Flow boiling enhancement by bubble mobility on heterogeneous wetting surface in microchannel

During flow boiling in microchannels, the physics of a bubble is closely related to the heat transfer performance of different hydrophobic patterns. However, the heat transfer properties of various patterns are yet to be investigated. In this study, we conducted a numerical investigation into bubble coalescence characteristics and heat transfer performance of three patterns, namely crosswise, parallel, and dotted patterns, for flow boiling in a microchannel, and evaluated the influence of the hydrophobic area fraction for each pattern. In the transport equation, we employed a mass transfer model based on a two-phase mixture flow for the vaporization and condensation processes. In addition, we used the volume-of-fluid method to track the dispersed phase's interface using the local volume fraction. Although the parallel pattern at low mass flux facilitating bubble movement exhibited a good heat transfer performance, the dotted pattern displayed a better performance at high mass fluxes due to its higher nucleation site density. Additionally, very wide or narrow hydrophobic areas are unsuitable for heat transfer. Narrow areas limit bubble nucleation. A hydrophobic area fraction of 0.165 for the crossed pattern and of 0.32 for the parallel and dotted pattern produced the best heat transfer performances.