A plane probe technique was developed to measure the thermal conductivity (k) and thermal diffusivity (a) of 7.5 cm diam core samples at room temperature. This develop¬ment was undertaken to provide data on samples of interest to the Geologic Disposal Evaluation Program. This plane probe was formed by sandwiching a spiral planar heater between a specimen of known k and a (NBS gum rubber) and a specimen of unknown k and a which was instrumented with a thermocouple. The probe was interfaced with a PDP 8 computer for automatic operation, data acquisition, and computation of k and a values. At time zero a controlled amount of power was supplied to the heater and the thermo¬couple response was recorded for the duration of the power application (∽100 s). Reliable results were obtained with a rise in specimen temperature of 1 to 2°C (2 to 4 °F). The computations of k and a used an exact mathemat¬ical analysis of the system, rather than the approxima¬tions normally used. Specimens of NBS gum rubber, Pyroceram Code 9606, and lavite were used to study technique variables such as applied load, interfacial resistances, and thermo¬couple placement.
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