Thermal contact resistances in a thermal conductivity test system Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8g84mq398

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  • The thermal contact conductance (TCC) between two machined pieces of stainless steel was studied. A guarded hot plate thermal conductivity test fixture was designed and built for the experiment. Factors investigated included the contact pressure, surface roughness, interface material and average test temperature. The contact pressure at the interface ranged from 80 to 800 psi. The mean surface roughness of the opposing surfaces was 2.8 μin (.0708 μm) parallel to the sanding direction and 1.9 μin (.0482 μm) perpendicular to the sanding direction. Interface materials included air, indium foil, copper foil, Teflon tape, silver filled paint and thermal grease. Average test temperatures ranged from 0°C to 100°C, in 20°C increments. With air alone in the interface gap the TCC was nearly insensitive to contact pressure. The thermal grease and silver filled paint most increased the TCC over air alone while being nearly insensitive to pressure. With indium foil the TCC was similar to air, but improved somewhat with increasing pressure. With copper foil the TCC was lower than air alone, but increased with increasing pressure. The Teflon tape had a lower TCC than air at low contact pressure, but a higher TCC than air at higher pressures. In general the TCC improved somewhat at higher temperatures. The ability of an interface material to improve the TCC is more a function of its flow stress and wetting ability than its thermal conductivity. An existing mathematical model was used to predict the TCC with air as the interface material, and was found to over-estimate the TCC by an order of magnitude. It was found that the model did not accurately predict the effective surface spacing for very smooth surfaces as used in this work. When a modification for smooth contact surfaces was incorporated into the model it yielded results that were consistent with experimental results.
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