Among the indirect measurement approaches, Schock and Miquel [9] performed regression of flat sheet membrane performance data to determine the mass transfer coefficient in a plane,feed spacer filled channel using the combination of film theory and an empirical membrane transport model. This empirical transport model assumes that the permeate flux is linearly dependant on the difference between applied pressure and osmotic pressure. The authors used a dimensionless correlation to describe the mass transfer coefficient, in the form of Eq.