Numerical investigation of flow boiling heat transfer in manifold microchannels

The manifold microchannel (MMC) has drawn much attention due to its excellent convective heat transfer performance. Flow boiling in MMC can reach high heat transfer coefficient, however the research of which is rare in the literature. In this study, transient subcooling flow boiling heat transfer in MMC is numerically studied by a phase change model that renders the phase interfacial temperature converged to the saturation temperature. Effects of heat flux, subcooling, bottom channel height, and outlet/inlet width ratio are investigated in terms of vapor dynamic behaviors, thermal resistance, heat flux with the lowest thermal resistance and pressure drop. A lower subcooling promotes the occurrence of nucleate boiling and leads to lower thermal resistance, however the thermal resistance starts to rise earlier. In addition, too high bottom channel height deteriorates the convective heat transfer while too low bottom channel height leads to worse heat transfer at the upstream corner, and thus there exists an optimal channel height. Moreover, there also exists an optimal outlet/inlet width ratio which avoids the local worse heat transfer at upstream corner or vapor blockage in the outlet channel. Based on the results in the present study as well as in the literature, a new flow-boiling heat transfer correlation is developed for nucleate boiling in MMC. The new correlation agrees well with existing results, with mean absolute deviation (MAD) about 7.87%, much lower than MAD of 200% obtained by existing correlations. The present work is helpful for understanding flow boiling processes and providing flow-boiling heat transfer correlations in MMC.