Novel spacer geometries for membrane distillation mixing enhancement

Abstract

Membrane distillation is an emerging promising desalination method that requires further improvement in order to become industrially viable. Due to the fact that evaporation is the primary process in membrane distillation, one strategy to boost membrane permeate flux is to optimize the energy supply to the water interface by increasing mixing in the hot channel via the use of optimized spacers. Contemporary spacer designs predominantly induce turbulence, resulting in elevated pumping energy requirements. This study introduces novel spacer geometries, inspired by industrial mixer designs, to surmount the limitations of conventional spacer configurations. The mixing efficiency, thermal performance, and pressure drop induced by the two novel geometries are studied and compared to those of commonly utilized spacer designs. It is confirmed, that the first of these novel geometries significantly enhances mixing, whereas the other causes a lower pressure drop and appears to be a viable solution when a spacer is a necessary structural component. In the course of the analysis, it is also shown that the coefficient of variation coupled with the Nusselt number at the membrane can be used to assess spacers' performance.