Mathematical modeling of influence of porous structure a membrane on its vapour-conductivity in the process of membrane distillation

Abstract

Membrane distillation (MD) is a perspective method of separation and concentration of inorganic aqueous solutions. The driving force of MD is temperature difference on both sides of a hydrophobic porous membrane, which separates two aqueous solutions with different temperatures and concentrations. The coefficient of vapor conductivity is one of more important parameters of water vapor transfer through hydrophobic microporous membrane. The influence of membrane porous structure on vapor conductivity coefficient was studied theoretically using the pore network as a model of porous medium. The pore networks were considered as a long and straight cylindrical capillaries arranged around the bonds of two- or three-dimensional lattices with fixed coordination number z for lognormal pore size distribution. The effective-medium theory (EMT) and smooth field approximation (SFA) were used for describing of mass-transfer through the porous membrane. It was shown that the vapor conductivity coefficient value decreases with increasing of the pore dispersion d and decreasing of mean radius porous « rå, grows with increasing of coordination number z. As a result, MD process is more effective using the porous membrane with narrow pore size distribution.