The influence of back-shock frequency on the net flux at different transmembrane pressures and cross flow velocities has been studied. The mathematical model used in the investigation solves the continuity equation in a two-dimensional domain near the membrane surface. An osmotic pressure model is used to calculate the concentration at the membrane surface. The highest value of the normalized net flux was found at high transmembrane pressure and high cross-flow velocity. The normalized net flux at optimal conditions was 1.36 times higher than the flux without back-shocking. The optimal forward filtration time at the highest transmembrane pressure and the highest cross-flow velocity is approximately 5 s, corresponding to a frequency of 0.18 Hz. The optimal forward filtration time decreases as a function of both increasing transmembrane pressure and increasing cross-flow velocity. (C) 2016 Elsevier B.V. All rights reserved.