Analytical Model for Capillary Evaporation Limitation in Thin Porous Layers

摘要

Fluid flow and heat transfer in thin porous layers are of fundamental importance in numerous applications, including the development of high power-density electronics cooling devices, loop heat pipes, aerospace radiators, as well as micro fuel cells. A two-dimensional analytical model has been developed to evaluate the pressure distribution and capillary evaporation limitation in a uniformly heated thin porous layer and the effects of the porous structure and properties of the working fluid on the capillary evaporation process. Two types of porous materials, sintered powder and layers of screen mesh, with different characteristics were investigated. The results indicated that the maximum capillary evaporation heat transfer is proportional to the thickness and the permeability of the thin porous layer, but that increasing the thickness of the porous layer can result in higher superheat. Higher Bond numbers were shown to correspond to higher capillary evaporation heat-transfer limitations. By comparison, the sintered wick structure had a significantly higher effective conductivity and a higher capillary pumping pressure than the mesh screen. As a result, the maximum evaporation heat-transfer rate for the sintered powder layer was much higher than for any of the mesh screen layers evaluated.