Numerical study of flow boiling heat transfer in Ω-shaped reentrant microchannels

Flow boiling process in a unique type of Ω-shaped reentrant microchannels was numerically investigated by the comparison of conventional rectangular microchannels in this study. Three-dimensional numerical models were developed and validated. The bubble behaviors, fluid velocity, temperature distributions and heat transfer process were explored for the flow boiling of reentrant microchannels. The effects of structural parameters of reentrant microchannels, i.e., the upper slot width and circular cavity radius, were examined for optimization. It was found that the unique Ω-shaped configuration of reentrant microchannels contributed favorably to the bubble nucleation, and induced uniform annular flow with more stable thin film evaporation. Numerical simulation results showed that reentrant microchannels presented a 10%−37% enhancement in the flow boiling heat transfer performance than the rectangular microchannels. Reentrant microchannels with middle upper slot width of 0.4 mm and middle circular cavity radius of 0.4 mm facilitated the bubble detachment and elongation to form gas column, and contributed to more uniform liquid film with stable thin film evaporation. They present the best flow boiling heat transfer performance among the reentrant microchannels samples with different upper slot widths and circular cavity radius, and should be selected as the optimum for the cooling of high heat-fluxes devices. This study elucidates the underlying behaviors of flow boiling process in the unique reentrant microchannels, and sheds lights on the development and optimization of enhanced microchannels heat sinks for high heat-flux dissipations.