Development of Needle Probe Method to Measure Thermal Conductivity of Rocks Simply at High Temperature and High Pressure

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Thermal properties of rocks at elevated temperature and high pressure have been highly concerned in geothermal energy development and in many fields of engineering. This paper describes development of a needle probe method -a transient hot wire method for simple and fast laboratory measurements of temperature and pressure dependence of the thermal conductivity of rocks and other poor conductors. A cylindrical sample of high purity fused quartz as a standard material of the thermal conductivity and samples of two granite are heated by a thin needle probe having 2.0 mm 0. D. and 80 mm effective length, the resulting temperature increase at the effective center point of the probe being monitored by a thermo-couple, a digital voltmeter and a pen recorder. The experimental temperature data to yield values of the conductivity is obtained in about fifteen minutes. Conductivity values of fused quartz and the granite specimens are presented in the temperature range 300-800°K. The absolute accuracy better than ±3.0 % verified by measurement of the standard sample for this method. The thermal conductivity of the granite specimens exhibitsaT<SUP>-1</SUP> dependence on temperature, T, as expected for these type of rocks. Sample preparation is simple and not critical. The method described is well suited for measurement of the variation of thermal properties with temperature and pressure.
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