Immiscible Fluid Disposition and Permeability in Thin Porous Structures*

The disposition of immiscible fluid phases in porous media is a key characteristic determining multiphase transport properties within a structure. For bulk porous media, the saturation/capillary pressure and saturation/permeability relationships describe this mechanism and have been characterized for a wide array of porous structures. For thin porous structures without delineated internal pores, such as free standing meshes, these relationships are less clearly defined. Here we measure the effective permeability of metallic mesh with liquid-vapor interfaces at both sides at a range of capillary pressures. As expected, increasing capillary pressure reduces the liquid volume present in the structure and the corresponding permeability. We characterize the evolution of the liquid vapor meniscus with capillary pressure and relate this to the measured flow resistance. We also explore the degree to which these results can be generalized via dimensional analysis of the capillary pressure/permeability relationship. Finally, we consider the design of porous structures for specific two-phase transport problems such as liquid-vapor phase change heat transfer.