Experimental and theoretical investigation of air gap membrane distillation process for water desalination

Abstract

This study features an experimental and theoretical investigation of the performance of air gap membrane distillation (AGMD) system using flat-sheet poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) membrane for water desalination. To provide better understanding of the factors affecting the AGMD process, the impacts of system operating parameters such as feed temperature, feed flow rate, and feed concentration on permeate flux were studied. The performance of the AGMD process was statistically optimized using the design of experiment (DOE) and Taguchi techniques. Furthermore, a theoretical model describing heat and mass transfer analysis in AGMD was used. The system performance was mostly dominated by the effect of feed temperature and feed flow rate, while feed concentration had a considerable effect on flux. It was found that the permeate flux increased by about 3.8 fold with the increase of feed temperature from 45 to 65°C for 35g/L NaCl solution. The permeate flux increased by about 30%, while the feed flow rate increased from 0.25 to 0.55L/min. The rejection factor was found to be greater than 99.9% and the permeate conductivity was less than 20μS/cm. The theoretical model results were found to have good agreement with the experimental data as the maximum deviation of model results was within 20%. The model was also used to predict thermal efficiency and temperature polarization of the AGMD system. The maximum thermal efficiency of the system was 96% and the gain output ratio (GOR) was 4.87.