CFD-assisted design improvement of a bench-scale nanofiltration cell

Abstract

CFD simulation was carried out with the aim to improve the design of a bench-scale nanofiltration cell and to increase the filtration performances. The laminar fluid flow in the flat circular filtration cell was simulated. Design variables considered were feed chamber thickness, number and distribution of the inlet/outlet pipes, sequential mode inlets, addition of grooves on the top surface of the cell. With the simulated design modifications, the velocity and the wall shear stress could be sharply increased and the size of the recirculation areas could be lowered. Two sequential mode inlets permitted to obtain high velocity and wall shear stress fluctuations in the cell. So, one can expect a sweeping of the membrane surface which should greatly hinder the polarization layer development and membrane fouling. A sharp enhancement of the nanofiltration flux was observed experimentally with the new designed cell, built including the suggested modifications. The addition of grooves on the cell top was simulated and showed intense velocity and wall shear stress fluctuations. The 2D study demonstrated that the groove size and the groove interval play a significant role. So, for small bench-scale cells when the use of retentate spacers is not convenient, the alternative would be to add grooves opposite to the membrane side in order to create velocity fluctuations.