n~<A ' u

JjL C.

NATIONAL BUREAU OF STANDARDS REPORT

2531

PROGRESS REPORT

for

Dec. 1, 1952 to April 30, 1953

on

GREASE FILTER TEST METHODS

by

C. W. Coblentz

P. R. Achenbach

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engagt i in technical work. In general, each section is engaged in special*

ized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Applied Electricity. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Gage.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State

Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy.

Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pine Substances.

Mechanics. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. Capacity, Density, and Fluid Meters. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure. Chemistry of Mineral Products.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Machine

Development.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

Ordnance Development. These three divisions are engaged in a broad program of research

Electromechanical Ordnance, and development in advanced ordnance. Activities include

Ordnance Electronics. basic and applied research, engineering, pilot production, field testing, and evaluation of a wide variety of ordnance materiel. Special skills and facilities of other

NBS divisions also contribute to this program. The activity is sponsored by the Department of

Defense.

Missile Development. Missile research and development: engineering, dynamics, intelligence,

instnimentation, evaluation. Combustion in jet engines. These activities are sponsored by the

Department of Defense. • Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-4715 May 29, 1953 2531

PROGRESS REPORT

for

Dec. 1, 1952 to April 30, 1953

on

GREASE FILTER TEST METHODS

*>y

C. W. Coblent

P. R. Aehenbaeh

Heating and Air Conditioning Section

Building Technology Division

for

Bureau of Ships

Department of the Navy

Washington, D. C.

The publication, reprln

unless permission isobt

25, D, C, Such permls:

cal ly prepared If that

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

iart, Is prohibited

ards, Washington

t has been specifl1 for Its own use.

Progress Report

Dee, 1, 1952 to April 30* 1953

on

GREASE FILTER TEST METHODS

LOADING RATES OBSERVED ON U.S.S. TARAWA

The examination of the grease deposits from the air

samples taken in the crew’s galley of the U. S. S. Tarawa

has shown that the grease content of the air varied widely

during the frying operations . Samples were taken on filter

paper,, in sampling tubes filled with glass wool, and on

microscopic slides by means of an impactoro In all cases,

the sampling was done about half way between the respective

cooking facility and the nearest filter by drawing a measured volume ©f air through the sampling device. The

weight increases of the sampling tubes and the filter papers

were determined by weighing them to the nearest 0.1 mg before

and after the test, the sampler having been thoroughly dried

in a desiccator before each weighing. The grease samples

collected on microscopic slides on the U, S. S, Tarawa were

compared as to their density with deposits from equal air

volumes of known grease content In the grease filter test

apparatus at the National Bureau of Standards. These

comparisons confirmed the data obtained with the two other

sampling methods used on the U. S. S. Tarawa.

Fig. 1 is a 450 x magnification of a grease deposit

obtained during the frying of steaks on the griddle on board

ship. The particles range from the limit of resolution of

the microscope to relatively few of fifty microns diameter

or more.

Fig. 2 Is a mierophotograph of the same magnification

of grease accumulated on the surface of one of the filters

above the deep fat fryers. The range of the particle size

Is approximately the same as in Fig. 1. It will, however

Fig. 2 than in Fig. 1 and fewer small particles in Fig. 2

than In Fig. 1. This Is believed due to the fact that a

larger percentage of the bigger particles Is retained on

'

Fig. 1

mm

Fig, 2

“ 2°

Fig. 3 is a microphotograph with the same magnification

of grease deposits taken from the duct behind the filter above

the deep fat fryer. The range of the particle size, again, is

about the same| this time, however, the proportion of bigger

particles is very much smaller. There are few agglomerations

and little adhesion of the particles to the fiber fragments

in Fig. 3«

The following table shows the average values of the

grease content of the air computed from the samples taken

with filter paper and glass wool samplers for different

frying operations on the U. S. S. Tarawa. Also shown are

the equivalent loading rates for a 20 x 20 in. filter as determined in the grease filter test apparatus. The filtering efficiency measured on a Farr #4 filter in the grease

filter test apparatus is shown in the table for each loading

rate and corresponding grease content as observed on board

ship. The results reported on the Farr #4 filter are representative of the impingement filters most used. The deviation

in the efficiencies of other similar filters at the observed

grease contents of the air are small.

Equivalent Observed

Grease Content Loading Rate Efficiency

Frying Operation of Air ^ of 20x20 in, of Farr Filter

mg/ft3 Filter in Laboratory

2

Steak on Griddle l.?8 92 90

Fish In Deep Fat Fryer 0.87 42 84

Potatoes on Griddle 0.42 19 79

Corn Fritters in Fryer 0.22 9 75

The values indicate a wide range of loading rates depending on the kind of cooking operation. It can be expected that

the loading rates would vary in excess of ±100$ at different

times due to temperature of the grease and depending on the

ventilation rate just above the ranges. The lowest efficiency observed in the laboratory corresponding to the grease

contents observed on the U. 'S. S. Tarawa was 75$ and it

increased to 90$ at the highest grease concentration in the

air.

Out of a group of 13 filters taken from several Navy

vessels that were tested here in the early part of 1951* the

most heavily loaded grease filter of the group was used in

the hood above the griddles on the U. S. S. Coral Sea. This

filter was said to have been in continuous operation for four



=3

"

weeks at a face velocity of 468 fpm and was found to contain

a total load of 2.27 oz> equivalent to JO grams on a 20 x 20 in

filter o An analysis of the deposits showed that 37$* or

about 26 grams 9 of the filtrate was fat. Assuming that all

fat had been collected on this filter during a one hour daily

operation of the griddles^ an average loading rate of less

than 1 gram per hour would be indicated for this kind of

operation.

However9 actual tests made over griddles on board the

U. Bo S. Tarawa showed loading rates as high as 92 g/hr at

conditions which should be similar to those on the U. S. S.

Coral Sea. Considering that some additional grease was probably being collected in the filter on the U. S. S. Coral

Sea during the estimated 23 hours of the day when there was

no frying done on the griddles,, there is a ratio of approximately 1 to 100 between the loading rates for the two ships.

In our opinion there probably was not actually that much

difference in the loading rates during similar operations

in the two installations.

Efficiency Tests at 800 ft/min Face Velocity

A series of 70 tests was made to determine the efficiency

of grease filters operating at 800 ft/min face velocity. Based

upon the information obtained about the loading rates to be

expected in actual operation from the above described sources

all these tests were conducted at loading rates below 10 g/hr.

The grease filter test apparatus was originally equipped

for handling air flow rates up to 1000 CFM corresponding to

400 ft/min face velocity with the standard 20 by 20 inch

filters. By cutting the frames and filter elements the size

of the net face area was reduced to 1 sq ft on two specimens.

By means of a special adapter these filters could be tested

without alteration of the test apparatus at 000 ft/min face

velocity with an air flow rat® of 800 CFM. Isokinetic air

flow through the sampler tubes was used as previously described

The filters tested were a Farr jfk and an Air^Maze Greastop

Fig. k and 5 show graphs of the efficiency plotted against

the loading rate.

The efficiency of the filters appears to be best represented by a straight line on the semi => logarithmic paper as the curve of the least mean distances of the points of observation. The efficiency of the Air-Maze filter was found to be

OBEA

Loading

Rate

,

g/hr

GREASE FILTER TE3T METHODS.

Efficiency, percent

-fcslightly higher than that of "the Farr filter, concurring with

the observations made at ^00 ft/min face velocity as reported

in Progress Report No, 1772, Shted July 8, 1952

A comparison of the filter efficiencies observed during

previous tests at tOO ft/min face velocity with those observed

in the tests at 800 ft/min face velocity on the basis of equal

loading rate per unit area requires consideration of the

difference in filter sizes used in these tests. The net face

area of the 20 x 20 in. filters used for determining the

efficiency at 400 ft/min face velocity was 2.2^ sq ft. Therefore, the efficiencies of these filters at a 10 g/hr loading

rate must be compared with the efficiencies of the 1 sq ft

filters used for the 800 ft/min face velocity tests at a loading rate of 10 - 4.5 g/hr.

272?

Based on the curves drawn through the plotted points

the filter efficiency of the Farr filter tested at 800 ft/min

face velocity at k„5 g/hr loading rate was 8l$ and that of

the Air-Maze 86$. Previous tests at 400 ft/min face velocity

indicated that at 10 g/hr loading rate the corresponding

efficiencies were 75$ and 8 The actual efficiency at a

given loading rate cannot be stated with great precision

because there was considerable scattering of the plotted

values in Fig. k and 5 as well as in the corresponding data

at lower face velocity. Deviations in efficiency of ±5$ or

greater were observed for the same loading rate.

A more informative comparison can be obtained of the

difference in the efficiency of the filters operating at

400 and 800 ft/min face velocity by plotting the efficiencies

against the grease contents of the air approaching the

filters. The grease content of the air for a one hour period

was determined by dividing the loading rate by the efficiency.

The grease content of 100,000 cu ft was obtained by dividing

the hourly grease content by the hourly flow rate through the

filter and multiplying by 100,000. For convenient plotting

on the available semi-logarithmic paper, the grease content

was also calculated for ^3,700 cu ft. The following table

shows the values determined for the Farr jfk and Air-Maze

Greastop filters. The values for the efficiency used in

this table are the average values taken from Fig. 4 and Fig. 5

in this report and also from Fig. 1 and Fig. 2 of the July 9,

1952 progress report.
• '

r ;

.

'

.

-

.

'
-5-

Farr #4

Efficiency, $ 62 66.5

Grease

Content

of Air, g/hr 1.61 3.01

" g/lo5ft3 2 .80 5.23

" gA3700 ft 3 1.22 2.29

Air-Maze Greastop

Efficiency, $ 76 78

Grease

Content

of Air, g/hr 1.32 2.56

" g/lo5ft3 2.29 4.45

" gA3700 ft3 1.00 1.94

69 72 76 51

4.35 6 . 9k 13.17 1.96

7»56 12.06 22.87 4.09

3-31 5*27 9.98 1.79

79-5 81 83 57

3 <>76 6.16 12.05 1.75

6.54 10.70 20.91 3.65

2.85 4.68 9.15 1.59

83 ! 96.5 i

3.08 4.11

!

6.03 10.37

6.42 8.58 12.68 21.61

2.81 3.75 5.50 9.44

69 76.5 86 98

2.90 3-93 5.80 10.20

6.05 8.20 12.10 21.26

2.64 3.58 5.28 9.30

Relation of the Loading Rate, Filter Efficiency, and Grease

Content of the Air at 400 and 800 ft/min Face Velocity,

Loading Rate,

g/hr

1

4oo ft/min Face Velocity

10

800 ft/min Face Velocity

4-

10

65 73

Figo 6 and j show graphs of the efficiency plotted against

the grease content of the air approaching the Farr and AirMaze filters, respectively . The graphs indicate that

changes in the grease content of the air had a greater

effect Jon the efficiency at 800 ft/min face velocity than

it had at 400 ft/min. It will he noticed that for both

filters the efficiency at 400 and 800 ft/min face velocity

is equal at approximately 3 to 4 grams grease content per

^3^700 cu ft of the air, at the intersection of the two

curves. This corresponds to a loading rate of about 3 to 4

g/hr for the two filters. The curves also show that the

efficiency at lower values of the grease content than 3 to 4
Semi-Lo*arithmic.

1

Cycle

>*.

10

to

the

Inch.

6th

line*

accented.

50

Eff let ®ncv

60

t

100

Fig. 6
S«mi-LoK*rithroic.

1

Cyc*«

X

10

Co

Ih*

inch.

Efficiency

Fig. 7

-6-

grams per 43^,700 eu ft of air xs smaller at 800 ft/min

face velocity than that at 400 ft/min face velocity and vice

versa at higher grease contents

The centrifugal forces caused by the changes of

direction of the air passing the filter media throw airborne grease particles from the air stream and make them

adhere to the filter medium . The force acting to eject

the grease particles from the air stream increases with the

size of the particles and also with their velocity which in

turn is a function of the face velocity at which the filter

is being operated., The size of the particles will increase

with the grease content of the air and change with the temperature of the grease 9 the length of time -it 'has been heated

and the type of the grease used„ The analytical evaluation

of the effect of these numerous variables on the efficiency

of the filters appears extremely complex and not within the

scope of these particular tests

Paper Filters

The difficulty associated with proper cleaning of grease

filters on board ships prompted an investigation of the

feasibility of substituting expendable paper filters for the

permanent impingement type filters . Out of a great number of

commercial filter papers a group of four papers was selected

which had a low flow resistance to air and promised good

absorptivity for grease . The air flow rate ’through the clean

filter papers obtained with a pressure drop of 2 in, W.G.

across the paper was found to vary from 22 to 36 GEM per

sq ft area. The flow rate was also determined after the

filter papers were partially loaded with grease and it was found that the Eaton-Dikeman paper #64Op which had the best

characteristics s passed only 20 . 5 CFM per sq ft with a

grease load of 0.1084 g per sq ft area at the same pressure

drop of 2 in. W.G.

A pressure drop of 2 in, W.G. across the filtering

medium was considered the maximum permissible for design

purposes „ Taking into account the possibility of increasing

the area of the filter paper to ten times the face area of

the filterp by arranging the paper in a zigzag pattern the

total filter paper area that could be used in a 20 x 20 in.

filter frame with a 2.24 sq ft face area would be 22

sq ft.

With a load of 0.1084 g per sq ft this paper filter could

hold a grease load of 0.1084 x 22.4 = 2.42 g and pass an

air flow of 20.5 x 22.4 - 460 CFMp corresponding to a face

-7-

veloeity of 205 ft per minute. At 400 ft/min face velocity

the pressure drop across the filter paper would be near

8 in. W.G.

The measurements on board the U. S. S. Tarawa showed

that loading rates of the filters rangea up to 92 g/hr or

38 times as much grease was retained by the impingementtype filter in an hour 8 s cooking time as can be held by the

filter paper at a lower than normal face velocity and a higher than desirable pressure drop.

This determination was considered to he adequate evidence

that the method of abstracting grease from the cooking air

by means of paper filters would not be practical.

Grease Deposits in Duets

In order to obtain some information on the amount of

grease deposited in a cold duct downstream of a filter

the connecting duct between the grease filter test apparatus

and the exhaust blower at the National Bureau of Standards

was disassembled and inspected. This duct is 15 ft long and

contains an orifice flow meter for measuring the air flow

rate through the test filter. The diameter of this duct is

12 in. and the average air velocity is about 1200 ft/min.

The duct had been in operation for 2-1/2 years , approximately

2500 hrs of testing without being cleaned wheto It was inspected. Grease accumulations were found on the bottom of

the section containing the orifice plate and the two adjoining sections 9 whereas the upper parts and the sides of these

three sections and all the other sections were practically

clean.

Fig. 8 is a photograph of the duct section that holds

the orifice plate 9 looking toward the test apparatus, i.e.

upstream. The greatest depth of the grease accumulated on

the bottom of the duct was approximately 3/8 in. downstream

and 1/2 in. upstream of the orifice. Fig. 9 shows the section

of duct adjacent to the orifice section in an upstream

direction. It can be seen that the grease deposit on the

bottom of this section extends to about i/3 of its length.

It appears from these photographs that the grease in the

duct had been separated from the grease-laden air by the

turbulence caused by the orifice plate and that it flowed

off in both directions to the bottom of the ducts. The

results of this inspection lead to the opinion that very

little grease would have been deposited downstream of the

filter in a smooth-flowing air stream of adequate velocity.
.

<?

>

t

-

' si

,

.
' V

Fig. 8

Fig, 9

-8-

This assumption is supported by the fact that the guide vanes

and the wheel of the exhaust blower had so little grease cover

that no cleaning was required* There was no appreciable grease

deposit in the bottom of the blower housing. The puddling of

the grease shown in Fig. 8 and 9 indicates that the grease

was warm enough to flow into the bottom of the duct during

some periods of operation.

Further investigation appears desirable to ascertain the causes of grease deposits in ducts with and without a grease

filter in the system with special attention given to the presence

of lint in the air.

Water Cooled Filters

An Air-Maze Greastop filter was taken apart and 13 copper

tubes , l/k in. O.D., were imbedded in alternate crimps of the

filter screen near the middle of the 2 in. thick filter media.

The copper tubes were extended through the filter frame and

were manifolded in a 1 in. pipe on either end of the filter as shown in Fig. 10. City water at a temperature of about 55 °F was passed through the tubes at a rate of 5 gal/min cooling the

grease-laden air from 110 °F to 106°F.

Eight; tests of 7=l/2 hours each were made with this filter

at loading rates ranging from 3.3 g/hr to 11.0 g/hr. The

filtering efficiency in six of these tests was 3^<>3# - O.l#

which compares rather unfavorably with an efficiency of about

80# determined for the same filter in an unaltered condition

and at the same loading rate. The decrease in efficiency is

believed to have been caused by spreading apart the filter

media with the water tubes about midway through the filter

media.

Fig. 11 is a photograph of a 16 x 16 x 3 inch cooling

coil with three rows of tubes and six fin® per inch that was

tried out as a grease filter. The three coils were so manifolded that the water flowed through the coil in both directions

to obtain a more equal cooling over the entire a£©&° The coil

was fitted into a wood frame , 20 x 20 in. outside , for con- venient installation in the test apparatus. Because of the

heavy weight of this coil it was considered impractical to

determine the weight of the grease deposit by weighing the

coil before and after each test. The efficiency was determined by installing sampling tubes upstream and downstream of

the coil in the test apparatus. The filtering efficiency, then,

was the difference between one and the ratio of the weight
v £ ~,V.;

s;

'

‘ ^' • " ' .

•- --

V

•

J.'i

'

.

.

'
Fig., 10

Fig.

11

-9-

increase of the sampler tube installed downstream (wj) to that

installed upstream of the coil (w2 )

Efficiency = (l - ^ )100 or w2

E = x 100$.

w2

The coil was . operated for a total of 18 hours with water at a

temperature of about 55°F flowing through it. The average

efficiency was 62.8$ at an average loading rate of 46 g/hr

computed on the basis of a 20 x 20 in. filter.

A series of tests was then made to investigate the difference

of the grease retaining ability of this coil when cooled with tap

water and when it was not cooled.

For this purpose the grease filter test apparatus was operated under steady state condition and air samples were

taken downstream of the coil during l-l/2 hr periods alternately

with water flowing through the coil and w&Sh, the y*te» shat off.

Sufficient time was allowed for the coil to heat up or cool off

before installing the new sampling tube in each cycle. It was

found that the average weight increase of the downstream sampling

tubes operated with a cooled coil was 5»8 mg and when the coil

was at air temperature the weight increase was 7*5 ®g, about

30$ higher.

This test indicated that the retention of grease in the

cooled coil was the result of both condensation of 'vapor and

adhesion of liquid particles. In a coil or filter at ambient

temperature very little condensation of grease vapor can occur

because very little heat is transferred in the coil| therefore,

only liquid particles can be retained.

Based on the experience gained in the above described

test a filter has been built the filter medium of which consists

of a stack of flat aluminum fins. Fig. 12 is a photograph of,

this experimental model which has 475 fins of 0.001 in. and 60

fins of 0.002 in. thickness. Two gages of material were used

as the thinner material was not available in sufficient quantity

and could not be readily procured. The fins are separated from

each other by five crimps, and the heavier material can be

noticed on the right hand side of the photograph.

Two tests have been evaluated, to date, and showed an

efficiency of 58$ and 62$, respectively, at a loading rate of
'

,

.

..

'

-
Fig. 12

-10 -

13 .4 g/hr at 400 ft/ndn face Telocity. The efficiency of the

Air-Maze P-5 filter at the same condition was 67#

The efficiency of this filter at various loading rates and

its loading capacity -will be further investigated. If these

tests show satisfactory results, some modifications of the

fin arrangement will be made to determine the optimum operational characteristics.

The advantage anticipated for a finned filter of this type

would be that no cumulative clogging with linfc would be likely

between the filter faces such as occurs in wire mesh filters.

These filters, if shown to have acceptable efficiency, should be

easier to clean and last indefinitely.

The Gaylord Industries, Portland, Oregon, has advised us that they have shipped their ClearAir system here, for testing.

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.