Analysis of non-equilibrium rarefied gas flows induced by evaporation from nanoporous membranes

Abstract

High-heat-flux cooling devices have been attracting attention due to the increasing power density of semiconductor devices. Nanoporous membrane-based evaporative cooling devices were recently reported which can dissipate a heat flux of ~1 kW/cm2. The optimized design of these devices requires the understanding of the non-equilibrium gas flow near a liquid–vapor interface, which is called the Knudsen layer. Although the one-dimensional Knudsen layer has been intensively investigated, the two- and three-dimensional Knudsen layers are not well understood because the change in the interfacial shape and position affects the overall heat and mass transfer flux in evaporation from a nanoporous membrane. In this study, we clarify how the evaporating flow velocity, the shape and position of the liquid–vapor interface, and the Knudsen number affect the number density at downstream and the apparent mass accommodation coefficient at the porous outlet.