Flow boiling heat transfer in microchannels

Flow boiling heat transfer to water in microchannels is experimentally investigated. The dimensions of the microchannels considered are 275 x 636 and 406 x 1063 mu m(2). The experiments are conducted at inlet water temperatures in the range of 67-95 degrees C and mass fluxes of 221-1283 kg/m(2) s. The maximum heat flux investigated in the tests is 129 W/cm(2) and the maximum exit quality is 0.2. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows. In this model, specific features of flow boiling in microchannels are incorporated while deriving analytical solutions for the convection enhancement factor and nucleate boiling suppression factor. Good agreement with the experimental measurements indicates that this model is suitable for use in analyzing boiling heat transfer in microchannel flows.