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 ��in (.0708 ��m) parallel to the sanding direction and 1.9 ��in (.0482 ��m) 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. / Graduation date: 1999

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Xie Jian Li. / "August 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 106-109). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

The low thermal conductivity of gallium arsenide compared to silicon results in self-heating effects in GaAs MESFETs that limit the electrical performance of such devices for high power applications. To date, analytical thermal models of self heating in GaAs MESFETs are based on the assumption of a uniformly heated channel. This thesis presents a two dimensional analysis of the electrothermal effect of this device based on the two dimensional power density distribution in the channel under various bias conditions. The numerical simulation is performed using the finite difference technique. The results of the simulation of an isothermal MESFET without heat effects is compared with various one dimensional analytical models in the literature. Electro thermal effects into the two-dimensional isothermal MESFET model allowed close examination of the temperature profile within the MESFET. The large gradient in power distribution results in a localized heat source within the channel which increases the overall channel temperature, which shows that the assumption of a uniformly heated channel is erroneous, and may lead to an underestimation of the maximum channel temperature. / Graduation date: 1992

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No description available.

A unified and systematic study of one-dimensional heat conduction based on thermal relaxation is presented. Thermal relaxation is introduced through the constitutive equation (modified Fourier's law) which relates this heat flux and temperature. The resulting temperature and flux field equations become hyperbolic rather than the usual classical parabolic equations encountered in heat conduction. In this formulation, heat propagates at a finite speed and removes one of the anomalies associated to parabolic heat conduction, i.e., heat propagating at an infinite speed. In situations involving very short times, high heat fluxes, and cryogenic temperatures, a more exact constitutive relation must be introduced to preserve a finite speed to a thermal disturbance. The general one-dimensional temperature and flux formulations for the three standard orthogonal coordinate systems are presented. The general solution, in the temperature domain, is developed by the finite integral transform technique. The basic physics and mathematics are demonstrated by reviewing Taitel's problem. Then attention is turned to the effects of radially dependent systems, such as the case of a cylinder and sphere. Various thermal disturbances are studied showing the unusual physics associated with dissipative wave equations. The flux formulation is shown to be a viable alternative domain to develop the flux distribution. Once the flux distribution has been established, the temperature distribution may be obtained through the conservation of energy. Linear one-dimensional composite regions are then investigated in detail. The general temperature and flux formulations are developed for the three standard orthogonal coordinate systems. The general solution for the flux and temperature distributions are obtained in the flux domain using a generalized integral transform technique. Additional features associated with hyperbolic heat conduction are displayed through examples with various thermal disturbances. A generalized expression for temperature dependent thermal conductivity is introduced and incorporated into the one-dimensional hyperbolic heat equation. An approximate analytical solution is obtained and compared with a standard numerical method. Finally, recommendations for future analytical and experimental investigations are suggested. / Ph. D.

An experimental investigation was carried out to determine the feasibility of using thermal conductivity measurements to detect moisture concentrations in a highly porous glass fiber insulation. A new technique employing thermistor probes was used to measure thermal conductivity over a range of low moisture contents. The results indicate that the material's thermal conductivity is a strong nonlinear function of the moisture concentration. The sensitivity of the moisture content to thermal conductivity is greatest for moisture contents less than 25 per cent for the material tested. A numerical procedure for predicting the temperature and moisture distributions in a highly porous material is detailed. / Ph. D.