Infrared (IR) thermography was used to measure the local heat transfer coefficients within two plate heat exchanger geometries. The chevron patterns were machined into polycarbonate and IR transparent calcium fluoride plates, both of which were electrically heated using flexible film heaters at heat fluxes up to 0.8 W cm-2. The test fluid was a refrigerant (HFE7100) at mass fluxes between 25 and 100 kg m-2 s-1 , and qualities from 0 to 0.9. The apparatus and data reduction technique were validated by comparing the single-phase heat transfer and pressure drop data against the prediction methods from the literature. Adiabatic flow visualizations were conducted to link the flow patterns with the observed heat transfer. The frictional pressure gradient and heat transfer coefficient were compared with available correlations. It was shown that the heat transfer coefficient and the frictional pressure gradient increased with mass flux and quality. The comparison indicated the need for new prediction methods for predicting the local thermalhydraulic performance over a wide range of operating conditions.

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Flow boiling heat transfer is an important mechanism across a wide variety of engineering disciplines. The prediction of the heat transfer rate as a function of flow conditions and temperature has been based almost exclusively on experimentally derived correlations. The quality of these correlations depends on the accuracy and resolution of the measurement technique. In addition to the complexities of flow boiling phenomenon in earth gravity, engineering design of space systems requires knowledge of the gravity dependence for heat transfer prediction. Current research has shown significant variations in the heat transfer during pool boiling as a function of gravity magnitude. Research into flow boiling in variable gravity environments is very limited at this time, and such data is needed if multiphase systems are to be designed for space applications. The objective of this study is to develop, validate, and use a unique infrared thermometry method to quantify the heat transfer characteristics of flow boiling over a range of gravity levels. This new method allows high spatial and temporal resolution measurements, while simultaneously allowing the flow to be visualized. Validation of this technique is demonstrated by comparison with accepted data in earth gravity environments. Measurements taken in high, earth, and zero gravity environments are used to show how the heat transfer characteristics change with gravity.

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