Generalization and prognostication of mass exchange characteristics of electrodialyzers operating in overlimiting current regimes with use made of similarity theory and compartmentation method

Abstract

A semiempirical approach, which allows one to perform generalization, prognostication, and scaling of the mass exchange characteristics of electrodialyzers intended for the desalination of dilute solutions in the overlimiting current regimes, is proposed. The approach is based on modern theoretical notions concerning the dependence of mass transfer on conjugated effects of concentration polarization, such as electroconvection and the exaltation effect and makes use of the similarity theory principles. As a result, there are obtained sufficiently simple equations that describe to within a satisfactory accuracy characteristics of the process of electrodialysis (mass transfer coefficient, Sherwood number, solution desalination degree, and so on) as functions of four parameters, namely, the input concentration, the solution flow rate, the potential drop across the paired chamber of the membrane stack of an electrodialyzer, and the length of the desalination channel. For scaling the obtained dependences with respect to a channel length a compartmentation method is used. Results of experimental investigations and calculations of electrodialyzers with desalination channels without a filler, or containing an inert separator, a monolayer of an ion-exchange resin, a profiled membrane, are presented.