Spacer Design for Membrane Distillation Module Using CFD

Abstract

Membrane processes are used widely to desalinate water. Major techniques for this purpose include Reverse Osmosis (RO), Multi-stage Flash Distillation (MSD), Membrane Distillation (MD) and Multi-effect Distillation (MED) with RO being most used. Higher salt rejection rate of MD (99%) than that of RO (96%) makes it a better option for water desalination. Direct Contact Membrane Distillation (DCMD) is the easiest configuration among others for MD at low temperature and pressure conditions thus reducing cost. CFD study of impact of spacer in feed and permeate channels has been conducted by considering the effect of velocity, membrane thickness, spacer filament distance and their arrangement variants. Temperature Polarization Index (TPI) and Vapor Flux are used as the evaluation criteria for performance of a combination. Study shows that TPI is lower and thus performance of DCMD setup is better for a combination of high feed and permeate velocity, larger filament diameter arranged mid channel using a thicker membrane in a counter flow arrangement. This can be used to design an effective hybrid desalination system to attain maximum flux.