NATIONAL BUREAU OF STANDARDS REPORT

lT\ r't ~

6952

PERFORMANCE TEST OF AN ELECTRO-CELL

ELECTROSTATIC AIR CLEANER, MODEL 2-24

manufactured by

American Air Filter Company

Louisville, Kentucky

by

Carl W. Coblentz and Paul R. Achenbach

Report to

General Services Administration

Public Buildings Service

Washington 25^ D. C.

(I. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY
THE NATIONAL BUREAU 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, 1950. 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; in- vention anil 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,

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divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers. These papers- appear either in the Bureau’s own series of publications or in the journals

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

m% PROJECT NBS REPORT

'1003-30-10630 September 2, i960 6952

PERFORMANCE TEST OF AN ELECTRO-CELL

ELECTROSTATIC AIR CLEANER, MODEL 2-24

manufactured by

American Air Filter Company

Louisville, Kentucky

by

C. W, Coblentz and P. R» Achenbach

Mechanical Systems Section

Building Research Division

to

General Services Administration

Public* Buildings Service

Washington 25.* D. C.

NATIONAL BUREAU OF STANE

|r, tended for use yvlthin the Goy

to additional evaluation and revie Jilting cf this

1 Report, either in w

the Office of the Director, Nation

r.ov/evor, by the Government age

to reproduce additional copies fa

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

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

ess accounting document*

ly published it Is subjected

induction, or open-literature

Is obtained in writing from

It permission Is not needed,

iared if that agency wlshe*

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FOR OFFICIAL USE ONLY
.

.

VJBO m JA!3m3 5101
PERFORMANCE TEST OF AN ELECTRO-CELL

ELECTROSTATIC AIR CLEANER, MODEL 2-24

manufactured by

American Air Filter Company

Louisville, Kentucky

by

C. W. Coblentz and P. R. Achenbach

1 . Introduction

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

an Electro-Cell electrostatic air cleaner were determined.

The scope of this examination included the determination of

the arrestance of the particulate matter in the laboratory

air and of Cottrell precipitate, the pressure drop, and the

dust-holding capacity of the specimen.

2 . Description of Test Specimen

The device was manufactured and supplied for test purposes by the American Air Filter Company of Louisville,

Kentucky, and was their high-velocity Electro-Cell, Model

2-24.

The outside dimensions of the collector cell were 19 3/4

in. high, by 23 3/4 in. wide, and 10 in. deep. There were

seven ionizer wires. The grounded elements between these

ionizer wires were extensions of some of the grounded plates

with cut-outs provided for the intermediate ionizer supports.

The cell had 63 charged plates and 62 grounded plates, each

5 9/16 x 19 3/4 in. in size. Six of these grounded plates,

the extensions of which served as grounded elements between

the ionizer wires, were 4 in. longer than the other plates,

and had a thickness of 0.0437 in., whereas all other plates

were 0.0218 in. thick. The plates were arranged 5/32 in.

center-to-center . The effective or net face area of the

collector cell was 2.87 square feet and the gross face area

was 3.26 square feet. The cell was equipped with a 2-in.

thick after filter, American Air Filter Co. type Amer-Glas.

The adhesive used on both the after filter and the plates

was designated as type NCC (Viscosine) ; it appeared to be

a light detergent oil.

- 2 -

The power pack supplied with the unit was built by the

General Electric Co. It was their type SG-3V and was designed for 13 . 4 KV ionizer voltage and 4.0 KV plate voltage.

The arrestance measurements were made in accordance with

the "NBS Dust Spot Method" described in a paper by R. S. Dill

and entitled "A Test Method for Air Filters " (ASHVE Transactions, Vol . 44, p. 379 , 1938).

For test purposes, the collector cell was installed in

the test apparatus and carefully sealed to prevent inward

leakage of air 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 two feet upstream and eight feet downstream of the

test specimen at equal rates and passed through known areas

of Whatman No. 4l filter paper. The change of the opacity

of these areas was determined with a sensitive photometer

which measured the light transmission of the same spot on

each sampling paper before and after the test. The two

sampling papers used for each test were selected to have

the same light transmission readings when clean.

For determining the arrestance of the filter, with Cottrell precipitate as the test dust, different size areas of

sampling papers were used upstream and downstream of the

filter in order to obtain a similar increase of opacity on

both sampling papers.

For each arrestance determination with Cottrell precipitate, the upstream sample of the aerosol was collected on one

filter paper for about half of the test period and on a second

filter paper during the remainder of the test period. The

downstream sampling paper collected the dust for the entire

test. This method was used to avoid too large differences

in the dust spots when determining Cottrell precipitate arrestance values on the order of 99 percent. The arrestance,

A (in percent), was then calculated by the formula:

3 . Test Method and Procedure

-3-

where Sp and Sp are the upstream and downstream sampling areas

and AUq, AU2 , and AD the observed changes in the opacity of the

two upstream and one downstream sampling papers,, respectively.

For determining the arrestance of the particulate matter

in the laboratory air, equal sampling areas were used for the

upstream and downstream samplers. A similar increase of the

opacity of the upstream and downstream filter papers was

obtained by passing the sampling air through the upstream

paper only part of the time while operating the downstream

sampler continuously. This was accomplished by installing

one solenoid valve in the upstream sampling line and another

one as a by-pass for the sampler and first solenoid valve.

The valves were operated by an electric timer and a relay

so that one was open while the other one was closed during

any desired percentage of the 5-mi nute timer cycle., reversing

the position of the two valves during the remainder of the

cycle. The arrestance, A (in percent), was then determined

with the following formula:

A = 100 - T x AD

AU

where T is the percentage of time during which air was drawn

through the upstream sampler, AU and AD being the changes of

opacity of the sampling papers, as previously indicated.

After installing the device, the power pack was connected to the laboratory electric supply line and suitable

transformer taps were selected. A measurement of the static

voltages with a line voltage of 117 volts showed 13.8 KV

ionizer voltage and 4.3 KV plate voltage. By means of a variable voltage transformer, the line voltage was adjusted,

during subsequent readings of the static voltage, to 117 ±

1/4 volts, but was allowed to drift during the test runs.

Six arrestance determinations were made immediately

after installation with air flow rates in a range from 1312

to 2300 cfm. Thereafter, several arrestance measurements

were made with Cottrell precipitate. A total of 16 arrestance measurements were made during the loading period

while 1119 grams of dust and lint were introduced into the

system. The loading of the test specimen was concluded

when 2/3 gram of dust had been introduced for each cfm

rated air flow (1094 grams).
*
-4-

4. Test Results

A Summary of the test results is presented in Table 1

which shows the air flow rates,, dust load, pressure drop,

and arrestance values observed with the particulate matter

in the laboratory air as well as for Cottrell precipitate

as the aerosol. The effect of the dust load on the pressure drop and on the arrestance of the particulate matter

in the laboratory air are plotted in Fig. 1. The effect

of the air flow rate on the arrestance of the device with

clean plates is shown in Fig. 2. The curves in these two

graphs are drawn as smooth curves approximating the lines

of least mean square distances.

Table 1

Performance of

American Air Filter Co. Electro-Cell 2-24

Air Flow Rate Dust Load Pressure Drop Arrestance Aerosol

cfm grams in. W. G. ~ir **

1312 0 0.181

98.2*

A

1640 0 0 . 266 95.9* A

1968 0 0.288 93.1 A

2300 0 0.378 88.5 A

1640 10 0.275 98.9 C

1640 228 0.300 99- -4 C

1640 477 0.332 99.3 c 1640 477 0.332 95.1 A

1640 684 0.367 94.4 A

1640 705 0.375 99.1 C

1640 892 0.419 93.1 A

1640 953 0.434 99-3 C

1640 1099 0.478 92.0 A

1640 1119 0.480 99.1 C

* Average of two tests.

** A - Particulate matter in laboratory air.

C - Cottrell precipitate in laboratory air.
.

.
-5-

At the rated flow rate of 1640 cfm, the pressure drop

Increased from an initial value of 0.266 in. W.G. to a final

value of 0.480 in. W.G. after a dust load of 1119 grams had

been introduced into the system. During this time., the arrestance of atmospheric dust decreased from 95.9 percent to

92.0 percent. The arrestance of Cottrell precipitate has

not been plotted but was determined in six test runs to be

in the range from 98.9 to 99.5 percents averaging 99-2

percent

.

The relation of arrestance of the particulate matter

in the laboratory air to air flow rate for the clean unit

is plotted in Fig. 2 and shows a decrease from 98.2 percent

at 1312 cfm air flow to 88.5 percent at 2300 cfm air flow

rate

.

An examination of the collector cell after the conclusion of the test showed that all plates were evenly

covered with a light layer of dust. The number of electrical discharges observed did not exceed 18 per minute

and was considerably less during most of the performance

test

.

USCOMM-NBS-DC

IRICAN AIR FILTER COMPANY ELECTRO-CELL 2-24

LUST load, grams

AMERICAN AIR FILTER COMPANY ELECTRO-CELL 2-24

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

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» Office of Weights and Measures.

Boulder, Colorado

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