An experimental study on the performance of an electro-dialysis desalination using hollow cubic assembled porous spacers fabricated by a 3D printer

In order to improve the performance of a filter press type electro-dialysis (E.D.) system, 5 types of hollow cubic assembled porous spacer fabricated by a 3D printer were applied instead of the conventional mesh spacers. The effects of structure of porous spacers on the E.D. system performance were experimentally investigated in terms of limiting current density, stack voltage and pressure drop. It was found that the porous spacer with vertical staggered arrangement normal to membrane surface and with smaller interfacial surface area between spacer and membranes contributes a higher limiting current density, which is about 2.5-3.0 times higher than that of E.D. system without spacer. Moreover, this spacer filled in E.D. system results in a relative lower electrical resistance and a smaller pumping power compare to other spacers. Since the vertical staggered structure is able to mix the flow (i.e. mechanical dispersion), supplies ions in the flow towards membranes, and suppresses concentration polarization, so that increases the LCD at expense of slightly increase in electrical resistance. Moreover, dimensionless mechanical dispersion coefficient towards membranes was estimated by fitting the experimental data with the analytical solution proposed in previous paper. Finally, a suggestion for making a good porous spacer has been proposed.