Influence of Microporous Membrane Properties on DCMD

It would very useful if one can predict the performance of a microporous hydrophobic membrane in Direct Contact Membrane Distillation (DCMD) just from the nominal  properties of the membrane if the boundary layer heat transfer coefficients are known. To evaluate the influence of membrane properties on their performance in desalination by the DCMD process, a variety of microporous hydrophobic flat sheet membranes of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) were studied over a range of hot brine temperatures, 65-85deg C. The membranes had a wide range of values of the pore size and thickness. Experiments were done using two different flat membrane test cells, one made out of stainless steel and the other from chlorinated polyvinyl chloride (CPVC). Membrane properties, such as the maximum pore size were experimentally determined.  Mass transfer modeling involved both the Knudsen and the transition regimes. The boundary layer heat transfer resistances in the membrane cells and the membrane surface temperatures were determined from experimental data via Wilson plots. Good agreements of membrane mass transfer coefficients and water vapor fluxes were found between the model simulations and the experimental results.