A New Method for Thermal Diffusivity Measurements in Metals Utilizing the Thermo-Electric Effect
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A NEW METHOD FOR THERMAL DIFFUSIVITY MEASUREMENTS IN METALS UTILIZING THE THERMO-ELECTRIC EFFECT **
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ISAAC SHAI , URI LAOR AND ILAN GILAD * The Pearlstone Center for Aeronautical Engineering Studies, Mechanical Eng. Dept., Ben-Gurion University of the Negev, P. 0. Box 653, Beer-Sheva 84105, Israel "**Nuclear Research Center - Negev, P. 0. Box 9001, Beer-Sheva 84190, Israel ABSTRACT A new method for the measurement of the thermal diffusivity in metals, using transient conditions, is demonstrated. This method is using the principle of superposition of thermal loads. Only time measurements are required, and no accurate temperature and heat flow rate measurements are needed. The method utilizes the Seebeck effect for the measurement of the time dependence of the temperature. A solution of the heat transfer equation for the model pertinent to the described method is derived, and results obtained for several materials are presented.
INTRODUCTION The thermal conductivity of solids is an intrinsic physical property of the material, and is of great importance in determining heat flow rates and temperature distribution in the solid. Many experimental methods for the measurement of the thermal conductivity of solids are described in the literature. Most of these methods are based on the conductive heat transfer equation solution, with well defined boundary conditions. All of the measurements are performed by applying a thermal load to the sample, and monitoring the resulting temperature distribution in the sample. The measurements are performed under either steady state or transient conditions approximating the boundary conditions used in the analytical solution. The temperatures and heat transfer rates are measured at selected locations from which the thermal conductivity can be deduced. In the steady-state measurements, a constant heat flux is driven through a sample of fixed cross section. The temperatures at a few points along the sample are measured, and the thermal conductivity is calculated using Fourier's equation [1]. Other methods are performed under transient conditions [2], where the physical property measured is the thermal diffusivity rather than the thermal conductivity. Each of these methods is based on a geometrical model on which specific thermal load and boundary conditions are induced. The differential equation describing the thermal conditions is solved using the chosen boundary conditions. The solution yields a relation between the measured temperature values and the thermal diffusivity [3]. All those methods are based on accurate heat flow rate and temperature measurements using thermocouples, thermistors or infrared detectors. The accuracy of the temperature
Mat. Res. Soc. Symp. Proc. Vol. 234. @1991 Materials Research Society
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measurements is of major importance to the accuracy of the thermal diffusivity values obtained. Recently, a new method for the thermal diffusivity measurement in solids, under transient conditions using the principle of superposition of thermal loads, has been pres
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