NATIONAL BUREAU OF STANDARDS REPORT

6428

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT

AIR FILTERS TYPE P-5

MANUFACTURED BY

AIR-MAZE CORPORATION

CLEVELAND, OHIO

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.

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT MBS REPORT

1000-12-4801 June 4, 1959 6428

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT

AIR FILTERS TYPE P-5

MANUFACTURED BY

AIR-MAZE CORPORATION

CLEVELAND, OHIO

by

Carl W. Coblentz 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 S' intended for use within the

to additional evaluation and

listing of this Report, either the Office of the Director, h however, by the Goverrimen

to reproduce additional cop

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

rrmally published u is 3u,r. u »

, reproduction, or open-literature

ssion is obtained In writing from Such permission is not needed,

y prepared If that agency wishes

<NSS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TESTS OF TWO CLEANABLE

IMPINGEMENT AIR FILTERS TYPE P-5* 1 IN. AND 2 IN. THICK

MANUFACTURED BY

AIR-MAZE CORPORATION

CLEVELAND* OHIO

by

Carl W. Coblent z and Paul R. Achenbach

1. INTRODUCTION

The performance characteristics of two cleanable viscous

impingement air filters were determined to provide information

for evaluating the relative economy of cleanable versus throwaway 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 in this report were obtained on

two new filters and include determination of the arrestance and

pressure drop as related to the specific dust load for face

velocities of 360 ft/min and 54-0 ft/min and information on the

cleanability of the test specimens.

2. DESCRIPTION OF TEST SPECIMENS

The two test specimens were of the cleanable viscous impingement type and were manufactured and supplied by the AirMaze Corporation of Cleveland* Ohio. They were both identified

as their type P-5., but were of different thicknesses. Both

filters measured 19 1/2 in. square on the outside and had a free

face area of 18 in. square* i.e.*,2.25 sq ft. The nominal 1 in.

thick filter had an actual thickness of 15/16 in. and the nominal

2 in. thick filter was 1 7/8 in. thick.

The filter media consisted of strips of 16-mesh crimped screen

wife. The width of these strips was 7/8 in. and 1 3/4 in.* respectively* and the strips were 19 in. long after crimping and

were piled up 19 in. to cover the area of the filters. There

were three 1/8 in. thick steel rods placed through the middle of

- 2 -

the pile of strips to provide rigidity in the direction of the

air flow. The frames were made of 21 gage sheet steel bent into

a continuous U-shaped channel.

The filters were oiled with an adhesive furnished by the

manufacturer, identified as "Filterkote G.”

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 tests 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.
,*

.
- 3

-

4. TEST RESULTS

The data on pressure drop and arrestance observed for different dust loads are summarized in Tables 1 to k, inclusive.

An asterisk (*) behind the value of arrestance indicates that

this value presents the average of two test runs.

Table 1

Performance of P-5 Filter (l in. thick)

at 360 ft/min Face Velocity

Dust Load

g/sq ft

0

3

46

88

130

173

182

Pressure Drop

in. W. G.

0.055

O.O56

0.086

0.132

0.240

0.450

0.526

Arrestance

50*

55

61

64

67

74*

Table 2

Performance of P-5 Filter (l in. thick)

at 540 ft/min Face Velocity

Dust Load

g/sq ft

0

5

59

105

132

162

Pressure Drop

in. W. G.

0.125

0.130

0.225

0.375

0.530

O.85O

Arrestance

Jo52*

64

70

80

81*

-4-

Table 3

Performance of P-5 Filter (2 in. thick)

at 360 ft/min Face Velocity

Dust Load Pressure Drop Arrestance

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

0 0.046 -

Qu 0.048 52*

54 0.072 53

102 0.102 58

149 0.132 60

197 0.190 61

244 0.290 63

300 0.525

Table 4

71*

Performance of P-5 Filter (2 in.

at 540 ft/min Face Velocity

thick)

Dust Load Pressure Drop Arrestance

g/sq ft in. W. G.

0 0.128 - 5 0.129 57*

59 0.172 61

114 0.220 66

168 0.290 73

221 0.406 76

270 0.640 - 293 0.820 81*

The dust load per square foot net face area is the weight

of dust and lint introduced into the test apparatus minus the

fall-out in the upstream portion of the test duct divided by

the net face area of the filter. The total fall-out was determined at the end of each test by sweeping out the upstream portion of the test duct. For computing the dust load per square

foot net face area the amount of dust and lint introduced into

the test apparatus was multiplied by one minus the ratio of fallout to the total dust introduced according to the following
.

-
-5-

f ormula:

L _ D x (1 - F)

A

where: L = dust load,, g/sq ft

D = dust and lint introduced,, g

A = net filter area, sq ft

total fall-out

F = total dust and lint introduced * at the end of the test

The values of the above tables are graphically presented in

Fig. 1 and Fig. 2 as smooth curves that approximate the curves

of the least mean square distances of the individual points of

observation

It will be noted that the arrestance increased with increasing dust loads,, but the rate of increase varied for the two filters and also with the face velocity. For both filters the increase of the arrestance was from 20 to 30 percent., and the arrestance at equal dust loads was higher at the higher air velocity.

The dust loads indicated by these graphs at 0.5 in. W.G. pressure drop for 360 ft/min face velocity and at 0.8 in. W.G. for

540 ft/min face velocity are shown in Table 5 as "Dust Holding

Capacity”. Also shown in this table are the mean arrestance values

of each filter for each of the two face velocities during the period

in which the capacity dust load was being deposited. As was to

be expected,, the dust holding capacity of the 1 in. thick filter

was considerably lower than that of the two-inch thick one. However, the mean arrestance was found to be the same for both filters

at either face velocity.

Air Maze - P-5 (l in. thick)

100 200 300

Dust Load, grams per square foot

0

Air Maze - P-5 (2 in. thick)

Dust .Load, grams per square foot

- 6 -

Table 5

Dust Holding Capacity

Thickness of Filter, in.

and Mean

1

Arrestance

2

Face Velocity, ft/min 360 540 360 540

Final Pressure Drop, in. W.G. 0.5 0.8 0.5 0.8

Dust Holding Capacity, g/sq ft 180 158 296 293

Mean Arrestance, % 60 68 60 68

The weights of the oiled and drained filters determined before

installation in the test apparatus and also their pressure drop at

both face velocities are shown in Table 6 for the new filters and

after each loading and cleaning cycle

Table 6

Cleanability of Filters

Weight Pressure Drop, in. W.'

Thickness and of Filter at Face Velocity

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

1 in. thick

New 2412 0.055 0.110

After 1 loading and cleaning 2477 0.060 0.125

After 2 loadings and cleanings 2535 O.O85 0.170

2 in. thick

New 3455 0.046 0.105

After 1 loading and cleaning 3630 0.060 0.128

After 2 loadings and cleanings 3815 0.071 0.141

The cleaning of the filters was performed with a stream of

about 150 F water and was continued until the waste appeared clean.

The increase of the weight of the filters after each loading and

cleaning cycle indicates that a considerable part of the dust had

not been removed by careful washing of the filters. This fact is

corroborated by the steady increase of the pressure drop values of

the filters after each loading and cleaning cycle.

USCOMM-NBS-DC
.
0. vS. foEPARTMENT OK COMMENCE

f,t>wln Ij. Slt-jUtflU, Secretary

NATIONAL lUmteAU Of' STANDARDS

A. V, AmIii, Director THE .NATIONAL KOTIKAIT OE STANI»AKI».S

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