An improved model incorporating constriction resistance in transport through thin film composite membranes

An improved Wheatstone bridge resistance model for diffusion through a thin film composite (TFC) membrane has been proposed. The constriction resistance encountered by the diffusing species in seeking out a pore in the support membrane to diffuse through is quantified. This resistance model has been validated for a range of parameters against a rigorous two dimensional numerical analysis of the diffusion process through a TFC membrane. An analytical solution has also been developed for the case when the support membrane matrix can be considered to be impermeable. It is shown that when the support membrane surface porosity is greater than 10(-3) but less than 0.6, the accurate prediction of flux through a TFC membrane requires a two dimensional analysis. It is shown that the improved Wheatstone bridge model with constriction resistance is accurate through the entire range of parameters.