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In the direct contact membrane distillation (DCMD) system, the temperature polarization due to boundary layer formation limits the system performance. This study presents the experimental results and heat transfer analysis of a DCMD module coupled with a salinity gradient solar pond (SGSP) under three different flow channel configurations. In the first case, the feed and permeate channels were both empty, while in the next two cases, the feed and permeate channels were filled with a porous spacer material. Two different spacer geometries are examined: 1.5 mm thick with a filament angle of 65°, and 2 mm thick with a filament angle of 90°. The study considers only the heat transfer due to conduction by replacing the hydrophobic membrane normally used in a DCMD module with a thin polypropylene sheet so that no mass transfer can occur between the feed and permeate channels. The Reynolds number for all three configurations was found to be between 1000 and 2000, indicating the flow regime was laminar. The flow rate through both the feed and permeate sides was the same, and experiments were conducted for flow rates of 5 L/min and 3 L/min. It has been found that the highest overall heat transfer coefficient was obtained with the spacer of 2 mm thickness and filament angle of 90°. [ABSTRACT FROM AUTHOR]

This research aimed to examine the effect of the thermal conductivity model of hydrophobic membranes on performance modelling of direct contact membrane distillation systems. The parallel, series, and two types of Maxwell models were studied. Simultaneously, an iterative numerical model was developed to choose the most appropriate model by analysing the mass flux (Jw) and the heat transfer rate (Q-P). Comparison with the experimental results, showing that Maxwell Type II was the most appropriate for modelling the thermal conductivity of the membrane. Also, based on the chosen model of membrane thermal conductivity, the direct contact membrane distillation performance (the global heat transfer coefficient, temperature polarization coefficient, energy efficiency, and gain output ratio) was studied. It was found that the membrane thermal conductivity model with a higher value of membrane thermal conductivity (km) resulted in an underestimation of the predicted mass flux, temperature polarization coefficient, and energy efficiency. In contrast, the total heat transfer coefficient and predicted heat rate were overestimated. The gain output ratio values seemed not to be affected by this choice with only 8% deviation among the four models. [ABSTRACT FROM AUTHOR]