Experimental Measurement of Thermal Conductivity of an Unknown Material

The objective of this study was to determine effective thermal conductivity of an unknown material sample for sample temperatures up to 1000 degrees Celsius. A steady state, one-dimensional heat conduction test setup was designed, fabricated, assembled, and used to determine thermal conductivity of the sample. The measurement was accomplished by applying a heat flux from a radiant heater through a stack consisting of the test sample, reference plates, heat spreaders, and insulation layers. The heat transfer equation for steady state, one-dimensional conduction relates thermal conductivity of the sample to the thickness and cross-sectional area of the sample, the temperature difference across the sample, and the one-dimensional heat transfer rate through the sample. Thus, the thermal conductivity was calculated and assigned to the mean temperature of the sample for each particular run. One-dimensional heat transfer was maintained by guard heaters and insulation placed around the stack to reduce heat losses to the surroundings. Heat transfer through the sample was determined by subtracting the heat losses from the main power supply. A novel feature of the final-design configuration utilizes a "cold side" heater at the cold end of the stack to elevate the temperature within the stack without significantly increasing the power supply to the main heater. The experimental thermal conductivity results ranged from 4.90 to 9.93 W/(m K) over a temperature range between 208 and 865 degrees Celsius. A correlation for thermal conductivity over the temperature range is presented. With an uncertainty analysis of the thermal conductivity results, it was shown that the average calculated uncertainty was 3% of the final results.