NATIONAL BUREAU OF STANDARDS REPORT

6498

PERFORMANCE TEST OF A WESTINGHOUSE

"PRECIPITRON" ELECTROSTATIC AIR CLEANER

by

Carl W. Coblentz and Paul R. Achenbach

Report to

General Services Administration

Public Buildings Service

Washington 25., L. C.

SI. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUKEAU 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, 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

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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 back 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 cither 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 presents

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

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Information on the Bureau’s publications can be found in N BS CirciHar 460, Publications of

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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 NBS REPORT

1003-30-10630 August 5, 1959 6498

PERFORMANCE TEST OP A WESTINGHOUSE

"PRECIPITRON" ELECTROSTATIC AIR CLEANER

by

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning,, Heatings and Refrigeration Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25 j> 0. C.

NATIONAL BUREAU OF S' intended for use within the

to additional evaluation and

listing of this Report, either the Office of the Director, N however, by the Governmen

to reproduce additional cop

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

rrmally published it is subjected

1 reproduction, or open-literature

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

r prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY

PERFORMANCE TEST OF A. WESTINGHOUSE

"PRECIPITRON" ELECTROSTATIC AIR CLEANER

by

Carl W. Coblentz and Paul R. Achenbach

1. INTRODUCTION

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of a Westinghouse electrostatic air cleaner were determined. The scope

of this examination included determination of the arrestance of

particulate matter suspended in the laboratory air and of Cottrell

precipitate, pressure drop, dust holding capacity and cleanability

of the specimen.

2. DESCRIPTION OF TEST SPECIMEN

The air cleaner was manufactured and supplied by the Westinghouse Electric Corporation, Sturtevant Division, of Boston,

Massachusetts, and was designated "Precipitron”. The collector

cell was identified as the manufacturer’s type CB 2025:, serial

#496D151G04, the power pack was type RC5, serial #S496D519G01

.

The manufacturer also furnished an adhesive "Dustic Type B” which

was applied to the test specimen as directed.

The collector cell assembly was mounted in a sheet steel

housing. It was provided with a lint screen, Farr type #5706, as

a prefilter, and a Farr type #5611 after-filter. The lint screen

consisted of a single 8 -mesh wire screen installed in a U-shaped

steel frame. The after-filter was similar to the Farr type 44,

I in. thick. The outside measurements of the collector cell were

24 1/2 ” x 19 3/4” and were the same as that of the prefilter and

after-filter. The face dimensions of the cell were 18 3/8” x 22 1/8”.

It contained 117 plates, each measuring 19 1/2” x 5"; or 158 sq ft

total plate surface. The collector plates were 0.020 in. thick and

spaced approximately 0.192 in. on center. The unit was equipped with

II ionizer wires and grounded separators which consisted of 2 1/2

” x 1/8” metal strips. The cell housing was provided on either side

with a transition piece for adapting it to the NBS test apparatus.

The manufacturer had rated the filter for an air flow of 1740 cfm

which corresponded to a net face velocity of 615 ft/min, based on a

C!

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net inlet area of 2.82 sq ft after deducting the area taken up

by the plates, or to a gross face velocity of 518 ft/min, based

on the 3-36 sq ft area of the face of the collector cell.

Arrestance determinations were made by the NBS "Dust Spot

Method” using the following aerosols: (a) the particulate matter

in the laboratory air and, (b) Cottrell precipitate. The test

method is described in the paper ”A Test Method for Air Filters",

by R. S. Dill ( ASHVE Transactions, Vol. 44, p. 379, 1938).

The sampling air was drawn from the center points of the test

duct one foot upstream and eight feet downstream of the air cleaner

assembly at equal flow rates and passed through known areas of

Whatman No. 4l filter paper. For determining the arrestance with

the particulate matter in the laboratory air, the samples were drawn

at equal rates for periods of one hour to 3 1/2 hours, depending

on the dustiness of the outdoor air. In order to obtain a similar

increase of opacity on the upstream and downstream sampling papers,

an upstream sampler area of 0.884 sq in. and a downstream area of

0.3533 sq in. were selected and an electric timer that operated

two solenoid valves in the sampling line was set to pass the sampling air through the upstream sampler only 20 percent of the time

using a five minute cycle, while bypassing the sampler the rest of

the time. The downstream sampling air was drawn through the sampling

paper all of the time. The resultant arrestance A (in percent) was

then computed by the following formula:

where AD and AU were the observed values of the change in opacity

of the downstream and upstream samplers, respectively. Under these

conditions, an arrestance of 92.0 percent would have been indicated

if the dust spots on the upstream and downstream sampling papers

had shown the same change of opacity. The change of opacity was

determined with a sensitive light transmission photometer which

measured the same areas on the sampling papers before and after the

tests. The two filter papers used for each test were selected to

have the same light transmission readings when clean.

3. TEST METHOD AND PROCEDURE
-

*
For determining the arrestance with Cottrell precipitate,,

an upstream dust spot area of 2.685 sq in. and a downstream area

of 0.2651 sq in. were selected. Two filter papers were used successively in the upstream sampler and each operated during the

dispersion of 10 grams of dust into the test apparatus, whereas

only one sampling paper was used in the downstream sampler for

the total 20 grams. All three sampling papers were selected for

equal light transmission when clean. If AUn and AU? are the changes

of the opacity of the two upstream papers the resulting arrestance

then was:

Under this condition, an arrestance of 95.06 percent would have

been indicated if all three sampling papers had shown the same

change of opacity.

The power pack was connected to the 115-volt A.C. laboratory

power supply through a variable transformer, the output voltage

of which was maintained at 120 ± 2 volts during the operation of

the test specimen. When the ionizer and plate voltages were measured with a sensitive electrostatic kilovolt meter tne input to

the power pack was adjusted to 120 ± 1/4 volts. The high voltage

current could be observed on a milliammeter mounted on the front

panel of the power pack.

The following procedure was employed in testing the filter:

After the clean and oiled unit had been installed in the test apparatus, the housing was carefully sealed to eliminate air leakage.

It was then determined that the ionizer and plate voltages corresponded to the values recommended by the manufacturer, i.e., ionizer

11.1 KV, collector plates 5-0 KV. Two determinations of the arrestance of the clean unit were then made at the rated air flow rate

of 1740 cfm and also at air flow rates of 2088 cfm and 1392 cfm

(20 percent above and below the rated air flow rate, respectively).

During these tests, outdoor air was drawn into the test apparatus

through a nearby window and used as the aerosol.
,* .

-

•
-4-

Following these initial arrestance determinations, the arrestance of the test specimen was determined with laboratory air

into which Cottrell precipitate at a concentration of one gram per

thousand cubic feet was dispersed at the rated air flow rate of

1740 cfm. The loading of the filter was then begun with 4 percent

of cotton lint added to each 96 percent of Cottrell precipitate,

by wei'ght, each separately dispersed into the air stream. The lint

used for this purpose was No. 7 cotton linters previously ground

in a Wiley mill with a four-millimeter screen. The lint was dispersed into the air stream through an aspirator operating at approximately 35 psi inlet pressure. At selected intervals, as the

loading progressed, arrestance determinations were made using either

the laboratory air alone or laboratory air with Cottrell precipitate

as the aerosol. No lint was dispersed into the test apparatus during

these latter arrestance determinations, but an appropriate amount

of linters was added to retain the ratio of 4 to 96 , after each

arrestance determination. The pressure drop across the test specimen, and the ionizer and plate voltages were recorded at intervals

during the test. The test was to be discontinued after 1160 grams

of Cottrell precipitate and lint (i.e., 2/3 gram per cfm of rated

air flow) had been dispersed into the test apparatus or when the

pressure drop had reached 1 in. W.G.

The cleanability of the filter cell, prefilter and after-filter

was determined after they were removed from the test apparatus. A

stream of cold water from a high pressure hose nozzle was used for

cleaning all three components.

4. TEST RESULTS

The test results have been summarized in Table 1 which shows

the air flow rates at which the unit was operated, the cumulative';

dust loads, the ionizer and plate voltages and their combined current, the pressure drops across the unit and the arrestance values

determined with the particulate matter of the laboratory air as the

aerosol and with Cottrell precipitate.

A maximum of about three audible discharges per minute occurred

when Cottrell precipitate was dispersed into the test apparatus.

No discharges were noticed while the test specimen was operated

with laboratory air only.
-
-5-

Table 1

Performance of Westinghouse Precipitron

Air Flow

Rate

Dust

Load

Voltage

Ionizer Plate Current

Pressure

Drop Arrestance

Aerosol

Used

cfm grams KV KV ma In. W.G. **

2088 0 11.1 5.0 1.2 0.300 91.4* A

1740 0 11.1 5.0 1.2 0.208 95.7* A

1392 0 11.1 5.0 1.2 0.147 97-7* A

1740 20 11.05 5-0 1.2 0.210 99.5 B

1740 228 11.05 5.0 1.2 0.311 95.1 A

1740 415 11.1 5.0 1.15 0.738 99.1 B

1740 415 11.1 5.0 1.15 0.744 93.7 A

1740 435 11.1 5.0 1.15 1.02 93.5* A

* Average of two tests.

** A = Particulate matter in laboratory air.

B = Cottrell precipitate in laboratory air.

5 . SUMMARY

A. Performance

At the rated air flow rate of 1740 cfm (615 ft/min net face

velocity) the arrestance of particulate matter in the laboratory

air was 95-7 percents before any Cottrell precipitate had been dispersed into the test apparatus. When the air flow rate was increased by 20 percent to 2088 cfm the arrestance dropped 4.3$, to

91.4 percent. Under the same conditions, it increased 2$, to 97*7

percent when the air- flow rate was decreased by 20% to 1392 cfm.

Subsequent to this series of tests the unit was operated only at

the rated air flow rate of 1740 cfm. It was found that the arrestance of atmospheric dust decreased to 93.5 percent when the

dust load reached 435 grams and the pressure drop had gone up to

1.02 in . W. G.

Two tests made with Cottrell precipitate as the aerosol showed

99*5 percent and 99.1 percent arrestance. The high voltage measurements remained practically constant throughout the test.

- 6 -

The pressure drop at 17*40 cfm air flow rate was 0.208 in.

W.G. when the unit was clean and increased to 1.02 in. W.G. when

a dust load of 435 grams was dispersed into the test apparatus.

A layer of lint approximately 1/4 in. thick covering the lint

screen may have produced a considerable portion of the pressure

drop increase. The total load was only 1/4 gram per cfm of rated

air flow when the pressure drop reached the limiting value of 1

in. W.G. It was not determined whether the relatively rapid increase in pressure drop was due primarily to the lint accumulation

on the prefilter or the close spacing of the plates in the collector cell or a combination of these two factors.

B. Cleanability

The filter was subjected to the cleaning process described

under Test Method and Procedure. No difficulty was experienced

in cleaning the collector cell, the lint screen or the afterfilter with a cold water stream, using moderate care.

C. General

On completion of the dust loading test, the unit was removed

from the test apparatus for a visual examination. All components

of the collector cell were coated with dust. The heaviest deposits were observed on the leading edges of the negative plates

where the layers were estimated to be about 1/32 in. thick. Only

very small lint particles were noticed on the surface of the collector cell but the after-filter had a solid cover of lint on its

front side. The back side of the after-filter was completely clean

and did not indicate that dust had been carried through during the

test. The dust deposits on the collector plates as well as on the

after-filter appeared to be well saturated with oil.

An examination of the test apparatus after the test revealed

that no visible traces of dust could be found in either the upstream or downstream part of the test apparatus.

USCOMM-NBS-DC

U.S. DEPARTMENT OF COMMERCE

Kmlrrirk II. Mueller. .Vetiiig Secretary NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

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

laboratories in Boulder, Colorado, 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 and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

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

Length. Engineering Metrology.. Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid Slate 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. Electrodeposition. 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.

Building 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.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

9 Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radio Systems Application Engineering. RadioMeteorology. Lower Atmosphere Physics,

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Communication and Systems, Low Frequency and Very Low Frequency Research. High Fre- quency and Very High Frequency Research. Ultra High Frequency and Super High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.
NBS