NATIONAL BUREAU OF STANDARDS REPORT

6954

PERFORMANCE TESTS OP A PRAM THROW-AWAY TYPE AIR FILTER

manufactured "by

Pram Aire Corporation

Division of Pram Corporation

Providence, Rhode Island

by

Carl W* Coblent z and Paul R« Achenbach

Report to

General Services Administration

Federal Supply Service

Washington 25

t

D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL OSE ONLY
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The I'unclions 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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Publications

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of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

HBS IFROiCCT NB8 REPORT

1003-30-10630 September 8, i960 695^

PERFORMANCE TESTS OP A PRAM THROW-AWAY TYPE AIR FILTER

manufactured by

Pram Aire Corporation

Division of Fram^ Corporation

Providence, Rhode Island

by

C, W. Coblentz and P. R. Achenbach

Mechanical Systems Section

Building Research Division

to

General Services Administration

Federal Supply Service

Washington 25> L. C.'

IMPORTANT NOTICE

NATIONAL BUREAU OF 8T/

IritenHedl For use yvlthin the ( to additional evaluation and n

llsti(i^ cf this' Report, either ii the Office of the Director, Nal

hov/ovor, by the Government 1 to reproduce additional copiei

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ogress accounting documenU

nally published it la subjected

eproductlon, or open-llteraturo

Ion Is obtained In writing front Such permission Is not neededi

trepared if that agency wlahei

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY
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PERFORMANCE TESTS OF A FRAM THROW-AWAY TYPE AIR FILTER

manufactured by,

Fram Aire Corporation

Division of Fram Corporation

Providence,, Rhode Island

by

Carl W. Coblentz and Paul R» Achenbach

lo Introduction

At the request of the Federal Supply Service, General

Services Administration, the performance characteristics of

two specimens of the Fram throw-away type air filter were

determined. The scope of this examination Included the arrestance of Cottrell precipitate in laboratory air, the pressure drop, and the dust-holding capacity of the specimens at

370 ft/min face velocity.

2 . Description of Test Specimen

The filters were manufactured and supplied for test

purposes by the Fram Aire Corporation, Division of Fram

Corporation, of Providence, Rhode Island, and were intended

to be identical in construction. The test specimens were

nominal 20 x 20 x 1 in. filters and measured I 9 3/^ in.

square and 15/16 in. thick on the outside. The filter'

medium was held in a cardboard fra?ne with channel-shaped

cross section which left a net face area of I 7 7/8 in.

square, l.e., 2.22 sq ft.

The weights of the two specimeris were 240 and 235

grams, respectively (approx, 8 1/2 oz). The filter media

were of a light plastic felt about 1/2-in. thick. The

medium would not sustain combustion and according to the

manufacturer’s claims was treated with a bactericidal

substance. A perforated metal sheet was Installed in the

frame to support the downstream face of the filter media.

3 . Test Method and Procedure

The filter was tested at a face velocity of 370 ft/min

corresponding to an air flow rate of 820 cfm. The arrestance determinations were made with the NBS ’’Dust Spot

Method” described in a paper by R. S, Dill entitled, ”A

- 2 -

Test Method for Air Filters/' (ASHVE Transactions j Vol. hk

,

p. 379, 1938). The filter under test was supported in a frame which fitted the test apparatus and was carefully

sealed to prevent any by-pass of air or inward leakage

into the test apparatus, except through the measuring

orifice. The desired rate of air flow through the filter

was established, and samples of air were drawn from the

center points of the test duct 2 feet upstream and 8 feet

downstream of the test specimen at equal rates, and passed

through known areas of Whatman No. 4l filter paper. The

arrestance determinations were made with laboratory air

into which Cottrell precipitate was injected and diffused

at a ratio of 1 gram per 1,000 cu ft of air.

The two sampling papers used for each arrestance determination were selected to have the same light transmission when clean. The light transmission was measured

with a sensitive photometer on the same portion of each

paper before and after the test. In order to obtain similar increases of opacity with both samplers, different size

areas were used upstream and downstream of the filter. The

arrestance, A (in percent), was calculated by the following

formula

:

A = _ ^X

^

Su AU

X 100

where Sp and Sp are the downstream and upstream areas and

ad and AU the observed changes in the opacity of the downstream and upstream sampling areas, respectively.

Whereas the arrestance determinations were made with

Cottrell precipitate only, cotton lint was added during

the loading process in a ratio of 4 parts to every 96 parts

by weight of Cottrell precipitate, including that amount

used for arrestance measurements. The Cottrell precipitate had been previously sifted through a 100 mesh screen

and the cotton lint was prepared by grinding No. 7 cotton

llnters in a Wiley mill with a 4 millimeter screen.

Arrestance determinations were made at the beginning

and at the end of the loading period of each test specimen

and at several intermediate load conditions. The pressure

drop across the filter under test was recorded after each

increment of 20 grams of dust had been introduced into the

test duct. The test was terminated when the pressure drop

reached O.5 in. W.G.
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4. Test Results

A summary of the test results of the two specimens is

presented in Table 1 which shows the dust load, pressure

drop, and the arrestance values.

Table 1

Performance of a Fram Throw-away Type Air Filter

1 inch Nominal Thickness, 370 ft/min Face Velocity

Dust Load

g/sq ''ft

0

5

39

72

126

Pressure Drop

in. W.G.

FIRST SPECIMEN

0.120

0.131

0.220

0.310

0.496

Arrestance

54*

66* 69

76*

SECOND

0 0

5 0

47 0

100 0

135 0

SPECIMEN

110 — 116 50

214 65

353 73

505 73

* Indicates average of two arrestance determinations.

The ’’Dust Load” shown in this table is the dust received by 1 sq ft net filter area. It is the weight of the

Cottrell precipitate and lint Introduced into the test apparatus divided by the net face area of the filter and diminished by the percentage of dust fallout upstream of the

filter. This dust fallout was determined at the conclusion

of the test by sweeping out the test duct and calculating

the percentage of fallout to the total dust Introduced.

It will be noted that the pressure drop and the arrestance of the first specimen was a little higher than

that of the second one, associated with a slightly higher

weight of the first specimen. The initial arrestances of

the filters were 54^ and 30%, and the final arrestances,

76 ^ and 73^^ respectively. The pressure drops of the
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clean filters were 0.120 and 0.110 in. W.G., respectively.

The dust-holding capacity^ which is the dust load per unit

area at the final pressure drop of 0.5 in. W.G., averaged

130 g/sq ft. The first specimen, presumably because of its

higher arrestance, had a dust load of 126 g/sq ft at 0.496

in. W.G., whereas the second specimen showed 135 g/sq ft

at 0.505 in. W.G.

Figure 1 presents a graph of the values shown in Table

1 with smooth curves approximating the line of the least

mean square distances from the points of observation of both

specimens. The average arrestance of approximately 67^ is

taken as the imaginary horizontal line which would enclose

equal areas above and below the arrestance curve.

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U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Bouldei;, Colo., is suggested in the following listing of the divisions and sections engaged in technical work. In

general, each section carries out specialized research, development, and engineering in the field indicated by its

title. A brief description of the activities, and of the resultant publications, appears on the inside of the front cover. WASHINGTON, D.C. ELECTRICITY, Resistance and Reactance. Electrochemistry. Electrical Instiniments. Magnetic Measurements.

Dielectrics. METROLOGY. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering

Metrology. Mass and Scale. Volumetry and Densimetry.

HEAT. Temperature Physics. Heat Measurements. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Reseav.ch. Equation of State. Statistical Physics. Molecular Spectroscopy.

RADIATION PHYSICS. X-Ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological

Equipment. Nucleonic Instrumentation. Neutron Physics.

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Polymer Structure. Plastics. Dental Research.

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MINERAL PRODUCTS. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and

Microstructure.

BUILDING RESEARCH. Structural Engineei'ing. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. APPLIED MATHEMATICS. Numerical Analysis. Computation. Statistical Engineering. Mathematical

Physics.

DATA PROCESSING SYSTEMS. Components and Techniques. Digital Circuitry, Digital Systems. Analog

Systems. Applications Engineering.

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Atomic Physics.

INSTRUMENTATION. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical

Instrumerrts. Basic Instrumentation.

Office of Weights and Measures. BOULDER, COLO.

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Liquefaction.

IONOSPHERE RESEARCH AND PROPAGATION. Low Frequency and Very Low Frequency Reseai’ch. Ion- osphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Seiwices. RADIO PROPAGATION ENGINEERING. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation -Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

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