Doctoral Dissertations

Date of Award

8-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Robert J. Krane, J. R. Parsons

Committee Members

J. W. Hodgson, V. Alexiades

Abstract

A numerical investigation was performed to develop a three-dimensional numerical model to simulate a "generic" heat sink configuration in a table model television receiver cooled by natural convection and thermal radiation. The model was used to perform a parametric study to provide information on the size and aspect ratio of the heat sink, the effects of changing its coating emissivity, the effects of horizontal component board temperature, and the effects of shrouding the heat sink. For the present study, the heat sink was assumed to be a vertical, rectangular flat plate with a single electronic component attached to it, and mounted on a heated, upward-facing, rectangular isothermal surface (component board). Five geometric configurations were analyzed. Configuration "A" consists only of the heat sink and component board. In configuration "B", four vertical plane walls form partial enclosure for the heat sink and the component board. The heat sink is shrouded by two heated, vertical plane surfaces in configuration "C". In configuration "D", a top horizontal surface with a vent at the center is added to the partial enclosure of configuration "B". In the fifth configuration "E", the component board and heat sink are contained in a sealed enclosure, and the enclosure walls are maintained at ambient temperature. The developed numerical model, which is based on the SIMPLER algorithm, solved the fully-coupled, three-dimensional, transient natural convection, conduction, and radiation heat transfer processes that occur in each of the above five configurations. The flow field for configurations B, C and D never reached steady state due to the unsteady nature of the natural convection flow in the configurations. The flow field was observed to be essentially steady in configuration "E". Air flowing in the domain through the bottom opening of the partial enclosure played a major role in cooling the heat sink and component by natural convection. Shrouding the heat sink significantly increased the component (silicon chip) temperature as compared to that of other configurations. Parametric study of configuration "B" showed that the component temperature was very sensitive to the thickness and the emissivity of the heat sink, and the component board temperature. The sensitivity of the component temperature on surface emssivity emphasizes the importance of radiative heat transfer to the cooling of the component. Finally, parametric study of configuration "C" showed that the component temperature was also very sensitive to the shroud temperature in a typical television receiver.

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