Electronics of all types, particularly those in the military aviation arena, are decreasing in size while at the same time increasing in power. As a result, newer high-heat-flux electronic components are exceeding the cooling capabilities of conventional single-phase military aviation coldplates and coolants. It is for this reason that we have been investigating new methods to cool the next generation of high-heat-flux military aviation electronics. In this work, a novel method of inducing two-phase conditions within a microchannel heat exchanger has been developed and demonstrated. Micro-orifices placed upstream of each microchannel in a microchannel heat exchanger not only cause an improvement in flow distribution, but can also induce cavitation in the incoming subcooled refrigerant and result in favorable two-phase flow regimes for enhanced heat transfer. In this study, R-134a is used as the coolant in the cavitation enhanced microchannel heat exchanger (CEMC-HX) which has been integrated into a vapor compression refrigeration system. Multiple micro-orifice geometries combined with a fixed microchannel geometry (nominally 250 μm × 250 μm) were investigated over a range of applied base heat fluxes (10–100 W/cm2) and mass fluxes (500–1000 kg/m2-s). Two-phase heat transfer coefficients exceeding 100,000 W/m2-K at refrigerant qualities of less than 5% have been demonstrated due to the achievement of preferential, cavitation-induced, flow regimes such as annular flow. To the author’s knowledge, this is the highest heat transfer coefficient ever reported in the literature for R-134a. Additionally, a four term two-phase heat transfer correlation was developed that achieved a mean absolute error (MAE) of 25.5%.
- Heat Transfer Division
Cavitation-Enhanced Microchannel Heat Exchanger Demonstration and Heat Transfer Correlation Development Using R-134a
Sole, JD, Shelofsky, BJ, Scaringe, RP, & Cole, GS. "Cavitation-Enhanced Microchannel Heat Exchanger Demonstration and Heat Transfer Correlation Development Using R-134a." Proceedings of the ASME 2012 Heat Transfer Summer Conference collocated with the ASME 2012 Fluids Engineering Division Summer Meeting and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. Volume 2: Heat Transfer Enhancement for Practical Applications; Fire and Combustion; Multi-Phase Systems; Heat Transfer in Electronic Equipment; Low Temperature Heat Transfer; Computational Heat Transfer. Rio Grande, Puerto Rico, USA. July 8–12, 2012. pp. 607-615. ASME. https://doi.org/10.1115/HT2012-58109
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