NATiONAL BUREAU OF STANDARDS REPORT

3^11

PERFORMANCE TESTS OF A CLEANABLE

IMPINGEMENT TYPE AIR FILTER

”E Z KLEEN” RP 9102

by

Henry E, Robinson

Thomas W. Watson

Rerort To

General Services Administration

Public Buildings Service

Washington, 25, D.C,

<:nbs>

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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©Office of Basic Instrumentation ©Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4^30 December 7, 1954 3^11

PERFOR]V'!ANCE TESTS OF A CLEANABLE

IMPINGEMENT TYPE AIR FILTER

"E Z KLEEN” RP 9102

by

Henry E, Robinson

Thomas Watson

Heating and Air Conditioning Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25, D.C»

<^BS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, rep

unless permission Isi

25, D, C. Such pern

cally prepared If th

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

in part, is prohibited

indards, Washington

sort has been specifiport for its own use.
AI

iv
PERFORMANCE TESTS OF A CLEANABLE

IMPINGEMENT TYPE AIR FILTER

”E Z KLEEN" RP 9102

1, INTRODUCTION

At the request of the Public Buildings Service,

General Services Administration, the performance characteristics of a cleanable impingem.ent type air filter

were determined to provide information to assist in the

preparation of new air filter specif ications

The test results presented herein were obtained on

a specimen filter submitted by its manufacturer at the

request of the Public Buildings Service and included determinations of dust-arresting efficiency with two aerosols (atmospheric air and Cottrell precipitate), pressure

drop, dirt load and cleanability of the specimen,

2, DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Research Products

Corporation of Madison, Wisconsin, and was of the cleanable viscid type, 20 x 20 x 2 inches in nominal size. It

was identified by nam.eplate as an ”E Z Kleen RP 9102” air

filter. The filtering media was composed of many layers

of expanded metal (thin aluminum sheet or heavy foil)

arranged one after the other, as follows, starting at the

upstream face: one 4-1/2 inch square mesh wire grid; two

coarse (EM 3/^ x 1/2 inch mesh) ; one fine (EM 1/4 x 3/^

inch mesh) ; eleven layers of fine and coarse media arranged

alternately; two la^’-ers EM 3/S x 1/2 inch m.esh; three layers EM 1/4 X 3/S inch mesh; one 4-1/2 inch s<^uare mesh wire

grid. The layers of media were corcipressed to a thickness

of about 1-3/S inches and surrounded at the edges by an

aluminum metal frame. The filter had actual outside dimensions of 19-5/S X 19-5/S X 1-7/S inches, leaving a f^'^ee

opening IS-I /4 inches square ( 2.31 ft^ net face area) and

weighed l.S lb, when clean, without oilo

The manufacturer submitted an adhesive designated as

"Filter Coat No. 3” for oiling the filter. This was done

in preparation for test by immersing the filter in the

liquid and letting excess fluid drain off with the filter

standing on edge for a minimum of 20 hours prior to the

test. The liquid that V7as submitted was stated by the

manufacturer to consist of one part of "Filter Coat No, 3’^

and one part of water*
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3. TEST METHOD AND PROCEDURE

Efficiency determinations were made by the NBS

”Dust-Spot Method” using the follov/ing aerosols:

(a) outdoor atmosph^'ric air drawn through the laboratory without addition of other dust or contaminant;

and (b) Cottrell precipitate, dispersed in the outdoor

atmospheric air. The test method is described in the

paper ”A Test Method for Air Filters” by R. S. Dill

(ASHVE Transactions, Vol. AA, P379, 1938). In conducting the tests air was sampled from the test duct at

equal rates, from points one foot upstream and eight

feet downstream of the filter, and passed through known

areas of Whatman No. 41 filter paper. The areas of the

filter papers used upstream and downstream, or the times

during which the air was sampled upstream and downstream,

were selected experimentally so that the change in transmission of light through the two filter paper spots would

be about the same. The filter efficiency was calculated

by means of the formula,

Efficiency, percent = 100 £2 . _£l

0l

‘ T2

where A represents the dust spot area, 0 the change in

light transmittance of the filter paper as measured be

fore and after the deposition of dust, and T the time

during which the air samnle was drawn. Subscripts 1

and 2 refer to the upstream and downstream positions,

respectively.

Three efficiency-measuring techniques, or modifications based on the above formula were used, depending on

the apparent efficiency of the filter with the different

aerosols. For the tests made, techniques L, M and N were

used, as indicated in Table 2,

All light transmission measurements were made with

the photometer illumination at a constant intensity as

determined by measurements on a reference of constant

transmission characteristics. The filter papers used

upstream and downstream were selected to have equal light

transmissions when clean.
rSaasiigf,
- 3 -

The efficiency of the filter in arresting particulate matter in atmospheric air was determined by means

of two tests of the L and F types, as described above,

V7ith the filter clean. Following these, the efficiency

of the filter in arresting Cottrell precipitate was

measured by mieans of two N-type tests, after which was

begun the process of loading the filter with a mixture"

of 4 percent of cotton lint and 96 percent of Cottrell

precipitate, by weight, separately dispersed in the air

stream. The lint used for this purpose was No, 7 Cotton

linters previously ground in a Wiley mill with a 4-niillim.eter screen. At suitable periods as loading progressed,

the efficiency'’ of the filter was determined using Cottrell

precipitate in outdoor air. The pressure drop was recorded

at intervals during the test. The dirt-loading was continued until the pressure drop increased to approximately

0.50 inch W.G. The efficiency was again determined with

Cottrell precipitate and then v;-ith atmospheric air as the

aerosols.

The filter was then rem.oved from the test duct and

cleaned by means of a fine spray of cold water from a

hoze nozzle, and rinsed under a low-pressure flow of hot

water.

After being dried the filter was reoiled and after

draining and drying approximately 22 hours was reinstalled

in the test duct for pressure drop mieasurements at various

air flows.

4 . test results

Table 1 presents data as to the pressure drop, at

several rates of air flow, of the clean and oiled filter,

and also of the same filter after it had been loaded with

dirt, cleaned and reoiled.

The performance of the filter at SOO cfm is summarized in Table 2, for both aerosols A and C. The performance

of the filter in regard to aerosol C (Cottrell precipitate

in atmospheric air) is also shown graphically in Figure 1,

- 4 -

The efficiency of the filter in arresting aerosol A

(atmospheric particulate matter), both initially, and

after its resistance had been increased to 0,5 inch W.G.,

is indicated in Table 2,

Observation of the filter at the end of the dirtloading test revealed that the greater part of the

arrested dust and lint was found on the upstream f'ece

and had not penetrated the media beyond' a depth of about

3/4 inch. The doTvnstream face of the media was slightry

darkened with dust at the end of the loading test.

The pressure drops recorded in Table 1 indicate that,

after the filter had been subjected to loading with the

dust-lint mixture and had been cleaned and reoiled, its

increase in pressure drop at SOO cfm was 0,013 inch W,G.

The weight of the unoiled filter after it had been cleaned

and dried following the dirt-loading test was 0,2 lb, greater than that of the unoiled filter initially. The increase

of weight of the filter due to oiling was 0,27 lb. initially,

and 0,45 lb. for the second oiDing. The latter increase was

probably due in part to absorption of oil by dirt entrapped

in the frameedges. After the tests were completed the media

and frame were separated for observation. It was noted

there was a deposit of stiff sludjre and dirt in the peripheral

media behind the edges of the overlapping metal frame that was

not removed by the cleaning process. This could account for

the increase in weight, and part if not all of the pressure

drop increase of the filter. In view of the fact that the

filter appeared thoroughly clean in all of the media except at the edges, it is believed it can be considered as satisfactorily cleanable with careful treatment,

After the unit had been removed from the test duct,

the section of the duct 5 feet long downstream of the unit,

and upstream of a 3/4 inch thick wood strip fastened flat

across the bottom of the test duct, was carefully swept

out v/ith a fine brush. The amount of material obtained

from, the duct by this sweeping was 13.^ grams, or 2,5 percent of the dust load reaching the filter, constituting the

fall-out in the first 5 feet of the duct from the air passed

through the filter, and consisting for the most part of

large dust particles.
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Cellophane tapes, stretched across the test duct downstream of the filter with the adhesive side facing upstream,

5i^'^icated upon visual and microscopic exam.ination after exposure to the air stream that large numbers of particles of

sizes up to approximately 150 microns, and some lint, had

passed through the filter during the dirt-loading tests*

Particles much smaller than 5 microns were observed in

quantity by macroscopic examination of the downstream filter papers obta-ined in tests with both aerosols.
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TABLE 1

PRESSURE DROP OF CLEAN OILED FILTER

Air Face Pressure Pressure

Flow Velocity Drop (1) Drop (2)

cfm fpm inch W.G, inch W.G

1200 520 0.190 0,227

1000 433 .133 .156

goo 346 .0S6 .099

600 260 1

—

1

tr\ • O .061

(1) Initial values for the clean filter

(2) Values for the filter after the dirt-loading test

cleaning operation, and reoiling.

TABLE 2

Performance of Filter at SOO CFM

Inlet

Aerosol (1)

Total

Dirt

Load (2)

Pressure

Drop

Eff. Keas.

Technique (3) Effi

grams inch V/.G. per^

A 0.0^6 M 0 — .0^6 L 3

C 7 .037 N 53

14 N 54

63 .102 N 57

14^ .130 - —

211 .152 N 61

303 .202 N 63

378 .262 N 65

471 .364 N 75

545 .502 N 75

A 545 . ‘^ll L 15

545 .513 L 16

(1) Aerosol A: Particulat e matter in atmospheric air at K

Aerosol C: Cottrell precipitate in atmospheric air (1 gram

per lOUO cf)

(2) Average mixture: lint, 96% Cottrell precipitate, by

weight.

(3) Efficiency-m.easurinp: technique:

L: Air sampled at equal rates through equal areas; upstream sampling time selected to yield approximately

eoual dust-spot opacities both upstream and downstream..

Air sampled at equal rates through equal areas for equal

times.

Air sam.pled at pq’ial rates for equal times; downstream

area selected to obtain approximately equal dust-spot

opacities both upstream and downstream.

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PRESSURE

DROP,

INCH

WG

EFFICIENCY,

PERCENT

30 0

load reaching filter GRAM S 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 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

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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 ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, 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.