CFD simulation and optimization of an energy-efficient direct contact membrane distillation (DCMD) desalination system

Abstract

In this paper, the CFD simulation and optimization of an energy-efficient direct contact membrane distillation (DCMD) desalination system in a counter-current flow mode are performed. Two-dimensional modeling was applied and the governing equations for momentum, heat, and mass transfer in the three regions i.e., feed channel, membrane, and permeate channel were solved and corresponding velocity, temperature, concentration fields, and the permeate water flux through the membrane was obtained. A two-step approach was considered to optimize the desalination system through the MD process. First, the model results were validated with the reported experimental data and good agreements were observed. The maximum deviation for the outlet concentration and hot stream outlet temperature with different feed velocities and temperatures was 0.33%. Then, the process was optimized for maximizing the permeate flux. Since the number of parameters was high, the response surface methodology (RSM) was used to find the optimum condition in order to obtain the maximum water flux. It was determined that the highest permeate water flux would be gained at the permeate temperature, the hot feed flow rate, the cold-water flow rate, the length and height of the channels of 35 °C, 20 lit/min, 10.25 lit/min, 20 cm, and 3 cm, respectively. At this optimum condition, a permeate flux of 53.5 kg/m2.h and a TPC of 0.82 are expected.