Thermal modeling of fluid flow and heat transfer in direct contact membrane distillation

•An optimization analysis was performed between water flux and Gain output ratio.•Study of effect of operating and geometric parameters on performance of the system.•Solar thermal energy is utilized to power a desalination process.•Polyethylene membrane exhibit the highest permeate water flux.•Polytetrafluoroethylene membrane provides the maximum Gain output ratio. In this paper, a mathematical model was developed, and numerical simulations were conducted to analyze the direct contact membrane distillation process (DCMD) utilizing solar energy. The objective is to identify the optimal operating point, flow parameters, dimensions, and membrane properties of membrane module in terms of permeate water flux and GOR. The novel aspect of this paper is to analyze the flow patterns in the feed and permeate regions on performance of DCMD to maximize water production by optimizing the balance between permeate water flux and GOR. Additionally, the study will identify the most suitable location for installing the MD system based on factors such as solar energy availability and average annual temperature. The results show that the polyethylene (PE) membrane provides the highest permeate water flux, while the polytetrafluoroethylene (PTFE) membrane provides the highest GOR. A significant increase in permeate water flux and GOR is observed when the flow changes from laminar to turbulent. The study also examines the effect of membrane module dimensions, where increasing the length decreases flux but increases GOR, while increasing the width increases flux but decreases GOR. The study also reveals that countries with high annual average temperatures produce higher permeate water flux and GOR. The paper also delves into the effect of membrane properties on water flux and GOR. It is observed that a membrane with high porosity, low thickness, and having a pore size greater than 0.14 µm is desirable.