NATIONAL BUREAU OF STANDARDS REPORT

24^7

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

(NO. W-230 "AIRSAr’)

by

Henry E. Robinson

Thomas W. Watson

Warren W. Hurt

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-4715 May 12, 1953. 24^7

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

(NO. W-230 "AIRSAN")

manufactured by

Air Filter Corporation

Milwaukee, Wisconsin

by

Henry E. Robinson

Thomas W. Watson

Warren W. . Hurt

Heating and Air Conditioning Section

Building Technology Division

to

Bureau of Ships, Code 327

Department of the Navy

Reference: NPO - 15479 Index No. NSM I 3 O-OOI

The publication, reprint

unless permission isobti

25,D.C. Such permiss

cally prepared If that !

)proved for public release by the

rector of the National Institute of

andards and Technology (NIST)

^ Q ^01 S

PERFORMANCE TESTS OF AN

’’AIRSAN” NO, ¥-230 AIR FILTER

I. INTRODUCTION

At the request of the Bureau of Ships, Code 327,

Navy Department (NPO-15479, Index No, NSM 13 O-OOI)

qualification tests were made to determine the performance of cleanable viscid-impingement type air filters

in accordance with Section 4»5 of Military Specification MIL-F-I6552 ( Ships) dated 1 October 1951 as modified by Amendment 1 dated 15 April 1952.

The tests were performed on specimen filters submitted by the manufacturer at the request of the Bureau

of Ships, and Included determinations of the dustarresting efficiency, pressure drop, specific dirt

load and cleanability of the specimens at three face

air velocities, namely 300, 6 OO and 900 feet per minute,

II, DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Air Filter

Corporation of Milwaukee, Wiscopsin, and was of the

cleanable viscid type, 20x20x2 inches in nominal size.

It was identified by nameplate a^'an ’^Airsan”, Catalog

number W-230. The filtering media was composed of

V-crimped, and flat, strips of 14-mesh screen wire,

assembled by piling one alternately on the other to

form triangular air passages, from the upstream to

downstream face, with a dog-leg bend at their midpoint, There were approximately three and one-half

V-jirimped layers per inch of pile. The strips of media

were surrounded at the edges by a ferrous metal frame.

The filter had actual outside dimensions of

19-9/16x19-7/16x1-7/^ inches, leaving a free opening

l^xl7-7/S inches (2.23 ft'^ net face area.) and weighed

11,1 lb. when clean without oil.

The manufacturer submitted an adhesive designated

as ''Film-Cor” for oiling the filter. This was done

in preparation for the test by immersing the filter in

the liquid and letting the excess oil drain off at a

temperature of 75°F with the filter standing on edge

for a minimum of I6 hours prior to the test.

- 2 -

III. TEST METHOD AND PROCEDURE

The dust-arresting efficiency of the filter was determined by the NBS ’’Dust Spot Method” using as a test

dust Cottrell precipitate at a concentration of one

gram per thousand cubic feet of air. The test method

is described in the paper ”A Test Method for Air Filters”

by R. So Dill (ASHVE Transactions, Vol. 44, p. 379,

193^)

Dirt-holding capacity was determined by supplying

to the filter air in which were dispersed cotton lint

and Cottrell precipitate in the approximate proportions

of and by weight, respectively. The average

rate of feed of the contaminants was not more than 25

grams per hour per square foot of net filter face area

at each face velocity. The lint used for this purpose

was No. 7 cotton linters ground in a Wiley mill with

4 mm screen.

The efficiency and dirt-loading tests were made

at three different air velocities, namely, 300 , 600 and

900 fpm.

In the tests at each velocity, the following uniform procedure was employed. The clean filter, after

oiling and draining as described above, was installed

in the test duct and its initial pressure drop was

measured at 300, 600 and 900 fpm air velocity. The

initial efficiency of the filter at the test velocity

was then determined, following which the process of

loading the filter with a mixture of lint and 96%

Cottrell precipitate by weight was started. At intervals the increasing pressure drop of the filter was recorded. At suitable periods as loading progressed, the

efficiency of the filter was determined using 100%

Cottrell precipitate. In addition, the efficiency of

the filter was determined at the end of a day of loading, and at the start of the next day, to ascertain

whether the rate of dirt loading was overtaxing the

wetting rate of the filter adhesive. The dirt loading

was continued, in general, until the rate of pressure

drop rise increased to approximately 0,004 inch W.G.

per gram of dirt mixture fed per square foot of filter

face area.
iAi1
- 3 -

The filter was then removed from the test duct

and cleaned by means of a stream of cold water from

a high-pressure hose nozzle, directed ^at -and into

the filter media. After drying, the filter was reoiled for subsequent tests or for measurement of its

initial pressure drop after the final cleaning,

IV. TEST RESULTS

The pressure drop of the clean oiled filter, in

inch W.G., at 300 , 600 and 900 fpm face air velocity,

was measured at the start of each of the tests, and

after the 900 fpm test, as shown in Table 1 . TABLE 1

-

Face Velocity, fpm oo 600 900

At start of 300 fpm test 0.055 . 1^0 .363

At start of 600 fpm test ,052 .177 .361

At start of 900 fpm test .052 .176 ,360

After 900 fpm test

Increase in P,D, after

.050 .174 .355

3 cleanings, percent 0 0 0

A summary of the test data obtained in dirt-loading tests conducted at 300, 600 and 900 fpm face

velocity is given in Table 2 . TABLE 2

Face Air

Velocity Dirt Load'i' Pressure Drop Efficiency

fpm grams/sq ft inch WG percent

300 0 .055 cx> 3 .055 51

5 .055 52

65 .070 50

96 .0^0 52 (P)

99 .OSO 53 (A)

135 .099 56

197 .14^ 62

236 .196 73 (P)

239 .200 71(A)

290 .370 76

293 . 3^0 75

319 .507 75

'^Average mixture: 4 . 0^ lint, 96 . 0^ Cottrell precipitate

by weight.

Average rate of dirt loading: 17.5 grams per square

foot per hour.

- 4 - Table 2 - continued

Face Air

Velocitv Dirt Load^i' Pressure Drop Efficiencv

fpm grams/sq ft inch WG percent

600 0 .177

6 .175 56

24 .197 60

.254 60

12 g .290 65(P)

134 .295 62(A)

1^0 .354 69

247 .456 75(P)

253 .477 70(A)

265 .495 71

320 .655 74

357 .505 75

^Average mixture; 4.1^ lint, 95 > 9% Cottrell precipi

Average

tate by weight,

rate of dirt loading; 20.9 grams per squar900

foot per hour,

0 .360

6 .365 62

15 .377 66

2^ .395 69

99 .500 73

109 .515 71(P)

11^ .525 71 (A)

202 .655 77

261 .755 77(P)

267 .760 69(A)

2S6 .500 73

373 1.015 76

^I'Average mixture; 4»0^ lint, 96.0^ Cottrell precipitate

by weight.

Average rate of dirt loading; 22,0 grams per square

foot per hour,

NOTE; Efficiencies marked (P) or (A) were determinations made at the end of a day, of loading, and

at the start of the next . day of loading,

respectively.

V. SUmARY OF RESULTS

A. Performance

The test data are plotted in Figure Ij which shows

the variation of the pressure drop and of the efficiency

of the filter as it v/as subjected to increasing specific

dirt loading at face velocities of 300 j 600 and 900 feet

per minute.

Table 3 presents values of the pressure drop (P.D.),

in inches of water, and of the approximate efficiency

(Eff,), percent, as taken from the curves of Figure 1,

at various specific dirt loadings.

TABLE 3

Spec. Dirt

Ldg, grams/ 0 100 200 \ 300

sq. ft (Initial)

Face Vel,

fpm P.D, Eff. P.D. Eff. P.D. Eff. P.D. Eff

300 .05 51 „ 0 g 54 .15 63 .41 74

600 .Ig 56 .26 61 . 3 ^ 71 .59 73

900 .36 61 .50 73 .65 77 0^3 73

Bo Cleanability

The pressure drops of the clean oiled filter at 300,

600 and 900 fpm face velocity recorded in Table 1 under

Test Results indicate that, after the filter had been

subjected to three loadings with the dust-lint mixture

and three cleanings and re-oilings, the recorded pressure

drops were slightly lower than they had been at the start

of the tests. The precision of the pressure drop readings is considered to be within a few thousandths of an

inch of water. It is believed the filter can be considered as satisfactorily cleanable.

C. General

The fact that efficiencies determined at the end of

a day of loading of the filter (those marked (P) in

Table 2) were approximately the same as, or were greater

than, those made at the start of the next day of loading

(those marked (A) indicates that the dirt loading'rates

to which the filter was subjected did not overtax the

wetting-rate of the filter adhesive and cause the filter

surfaces to become ^dry’’.

r

I ’00

Ih

I/O

r'UJ a. 60

li. UJ

I 40

|cD 1.0

|x .8

o

1

AIRSAN W-230

0 100 200 300 400 500

LOAD, GRAMS PER SQUARE FOOT FIG. I

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 hy Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measiurement 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

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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 firont 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

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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 Pubhcations, National Bureau of Standards, Washington 25, D. C.
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