Theoretical and experimental study in membrane distillation

Abstract

The performance characteristics of an air gap membrane distillation (AGMD) process for water desalination were investigated by conducting two long-run experiments. In the first test an 8-week continuous experiment was carried out using a PVDF membrane of 0.45μm pore diameter. The second test consisted of a 6-week run using a PTFE membrane of 0.5 μm pore diameter. Furthermore, the effect of hot side temperature, cold side flow rate and feed concentration were investigated. The experimental results obtained showed that the mass flux was steady over time and that it was affected only slightly by an increase in salt concentration. Permeate quality was dramatically affected when membrane wetting occurred, the cold side flow rate had a negligible effect on the permeate flux and the flux exponentially increased with an increase in hot side temperature. The effect of temperature gradient on mass transfer was clarified by applying the theory of non-equilibrium thermodynamics. The Soret coefficient indicates that the thermal diffusion coefficient is negligible in comparison with the actual mass transfer coefficient of the process.