Date of Award

Spring 1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical and Industrial Engineering

First Advisor

P. Hrycak

Second Advisor

Denis L. Blackmore

Third Advisor

Rajesh N. Dave

Fourth Advisor

Avraham Harnoy

Fifth Advisor

Lawrence Jay Schmerzler

Abstract

The heat transfer characteristics in stagnation flow are investigated through three cases in this study. The first is forced convection by an array of air jets; the second is free convection of a downward-facing heated round plate; the third is free convection of an upward-facing heated round plate.

The first case is investigated by systematic experiments which examine the heat transfer characteristics mainly by five air jets impinging normally to a flat plate, with varying nozzle diameters, and Reynolds numbers, at different distances between the nozzles and the plate. The empirical formulas of heat transfer around the stagnation point and over the entire plate are established. Compared to the single jet cooling, the
Nusselt numbers do not increase significantly by increasing the numbers of jets.

The second case is a theoretical study. The analytical solutions for the velocity and the temperature profiles, using the Prandtl number in the moderate range, have been obtained through the similarity transformation of the governing equations applicable to laminar flow. The Nusselt number expression is found to be a function of the 1/4 power of the Rayleigh number, for the prescribed surface temperature condition; and a function of the 1/5 power of the modified Rayleigh number, for the prescribed surface flux condition.

The third case is formulated by a mathematical model similar to the second case; however, the analytical solutions for the velocity and the temperature profiles have not been obtained. Yet, the Nusselt number expression from the model shows the 1/4 power dependence on the Rayleigh number, which agrees with the results of the second approach and with experimental findings.

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