Theoretical and experimental studies on air gap membrane distillation

Air gap membrane distillation (AGMD) is an innovative membrane separation technique for pure water extraction from aqueous solutions. In this study, both theoretical and experimental investigations are carried out on AGMD of different aqueous solutions, namely, tap water, salted water, dyed solutions, acid solutions, and alkali solutions. A simple mechanistic model of heat and mass transfer associated with AGMD is developed. Simple relationships of permeate flux, total heating or cooling load and thermal efficiency of AGMD with respect to the membrane distillation temperature difference are obtained. Effects of solution concentration and the width of the air gap in AGMD are analyzed. In the experimental study, the experiments were conducted using 1 μm PTFE membrane with a membrane distillation temperature difference up to 55°C. The AGMD system yields a permeate flux of pure water of up to 28 kg/m² h. Direct comparison of the experimental results with the proposed modeling predictions shows a fairly good match.