Local mass transfer during electrodialysis with ion-exchange membranes andspacers

Mass transfer during electrodialysis with ion-conducting spacers in the int ermembrane gap is modeled experimentally using a local-distribution analysi s of solutions. Due to emergence of back-flow regions near the spacers, loc al quantities (diffusion layer thicknesses, surface concentrations, Sherwoo d numbers) are distributed nonuniformly over the channel length. In a smoot h channel, due to concentration polarization, local mass transfer rates ste adily decrease along the solution supply coordinate, but introducing ion-co nducting spacers into the channel intensities mass transfer because of peri odic interruption of diffusion layers and formation of recirculation zones. Effect of geometrical size of spacers on the mass transfer is studied. It is found that the mass transfer rate is maximum for ion-conducting spacers with the ratio 3.5 < l/h < 4.0.