A Dynamic Technique for Measurements of Thermophysical Properties at High Temperatures
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A DYNAMIC TECHNIQUE FOR MEASUREMENTS OF THERMOPHYSICAL PROPERTIES AT HIGH TEMPERATURES
ARED CEZAIRLIYAN Thermophysics Division, National Bureau of Standards, Washinoton, D.C. 20234
ABSTRACT A technique is described for the dynamic measurements of selected thermophysical properties of electrically conducting substances in the range 1500 K to the melting temperature of the specimen. The technique is based on rapid resistive self-heating of the specimen from room temperature to any desired high temperature in less than one second by the passage of an electrical current pulse through it and on measuring the pertinent quantities, such as current, voltage The technique and temperature, with millisecond resolution. was applied to the measurements of heat capacity, electrical resistivity, hemispherical total emittance, normal spectral emittance, thermal expansion, melting temperature, heat of fusion, and temperature and energy of solid-solid phase Upper temperature of the measurements has transformations. been limited by the melting temperature of the specimen, at which point, the specimen collapses due to the gravitational force. In order to be able to extend the measurements to the liquid phase, performance of the dynamic experiments in a near-zero gravity environment is suggested.
INTRODUCTION Conventional steady-state and quasi steady-state techniques for accurate measurements of thermophysical properties are generally limited to temperatures below 2000 K. This limitation is the result of severe problems (chemical reactions, heat transfer, evaporation, specimen containment, loss of mechanical strength and electrical insulation, etc.) which are created by the exposure of the specimen and its immediate environment to high temperatures for extended periods of time (minutes to hours). An approach to minimize the effect of these problems and thus to permit the extension of the measurements to higher temperatures is to perform the entire experiment in a very short period of time (less than a second). It is in this context that most of the dynamic techniques for the measurements of thermophysical properties at high temperatures were developed. The developments of various dynamic techniques for the measurements of selected thermophysical properties of electrically conducting substances have The objective of this paper is to been reviewed in the literature (1-4]. describe briefly the technique developed at the National Bureau of Standards, summarize the investigations performed with the technique during the past The technique was applied to decade, and present some of the recent advances. the measurements of heat capacity, electrical resistivity, hemispherical total emittance, normal spectral emittance, thermal expansion, melting temperature, heat of fusion, and temperature and energy of solid-solid phase transformations.
50 METHOD AND MEASUREMENT SYSTEM The method is based on resistive self-heating of the specimen from room temperature to any high temperature (in the range 1500 K to its melting temperature) in less th
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