Title

Surface Geometry and Heat Flux Effect on Thin Wire Nucleate Pool Boiling of Subcooled Water in Microgravity

Document Type

Article

Journal/Book Title/Conference

Journal of the Utah Academy of Sciences, Arts and Letters

Volume

87

Publication Date

1-1-2012

Abstract

In the summer of 2010, a nucleate pool boiling experiment was flown on NASA’s Weightless Wonder to study nucleate boiling heat transfer in microgravity. The motivation for this research was to understand the effects of surface geometry and heat flux applied to a thin wire heater. This will further the understanding of the fundamental behaviors of boiling onset, steady state heat transfer, and bubble dynamics with respect to nucleate boiling, with the goal of creating efficient thermal management systems for space applications. Using three thin platinum wire geometries and five different power levels, subcooled water was boiled over a period of approximately 25 seconds during 15 parabolic arcs to simulate microgravity. To represent the trends in bubble behavior across hundreds of frames of video in a single graph, a new method, named relative bubble area analysis, was introduced and used to analyze the results of the experiment. It was determined that the efficiency of steady state heat transfer via nucleate boiling in microgravity is comparable to steady state heat transfer in terrestrial applications. Nucleate Pool Boiling 327 The three-wire geometry reduced the heat flux necessary to initiate boiling. Bubble dynamics show a transition from isolated bubbles to jets of small bubbles as heat flux increases. This can be confirmed both visually and with relative bubble area analysis. The implications of this research are that sustained convective heat transfer with subcooled water is possible in microgravity. A three-wire surface geometry was shown to initiate boiling at lower heat fluxes, which would provide minimal super heating of the surface, from lack of convection, before boiling heat transfer could begin.

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