Doctoral Dissertations

Date of Award

8-1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

M. Parang

Abstract

Thermally-induced convection heat transfer is investigated in a series of experiments and by numerical modeling. Applications and potential importance of this process are discussed for both gravity and microgravity. The design of an in-space experiment for studying the process in microgravity is presented. Heat transfer in air enclosed between two parallel plates and subjected to rapid heat addition from the upper plate is investigated experimentally. The transient fluid temperature was measured using a new and unique optical technique developed for this purpose. The temperature along a cross-section of the test volume was found by measuring the refractive effects on a planar laser sheet that traversed the test volume. The heated plate temperature was measured by thermocouple. The optical temperature measurement technique is adapted for the in-space experiment design. A system consisting of a series of prisms that amplifies the laser deflection is presented. This is necessary since the space experiment must be contained in a small volume. The ground experiments demonstrate that the experimental technique is suitable and feasible to implement in a space experiment. Numerical modeling of the process is investigated by first analyzing previous numerical work. Shortcomings of the previous work are discussed and several changes are introduced that improve the accuracy of the numerical scheme. Secondly, an alternative numerical scheme is presented that neglects the acoustic velocity perturbations. The convective effects of the bulk motion generated in the fluid by the heat addition are calculated by requiring that continuity be satisfied in a spatially homogeneous pressure field. The momentum equations are eliminated in this scheme, so the numerical solution is greatly simplified. The results of the latter numerical model are compared with the experimental results. Good agreement is found for short times, but at longer times the experimental temperatures are below the numerical results. The numerical model is also compared with other previous numerical and analytical works.

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