NATIONAL BUREAU OF STANDARDS REPORT

6400

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT

AIR FILTERS TYPES ALH-1 AND ALI-2

MANUFACTURED BY

AMERICAN AIR FILTER COMPANY

LOUISVILLE, KENTUCKY

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.

<NB£p>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions find Activities

The funrtions 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, 19S0. 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 hack 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 prestnts

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

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

Scries, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in N BS Circidar 160, Publications of

the National Bureau of Standards (#1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office, Washington 25, 1). C.

Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1000-12-4801 May 1, 1959

NBS REPORT

6400

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT

AIR FILTERS TYPES ALH-1 AND ALI-2

MANUFACTURED BY

AMERICAN AIR FILTER COMPANY

LOUISVILLE, KENTUCKY

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U. S. Air Force

Washington, D. C.

IMPORTANT NOTICE

the Office of the Director Standards and Technology (NIST) C, Such permission is not needed,

however, by the Governm October 9 ^01 S

dly prepared If that agency wishes

to reproduce additional c

’

to

NATIONAL BUREAU OF

intended for use within 1 to additional evaluation a listing of this Report, eitl

Approved for public release by the ; formally published it is subjected

ar progress accounting documents

NBS
.* .

‘

!
PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT

AIR FILTERS TYPES ALH-1 AND ALI-2

AMERICAN AIR FILTER COMPANY

by

C. W. Coblentz and P. R. Achenbach

1 . Introduction

The performance characteristics of a group of cleanable

impingement type air filters were determined 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 in this report were obtained

on two new filters and include determination of the arrestance

and pressure drop as a function of the specific dust load at

face velocities of 360 ft/min and 540 ft/mi n and information

on the cleanability of the filters.

2 . Description of Test Specimens

The two test specimens were of the cleanable viscous impingement type and were manufactured and supplied by the American Air Filter Company of Louisville, Kentucky. They were identified as types ALH-1 and ALI-2. The frames of these filters

were made of U-shaped channels of aluminum, approximately 0.063

in. thick. The filter media consisted of 4 in. wide strips of

corrugated and expanded aluminum sheet, approximately 0.010 in.

thick. Six of these strips were laid side by side with overlapping edges to form each layer of the media. There were two of

these layers in the 1-in. thick type and 3 layers of this material in the 2-in. thick filter. The direction of the strips

and the corrugations in adjacent layers was oriented by 90 degree

with respect to each other. The ALH-1 type filter had steel wire

grids on the upstream and downstream sides, made of wire with a diameter of 0.1 inch. The grids were comprised of five wires

running in each direction and welded at the cross-overs to form
,•

•

•
- 2 -

4 in. squares. The ALI-2 type had grids of expanded steel sheet

on both sides. The outside of the filters measured 19 7/16 in.

square and the free inside area was 18 in. square. The actual

thickness of the ALH-1 type filter was 7/8 in. and that of the

ALI-2 type filter was 1 7/8 in. The weights of the specimens

were 2 lbs (902 grams) and 5 lbs, 2 oz (2330 grams), respectively, when oiled and ready for use.

The adhesive used during the tests was supplied by the manufacturer and was identified as "Viscosine BA”.

3 . Test Method and Procedure

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

and 5^0 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.
.
-3-

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 data on pressure drops and arrestances determined

during the tests at both face velocities are summarized in

Tables 1 through 4. It should be noted that an asterisk (*)

behind the values of arrestance indicates that this value is

the average of two tests.

Table 1

Performance of Type ALH-1 at 360 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in. W. G. %

0 0.055 - 3 0.056 38*

96 0.095 45*

l 8 l 0.150 48*

249 0.215 52*

334 0.405 52*

368 0.508 52"

Table 2

Performance of Type ALH-1 at 5^-0 ft/min Face Velocity

Load Pressure Drop Arrestance

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

0 0.120 - 5 0.122 46*

68 0.139 47 * 186 0.182 47

249 0.216 46*

321 0.263 48

457 0.390 47 * 601 O .589 45* 692 0.807 46*

-4-

Table 3

Performance of Type ALI-2 at 360 ft/min Face Velocity

Load Pressure Drop Arrestance

g/sq ft in. W.G.

0 0.105 - 3 0.110 47*

63 0.120 53*

156 0.170 54*

266 0. 225 57

385 0.350 60*

471 0.508 62*

Table 4

Performance of Type ALI-2 at 5^0 ft/min Face Velocity

Load Pressure Drop Arrestance

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

0 0.240 - 5 0.240 57*

68 0.255 57

123 0.277 57*

195 0.309 57*

330 0.385 57*

457 0.465 57*

583 0.560 58* 710 O .705 59*

773 0.802 52*

Fig. 1 and Fig. 2 show the values of the pressure drop and

arrestance plotted against the specific dust load, using smooth

curves to approximately fit the individual points of observation.

The test results show that for both types of filters, the

pressure drop increased more slowly at 5^-0 ft/min face velocity

than at 360 ft/min face velocity. The change in pressure drop

caused by increasing the face velocity from 360 ft/min to 5^0

ft/min was 0.065 in. W.G. for the 1-in. thick filter and 0.135

in. W.G. for the 2-in. thick filter with the media clean in each

case

.

0 100 200 300 400 500 600 700 800

Dust Load, grams per sq ft

Dust Load, grams per sq ft

- 5

-

But the specific dust loads at 0.5 in. W.G. pressure drop_, as

indicated by the graphs, was 362 g at the lower face velocity

and 550 g at the higher face velocity for the ALH-1 type and

468 g and 518 g for the ALI-2 type. This seems to indicate

that the accumulation of dust and lint at the face of the filter was considerably heavier at the lower air flow rate and

that at the higher air flow rate a better dust loading throughout the thickness of the filter media occurred.

The arrestance of both types increased with the loading

of the filters during the 360 ft/min face velocity tests, but

it remained practically constant at the 540 ft/min face velocity tests. The 1-in. thick filter showed an overall slight

decrease of the arrestance at the higher flow rate whereas the

2 -in. thick type showed a constant arrestance during the first

60 percent of its loading, then increased slightly and dropped

off. This drop of the arrestance was probably caused by dust

being forced through the medium which had been fully loaded over

its entire depth.

The dust loads for both types as shown in Fig. 1 and 2 at

0.5 in. W.G. pressure drop for 36 O ft/min face velocity and at

0.8 in. W.G. for 540 ft/min face velocity have been tabulated

in Table 5 as "Dust Holding Capacity". Also shown in this table

are the mean arrestance values for each filter at both air flow

rates during the period in which the capacity dust load was being

deposited.

Table 5

Dust Holding Capacity and Mean Arrestance

(Determined from Fig. 1 and 2 ) Type of Filter

Thickness of Filter Media, in.

Face Velocity, ft/min

Final Pressure Drop, in. W.G.

Dust Holding Capacity, g/sq ft

Mean Arrestance, percent

ALH-1

1

360 540

0.5 0.8

382

“ 47

T90

47

ALI -2

2

360 540

0.5 0.8

"W

56

775

57
.
- 6 -

This table shows that the change of face velocity did not

affect the mean arrestance value of the 1 -in. thick filter and

increased by only one percent that of the 2 -in. thick filter.

The dust holding capacity increased at the higher face velocity

from 362 g to 690 g (91 percent) for the 1 -in. type and from

468 g to 775 g (56 percent) for the 2 -in. type.

The useful life of a filter of this type depends on its

structural stability as well as on its ability to be satisfactorily cleaned after each loading. The cleanability of each of

the test specimens was indicated by a comparison of the weights

and pressure drops of the oiled and drained filters when new

and after each of two loading and cleaning cycles.

Table 6

Cleanability of Filters

Condition of Filter

1-in. Thick Medium, Type ALH-1

New

After 1 loading and cleaning

After 2 loadings and cleanings

2 -in. Thick Medium, Type AL1-2

New

After 1 loading and cleaning

After 2 loadings and cleanings

[eight of

Filter

grams

Pressure Drop, in. W

360 ft/mi n 540 ft/r

902 0.055 0.128

892 0.050 0.120

890 0.055 0.125

2330 0.105 0.245

2318 0.105 0.240

2330 0.105 0.240

Table 6 shows that neither the weight nor the pressure drop

of the filters increased after two loading and cleaning cycles.

The deviations shown in the weights and pressure drop may be

caused by differences in the thickness of the oil coating on the

filter media.

USCOMM-NBS-DC

if. S. DEPARTMENT OK COMMERCE

Erwin L. Strium*. Srrrf'lnty

NATIONAL mmtCAU OF STANDARDS

A. V. Afttlil, l)irrcior THE NATW1VAI IHJREAIJ OE STA1VBAKBS

The scope of activities of the Notional Bureau of Standards at its headquarters in Washington,

D. C., find its major laboratories in Boulder. Colo., is suggested in the following listing of ihe divisions and sections engaged In technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated hy its title. A brief ‘description of

the activities, and of the resultant publications, appears on the inside front cover. WASHINGTON, II. C.

Klectrlclty Itltll Rlectraitlcw. Resistance and Reactance. Electron Devices. Electrical In- struments. Magnetic Measurements. Dielectrics,. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

Optics and Metrology* Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Kent* Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research.

Atomic and Radiation PliysIflN, Spectroscopy. Rodiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory.

Radioactivity. X-rays. High Energy Radiation. Nucleonic instrumentation. Radiological

Equipment. ' Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposilion. Molecular Structure and Properties of Gases. Physical

Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and

Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories, Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Itlllldlug Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Itnta Processing Systems. SEAC Engineering Croup. Components and Techniques. Digital

Circuitry. Digital Systems. Anolog Systems. Application Engineering.

* Office of Basic Instrumentation. * Office of Weights and Measures. IIOUMIHU* COLORAIM!

Cryogenic engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction.

Radio Propagation Pliy»*ic^. Upper Atmosphere Research, lonospherij Research. Regular Propagation Services, Sun-Earth Relationships. VI IF Research. Ionospheric Comimmieal ion Systems.

Radio Propagalion (Engineering. Data Reduction lusiriimcululion. Modulation Systems.

Navigation Systems. Radio Noise. I ropnsphcric Measurements. Tropospheric Analysis. Radio

Systems Application Engineering. Radio-Meteorology.

Radio SloniBrsrd*. High Frequency Electrical Slumlords. Radio Broadcast Service. High

frequency isnpc dame" Standards. Electronic Calibration Gcntcr. Microwave Physics. Microwave

Gircuit Standards.