Heat transfer, pressure drop and flow patterns of flow boiling on heterogeneous wetting surface in a vertical narrow microchannel

摘要

The micro-structured surfaces have a significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. As illustrated by previous studies, there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surfaces on the flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surfaces and original silicon surface was conducted with deionized water as the working fluid. Hydrophobic patterns perpendicular (HC) and parallel (HP) to the flow direction are compared. The subcooled boiling curves, heat transfer coefficient, and pressure drop were discussed with the variation of heat flux and mass flux, the trends of which were analyzed along with the flow patterns. The heat transfer coefficient of flow boiling on heterogeneous wetting surface HC was enhanced for up to 39.55% compared to a silicon surface with less pressure drop. During the boiling process, the dominant heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes. The easily formed bubble can be easily detached due to the supply of liquid from the hydrophilic regions nearby. With the increasing wall heat flux, the boiling heat transfer coefficient of the heterogeneous wetting surface HP is gradually lower than HC due to hydrophobic stripes parallel to the flow direction cannot restrict the bubbles from expanding in the axial direction.