Date of Graduation

1998

Document Type

Dissertation/Thesis

Abstract

The purpose of this investigation was to examine one possible method of heat transfer enhancement. A free annular jet was oscillated and impinged on a flat plate to determine the effects of oscillation on the subsequent heat transfer. The nozzle through which the jet was emitted was an axisymmetric bistable fluidic oscillator but was oscillated through mechanical and pneumatic means for this investigation. The frequencies investigated ranged from steady flow to 25 Hz. The investigation used two methods, computational and experimental. The computational fluid dynamics package FLUENT version 4.3 was used to determine instantaneous heat fluxes and determine the flow field. Experimental data were used to corroborate the computational results. Experimental data were obtained using a heated jet, 400{dollar}\\sp\\circ{dollar}F and 500{dollar}\\sp\\circ{dollar}F at the nozzle exit. The jet impinged on an aluminum plate where a constant temperature backwall boundary condition was maintained. Thermocouples were mounted at various points on the front surface of the plate in various configurations. These thermocouples on the front surface of the plate yielded instantaneous air temperatures directly below the surface at distinct radial positions and heat fluxes through the plate. The experiments were conducted at flow rates of 7.5, 10 and 13.4 scfm and spacings of 25 to 75 hydraulic nozzle diameters between the nozzle exit and plate. The computational data indicated increased overall heat flux by nozzle oscillation of 11 to 38 percent over that of a non-oscillating jet under identical nozzle to plate spacings and flow rates. Vortical structures formed by the oscillating nozzle were observed and are believed to be the mechanism for the increased heat transfer. The experimental evidence confirms, to an extent, the conclusions drawn from the computational evidence.

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