Transient permeate flux analysis: Model validation
An extended model integrating several particle back-transport theories has been proposed by Sethi and Wiesner to predict transient permeate flux as a function of operational parameters for constant permeate flux (CF) and constant transmembrane pressure (CP) cross-flow regimes. Filtration experiments using monodisperse latex suspensions of particles 0.02 μm, and 0.12 μm and 0.68 μm in diameter in a cross-flow flat slit membrane were carried out for model validation. In a separate set of filtration experiments with monodisperse latex particles 0.10 μm, 0.43 μm and 1.00 μm in diameter, the transient behavior of permeate flux in CP and CF modes of operation was compared. Significant differences between model calculations and experiments were observed. A slightly more complex structure at the cake-suspension interface was hypothesized to explain these differences. A representation of the cake with a gradually changing solids concentration allowed for better matching of the extended model and experimental results. The CP operation mode yielded a higher specific permeate flux resulting from a thinner cake or a cake with a lower average specific resistance. Experimentally observed differences between performance in CP and CF modes were less sensitive to the size of particles in the suspension than predicted by theory.