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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-1015 February 12, 1953 2263

Thermal Conductivities of Two Specimens of

Ferrous Alloys at Temperatures from 100®C to 700®C

by

H, E. Robinson

S. Katz

Heating and Air Conditioning Section

Building Technology Division

for

Lebanon Steel Foundry

Lebanon, Pennsylvania.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or repiodu from the Office of the Director, Nation which a report has been specifically Approved for public release by the

Director of the National Institute of

d unless permission Is obtained In writing

s not needed, however, by an agency for that particular report for Its own use. Standards and Technology (NIST)

on October 9, 201 5.

Thermal Conductivities of Two Specimens of

Ferrous Alloys at Temperatures from 100°C to 700®C

by

H. E. Robinson

S. Katz

I. INTRODUCTION

Two specimens, referred to as No. E-452^ (L205A)

and No. C-^507 (L23), were submitted by the Lebanon Steel

Foundry, Lebanon, Pennsylvania, for calibration measurements of thermal conductivity in the temperature range

from 100®C to ?00®C.

From information furnished by the Lebanon Steel

Foundry, the compositions of these ferrous alloy specimens were as follows:

No. E-452^ No. G-S507

{L 205A) 23 ) Carbon .30 # 3L 3^ Silicon .35 1.20

!4anganese .69 .74

Chromium .^0 20 . 3^

Nickel .75 9.43

Molybdenum .25 .07

Copper .0^ .10

Phosphorous .026 .020

Sulphur .036 .025

II. PREPARATION OF THE SPSCEffiNS

The general arrangement of the test apparatus is shown

in Figure 1, as amended to show an internal heater in the

bar specimens in place of the external heater previously

used.

The upper end of each specimen was drilled to provide

a well for circulation of the coolant and the lower end

was drilled to accommodate the heater. The internal heating element was made by winding nl chrome wire on a grooved

porcelain cylinder, which was then covered with alundum

for electrical insulation. Chromel-alumel thermocouples

were attached at intervals of about 4 cm. along the length

of the bar. One thermocouple was attached to the lower end
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of the specimen. Jhe completed specimen was supported

on a thin nichrome pin located in the bottom of a thickwalled stainless steel guard cylinder. The guard cylinder was also equipped with thermocouples and a heater

element, and at the top with a copper coil through which

the coolant was circulated. The specimen-guard assembly

vias suspended in a large sheet metal container and the

entire system insulated with a fine granular insulation.

III. TEST FiETHOD

Electrical energ3

r 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 v/ater at constant temperature was pumped through the well in the specimen and

through the coil on the guard cylinder. When steady

temperature conditions had been attained the emfs of

the thermocouples (reference junctions at OC) and the

current through and voltage drop across the bar heater

were measured by means of standard resistors and a precision potentiometer. Thermocouple readings were subsequently converted to degrees Centigrade, using data

determined by a calibration of the thermocouple wire.

To calculate the thermal conductivity, observed

temperatures of the bar and guard were plotted versus

position along the bar as abscissae and smooth curves

were drawn through the points along the bar and along

the guard. 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 detemined from the curves and

using the conductivit|: 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 cylinder (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 distance and temperature difference between them, and the

cross-sectional area of the specimen, to calculate the

average thermal conductivity for that span. 'Phe calculated heat loss from the bar below the first span was

less than 10 percent of the heat input; the total heat

loss for all six spans was from -9 to +6 percent of

the heat input in the various tests. It is believed
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that the various corrections could be evaluated with an

uncertainty of not more than about 20 percent, conse~

quently the uncertainty in the rates of heat flow used

in computing the conductivities is of the order of not

more than 2 percent.

IV. TEST RESULTS

The values of thermal conductivity obtained in the

tests v/ere plotted against mean temperature (Figures 2

and 3) and a straight line, determined by the method of

least squares, was drawn through the points. In the

case of specimen No. E-452^ two straight lines were

drawn because of a sharp change in the thermal conductivity at a mean temperature of about 200®C, Table I

lists thermal conductivities taken from these lines.

V. DISCUSSION OF RESULTS

The plotted points show some scatter from the least

mean square lines drawn through them over a range of mean

temperatures. The scattering about the straight line

evidenced by the points obtained for the same test condition is an inverse measure of the precision of the

measurements. Several factors may have contributed to

the scattering, namely, small random inaccuracies in

measuring the thermocouple locations on the bar, slight

heat conduction along the thermocouple wires near the

hot junctions and possible slight inhomogenieties of

the thermocouple v;ires.

To minimize heat conduction effects, No. 26 A.¥.

gage thermocouple wires were used, and the wires were

led away for a distance of a f^w centimeters in the plane

of the cross-section at the junction, in which the temperature should -be fairly uniform. However, since the

temperature gradients along the bar ranged from 5 to 3^

degrees C per centimeter in different tests, scane conduction effect on individual thermocouple readings

probably could not be avoided. The plot of bar temperatures versus position indicates some slight departures

from a smooth curve, of magnitude not greater than one

degree C in the extreme case. Since all of these factors were random in nature, their effect v^as probably to

decrease the precision of the measurements rather than

to affect the overall results in any one direction.
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Table^'l

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Mean Temperature Thermal Conductivity, watta/cmCdegC)

Hq,. E-452g No^...C-.81^

50 0*366 0.132

100 .376 .140

150 .3^7 .149

200 .397 .157

(200) (.400) - 300 ,3^6 .173

400 .372 i--.- 4-- .190

500

• ^ 1 1 .357 4 .206

600 .343 . .223

700 - S : - .239

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