Hierarchical biphilic micro/nanostructures for a new generation phase-change heat sink with 1800 W/cm2 CHF limit

Abstract

The physics of membrane-based microchannel boiling process is explained. Through a set of fundamental studies conducted on several membrane-based heat sinks designed with different configurations incorporating surface micro- and nanostructures, the nature of critical heat flux (CHF) limit and its active control is explained. It is commonly known that the occurrence of CHF is accompanied by the formation of significant vapor adjacent to the heated surface such that liquid cannot rewet the surface. In the new approach, flow is constrained within a hydrophilic microstructure by a superhydrophobic vapor-permeable nanofibrous membrane. A bubble bounded between the two structures is pulled away from the hydrophilic heated structure and discharged from the flow, thus leading to rewetting of the heat transfer surface. Hierarchical micro- and nanostructures designed on the heat transfer surface allow to substantially increase the surface wettability. The maximum heat flux removed is approximately 1800 W/cm2 with water used as the test fluid. Only vapor exits the heat sink. Hence, the heat sink exit vapor quality is 100%.