NATIONAL BUREAU OF STANDARDS REPORT

8001

PERFORMANCE CHARACTERISTICS OF FOUR MODELS OF

"DRI-PAK" DEEP-BED AIR FILTERS

manufactured by

American Air Filter Company

Louisville,, Kentucky

by

Carl W. Coblentz and Raul R. Achenbach

to

General Services Administration

Public Buildings Service

Washington 25 * D.C.

<NB§>

U. S. DEPARTMENT OF COMMERCE

NATIONAL RUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARD

Functions and Activities

The functions of t lie National Bureau of Standards are set forth in the Act of Congress,

March 3, 1901, as amended by Congress in Public Law 019, 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; invention and development of devices to serve special needs

of the Government; and the development of standard practices, codes, and specifications. Tin 1 work includes basic and applied research, development, engineering, instrumentation, testing,

evaluation, calibration services, and various consultation and information services. Research

projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s unique competence is required

The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's research are published either in the Bureau’s own series of publications or in the journals of professional and scientific societies. The Bureau publishes

three periodicals available from the Government Printing Office: The Journal of Research,

published in four separate sections, presents complete s< ientifio and technical papers; the Technical News Bulletin presents summary and preliminary reports on work in progress; and the

Central Radio Propagation Laboratory Ionospheric Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also

five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks,

Miscellaneous Publications, and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular 460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25),

and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957

($1.50), and Miscellaneous Publication 240, July 1957 to June 1960 (includes Titles of Papers

Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-30-10630 June 11, 1963 8001

PERFORMANCE CHARACTERISTICS OF FOUR MODELS OF

"DRI-PAK" DEEP-BED AIR FILTERS

manufactured by

American Air Filter Company

Louisville, Kentucky

by

Carl W. Coblentz and Paul R. Achenbach

Mechanical Systems Section

Building Research Division

Report to

General Services Administration

Public Buildings Service

Washington 25., D.C.

NATIONAL BUREAU OF

for use within the Governme

and review. For this reason, whole or in part, is not au Bureau of Standards, Wash

the Report has been specific

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

;ress accounting documents intended

is subjected to additional evaluation

ire listing of this Report, either in the Office of the Director, National by the Government agency for which

I copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE CHARACTERISTICS OF FOUR MODELS OF

THE "DRI-PAK" DEEP-BED AIR FILTERS

manufactured by

American Air Filter Company

Louisville,, Kentucky

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

four deep-bed dry media air filters, type Dri-Pak Models

1060, 2060, 2090, and 2100 manufactured by the American

Air Filter Company, Louisville, Kentucky were determined.

The scope of this examination included the determination

of the arrestance of the particulate matter In the

laboratory air and measurement of the pressure drop at

different dust loads when the filters under test were

operated at their rated air flow rate.

2 . Description of Test Specimen

The test specimens were supplied by the American Air Filter

Company of Louisville, Kentucky and were stock samples of

their Dri-Pak series 1000 and 2000 filters, i.e., designed

for nominal air flow rates 1000 cfm and 2000 cfm,

respectively. The approximate arrestance of the various

media used in these filters, when tested by the NBS

Dust Spot Method, using the particulate matter in the

laboratory air as the aerosol, was indicated by the three

digits following the initial series number as a percent,

060, 090, and 100.

All specimens had identical steel face plates 24 in. square

with 36 stamped square holes, symmetrically arranged. The

sides and corners of these holes were well rounded for reducing the entrance air turbulence and to provide rigidity

to the plate. The holes were arranged in six rows with a

- 2 -

bag of filter media bonded to the downstream side along each

row of holes. In order to avoid direct contact of adjacent

bags, when they were inflated by the air pressure, the bags

were stapled so that it appeared as if there was a pocket

of media extending downstream from each inlet hole and the

pockets of each row were connected. The media consisted

of fiber glass mats about 1/4 in. thick and supported on

the downstream side by a flexible mesh. A microscopic

examination of the different media indicated that the glass

fibers in the model 1060 and 2060 media were about 5 microns

in diameter, whereas the fibers of the model 2090 and 2100

media were less than 3 microns in diameter. The useful

media area was approximately 90 sq. ft. for the 2000 series

specimens and 45 sq. ft. for the 1000 cfm filters,

indicating a net media velocity of about 22 ft/min.

The test specimens were furnished folded and occupied a space of about 24 x 24x 4 in. The weights of the test

specimens were as follows:

A holding frame made of sheet steel was provided with

rubber seals and steel springs to hold the face plate as

well as a panel type pre-filter, if such was to be used.

The assembly of filter banks is accomplished by riveting

together these holding frames. Some 2-inch Amer-Glass

throw-away type panel filters were also furnished by the

manufacturer in order to determine the effect of prefilters on the dust holding capacity of these deep-bed

filters

.

Model 1060

Model 2060

Model 2090

Model 2100

2240 grams (5 lbs.)

2750 grams (6 lbs. 1 oz.

2550 grams (5 lbs. 9 oz.

2420 grams (5 lbs. 5 oz.

-3-

3 . Test Method and Procedure

The arrestance determinations were made with the NBS Dust

Spot Method as described in a paper by R. S. Dill entitled

"A Test Method for Air Filters" (ASHVE Transactions,, Vol.

44, p. 379j 1938). The filter under test was installed

in the air filter test apparatus and carefully sealed to

prevent bypass of air or inward leakage into the test

apparatus except through the measuring orifice. After

establishing the correct air flow rate through the filter,

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. Arrestance determinations were made with the particulate matter in the

laboratory air as the aerosol and also with Cottrell

precipitate injected into the air stream at a ratio of 1

gram per 1,000 cu. ft. of air.

The light transmission of the sampling papers was measured

on the same area of each paper before and after the test

and the two sampling papers used for any one arrestance

determination were selected to have the same light transmission when clean.

For determining the arrestance of the particulate matter

in the laboratory air, equal sampling areas were used in

the upstream and downstream samplers. A similar increase

of the opacity of the two sampling papers was obtained by

passing the sampling air only part of the time through the

upstream paper while operating the downstream sampler

continuously. This was accomplished by installing one

solenoid valve in the upstream sampling line and another

one in a line bypassing the sampler. The solenoid 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-minute 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 formula:

AD

A = 100 - T x

- 4-

where T is the percentage of time during which air was

drawn through the upstream sampler, and AU and aD are the

observed changes in the opacity of the upstream and downstream sampling paper, respectively.

For determining the arrestance of the filter with Cottrell

precipitate as the test dust, different size areas of

sampling paper were used upstream and downstream of the

filter in order to obtain a similar increase of opacity on

both sampling papers. The arrestance was then calculated

by the formula:

A = (1 - ^2 x —) x 100

Su AU

7

where the symbols A, AU, and AD are the same as indicated

above and Sp and Sp are the upstream and downstream

sampling areas. Only a few arrestance determinations were

made using Cottrell precipitate. These arrestance determinations were made with Cottrell precipitate only, while

cotton linters were added during the loading process in a ratio of 4 parts to every 96 parts Cottrell precipitate,

including that amount of Cottrell precipitate used for

arrestance measurements. The lint used had been

previously prepared by grinding No. 7 cotton linters

through a Wiley mill with a 4-millimeter screen while the

Cottrell precipitate had been sifted through a 100-mesh

screen, eliminating all particles larger than about 150

micron size.

The pressure drop across each filter was recorded at the

beginning and at the end of the test, after each arrestance

determination, and after every 20-gram increment of

Cottrell precipitate that was introduced into the test

apparatus to load the filter. The models 1060 and 2060

were loaded until the pressure drop had increased 0.5 in.

W.G. above that of the clean filters, whereas the models

2090 and 2100 were loaded until the final pressure drop

reached 1 in. W.G. One model 1060 specimen was operated

without pre-filter and a second specimen was tested with

three Amer-Glass pre-filters, successively.

-5-

Some arrestance determinations were made with Cottrell

precipitate as the aerosol on models 2060 and 2090. Since

these values approached 100 percent, they were not considered

significant for this series of filters, therefore, all

arrestance determinations on the two other models were

made with the particulate matter in the laboratory air, only.

4. Test Results

All test specimens were furnished folded to the downstream

side of the face plate, held together by a strip of paper.

When a filter was introduced in the holding frame the paper

strip was cut and the filter media unfolded due to the

air pressure. No damage to any of the test specimens was

noticed during the installation, however, a number of

pockets in the bags of each filter did not open up

immediately, causing an increased air flow through those

pockets which had opened up. It was then necessary to

cover the inlet of a large number of the inflated pockets

to raise the pressure drop across the remainder. This

procedure was repeated until all of the pockets were

Inflated.

The performance of the four different models was as

follows

:

A. Model 1060

The performance data of this model are shown in Table 1,

indicating that the pressure drop of the clean filter at

the rated air flow rate of 1,000 cfm was 0.200 in. W.G.

The arrestance for the particulate matter in the laboratory

air was initially 37.2 percent and it increased to 61.7

percent when the pressure drop reached 0.578 in. W.G. and the

dust load was 1413 grams. The dust load is reported as

the weight of Cottrell precipitate and lint introduced into

the test apparatus diminished by the percentage of fallout

upstream of the filter. The fallout was determined at the

conclusion of the test by sweeping out the test duct

upstream of the filter and calculating the ratio of fallout

to the dust introduced into the system.
- - i
- 6 -

The data in Table 1 are shown graphically in Figure 1

where the arrestance and pressure drop values are plotted

against the dust load and smooth lines drawn to approximate

the curves of least mean distances. The dust load

corresponding to 0.700 in. W.G. pressure drop was 1,610

grams and the average arrestance during the loading of the

filter was approximately 57 percent.

The performance of the Model 1060 filter with an Amer-Glass

prefilter is shown in Table 2. Three prefilters were loaded

during this test and the Initial pressure drop and arrestance was determined with a fourth one. About 400 grams of

Cottrell precipitate and lint was introduced for each of

the first three prefilters. This dust load increased the

combined pressure drop across prefilter and Dri-Pak about

0.45 in. W.G. for the first two prefilters and about

0.61 in. W.G. for the third prefilter as compared to the

initial pressure drop with both filters clean. It will be

noted that the arrestance of the combination with clean

prefilters was not significantly different from that determined when the Dri-Pak filter was operated without a prefilter. The arrestance of the combination increased by 6

percent to 11 percent as the prefilters loaded up. After

a dust load of 1206 grams had been added to the system,, the

pressure drop of the combination with a clean prefilter had

increased from 0.288 in. W.G. to 0.423 in. W.G. Assuming

that each prefilter had the same initial pressure drop,, the

pressure drop across the Dri-Pak deep-bed filter increased

0.135 in. W.G. during this loading period. In Figure 1 It

is shown that a dust load of about 700 grams increased the

pressure drop of the Dri-Pak filter the same amount when

operating without a prefilter.

Figure 2 indicates that the average arrestance of the two

filters in series was about 43 percent during the addition

of the 1200 grams of Cottrell precipitate and lint. The

average arrestance of the Dri-Pak filter operating by itself was about 53 percent during the addition of the first

1200 grams of the same aerosol, as shown In Figure 1.

-7-

However, the Dri-Pak filter was probably between one-third

and one-half loaded after the addition of 1200 grams of

dust when the prefilter was used. The average arrestance

of the Drl-Pak filter, operating by itself, was about 49

percent during the first third of the loading period, as

shown in Figure 1. Thus it appears that the arrestance of

the combination of the two filters might be lower than for

the Dri-Pak filter by itself during a full loading period.

It should be recognized, however, that the effect of a prefilter in a given installation would depend somewhat on

the distribution of particle size in the dust and the

amount of lint involved at that installation. The results

described above are related specifically to the performance

with Cottrell precipitate and lint as the aerosol.

Table 1

Performance Characteristics of

the Dri-Pak Model 1060 without Prefilter

Pressure Drop Dust Load Arrestance

in. W.G. grams %

0.200

0.243

0.277

0.319

0.330

0.358

0.442

0.520

0.578

0.712

0

202

404

606

646

808

1009

1211

1413

1615

37.2*

49.3

53.6*

55.6*

57.5

61 . 2

* 59.5

60 . 1* 61.7*

58.7*

*Average of two tests

-8 -

Table 2

Performance Characteristics of the

Drl-Pak Model 1060 with Amer-Glass Prefilter

Pressure Drop Dust Load Arrestance,

in. W. G. grams %

Dri-Pak Prefilter

Combination Only Combination Only Combination

0.288 0 0 39-5

0.434 — 203 203 43.5

0.740 — 388 388 45.1

0.392 0.294 388 0 36.8*

0.750 0.300 797 409 44.8

0.421 0.300 797 0 39-5

0.903 0.308 1206 409 50.6

0.423 0.308 1206 0 43.1

*The Dri- Pak filter was removed from test apparatus and

the collected dust was dislocated in the pockets

.

IIIIIIIIN z I1

IIIIIIII

EL 1060


-

'• •
- 11 -

B. Model 2060

The pressure drop,, dust load,, and arrestance values determined with the Dri-Pak Model 2060 are shown in Table 3 . The initial pressure drop of this filter was 0.342 in.

W.G. and it increased to 0.594 in. W.G. when the dust load

had reached 1,666 grams, At that time it was noticed that

a number of pockets in the filter had not opened up. By

closing up the inlet openings of some of the operating

pockets temporarily, these pockets were opened up by the

force of the increased air pressure. As a result of the

increase in filter area the pressure drop decreased to 0.485

in. W.G., i.e., by 0.109 in. W.G. It can be assumed that

the Initial pressure drop of the test specimen would have

been lowered by a similar amount if all pockets had opened

up at the beginning of the test. The final dust load of

3,937 gnams at a pressure drop of 0.485 in. W.G. was based

on a 0.5 in. W.G. increase above the 0.342 in. W.G.

initial pressure drop. The final pressure drop recommended

by the manufacturer was only 0.7 in. W.G. From Figure

3* in which the arrestance and pressure drop values of

Table 3 for the Model 2060 filter have been plotted against

the dust load, it can be determined that the dust load of

this filter at 0.7 in. W.G. pressure drop was 3*100 grams.

The initial arrestance of the filter was 43.8 percent and

the average value for the entire loading period was about

.57 percent.

The upper curve of Figure 2 shows a considerable scattering

of the individual arrestance values, which was caused in

part by the dislocation of the dust in the filter pockets

that occurred every time the air flow was cut off. Also

evident in the lower curve of Figure 3 is the decrease in

pressure drop that resulted from forcing open several

pockets of the filter media which had remained closed

during the early part of the operation of this specimen.

- 12 -

Two arrestan.ee determinations made with Cottrell precipthe aerosol Indicated 97',6 percent when the

1 and 98.5 percent with a dust load of 1.458

Table 3

Performance Characteristics of

the Dri-Pak Model 2060 without Prefilter

ssure Drop Dust Load Arrestance

1. W.G. grams %

0.342 0 43.8 97.6*

0.359 208 53.7

0.388 417 59.6

0.418 625 58.9

0.455 833 55-6

0.500 1042 66.6

0.535 1250 55.5

O.56O 1458 56.4 98.5*

0.594 1666 —

0.485** 1666 54.8

O.56O 1875 58.5

0.584 2083 62.2

0.607 2291 59.2

0.634 2500 57.9

0.652 2708 57-7

0.678 2916 64.9

0.708 3125 57.2

0.729 3333 62.2

0.750 35^1 56.3

0.794 3749 56.5

0.845 3937 56 .

8

*Cottrell precipitate as the aerosol.

**Forced open closed filter pockets.

AMERICAN AIR FILTER COMPANY DRI-PAK MODEL 2060

-14-

C. Model 2090

The performance of Model 2090 Drl-Pak filter is indicated

by the values for pressure drop, dust load, and arrestance

shown in Table 4. The initial pressure drop of this

specimen was 0.268 in. W.G., its dust-holding capacity at

a final pressure of 1 . 005 in. W.G. was 2,789 grams. The

arrestance of the clean filter determined with the

particulate matter in the laboratory air was 56.5 percent; it reached 90.0 percent for the first time with a dust load of 417 grams and a maximum of 93-7 percent with

a dust load of 1937 grams. The arrestance of Cottrell

precipitate showed values of 99-1 percent and 99-5 percent during the early part of the loading period.

The dust-holding capacity of this model based on the

recommended final pressure drop of 0.8 in. W.G. was 2,500

grams and the average arrestance approximately 90 percent.

The performance data for the Model 2090 Dri-Pak filter

from Table 4 were plotted in Figure 4 and smooth curves

were drawn through the observed values.

-15-

Table 4

Performance Characteristics of

the Drl-Pak Model 2090 without Prefilter

isure Droo Dust Load Arrestance

l. W.G. grams %

0.268 0 56.5 99.1*

0.312 208 82.0

0.342 417 90.0

0.372 625 89.2 99.5*

0.398 833 85.3

0.421 1042 91.1

0.453 1250 90.6

0.471 1354 92.6

0.5H 1562 92.6

0.544 1729 93.0

0.604 1937 93.7

0.660 2145 91.3

0.740 2354 92.1

O .813 2476 92.3

l o 005 2789 90.4

Cottrell precipitate as the aerosol.

AMERICAN AIR FILTER COMPANY, DRI-PAK MODEL 2090

-17-

D. Model 2100

The first two specimens of the Dri-Pak Model 2100 were found

to have holes in the media, the cause of which could not be

determined. The manufacturer’s representatives stated that

these two specimens had not been assembled in the regular

production line and had received no quality control

inspection. The three replacement filters then furnished

by the manufacturer did not reveal any holes after being

installed into the test apparatus. Only one of these

three filters was loaded to capacity, identified as

Specimen A in Table 5. The initial pressure drops and

arrestances of the two other specimens are also presented

in Table 5.

It will be noted that the initial pressure drop of the

three specimens ranged from 0.400 In. W.G. to 0.425 in.

W.G. and the arrestance values were between 87.9 percent and

89.5 percent. These differences in the Initial performance

of deep-bed filters of this type do not seem excessive.

Specimen A had a maximum arrestance of 98.7 percent at a dust load of 4l6 grams and a pressure drop of 0.480 In. W.G.

The performance data for Specimen A, shown In Table 5, were

plotted in Figure 5 and smooth curves approaching the lines

of least mean distances were drawn. The average arrestance

of this specimen was approximately 97.5 percent and the

dust-holding capacity based on a recommended final pressure

drop of 1.0 In. W.G. was 1350 grams.

Table 5

Performance Characteristics of

the Dri-Pak Model 2100 without Prefilter

sure Drop

.. W.G.

Dust Load

grams

Arrestance

%

0.400

Specimen A

0 89.5

0.437 208 98.2

0.480 4l6 98.7

0.546 667 96.6

0.646 937 98.0

0.905 1271 97.8

1.03 1355 97.5

0.425

Specimen B

0 87.9

Specimen C

AMERICAN AIR FILTER COMPANY, DRI-PAK MODEL 2100

- 20-

Summary

Table 6 summarizes the pertinent data determined in the

tests of the four models of the Dri-Pak filter. It shows

the air flow rate, initial pressure drop., the final pressure

drop recommended for each model by the manufacturer, and

the dust load of the filters corresponding to the final

pressure drop. Also shown are the arrestance of the

particulate matter when the filters were clean and the

average arrestance values for the entire loading period.

It should be noted that the initial pressure drop of the

Model 2060 filter would have been lower than the observed

value of 0.342 in. W.G. if all of the pockets had been

opened at the time of installation of this filter.

Although the initial arrestance of the Model 2060 filter

was higher than that of Model 1060 it was found that the

average arrestance, 57 percent, was the same for both

models and the dust load for the Model 2060 at the final

pressure drop of 0.7 in. W.G. was close to double that of

the other filter which had about half as much media area.

Figure 6 shows the observed arrestance values plotted

against the pressure drop for the four filter models.

It will be noted that the increase In pressure drop from

the initial value to that at which the filters first

reached the average arrestance, shown in Table 6 , differed

considerably with the four models. This Increase in

pressure drop is shown in Table "J

which also presents the

corresponding values of the dust loads that had been

introduced Into the filters when the average arrestance was

first reached. These latter values were taken from

Figures 1, 3 , 4, and 5* respectively.

Summary

of

Performance

of

Pour

Drl-Pak

Deep-Bed

Air

Filters

- 21 -

o

o

i—

CM

O O O LPi 040LH • o • • on om>-

C\1 O rl I—I CO CF\

o

CT\ o

CM

co O VO O LT\ CM 00 h- • o • • mvo o

CM O O CM LOCT\

o

VO

o

CM

CM 0-0- o co o co t—co • O o • i—I CO t

cm o o co^r lo

o

VO

o

I—

o

O O O CM CMNO • o » • vo £— t

i—I O O i—I CO LP\

o

• CQ ^ E

cd

• 3

C bo

•H

•s *> a

• a o o o g

• U P

:s p

0

• CD U

a g 3

S *H 3 cQ

<Oi CQ CQ O * CQ CD a CD * o G a

0 G a

4-0 P i—1 0 0

eg H cd o o

a 0 cd 0 G 3

G c a 0 0

£ 3 a a a a

o w a 0 co G a cq 4-o 0 0

CD a 0 p 0 3 G P G 0 G G

S 3 a o x3 < <

3 a c 0

55 < a 0 o a 0

0 E P 0 hO a o a e a 0

o 0 a o a a g

p a a o cq a 0

o eg C 0 3 a > S a a a p a <

Pressure

Drop

Increase

and

Dust

Load

- 22 -

o OJ o o o 1—

• 1—

OJ o iH coco

o o

ov i—o

o • O CO00

OJ Oh H Ol

o =t

<D VO o o

O O • i—

i—

o

C OJ O 00 i—1 i—

cd -p

<D

PhPh <

CD

faQ O OJ

cd VO i—

o

Ph O • O 4h CD i—

O VO OJ PO ><

CD ft-p

TO

0)o

0

TOO 1—

u cd ft » -p CO O

-p • EH

03

Ph ft H • O

ft d to

•H >R. cd -P o

cd *> •'ft

ft CD (D p 03 03 rH

cd cd cd

0) CD ft

Ph Ph o

O o EH CMC H E H P

cd o

ft Ph ft

Ph O bCo

CD Ph Ph ft ft •> ft CD •> £ TO 03 TO d <D cd <D cd cd s Ph Q Ph CD Q

d ft d Ph ft H 03 03 O

CD 03 p 03 d P

ft CD 03 CD H 03 O Ph d Ph d

s ft ft Ph ft

-23-

A comparison of the data in Table 7 on the Models 1060

and 2060 air filters indicates the effect of the unopened

pockets in the latter specimen during the early part of

the test. It will be noted that the amount of dust load

required to increase the arrestance of the Model 2060

filter to the average arrestance value of 57 percent was

only half that required for the Model 1060 even though the

latter had only half as much filter area If both were

fully expanded. The Increase in pressure drop accompanying

the initial rise in arrestance to 57 percent was only

0.04 In. W.G. for the Model 2060 as compared to 0.12 in.

W.G. for the Model 1060. Since the design air velocities

through the media in both filters were equal, the failure

of some pockets to open initially In the Model 2060 filter

caused the air velocity to be higher in this filter at

the beginning of the test. This probably accounted for

some of the observed difference in Initial loading

characteristics and rate of Increase in arrestance.

AMERICAN AIR FILTER COMPANY, DRI-PAK SUMMARY

U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, 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

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. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. High Voltage. Absolute Electrical Measurements.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology. Mass and Volume.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.

Metallurgy. Engineering Metallurgy. Metal Reactions. Metal Physics. Electrolysis and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Ele- mentary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOULDER, COLO.

CRYOGENIC ENGINEERING LABORATORY

Cryogenic Processes. Cryogenic Properties of Solids. Cryogenic Technical Services. Properties of Cryogenic

Fluids. CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun- Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research. Troposphere and Space Telecommunications. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Spectrum Utilization Research. Radio-Meteorology. Lower Atmosphere

Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre- quency Utilization. Modulation Research. Antenna Research. Radiodetermination. Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Standards Physics. Frequency and Time Disseminations. Radio and Microwave Materials. Atomic Fre- quency and Time-Interval Standards. Radio Plasma. Microwave Physics.

Radio Standards Engineering. High Frequency Electrical Standards. High Frequency Calibration Services. High

Frequency Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency

Calibration Services.

Joint Institute for Laboratory Astrophysics- NBS Group (Univ. of Colo.).

USCOMN-N0S-DC