NATIONAL BUREAU OF STANDARDS REPORT

UU87

PERFORMANCE TESTS OF AN AIRMAT PL-2li

DRY-TYPE AIR FILTER

Henry E* Robinson

Thomas W. Watson

Report to

General Services Administration

Public Buildings Service

Washington 2^, D. C.

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 engaged in technical work. In general, each section is engaged in

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Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

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Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

NIBS PROJECT NBS REPORT

OOO-- 3 O-483O January 16, 1958 448?

PERFORMANCE TESTS OF AN AIRMAT PL-24

DRY-TYPE AIR FILTER

fey

Henry E* Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

To

General Services Administration

Public Buildings Service

Washington 25, D. C,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprii

unless permission Isob

25, D. C. Such permls

cal ly prepared If that

Approved for public release by the pa,,, is prohibl,ed

Director of the National Institute of

lards ' Washing,on _ . „ _ t has been speclfi- Standards and Technology (NIST) rt for its own use , on October 9, 2015.

PERFORMANCE TESTS OF AN AIRMAT PL-21*

DRY-TYPE AIR FILTER

by

Henry E. Robinson and Thomas W. Watson

lo INTR0DUCTI0N-5CAt the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

dry-type air filters were determined to provide information

to assist in the preparation of new air filter specifications.

The test results presented herein were obtained on a

specimen dry-type air filter submitted by its manufacturer

at the request of the Public Building Service and included determinations of dust arresting efficiency with two aerosols

(atmospheric air and Cottrell precipitate), pressure drop' and

dirt load.

2. DESCRIPTION "OF THE FILTER SPECIMEN

The filter was manufactured by the American Air Filter

Company, Inc. of Louisville, Kentucky and was of the renewable

media type, identified as an ''Airmat Type PL-2 I4 " air filter.

The filter cell and frame had overall dimensions of 2i*x2i*x8 l/2

inches deep, and had five-ply Viscosine-treated Airmat paper

filtering media, 2:6 inches wide, arranged in vee-folds approximately six inches deep, supported downstream by a six-mesh

wire retaining screen and held in place in the 'troughs by flat

rods supported by the top section of the frame. The net face

area of the filter cell was 3 . 1*8 sq. ft. and the area of the

medium effective for filtering was approximately 28 sq c ft.

The length of Airmat media required for one filling of the

frame was 1< ft. 10 in.

3. TEST METHOD AND PROCEDURE

Efficiency determinations were made by the .NBS n DustSpot Method” using the following aerosols^ (a) outdoor atmospheric 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 a paper U A Test Method foi

R. S. Dill ( ASHVE Transactions, Vol. M,!- 4 » Air Filters'* by

XIQ 1 QO p,)

#This report is submitted for in forma tic only. and i s not

released for use in connection with advertising or sales

promotion.

For these tests , the filter was installed in the apparatus and the desired rate of air flow through the cleaner

was established. Samples of air were drawn from the center

of the test duct, at points one foot upstream and eight feet

downstream of the filter and passed through known areas of

Whatman No. ijl filter paper. The areas of the filter papers

used upstream and downstream and 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

where A represents the dust spot area, 0 the change In light

transmittance of the filter paper as measured before and

after the deposition of dust,, and T the time during which the

air sample 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 measurement on a reference of constant transmission characteristics. The filter papers used upstream and downstream

were selected to have equal light transmissions when clean.

The efficiency of the filter in arresting particulate

matter in atmospheric air was determined by means of two

tests of the M and L types,, as described In Table 2, with the

filter clean. Following these,, the efficiency of the filter

in arresting Cottrell precipitate was measured by means of

two N-type tests, after which was begun the process of loading

the filter with a mixture of four 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 14 -millimeter screen. At suitable periods as the loading

progressed, the efficiency of the filter was determined

using Cottrell precipitate in outdoor air. Pressure drops

were recorded at intervals during the test. The dirt-loading

Efficiency, percent = 100

- 3

-

was continued until the pressure drop increased to approximate!;' G e 50 inch V.G, The efficiency was again determined

with Cottrell precipitate and then with atmospheric air as

the aerosols.

4, TEST RESULTS

Table 1 presents data as to the pressure drop of the clean

filter at several rates of air flow.

The performance of the filter at 1000 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, The efficiency of the filter in arresting aerosol A (atmospheric

particulate matter) , both initially, and after its pressure

drop had been increased to 0»5 inch W. G, is indicated in

Table 2,

Observation of the filter at the end of the dirt-loading

test revealed that the greater part of the arrested dirt was

found uniformly distributed on the upstream face. The downstream face of the media was uniformly darkened by dust. No

lint was visible on the downstream face of the media.

After the filter had been removed from the test duct,

the section of the duct five feet long downstream of the unit

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

the bottom' of the test duct was carefully swept out with a

fine brush. The amount of material ' obtained from the duct

by this sweeping xvas less than 1/4 gram.

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

indicated upon visual and microscopic examination after exposure to the air stream that some few particles up to approximately 40 microns in size had passed through, the filter during

the dirt-loading tests. Particles smaller than five microns

were observed in quantity by microscopic examination of the

downstream filter papers obtained in tests ,wi tip. both aerosols.

No lint was observed on the tapes during these tests.

TABLE 1

Air

Blow

cfm

1200

1000

800

PRESSURE DROP OF CLEM FILTER

Air Velocity

through Media

fpra

k3

36

29

Pressure

Drop, Initial

inch, W,G.

0.118

.093

.069

600 21 • OI4I4

TABLE 2

PERFORMANCE OF FILTER AT 1000 CFM

Aerosol (1)

Tot al

Dirt

Load (2)

Pressure Eff. Meas.

Technique ( 3 ) Effic:

A

grams inch W.G

0.093 M

perc

7

- .093 L 14

- .093 M 11

C 9 .098 N 83

18 .102 N 88

28 .109 N 90

98 . 166 N 93

137 .218 N 94

196 .33° N 94

225 ' *392 N 96

274 .492 N 97

279 .506 -

A 279 .512 M 43

279 .512 M 47

Cl)

( 2 )

(3)

Aerosol As

Aerosol G % Particulate matter in atmospheric air at NBS.

Cottrell precipitate in atmospheric air

(1 gram per 1000 cf )

Average mixture: 4.0 percent lint, 93.0 percent Cottrell

precipitate by weight.

Efficiency measuring techniques

L % Air sampled at equal rates through equal areas;

upstream sampling time selected to yield approximately equal dust-spot opacities of the upstream

and downstream filter papers.

Ms Air sampled at equal rates through equal areas for

equal times.

Ns Air sampled at equal rates for equal times j downstream areas selected to yield approximately equal

dust-spot opacities of the upstream and downstream

filter p ?rs.

!N30d3d ‘A0N3I0I3J3 9 ’M HONI ‘dOUQ 3HHSS3 dd

100

200

300

LOAD

REACHING

FILTER,

GRAMS

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

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