/ o,u -r

NATIONAL BUREAU OF STANDARDS REPORT

4751

Thermal Conductivity of a Specimen of Stainless Steel

Type 430

by

Lloyd E, Richards

Henry E. Robinson

Report to

U. S. Atomic Energy Commission

Haitford Operations Office

Richland, Washington

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
u. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

[NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C.. and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the di\ isions 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 reports and publications, appears on the inside back cover of

this report.

WASHINGTON, D. C.

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BOl LDER, COLORADO

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(fas Liquefaction.

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Extreme High frequency and Noise. Microyyave Frequency and Spectroscopy. Microwave

( arcuit Standards.
NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NBS REPORT

1000 “3 ^”U ^30 July 5 ? I953 I4 751

Thermal Conductivity of a Specimen of Stainless Steel

Type I43O

by

Lloyd E. Richards

Henry E. Robinson

Heating and Air Conditioning Section

Building Technology Division

to

U 0 S. Atomic Energy Commission

Hanford Operations Office

Richland,, Washington

<n9s>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re

unless permission I

25, D. C. Such pei

cal ly prepared if I

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

in part, is prohibited

tandards, Washington

sport has been specifieport for its own use,

I

THERMAL CONDUCTIVITY OP A SPECIMEN OP STAINLESS STEEL

TYPE I43 O

by

Lloyd E. Richards and Henry E. Robinson

I. INTRODUCTION

A specimen, designated as Stainless Steel Type I43 O

,

was submitted by the Atomic Energy Commission, Hanford

Operations Office, Richland, Washington for measurements

of thermal conductivity. The measurements were authorized by order number HA-56- 2723 , requisition number

G-272-667, appropriation and allotment number 899/60101*91

23 -61-91 “Ode

lie 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, and the upper end was cooled by water

circulated through the upper well. The heating element,

having about 53 ohms resistance, was made by passing

ni chrome wire through multiple-hole porcelain tubing.

Chromel-alumel thermocouples were attached at intervals of about I4 cm along the length of the bar by

peening the junctions into one millimeter holes about

2 millimeters deep in the side of the specimen. An

additional thermocouple was attached to the lower end

of tlie 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

-zequipped with a heater 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 was

insulated with a fine granular insulation of known

thermal conductivity characteristics.

III. TEST METHOD

Electrical energy from a constant 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. Cooling water at constant temperature was

pumped through the upper well in the specimen and

through the coil on the guard. When steady temperature conditions had been attained, the emf 1 s of the

thermocouples and the current through and the 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 0.3 degrees C per hour;

several readings taken over a period of three or more

hours after steady conditions were attained were

averaged for each test.

To calculate the thermal conductivity, 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 as

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, (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 thermocouples on the bar

was thus computed and used, together with, the measured
0
-

3

"

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

1 to II4 percent of the input, in the various tests.

It is believed that since the calculated values of

heat interchange could be evaluated with anuncertainty of not more than 20 percent, the uncertainties

in the rates of heat flow used in computing the thermal conductivities were of the order of not more

than 3 percent.

For each of the separate tests, the thermal

conductivity was computed for each of the six I4 cm

thermocouple spans on the bar, corresponding to tne

mean temperature existing in each span.

The precision of the measurements is 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

lei away from the hot junction 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 9 to 2^ 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 of

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.

IV. TEST RESULTS

The values of thermal conductivity obtained for

each test span were plotted against their corresponding

mean temperatures.

The results of the individual measurements are

shown in Figure 2, and are represented by a straight

line determined from the data by the method of least

squares

„

Table I lists thermal conductivity values for

various mean temperatures, as taken from the least

square straight line.

V. DISCUSSION OF RESULTS

Considerable scatter of the results was experienced with this specimen, as shown in Figure 2,

the departures being rather greater than have generally

been found in measurements of other types of stainless

steel. In view of the scatter observed in the earlier

test results, new thermocouples were substituted for

those originally used on the specimen, and a few tests

were made, with substantially the same results and

scatter. Finally, the bar was turned end for end in

the apparatus, and retested. The corresponding e results

are shown in Figure 2 by points plotted as open circles,

solid circles, and triangles, respectively.

It does not seem possible to account for the low

temperature scatter on the basis of a systematic error

in the measurements. The data show that the scatter

resulted from irregularities in the temperature gradient

along the specimen. For this reason a new set of

thermocouples was installed, and the specimen was also

tested in a reversed position, but the irregularities

persisted. The possibility remains of a heat treatment

effect on the. metal of the specimen, but it is difficult to conceive of a low temperature effect of this

sort from what is known of the general composition of

this stainless steel.

TABLE I

Stainless Steel Type J43O

Mean Temperature

C°c)

0

100

200

300

I400

500

600

Thermal Conductivity

(Watts cm'-1- C” 1

)

0.22:0

0 .230

0.232

0.235

0.237

0.239

0.2,4a

700 0 o 2I4I4

53.0

CENTIMETERS

0 5 10 15 20

APPARATUS FOR MEASURING THE THERMAL

CONDUCTIVITY OF METALS

3, .WO SilVM - AllAllOnaNOD 3VWd3Hl

02

O UJ m

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

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