NATIONAL BUREAU OF STANDARDS REPORT

2291

PERFORMANCE TESTS OF CLEANABLE

IMPINGEMENT TYPE AIR FILTERS

’’ALUMALOY” RP 902

manufactured by

Research Products Corporation

Madison, Wisconsin,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

by

Henry E, Robinson

Thomas W, Watson
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, S^retary

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 February 17, 1953 2291

PERFORMANCE TESTS OF CLEANABLE

IMPINGEIVENT TYPE AIR FILTERS

"ALUMALOY” RP 902

manufactured by

Research Products Corporation

Madison, Wisconsin.

by

Henry E. Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

To

Bureau of Ships, Code 327

Department of the Navy

Reference: NPO - 15479 Index No. N3fl "I3 0-001

The publication, reprin

unless permission Isobt 25,0,C. Such permit;

tally prepared If that

Approved for public release by the art, Is prohibited Director of the National Institute of ardsiWaihington Standards and Technology (NIST) on October 9, 2015.

1 f«Hf. own u,e.

Performance Tests of an "Alumaloy" Air Filter

I. INTRODUCTION

At the request of the Bureau of Ships, Code 327, Navy Department (NPO-15479, Index No. NSM I 3 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 a specimen filter submitted by

its manufacturer at the request of the Bureau of Ships, and included

determinations of the dust-arresting efficiency, pressure drop,

specific dirt load and cleanability of the specimen at three face

air velocities, ramely 300, 6OO and 9 OO feet per minute.

II. DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Research Products Corporation

of Madison, Wisconsin, and was of the cleanable viscid type, 20x20x2

Dnj^hes in nominal size. It was identified by nameplate as an "RP 902

A]umaloy Industrial Washable Air Filter’^. The filtering media was

composed of many layers of expanded metal (thin aluminum sheet or

fo:l) arranged one after the other, as follows, starting at the upstream face: One layer EM 5/l6x9/l6 inch mesh; one 4-1/2 inch square

mesh wire grid; four layers EM 3/^xl/2 inch mesh; six layers

EM 1/4x5/1d inch mesh;three layers EM 3/^xl/2 inch mesh; six layers

EM 1 /4x 5/16 in6h mesh; one 4-1/2 inch square mesh wire grid; one

layer EM 5/l6x9/l6 inch mesh. The layers of media were slightly

compressed and surrounded at the edges by an aluminum metal frame.

The filter had actual outside dimensions of 19-3/4xl9-^/Sxl-7/S inches,

leaving, a free opening 15!-l/^xl5-l/6 inches (2.27 ft^ net face area)

and weighed 3.9 lb. when clean, without oil.

The manufacturer submitted an undescribed oil adhesive for oiling the filter. This was done in preparation for test by immersing

the filter in the liquid and letting excess oil drain off with the

filter standing on edge for a minimum of I6 hours prior to the test.

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. S. Dill (ASHVE Transactions, Vol. 44, p. 379, 193^).

2

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 differ

ent 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 4 percent lint and 96 percent 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 percent

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 over

taxing 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.

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

re-oiled for subsequent tests or for measurement of its initial pres

sure 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 300 600 900

At start of 300 fpm test .051 .1^2 .390

At start of 600 fpm test .050 .ISO .387

At start of 900 fpm test .050 .183 .395

After 900 fpm test .054 .200 .436

Increase in P.D. after 3 cleanings,^ 6 9 12

- 3 -

A summary of the test data obtained in dirt-loading tests con

ducted at 300, 600 and 900 fpm face velocity is given in Table 2,

Table 2

Face Air Velocity Dirt Load* Pressure Drop Efficiency

fpm grams/sqft inch WG percent

300 0 .051 •• 3 .051 42

6 .051 43

57 .071 45(P)

62 .071 45(A)

120 .102 54

164 .137 56(P)

167 .134 54(A)

1^2 .152 55

221 .200 57

252 .250 60

2^4 .313 65(P)

2^6 .317 64 (A)

299 .360 65

334 .514 73

* Average mixture: 4.0^ lint, 96 % Cottrell precipitate by weij

Average rate of dirt loading: 16,9 grams per square foot per hour.

0 .1^0

6 .1^0 54

12 .1^1 51

1^ .\t2 57

34 .204 50

43 .220 53

70 .254 54

91 ,2^g 59(P)

97 .2^7 5^(A)

143 .376 57

197 .510 61

236 .674 66(P)

242 .695 66(A)

254 .790 72

Average mixture: 1^,0% lint, 9^% Cottrell precipitate by weight.

Average rate of dirt loading: 20,7 grams per square foot per hour.
f

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i in ^

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- 4 - Table .2 - continued

Face Air Velocity

900

Dirt Load* Pressure Drop Efficien

grams/sqft inch WG percent

0 .395

9 .397 63

IS .400 64

73 .543 64

91 .593 66(P)

101 .630 66(A)

146 .610 66

1^3 1.005 66

193 1.060 76

Average mixture: 4 . 0^ lint, 96 , 0% Cottrell precipitate by weight.

Average rate of dirt loading: 22.2 grams per square foot per hour.

NoteEfficiencies 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. SUT®ARY OF RESULTS

A. Performance

The test data are plotted in Figure 1 , which shows the variation

of the pressure drop and of the efficiency of the filter as it was

subjected to increasing specific dirt loading at face velocities of

300,600 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.), in percent, as

taken from the curves of Figure 1 , at various specific dirt loadings.

Spec. Dirt Ldg.

grams/sq ft

0

( Initial)

Table 3

100 200 300

Face Vel. .fpm P.D. Eff. P.D. Eff. .P.D. Eff. . P.D

300 0.05 42 .09 51 .17 56 .36

600 .16 54 - .29 56 .52 61 — 900 .40 63 .63 66 - -

B. Cleanability

The pressure drops of the clean oiled filter at 300 , 6OO 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 dustlint mixture and three cleanings "and re-oilings, its average percentage increase in pressure drop was about 9 percent, or about 3 percent

average per loading and cleaning oD-eration. Almost all of the pres-
1

i

1

i

t

I

A'

. i
- 5 - sure drop increase of this filter occurred following the 900 ft/Mn

test. Examination of the media at that time indicated the cleaning

operation had removed practically all observable dirt. The increase

of pressure drop apparently was due to shifting or bending of the

thin metal of the media as a result of the cleaning operation.

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 those made at the start of the next day of loading ('those marked (A)) indicates that the dirt loading rate to which

the filter was subjected did not overtax the wetting-rate of the

filter adhesive and cause the filter surfaces to become “"dry”.
<
RESEARCH PRODUCTS "aLUMALOY" RP902

400

LOAD, GRAMS PER SQUARE FOOT FIG. I
1,
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

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