Visualization Study Of Pool Boiling Heat Transfer And Critical Heat Flux In Reduced Gravity

Team:Department of Mechanical Engineering, Texas A&M University

Abstract: An experiment is proposed in which water at vacuum pressure is heated with a sufficiently high heat flux to cause nucleate pool boiling and critical heat flux (CHF). Two different electric heater geometries are incorporated in the experimental apparatus which is designed to be operated aboard the NASA 930 aircraft at varying levels of gravitational acceleration. The heaters will be instrumented to obtain accurate values of nucleate boiling heat transfer coefficients and critical heat fluxes at various conditions. Additionally, part of the test chamber will be constructed of a clear material (polycarbonate), which will allow visualization of the pool boiling mechanisms. The experiment will be videotaped to provide both a simple means of data acquisition and an interesting outreach tool. Conventional theoretical predictions of pool boiling critical heat flux predict that CHF will decrease with decreasing pressure and increase with increasing gravitational acceleration. Previous experiments detected the expected qualitative trends, but found that conventional correlations do not accurately predict CHF under micro-gravity conditions. It is also apparent from previous results that the nucleate boiling heat transfer coefficients observed under micro-gravity conditions are sufficiently close to those at 1 g that very accurate means of heat flux and temperature measurements are required to distinguish between the two phenomena. A visualization study incorporating highly accurate data acquisition is required to observe and explain the physical mechanisms associated with pool boiling heat transfer in micro-gravity. The experimental design described in this proposal incorporates several features which make it partvicularly amenable to the research environment aboard the NASA 930 aircraft. Maintaining the test chamber at vacuum pressure allows the water to boil below 100F, thereby allowing safe operating temperatures and minimal heat loss to the surroundings. The use of a vacuum ejector to maintain the test chamber pressure and the use of nitrogen for cooling the working fluid allow a very simple, lightweight design.

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Tuesday, 27-Jan-2004 19:56:39 CST