Numerical Simulation of the Performance of Multistage Direct Contact Membrane Distillation

In this work, a multistage membrane distillation system was numerically examined. Specifically, this study addresses the effect of multi-staging on the reduction in temperature and concentration polarization and its impact in improving the DCMD productivity. Moreover, this study addresses the effect of co-current and counter-current flow arrangements on system performance. The numerical analysis provided detailed velocity, temperature, and concentration profiles of the direct contact membrane distillation system. A 2D numerical simulation of direct contact membrane distillation (DCMD) was conducted for a system with a length of 500 mm in a single stage in contrast with five stages. Results showed a significant improvement in performance up to 26.3% in the case of the five-stage system. The study also shows that increasing the number of stages for co-current operation has a greater impact on the percentage improvement of the permeate flux than counter-current operation. The counter-current configuration exhibited a better initial performance than the co-current configuration in permeate flux for a single stage by increasing the number of stages. Hence, the difference in the total permeate flux diminished and became less noticeable between the two configurations. Furthermore, the effect of multi-staging on improving permeate flux under different inlet conditions, including mass concentration, feed temperature, and velocity, was investigated. Results indicated that increasing the aforesaid inlet conditions improves the permeate mass flux through multi-staging. Specifically, an improvement of more than 30% is realized by increasing the number of stages in some inlet condition cases.