Experimental modeling of an air-gap membrane distillation module and simulation of a solar thermal integrated system for water purification

Membrane distillation is a novel process that could be adapted effectively for many water purification applications. In recent years, several bench, pilot and commercial scale membrane distillation systems with production capacities ranging from 20 L/d to 50 m(3)/d were developed and tested. In this work, a single cassette air-gap membrane distillation (AGMD) module was characterized to identify the effect of process parameters on distillate flux and thermal efficiency. Favorable conditions to obtain distillate flow rate of 1.5-3 kg/h were determined on a bench scale experimental setup. Factorial design of experiments was conducted and response surface methodology (RSM) was applied to develop an empirical regression model relating operating parameters with AGMD system performance indicators. Operating parameters including hot feed inlet temperature (T-Hin), cold feed inlet temperature (T-Cin), feed flow rate (V-f) and feed conductivity (C-f) were considered. Distillate flux (J(d)) and specific performance ratio (SPR) were selected as the performance indicators for the modeling. The developed regression model using RSM was tested by analysis of variance. Regression analysis showed agreement with the experimental data fitted with second-order polynomial model having determination coefficient (R-2) values of 0.996 and 0.941 for J(d) and SPR, respectively. Numerical optimization has been carried out to identify optimal set of operating conditions for achieving desired operation. Also, dynamic simulation of the membrane distillation module integrated solar thermal system has been reported along with validation of the system model by comparing with the experimental data obtained from a pilot scale setup located in UAE.