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This study describes the transient temperature distributions in a cooling apparatus for high-power semiconductor devices used in electric-railcar drive systems. The cooling apparatus is composed of heat pipes, air-cooled fin arrays, and a metal block which is used for attaching several semiconductor packages, In our numerical simulation model, we substituted solid elements for the heat pipes, and determined their thermal properties by experiment. As a result, we could obtain transient temperature distributions for the cooling apparatus through a heat conduction analysis. Calculated results showed that when the amount of heat generated in the devices changes, the temperature of the cooling apparatus changes more slowly than that of the devices. A comparison between the transient-temperature distribution calculations and the experiments confirmed the accuracy of the modeling and prediction method. Thus, these calculations can be used to provide data for packaging design, especially concerning thermal stress and fatigue in the packages. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 107–115, 1997

The thermal stress analysis of a silicon bulk single crystal with a diameter of 6 or 8 inches is performed in the cases of the [001] and [111] pulling directions by using a three-dimensional finite element program developed for calculating thermal stress in a bulk single crystal during the Czochralski growth. Elastic anisotropy and temperature dependence of material properties are taken into account in this program. The temperature distribution and shape of a silicon bulk single crystal which are required for the thermal stress analysis are obtained from a computer program for a transient heat conduction analysis which is specialized for the Czochralski growth. The stress components obtained from the thermal stress analysis are converted into the parameters related with dislocation density. The time variations of these parameters are shown in this paper. The relation between these parameters and the shape of the crystal-melt interface is discussed.

Numerical simulation was conducted to study the thermal history of Czochralski growth of large silicon single crystals. The computations were performed for various crystal diameters and emissivities of the crucible inner wall. The analysis gives the change of temperature distribution in the crystal and the shape of the solid-melt interface. The computed results show the importance of the effects of radiation from the crucible inner wall and the melt free surface on crystal growth. Also, increasing crystal diameter decreases the pull speed and increases the concavity of the solid-melt interface into the crystal. The result of this analysis is in good agreement with measurement of the pull rate on production apparatus, and the shape of the crystal-melt interface showed a tendency to qualitatively agree with the observations of X-ray diffraction.

The heat transfer performance of coaxial straight heat pipes in high-speed rotation has been analyzed. The parameters are the geometry of the pipe, the kind of working fluid, the mass of the working fluid charged in the pipe, the rotation rate and the heat load. As a result of the analysis, the distribution of film thickness in the pipe, the Nusselt number of the evaporator and condenser section, and the dryout conditions at the end of the evaporator section were found. The Nusselt number from the present analysis is compared with the experiment by Ohtsuka et al. The predictions are is good agreement with the experimental data in the condenser section, but are about 80 100% lower in the evaporator section.