NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1003-20-4707

NBS REPORT

January 29, 1953 2228

PROGRESS REPORT OH

WATER-VAPOR TRM3IESSI® IN REFRIGEIRATEI) WAREHOUSES

October 1 to December 31, 1952

by

P. J. Bovliteb, Jr,

Beating and Air Conditioning Section

for

Office of The Quartoxvaster General

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, orrepiod

from the Office of the Director, Natio which a report has been specifically Standards and Technology (NIST)

on October 9, 2015.

tro^reon report

KATL-fi-VAPOR TKAKSMISSIOS IS JftFaiGEBATE© VAKKHGtfGEB

October 1 to December 31? 1952

Construction of the apparatus for the measurement of water-vapor

transmission through warehouse panels was continued*

Several ttossle shapes were investigated to determine the shape for

ffipl ”4.nj\ air flow through a rubber bose frost the worm aide heater duct to

the humidifier hanging from the rotatable cantilever weighing device.

A suitable noasle was constiucted and installed. (Gee sJeeteb of previous

Progress Report Mo. 1995*}

Two units of Twindov windows were installed in the warm side of

the apparatus and in the desiceant box to facilitate reading of the dial

gages on the cantilever scale.

flexible hose© connecting the cold chamber and the desiccant oox

were insulated, vapor-proofed, ant installed » k glower was installed to

circulate air from the cold box to the desiccant box, Preliminary air

flow measurements were made and the heat gain to the desiccant box was

estimated, Calculations indicated that the temperature rise in the

desiccant box was too large so an auxiliary cooling coll was installed

in the box and connected to the present refrigeration system.

A solenoid-operated hose clamp was designed, constructed and

installed. 111® hose clamp controls the flow of air to the humidifier.

Calibrations for a new potentiometer, standard cell, watthour tauter

and the copper-constantan tnemocouple wire were obtained. Tables of

eaf versus temperature in steps of 0.1 degree F for a range of ~4o degress

F to 133 degrees F were calculated, based on the calibration of the wire.
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The uniformity of tbs wire was cheeked by treasuring the emf of three

thermocouples made from samples of wire taken froc the ends and the

middle of a 5-pound roU , The thermocouples checked each other at steam

and ice temperatures indicating good uniformity of the wire.

The results of water vapor permeance determinations on the polyethylene films used in the construction of the apparatus were received

and are as follows:

1. 0.002 in. thickness - 0.23 perms*

2. 0.004 In. thickness - 0.08 perms

* Perm * on© grain per square foot per hour per inch of Eg.

A meeting was held of Section personnel and a representative of the

Office of The Quartermaster General. The scope, conditions of test and

the type of test panels to be measured were discussed. Some preliminary

designs of test panels were, developed.

A visit was jsade to American Instrument Goctpany, Silver Spring, M&.

to examine hueddity-msasuring equipment and wiring sis^dlar to those on

order for the apparatus . The existing devices and proposed devices for

measuring humidity inside of building sections were discussed.

A short- talk was given on the construction and proposed operation

of the apparatus for the measurement of water vapor transmission to

representatives of the office of The -ruartermster General and the

University of Minnesota

.

A control board for the apparatus was designed and partly constructed.

Thenaooouples and. reference junctions for sixty-six temperature measurements were installed in the apparatus and on the control board.

The design of the apparatus is complete and the construc tion phase

of the apparatus is 90% complete. Some delay was experienced la the
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one instrument ms on hand arid that instrument has been promised in a

week,. Completion of the ©obstruction and the ©tart of the calibration

of the apparatus is expected to begin in February

,

At the request of i-ir * Feilxer of the Office of The -.'ajartenaaster

General detailed drawings of the rotatable cantilever weighing device

' were prepared end are being transmitted with this report. *£he

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, Pi3

a * m

where 4 «= deflection, inches

JP * load, pounds

L » length of beam, inches

1 m modulus of elasticity (approx. 19 X 10° psi)

k

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Since the deflection is linearly preportional to the load, provide* the

maxima® stress in the bar does not exceed, the elastic limit, intermediate

loads and deflections can be calculated by Interpolation if the

deflections under two known loads are determined, .;aeh of the bars used

for the we&sfriag device is dimensioned m that its deflection under

maximum load, is about inch, k dial gage with 0*0001 inch graduations is used to divide this deflection range into approjdraateiy XA

parts, so that loads on the bar can be measured with an accuracy of

about l/toO of toe difference between the maximum and mUxLmm loads

placed on the bar. A dial g&ge was selected for this purpose, instead

of an electrical strain gage or similar device because Its deflection
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indications are not subject to change with time. A suitable gage,

Model &-21, ms purchased from Federal Products Corporation, Hfeh Eddy

Street, Providence 1, R. I.

Beryllium copper was chosen for the cantilever because of Its

properties of high proportional elastic limit (70-80,000 psi), snail

hysteresis, and a comparatively straight etrass-strsdLa cur.'e . The

beryllium copper bars {BttCtWO 23) were purchased from, the Beryllium

Corporation, Beading, Be., and were heat treated one hour at 660 degrees

f upon the advice of Mr. J. T. Richards, Development Engineer, for the

Beryllium Corporation.

To assure that the maximum stress in each bar would not exceed half

of the elastic limit of the metal, to provide a safety factor of two or

sore, under the taaxiisuia design load, the stress was computed by means of

the formula

s * m/i

whore a m Bending stress, psi

U * Bonding Moment, in-lb

C * Distance from the neutral axis, inches

k

X * Moment of Inertia, in

The two weiring devices were assembled and the performance of two

of the cantilever bars wider load ms investigated. It ms found during

experimental measurements that the load, deflection curves of the assembled

devices closely approximated straight lines over the working load range,

but that a slight vibration of the system was necessary to assure

reproducibility of dial gage readings by overcoming Its frictional
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resistance. k doorbell feassor ms attached to tea gage-supporting

arta of each of the cantilevers to overcome frictional realstance

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It ms found necessary to devise a poategraph arrangement to relieve

tension in the hose between tee cantilever load and the fixed end of

the hose connecting it. In me, the load deflection characteristics

of each beast will he dot©reined in place by msmurm&ntG with known

loads Just before and after each test

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