METHOD AND APPARATUS FOR MEASURING THE THERMAL CONDUCTIVITY AND THERMO-ELECTRIC PROPERTIES OF SOLID MATERIALS

• US 3,733,887 A
• Filed: 01/31/1972
• Issued: 05/22/1973
• Est. Priority Date: 01/31/1972
• Status: Expired due to Term

• Current Assignee: Allen D. Reich, Marland L. Stanley
• Original Assignee: Allen D. Reich, Marland L. Stanley
• Inventors: Stanley, Marland L., Reich, Allen D.
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US05/222,265
• Time in Patent Office: 477 Days
• Field of Search: 73/15 324/32
• US Class Current: 374/44
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18

Abstract

A METHOD AND APPARATUS FOR MEASURING THE THERMAL CONDUCTIVITY, SURFACE HEAT TRANSFER COEFFICIENTS AND THE THERMO-electric power of materials, involving the employment of the Peltier effect to establish the temperature difference across, while simultaneously measuring the rate of heat flow through, the investigated sample material. A predetermined current is applied to a thermoelectric couple sensor to produce a temperature difference across the thermoelectric couple sensor by controlling the temperature of the cold junction of the sensor. The thermal conducting body is engaged with the cold junction of the sensor. The current is then adjusted by a predetermined amount to re-establish the temperature differential. By measuring the change in the current required to restore the temperature differential, the thermal conductance of the body may be determined.

Claims

1. The method of determining the thermal conductance properties of a body comprising the steps of:

applying a predetermined current (Ic) to a thermo-electric couple sensor (c) to produce a temperature difference ( Delta Tc) across the thermo-electric couple sensor by controlling the temperature of the cold junction, T4, of the sensor, engaging the thermally-conducting body, having a predetermined temperature, with the cold junction of the sensor, adjusting the current (Io) by an amount Delta I to re-establish the temperature differential ( Delta Tc), and measuring the change in current ( Delta I) which provides the thermal conductance of the body.

2. The method as defined in claim 1 including determining the thermal conductivity, Ks, of the body, the body having a uniform cross-section, involving the further steps of:

contacting one end of the body to a fixed temperature heat sink and while its other end is engaged with the cold junction of the sensor, determining the cold junction temperature, T4, of the sensor, measuring the body to obtain the length (Ls) and cross-sectional area (As) and determining the ratio lambda s Ls/As, and calculating, from the herein-identified measured and determined quantities and the predetermined electric resistivity ( Rho c), Seebeck coefficient (Sc), and length to area ratio (Lc/Ac lambda c) of the sensor, the thermal conductivity of the body by the formula;

Ks ( lambda s Delta I/ Delta Ts) (2ScT4-(2I + Delta I) Rho c lambda c)

3. The method as defined in claim 1 including determining the thermal conductivity, Ks, of the body and correcting for surface heat losses of the body, the body having a uniform cross-section and including the further steps of:

applying a predetermined current (Ic1) to a second thermo-electric couple sensor (C1) while the predetermined current (Ic) is applied to the first-named sensor (C) such that the cold junction temperature (T5) of the second sensor is elevated above the ambient temperature as the cold junction (T4) of the first-named sensor is lowered below the ambient temperature, contacting one end of the body to the cold junction of the second sensor while its other end is engaged with the cold junction of the first-named sensor (C), adjusting the currents (Ic and Ic1) to restore the previously-established cold junction temperatures (T4 and T5), measuring the changes in current ( Delta I and Delta I1) to establish the thermal conductance in and out of the body (Qin and Qout), measuring the ambient temperature (Te) and the cold junction temperatures (T4 and T5), measuring the body to obtain the length (Ls) and cross-sectional area (As) and determining the ratio, lambda s Ls/As, calculating Qin and Qout, from the herein-identified measured and determined quantities and the predetermined electrical resistivity ( Rho c and Rho c1) Seebeck coefficient (Sc and Sc1), and length to area ratios of sensor C (Lc/Ac lambda c) and of sensor C1(Lc1/Ac1 lambda c1) by the formulas Qin Delta I1( 2Sc1T5-(2Ic1 Delta I1) Rho c1 lambda c1)Qout Delta I(2ScT4-(2Ic + Delta I) Rho c lambda c), anD determining the thermal conductivity of the body by the formula Ks (Qin lambda s/Te-T4) (tan Square Root B/ Square Root B) where (Te-T4) cos h Square Root B + (Te-T5) (Qin/Qout) sin h Square Root B (Qin/Qout) (Te-T4)

4. The method as defined in claim 1 including determining the thermal conductivity, Ks, of the body and correcting for surface heat losses of the body and in which the body is a sample having a uniform cross-section, involving the further steps of:

applying a predetermined current (Ic1) to a second thermo-electric couple sensor (C1) while the predetermined current (Ic) is applied to the first-named sensor (C) such that the cold junction temperature (T5) of the second sensor is elevated above the ambient temperature as the cold junction (T4) of the first-named sensor is lowered below the ambient temperature, providing a reference body of uniform cross-section and known thermal conductivity, Kr, disposing the reference body and sample between the sensor (C) and a second thermo-electric couple sensor (C1) with the reference body engaging the sample, the reference body engaging the cold junction of the second sensor (C1), and the sample engaging the cold junction of the sensor (C), adjusting the currents of the sensors to provide a temperature between the sample and the reference body equal to the ambient temperature (Te), determining the ambient temperature (Te) and the temperatures (T4 and T5) of the cold junctions of the sensors, calculating, from the herein-identified measured and known quantities, the thermal conductivity of the sample by the formula Ks Kr (T5 - T4/Te -T4)