A research on water desalination using membrane distillation

Abstract

This research work aimed to investigate the performance of direct contact membrane distillation (MD) unit under different conditions. A mathematical model was developed to evaluate the experimental values of the membrane water mass flux, heat transfer coefficients, the membrane/liquid interface temperatures, the temperature polarization coefficient (TPC) and the evaporation efficiency. This model was solved numerically using MATLAB® software, and its results were used to predict the actual performance of the membrane unit. The MD coefficient was evaluated from the computer model data and was subsequently used to estimate water fluxes. Experimental tests were performed using 0.0572 m2 of poly-tetra-fluoro-ethylene membrane manufactured by membrane solution (85% porosity, 45-µm thickness, 0.22-µm nominal pore size). Feed solutions were aqueous NaCl solutions with 1,000–200,000 mg/L (0.1–20%) in concentration, its temperatures were 40–80°C and feed flow rate was 2 l/min. The temperature and flow rate of permeate water was fixed at 20°C and 3 l/min, respectively. The experimental observation showed that the vapour mass flux through the membrane pores increased with feed temperature, but decreased with feed concentration. It was found that the predicted mass fluxes agreed reasonably with the experimental data, except at a high feed concentration. The temperature polarization coefficients increased with concentration and decreased with increasing temperature. The membrane heat transfer rates and the permeate flux have been discussed in this paper.