FINITE-ELEMENT SOLUTION OF THE EQUATIONS GOVERNING THE FLOW OF ELECTROLYTE IN CHARGED MICROPOROUS MEMBRANES

Electrical double-layer effects are unimportant in flows through porou s media except when the Debye length kappa(-1) is comparable in magnit ude with the pore radius a, Under these conditions the equations gover ning the flow of electrolyte are those of Stokes, Nernst-Planck and Po isson. These equations are non-linear and require numerical solution. The finite element method provides a useful basis for solution and var ious algorithms are investigated, The numerical stability and errors o f each scheme are analysed together with the development of an appropr iate finite element mesh. The electro-osmotic flow of a typical electr olyte (barium chloride) through a uniformly charged cylindrical membra ne pore is investigated and the ion fluxes are post-computed from the numerical solutions. The ion flux is shown to be strongly dependent on both zeta potential and pore radius, kappa a, indicating the effects of overlapping electrical double layers.