Effect of concentration boundary layers on mechanical pressure in a double-membrane system

Abstract

A mechanical pressure model equations for a double-membrane system, in which a series of two (M l and M r) vertically mounted, flat, symmetric, polymer membranes separate three compartments (l, m, r) containing the heterogeneous non-electrolyte solutions of concentrations C k l, C k m and C k r was developed. These concentrations in initial moment fulfilled the condition C k l < C k m < C k r. The inter-membrane compartment (m) consists of an infinitesimal layer of solution. The volume of the compartments (l, m, r) fulfill the consists on V l= V r 170 V m. The experimental test were performed for binary (aqueous solutions of glucose or ethanol) or ternary (glucose solutions in 0.75 mol·l −1 solution of ethanol or ethanol solutions in 0.1 mol·l −1 aqueous solution of glucose) solutions. The linear dependencies of the mechanical pressure on the concentration difference in binary solutions and non-linear in ternary solutions were obtained. It is shown that the double-membrane system has amplifying properties of mechanical pressure in the intermembrane compartment of a double-membrane system. The experimental results were interpreted in terms of convective instability, which increases the value of solute permeability coefficients of the system: concentration boundary layer/membrane/concentration boundary layer.