NATIONAL BUREAU OF STANDARDS REPORT

6251

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT AIR FILTERS

VORTOX TYPES VN1 AND VN2

MANUFACTURED BY

VORTOX COMPANY

CLAREMONT, CALIFORNIA

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.

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NB8 REPORT

1000-12-4801 6251

December 23 > 1958

PERFORMANCE TESTS OF TWO CLEANABLE IMPINGEMENT AIR FILTERS

VORTOX TYPES VN1 AND VN2

MANUFACTURED BY

VORTOX COMPANY

CLAREMONT, CALIFORNIA

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

{

•tended, for use. wjthln tl 0. additional evaii/etton'aii listing of this Report, eltbi the Office of Ike Director,

however, by tke GovSrnme

to reproduce additional cc

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

formally published It Is sub{ectad

g, reproduction, or open*litereture

ilcslon Is obtained In writing from Suck permission Is not needed,

iy prepared If that agency wishes

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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PERFORMANCE TESTS OF TWO CLEANABLE

IMPINGEMENT AIR FILTERS TYPE VN1 AND VN2

MANUFACTURED BY

VORTOX COMPANY

CLAREMONT, CALIFORNIA

by

Carl W. Coblentz 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 540 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

Vortox Company of Claremont, California. They were identified

as their types VN1-20-20 and VN2-20-20. The measured outside

dimensions of each filter were 19-1/2 in. square; the VN1 type

was 1 in. thick and the VN2 type was 1-13/16 in. thick. Each

had a net filter area of 18 in. square, i.e., 2.25 sq ft.

The filter media consisted of multitudinous helical coils

of about 1/4 in. diameter and 1 in. long made of thin steel

wire and placed at random between the steel frame and the face

screens. The face screens consisted of two expanded steel sheets

on the inlet or upstream side and a 16-mesh wire screen and an

expanded steel sheet on the outlet or downstream side. The openings of the expanded steel sheets were diamond shaped.
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The manufacturer also submitted his ’’Panel Filter Adhesive

9974 " which was used for oiling the filter before each test.

3 . Test Method and Procedure

The performance of the filters was determined at 360

ft/mi n 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 veloctiy 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.

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4. Test Results

The data on pressure drop and arrestance observed during

the tests for different dust loads are summarized in Tables 1

to 4 inclusive.

Table 1

Performance of Vortox Filter VNl(l in. thick)

at 360 ft/min Face Velocity

Load Pressure Drop Arrestanc<

g/sq ft in. W,3 Go —%— 0 0.055 50*

46 o 0 095 51*

117 0, 182 55*

157 0.335 59*

181 0.405 60* 199 0.480 63

204 0.515

* Average of 2 tests

Table 2

Performance of Vortox Filter VNl(l in 0 thick)

at 540 ft/min Face Velocity

Load Pressure Drop Arrestanc

g/sq ft in 0 W.Go

0 Oo 125 56*

49 0.184 57*

121 0.325 59*

139 0.395 62* 166 o„ 470 62* 202 0.615 64*

229 0„805 66

* Average of 2 tests
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Table 3

Performance of Vortox Filter VN2(l-13/l6 in 0 thick)

at 360 ft/min Face Velocity

Load

g/sq ft

0

46

114

156

190

223

241

Pressure Drop —rri". W7CF.

0.070

0.102

0.165

0.232

0.315

0.445

0.505

Arrestance

fo

52*

53*

55*

60

62

66

70

* Average of 2 tests

Table 4

Performance of Vortox Filter VN2( 1-13/16 in. thick)

at 540 ft/min Face Velocity

Load

g/sq ft

0

49

85

166

202

238

262

Pressure Drop " "TnT Y7S~

0.170

0,243

0,301

0,475

0.610

0,745

0,850

Arrestance

%

64*

70

76*

78

77

75

* Average of 2 tests

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The preceding tables show the arrestance values and the

pressure drop as a function of the dust load per square foot

net filter area at face velocities of 360 ft/min and 5^-0 ft/

min.

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

of lint and dust introduced into the test apparatus minus the

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

the net face area of the filters.

Pig 1 and 2 present these same values graphically using

smooth curves to approximately fit the individual points of

observation.

The arrestance increased generally with increasing dust

loads, but the rate of increase varied among the two filters

and also with the face velocity. The change in arrestance

while loading the specimens ranged from 10 to 18 percent.

However, at 5^0 ft/min face velocity, the 1-13/16 in. thick

filter VN2, showed a rise in arrestance from 68 to 78 percent

at 2/3 of its load and, then a drop of 75 percent by the time

the filter was loaded to its maximum pressure drop.

The dust loads indicated by these graphs 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 are shown in Table 5 as ’’Dust

Holding Capacity” o Also shown in this table are the mean

arrestance values for each filter and each face velocity during

the period in which the capacity dust load was being deposited.

It will be noted that the dust holding capacity of the 1-13/16

in, thick filter is about 20 percent higher than for the 1-inch

thick filter at 360 ft/min face velocity and only 10/ higher

at the 540 ft/min face velocity whereas the mean arrestance was

only 3 $ higher at the low velocity but 13$ higher at the high

velocity operation for the thicker filter.
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Table 5

Dust Holding Capacity and Mean Arrestance

(Determined from Fig 1 and 2)

Filter Type

Face Velocity,

ft/min 360

Final Pressure Drop,

in„ W. Go 0.5

Dust Holding Capacity,

g/sq ft 202

Mean Arrestance,

$ 56

VNl VN2

540 360 540

CO 0 • 0.5 0.8

227 240 250

61 59 74

The weights of the oiled and drained filters and also the

values of the pressure drop for both face velocities are shown

in Table 6 for the new filters and after each cleaning cycle 0 This table indicates that the VNl type retained about 40 g of

the dirt collected in the first loading test without further

accumulation of dirt when it was cleaned the second time. The

type VN2(2 in. thick), however, increased its weight by almost

500 g after three loading operations with an increase in pressure

drop of approximately 250$. The dust holding capacity during

the third test, which is not reported here in detail, showed

that the dust holding capacity was only about one half of that

during the second run, both being run at the same face velocity,,

The cleaning of these filters had been performed with a stream

of water at a temperature of about 150 F and was continued

until the waste appeared clean.
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Filter Type and Condition

VN1

New

After 1 loading and cleaning

After 2 loadings and cleanings

VN2

New

After 1 loading and cleaning

After 2 loadings and cleanings

After 3 loadings and cleanings

in. W.G.

340 ft/min

3032 0.055 0.116

3070 0.062 0,125

3072 0 0 06 0 0.125

3990 0,070 0,150

4080 0,080 0.170

4375 0.150 0.305

4486 0,180 0,372

Table 6

Cleanability of Filters

Weight

of Filter Pressure Drop

grams 360 ft/mln

VORTOX FILTER VNI

DUST LOAD , GRAMS PER SQUARE FOOT

VORTOX FILTER V N 2

DUST LOAD GRAMS PER SQUARE FOOT

U. S. DEPARTMENT OF COMMERCE

Lewis L. Strauss, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL KHREAIJ OE STANDARDS

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