution of the void fractions disappeared toward theupper zone (z = 1300 mm). The middle zone (z = 700 mm) is
the transition zone of the flow structures.
8
P1
P3

(a)

P2
P4

6

α(t) [-]

3. Results and discussion

42

z = 700mm
z = 1300mm
z = 1900mm

0.1

(a)

0

1000

2000

3000

Time [s]

8
P1
P3

(b)

P2
P4

6

α(t) [-]

Frequency [-]

0.15

0.05

0

5

10

4

2

15

Deq [mm]z = 700mm
z = 1300mm
z = 1900mm

0.06

0

(b)

1000

2000

3000

Time [s]

8
P1
P3

(c)

P2
P4

6

0.04

α(t) [-]

Frequency [-]

0.08

0.02

4

2

0

500

1000

1500

2000

Vb [mm]
FIGURE 3. Statistical distributions of bubble
parameter; (a) Histograms of bubble diameter;(b) Histograms of bubble velocity.

0

1000

2000

3000

Time [s]FIGURE 4. Time-series void fraction obtained byfour-point simultaneously measurement: (a) z = 100
mm, (b) z = 700 mm (c) z = 1300 mm.

3.2 Time-series void fractions
The time-series void fractions are calculated at four points{P1: (x, y) = (-95 mm, -95 mm), P2: (x, y) = (-95 mm, 95 mm),
P3: (x, y) = (95 mm, -95 mm), P4: (x, y) = (95 mm, 95 mm)},and the results at z = 100 mm, 700 mm, 1300 mm are shownin Fig. 4. The origin of a coordinate system was placed at thecenter of a perforated plate. The void fractions at z = 100 mm
are located eccentrically in space, and the magnitude offluctuation is large. Furthermore, the region of high void
fractions moves to a circumferential direction with time.
Although the fluctuation of the void fraction decreases at z =700 mm, there is the spatial variation of the void fraction.
However, the spatial variation of void fraction at z = 1300 mm
almost disappears and magnitude of fluctuation becomes
small. Therefore, the large-scale fluctuation of the void
fractions fades out toward the upper zone of the bubble
column.
From these results, the flow structure in a bubble column
is divided into three zones. In the bottom zone (z = 100 mm),the void fractions were unevenly distributed in the spatial

4. Conclusion
In the present study, we discussed a large-scale structure ofa bubbly flow in a bubble column. We obtained histograms of
bubble diameters/velocities and the fluctuations of the void
fraction by the F-TOP measurement method. In conclusion,
we demonstrated that the large-scale structure of a bubbly
flow in a bubble column is divided into three zones from the
distribution of the void fractions. We obtained the helpful
results to elucidate a large-scale structure of a bubbly flow.
Moreover, we need to elucidate the details of a flow structure
due to the measurement of liquid-phase motion.

5. References
Higuchi, M. & Saito, T. 2010 Quantitative characterizationsof long-period fluctuations in a large-diameter bubble
column on point-wise void fraction measurements, Chem.
Eng. J., vol.160, pp.284-292.

- 57 -

7. Proceedings of Korean Students Presentation
Korean students presented three presentations in this program. The information of thepresentation was listed as follow.

Presentation 1
Title: Design and Manufacture of High Efficiency Horizontal Wind Turbine Blades
Presenter: Jongmin Kim and Heesung Lee

Presentation 2
Title: Vertical axis type wind turbine Design and manufacturing
Presenter: Chunggi Moon and Kyeongrock Jang

Presentation 3
Title: Flow analysis using the Magnus effect of circular cylinder
Presenter: Jeonghoon SongThe briefing papers of the presentation are shown from next page.

- 58 -

Presentation 1

Presenter: Jongmin Kim and Heesung Lee- 59 -

- 60 -

- 61 -

- 62 -

- 63 -

- 64 -

- 65 -

- 66 -

- 67 -

Presentation 2

Presenter: Chunggi Moon and Kyeongrock Jang

- 68 -

- 69 -

- 70 -

- 71 -

- 72 -

- 73 -

- 74 -

- 75 -

- 76 -

- 77 -

- 78 -

- 79 -

- 80 -

Presentation 3

Presenter: Jeonghoon Song- 81 -

- 82 -

- 83 -

- 84 -

- 85 -

- 86 -

- 87 -

- 88 -

- 89 -

- 90 -

- 91 -

- 92 -

- 93 -

8. Acknowledgment
The Short Term-Stay International Exchange Program between Japan and Korea waspromoted and financially supported by Japan Student Services Organization (JSSO). We
thank JSSO for its help in the financial support.
All of Japanese and Korean students greatly appreciate the chance to participate thisprogram created by Prof. Saito and Prof. Shin.
We also thank Mr. Hiragi (Director of Shizuoka University Motors) for leading us a tour to
Shizuoka University Motors’s factory. We also thank Mr. Noba (Fukuta Laboratory, Shizuoka
University), Mr. Matsushita and Mr. Tanaka (Sanada Laboratory, Shizuoka University) for
taking part in the program.

- 94 -