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

The motivation of this nucleate boiling research is to understand the effects of surface geometry and heat flux as 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 future space applications. Using three different thin platinum wire geometries and five different power levels, subcooled water was boiled over a period of approximately 30 seconds for 15 parabolic arcs to simulate microgravity. To represent the trends in bubbles behavior across hundreds of frames of video in a single graph, a new method, named relative bubble area analysis, is 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, and in some cases more efficient than, steady state heat transfer in terrestrial applications. 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, which is a result of the lack of convection, before boiling heat transfer could begin