A numerical analysis of the performance of compact pin-fin array heat exchangers was carried out using water and JP-4 fuel as the working fluids. Three different configurations were used with hydraulic diameters ranging from 0.137 to 0.777 mm, and volumetric area densities varying between 4.5 and 14.5 mm2/mm3. Numerical simulations were carried out to determine the performance of each heat exchanger over a series of Reynolds numbers in both the laminar and turbulent flow regimes. It was found that very large heat transfer coefficients (in the kW/m2K range) can be achieved compared to air for the same footprint. In addition, the simulations were used to predict the Reynolds number range for transition from laminar to turbulent flow which was found to vary depending on the compactness of the heat exchanger configuration. As a final point, this study also investigated the effects of boiling of the liquid within the heat exchanger on its performance. It was found that despite improved heat transfer rates due to latent heat removal, vapor formation and resulting fluid expansion effects could result in undesirable flow patterns at low Reynolds numbers. The results from this study would be useful in the design of micro-scale heat exchangers for applications in the micro-electronic and gas turbine industries.
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