NATIONAL BUREAU OF STANDARDS REPORT

5991

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT TYPE

AIR FILTERS

AIRSAN TYPES AF1-30 AND AF2-30

MANUFACTURED BY

AIR FILTER CORPORATION

MILWAUKEE, WISCONSIN

by

Carl W. Coblentz

and

Paul R. Achenbach

Report to

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U. S, Air Force

Washington, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

LY
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT MBS REPORT

1003-30-4889 July 24, 1958 5991

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT TYPE

AIR FILTERS

AIRSAN TYPES AF1-30 AND AF2-30

MANUFACTURED BY

AIR FILTER CORPORATION

MILWAUKEE, WISCONSIN

by

Carl W. Cob lent

z

and

Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U. S. Air Force

Washington, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ' Intended Tor use within tti 5c additional evaluation an

listing of this Report, elth< the Oltke of the Director,

however, by the Governme

to reproduce additional co,

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 201 5.

or progress accounting document®

9 formally published it is subjected

lng ( reproduction, or open-literature

•mission Is obtained In writing from

C, Such permission Is not needed,

ally prepared If that agency wlshee

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
: , j
PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT TYPE AIR FILTERS

AIRSAN TYPES AF1-30 AND AF2-30

by

Carl W. Coblentz and Paul R. Achenbach

1. Introduction

The performance characteristics of a group of cleanable

viscous Impingement air filters were measured to provide information for evaluating the relative economy of cleanable versus

throw-away types of filters. This investigation was requested

by the Defense Department through the Tri-Service program of

research and development at the National Bureau of Standards to

obtain the required data for the preparation of new air filter

specifications

.

The test results presented herein were obtained on two new

"Airsan" filters and include determination of the arrestance

and pressure drop as a function of specific dirt load and

information on cleanability for face velocities of 360 and 5^0

f t/min.

2 . Description of Test Specimens

The two test specimens were of the cleanable viscous impinge

ment type and were manufactured and supplied by the Air Filter

Corporation of Milwaukee, Wisconsin. They were their models

Airsan AF1-30 and Airsan AF2-30 with nominal sizes of 20 x 20 x

1 in. and 20 x 20 x 2 in., respectively; the actual outside

dimensions were 19 1/2 x 19 1/2 x 15/16 in. and 19 3/8 xl9 3/8 x

1 7/8, respectively. The inside opening of the frames of both

filters was 18 x 18 in. providing a net filter area of 2.25 sq ft

Both filters had a galvanized steel frame and grilles made

of expanded galvanized steel sheet on the front and back side to

hold the filter elements made of 16-mesh wire screen. The twoinch thick filter contained six layers of pleated screen with

5/8-in. pleats running alternately vertical and horizontal and

a flat screen between the downstream grille and the last pleated

screen. The one-inch thick filter was built symmetrically and

had no mark to indicate the direction of the air flow. It contained five layers of screening. A flat screen in the center

was sandwiched between two 3/8-inch pleated screens which in

turn were placed between two screens with 5/8-inch pleats which

ran at a 90-degree angle to the 3/8-inch pleats.

- 2 -

The adhesive used was supplied by the manufacturer, bearing

the trade mark ’’Film Cor.”

3 . Test Method and Procedure

The performance of the filters was determined at 360 ft/min

and 540 ft/min face velocity, i.e., at an air flow rate of 810

cfm and 1215 cfm, respectively. The clean filters were immersed

in the adhesive and left to dry in the laboratory at least 16

hours before being weighed and installed in the test apparatus.

The initial pressure drop at each air velocity was measured and

then the initial arrestance at the air velocity desired for that

test was determined with the NBS "Dust Spot Method" as described

in the paper, "A Test Method for Air Filters," by R. S. Dill

(ASHVE Transactions, Vol. 44, p. 379 ) 1938).

The aerosol used for the arrestance determinations was

Cottrell precipitate which had been sifted through a 100-mesh

wire screen. In order to simulate actual operating conditions

when loading the filters, four percent by weight of #7 cotton

linters, previously ground in a Wiley mill with a four-millimeter

screen, was fed simultaneously with the Cottrell precipitate.

The pressure drop of the filters was recorded after each increment of 20 g of dust introduced into the apparatus. Whereas

the arrestance measurements were made with 100 percent Cottrell

precipitate, cotton linters were added to retain a ratio of

four parts by weight to every 96 parts of Cottrell precipitate,

including that amount used for the arrestance measurements.

Arrestance determinations were made at the beginning and at

the end of the loading period for each filter and at several

intermediate load conditions. The filters were loaded with a

dust concentration of approximately 1 g dust in 1000 cu ft of

air until the pressure drop reached 0.5 in. W.G. in 360 ft/min

face velocity test and 0.8 in. W.G. in the tests with 540 ft/min

face velocity.

After the filters had been loaded to capacity, they were

cleaned with water and allowed to dry; then, oiled again as previously described, weighed and installed in the test apparatus

for determining any change in pressure drop and in some cases

for a new performance test.

4. Test Results

The performance observed on the two filters is shown in

Tables 1 to 7 .
ni

11i

ii

iii i

ii

iin

siiiii

si

si
-3-

Table 1

Performance of Airsan Filter AF2-30 (2 M thick) at

360 ft/mi n Face Velocity

Load Pressure Drop Arre stance

g/sq ft in. W.G. %

0 0.C80 54

7 0.081 55

26 0.110 56

48 0.145 59

70 0.203 60

92 0.325 66

111 0.525 77

Table 2

Performance of Airsan Filter AF2-30

540 ft/min Face Velocity

(2" thick) at

Load Pressure Drop Arrestance

g/sq ft in. W.G. ~T~

0 0.225 64

31 0.275 64

49 0.345 -- - 68 0.455 65

86 0.695 —

99 0.960 72

Table 3

Performance of Airsan Filter AF1-30

360 ft/min Face Velocity

(l" thick) at

Load Pressure Drop Arrestance

g/sq ft in. W.G.

0 0.075 51

22 0.100 55

44 0.141 61

66 0.250 62

73 0.325 —

88 0.568 70
II

II
-4-

Table 4

Performance of Airsan Filter AF1-30 (l" thick) at

540 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in. W.G. £

0 0.155 64

22 0.190 64

50 0.320 66

64 0.517 —

77 0.775 73

86 1.000 78

Tables 1 to 4 show the relation of the pressure drop and

arrestance to specific dirt load for the two filters at face

velocities of 360 ft/min and 540 ft/min. Fig. 1 presents a

graph of the values observed with the two-inch thick media and

fig. 2 those of the one-inch thick media. The values of the

dust holding capacity taken from the curves in figs. 1 and 2

for pressure drops of 0.5 in. W.G. at the 360 ft/min air velocity and 0.8 in. W.G. at 5^0 ft/min air velocity are given in

table 5. Also shown in the table are the mean arrestance values

for each filter and each face velocity during the period in

which the capacity dust load was being deposited.

Table 5

Dust Holding Capacity

(Determined from

Thickness of Filter Media

Face Velocity, ft/min

Final Pressure Drop, in. W.G.

Dust Holding Capacity, grams/sq

Mean Arrestance, percent

and Mean Arrestance

Figs1 and 2)

1” 2”

360 540 360 540

0.5 0.8 0.5 0.8

ft 85 78 110 92

60 67 61 65
.
-5-

Table 6

Cleanability of Airsan Filter AF2-30 (2” thick)

Weight

of Filter Pressure Drop , in. W.G.

Condition of Filter grams 360 ft/min 540 ft/min

New 2910 0.080

After 1 loading & cleaning 2995 0.115 0.237

After 2 loadings & cleanings 2995 0.110 0.225

tt 3tt tt »* 3011 0.119 0.235

ft 4

tf tt ft 3025 0.120 0.225

Table 7

Cleanability of Airsan Filter AF1 -30 (1" thick)

Weight

of Filter Pressure Drop , in. W.G.

Condition of Filter grams 360 ft/min 540 ft/min

New 2318 0.075 0.160

After 1 loading & cleaning 2312 0.077 0.155

After 2 loadings & cleanings 2320 0.075 0.160

Tables 6 and 7 show comparative data of the cleanability of

the filters. Unfortunately, no pressure drop measurement was made

of the new two-inch thick filter at the 540 ft/min air velocity.

But the weight increase after the first loading and cleaning as

well as lower dust holding capacities observed in subsequent tests

confirmed that in the first run this filter accumulated a basic

load that could not be cleaned out later. The weight and pressure

drop of the one-inch thick filter, as shown in table J, remained

practically unchanged after two loading and cleaning processes.

13 *

fM z

AIRSAN FILTER AF 2-30 (2" thick)

DUST LOAD

AIRSAN FILTER AF 1-30 (l M thick)

DUST LOAD

-nxi

0

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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