Enhanced air gap membrane desalination by novel finned tubular membrane modules

To increase the permeate flux of air gap membrane distillation (AGMD) process, two novel tubular membrane modules: small and large, are designed and tested for desalination. The small module having a membrane surface area of 166 cm2 is basically composed of a nonporous finned copper tube for cold flow and the grooves outside of the tube for both the air and the permeate. The modules with air gap thickness of 1, 2 and 2.3 mm, and grooves number of 4, 6 and 11 are compared for their permeate flux, respectively. The effects of operating conditions including the feed flow rate, feed temperature, cold temperature, and temperature difference between the hot feed and cold solution are investigated on the permeate flux. It is found that the permeate flux higher than 50 kg m−2 h can be obtained in the proposed AGMD-based finned tubular membrane module with 11 grooves when the operating conditions are controlled at both hot feed and cold water flow rates of 5 L/min, hot and cold temperature of 353 K and 303 K, respectively. The flux is about 2–5 folds of the experimental results reported for AGMD modules in literature. The module under solar driven operation are further studied for the periodic variation of permeate flux, i.e., the desalination energy of which is supplied entirely by solar thermal collector. The large module composed of 10 finned tubes with a membrane surface area of 1661 cm2 is finally tested for the scale-up effect at the lab.