Phase-separation of wetting fluids using nanoporous alumina membranes and micro-glass capillaries

Phase separation in two-phase microfluidic exchangers is a promising strategy for reducing the required pumping power. Past research has focused on using hydrophobic nanoporous structures in order to extract water vapor and retain liquid within the vapor-cooling device. This study focuses on characterizing the bursting pressure, the maximum Laplace pressure for liquid containment, of nanoporous alumina membranes and micro-glass capillaries. The pore size diameters of the alumina membranes have a nominal diameter of 170 nm that can produce a pressure drop of 1.5 kPa for wetting dielectric liquids. In order to contain higher Laplace pressures, the pore geometry for ´pinning´ of the fluid at the liquid-vapor interface needs to be optimized. Single glass micro-glass capillaries were used in order to study the ´pinning effect´ of wetting fluids for various micro-capillary diameters. The glass capillary diameters ranged from 250-840 μm with measured Laplace pressures up to ~0.9 kPa. Experimental results agreed well with an analytical model that calculates the Laplace pressure as a function of pore geometry.