NATIONAL BUREAU OF STANDARDS REPORT

4132

THERMAL CONDUCTIVITY OP A SPECIMEN OF STAINLESS STEEL

TYPE 302

by

Lloyd E, Richards

Henry E. Robinson

Report to

Naval Ordnance Laboratory

White Oak, Silver Spring, Maryland

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NBS REPORT

IOOO-3O-I483O June 7, 1955 4132

THERMAL CONDUCTIVITY OF A SPECIMEN OF STAINLESS STEEL

TYPE 302

by

Lloyd E. Richards

Henry E. Robinson

Heating and Air Conditioning Section

Building Technology Division

to

Naval Ordnance Laboratory

White Oak, Silver Spring, Maryland

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprli

unless permission Tsob

25, D, C. Such permls

cal ly prepared if that

. , , , , , ,1 oart, Is prohibited Approved for public release by the 1 v r

. . lards, Washington Director of the National Institute of

thasbeenspeclfi . Standards and Technology (NIST) r , for lts own use , on October 9, 201 5.

THERMAL CONDUCTIVITY OF A SPECIMEN OF STAINLESS STEEL

TYPE 302

I INTRODUCTION

A specimen, designated as Stainless Steel Type 302, was

submitted by the Naval Ordnance Laboratory of White Oak,

Silver Spring, Maryland for measurements of thermal conductivity. The measurements were authorized by I.P.R.jNOrd

03059, appropriations 17x1319 . 52 R&D, Navy.

II PREPARATION OF THE SPECIMEN

The general arrangement of the test apparatus is shown

in Figure 1.

The lower end of the specimen was heated by an electrical heating element inserted in the lower well of the specimen; the upper end cooled by water circulated through the

upper well during the high temperature runs and by acetone

during the low temperature runs.

The heating element, having about 50 ohms resistance,

was made by passing nichrome wire through a multiple-hole

porcelain cylinder l/2 inch in diameter. Thermocouples

( chrome1 -alumel for the high temperature runs, and copperconstantan for the low temperature runs) were attached at

intervals of about I4 cm along the length of the bar by

peening the junctions Into one-millimeter radial holes

about 2 mm deep in the side of the specimen. An additional

thermocouple was attached to the lower end of the specimen.

The specimen was supported on a thin nichrome pin located

in the bottom of a thick-walled stainless steel guard cylinder. The guard cylinder was also equipped with a heating

element and cooling coil and with thermocouples at appropriate positions.

The specimen-guard assembly was suspended in a large

sheet-metal container and the entire system Insulated with

a fine granular insulation of known thermal conductivity

characteristics

.

Ill TEST METHOD

Electrical energy from a d.c. source was supplied

to the heater elements and adjusted so that a minimum temperature difference between bar and guard existed at the

thermocouples just above the heaters.

- 2 - Cooling water at a constant temperature of about I4O C

was pumped through the well in the specimen and through the

coil on the guard. Acetone cooled with dry ice was used

for the low temperature runs. When steady temperature conditions had. been attained, the emf's of the thermocouples

and the current through and voltage drop across the bar

heater were measured by means of standard resistors and a precision potentiometer. Temperature conditions were considered satisfactorily steady when no thermocouple on the

bar changed temperature at a rate greater* than 0.5 degree

C per hour; several readings taken over a period of several

hours after steady conditions were attained were averaged

for each test.

To calculate the thermal conduct! vity, the observed

temperatures of the bar and guard were plotted versus position along the bar as abscissae and smooth curves were

drawn through the points. Corrections to the measured heat

input to the bar to account for heat interchange between

the bar and guard were made on the basis of the temperature

differences between them determined from the curves and

using the thermal conductance of the granular insulation

at the appropriate mean temperature. The corrections were

made for the heat interchange (a) between the lower end

of the bar and the guard s (b) between the bar and guard at

the heater region and (c) between bar and guard for each

thermocouple span. The average rate of heat flow between

any two adjacent thermocouples on the bar was thus computed

and used, together with the measured distance and temperature

difference between them and the cross-sectional area of the

specimen, to calculate the average thermal conductivity for

that span.

The maximum difference for any thermocouple span between

the computed heat flow in the span and the measured electrical input to the heater ranged from -2.0 to +ll|*5 percent of

the input, in the various tests. It is believed that since

the calculated values of heat interchange could be evaluated

with an uncertainty of not more than 20 percent, the uncertainty in the rates of heat flow used in computing the

thermal conductivities was of the order of not more than two

percent.

Foi'* each of the separate tests the thermal conductivity

was computed for each of the six thermocouple spans on the

bar, corresponding to the mean temperature existing in each

span.
, .
- 3

-

IV TEST RESULTS

The values of thermal conductivity obtained for each

test span were plotted against their corresponding mean

temperature, as shown in Figure 2, and are represented by

a curved line faired through the plotted values.

Table 1 lists thermal conductivity values for various

mean temperatures, as taken from the curve.

V DISCUSSION OF RESULTS

The plotted points show some scatter from the curve.

Such scatter is an inverse measure of the precision of the

measurements, as affected by such factors as small random

inaccuracies in determining the thermocouple locations on

the bar, slight heat conduction along the thermocouple

wires near the hot junctions, and possible slight inhomogeneities in the thermocouple wires. To minimize heat

conduction effects, the thermocouple wires were led away

from the hot junctions and wrapped around the bar for a few

centimeters in the plane of its cross section, in which the

temperature should be fairly uniform. However, since the

temperature gradients along the bar ranged from 3.5 to 33

degrees C per centimeter in the several tests, some conduction effect on individual thermocouple readings probably

could not be avoided.

Since the factors involved in inaccuracies in measurements of thermocouple positions and temperatures were random

in nature, their effect was probably to decrease the precision of the values obtained for each span rather than to

affect the overall results in any one direction.

The curve representing the conductivity of the specimen shows an increasing slope as the mean temperature decreases. This is in accordance with the conductivity data

shown for several stainless steels (not including Type 302)

in Figure 23, page i|3, of National Bureau of Standards Circular 556, ’’Thermal Conductivity of Metals and Alloys at

Low Temperatures”, which gives data for temperatures up to

27°C. The curve obtained for the Type 302 stainless steel

falls intermediately, in regard to both magnitude and

slope, between the curves for Types 30I4 , 316 and 3k7 in the

above reference, in the temperature range common to both

sets of data. This fact provides reasonable justification

for extrapolating

lower than -100°C

curves of C$$6 as

tures lower than

the curve for Type $02 to

by running it family-wise

a guide* if conductivities

100°C are desired for this

temperatures

wi th the

at temperametal sample

TABLE 1

Stainless Steel Type 302

Mean Temperature

(C)

Thermal Conductivity

(Watts cm^C"1

) -100 0.114

0 .130

100 0159

200 0177

300 .192

too .207

500 .222

600 .236

700 .251

53.0

CENTIMETERS

0 10 15 20

CIRCULATING

COOLANT

o

ro

i in

in

t

-

]

in

m

i

0 ~--

c:t o:

z

RUBBER STOPPER

VA

u

.35

1.35

8.2

:d

-22.0

10. 2—

OUTER

CONTAINER

GUARD CYLINDER

SPECIMEN (2-2.5 CM.

DIA.)

INSULATION

BAR HEATER

GUARD HEATER

- SUPPORT CAP

SUPPORT PIN

NOTES

I. Dimensions in Centimeters.

2 x Indicates thermocouple positions.

APPARATUS FOR MEASURING THE THERMAL

CONDUCTIVITY OF METALS

NBS

Fig. 1

0 t -lNO S11VM - AllAllOnQNOO “IVWdBHl

IOO

200

300

400

500

600

700

TEMPERATUREC

Fig.

2

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

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publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.
j