A comparative analysis of commercial flat sheet and capillary membranes for membrane distillation applications

Performance of two commercial membranes, in flat sheet (FS) and capillary (Cap) configurations, has been analyzed for desalination through membrane distillation (MD). The performance of the membranes for large scale applications has been compared in terms of flux, pressure drop, pore size requirements and specific thermal and electric energy consumption. The calculations demonstrate that the FS membrane, characterized by relatively (~11 times) lower thickness, larger (33%) pore size and high (~20%) overall porosity compared to the Cap membrane, performs better in terms of trans-membrane flux and specific thermal energy consumption (maximum 36% less specific thermal energy consumption compared to the Cap membrane). However, the electric energy consumption associated with pumping the fluid inside the flow channels for FS membrane was nearly two orders of magnitudes higher than the Cap membrane. Furthermore, when pore size and contact angle for membranes in the two configurations are the same, the FS membranes are more prone to wetting than the Cap membrane when operating under the same conditions. The study also demonstrates that for a given module size and operating conditions, there exists an optimum freshwater recovery factor at which specific thermal energy consumption is the minimum.