Thermal contact conductance across epoxied contacts at cryogenic temperatures.

摘要

This work represents a compilation of investigations of thermal contact conductance (hc) or boundary resistance ( Rb) across amorphous, or epoxied, contacts.;A Monte Carlo (MC) Model is proposed and developed as a complement to the Acoustic Mismatch (AMM) and the Diffuse Mismatch (DMM) models. The AMM and DMM are combined into a single, Mixed Model that determines R b based on both specular and diffuse transmission. A regime map is developed which delineates 3 regimes describing the R b, predictions made by the AMM, DMM and Mixed models.;A third model, the Scattering Mediated Acoustic Mismatch Model (SMAMM), is investigated to verify the effects on Rb when different scattering mechanisms are used in the determination of the scattering time, tau. The results show that Rb has strong temperature dependencies for some scattering mechanisms when small magnitudes of tau are used.;Based on the SMAMM, a fourth model is developed for the transmission of heat through a solid slab. The Slab Model takes into account interference effects occurring in acoustically thin materials. When compared to experimental data, the model results are quite promising within this niche.;Two independent experimental investigations of the thermal properties across epoxied contacts are conducted. The samples include titanium/epoxy/titanium and copper/epoxy/copper contacts. To date very little data is available on the thermal properties of titanium at low temperatures. The experimental results demonstrate that the thermal conductivity decreases with decreasing temperature in a fairly linear manner for all titanium samples. However, the conductivity for the pure grades of titanium is greater than that of the titanium alloys for all temperatures. Although several investigations on the h c of epoxied joints have been reported, very few, if any, span the temperature range of 50--250 K considered here. In general, the hc across the interface for all samples increased with increasing temperature. From the experimental data, it was possible to extract the thermal conductivity of the epoxy and the Rb at the copper/epoxy interface. The thermal conductivity is shown to follow a T1.29 relation, which is consistent with the Literature. The SMAMM was successful in predicting the Rb across the copper/epoxy contact, though an extremely small tau was necessary. This indicates the influence of other physical phenomena not yet accounted for in the models investigated here.