Eulerian, two-fluid CFD simulations were carried out to investigate the hydrodynamic features of changing the level of liquid that are responsible for flux enhancement in the airlift submerged flat-sheet membrane system. The proposed model is in good agreement with the experimental results in terms of gas hold-up. It was shown that by decreasing the liquid level, the intensity of mixing and distribution of liquid phase velocity in the riser was improved while the shear stress on the membrane surface was reduced. With the lower liquid level, the shear stress distribution restricted only to certain parts of the membrane, whereas at higher level of liquid the shear stress spreads over a large part of the membrane. Wall shear stress is probably the major factor responsible for reduction of fouling in membrane systems. Greater shear stress of the liquid will minimize the extent to which particles will settle on the membrane, thus, fouling will be reduced and flux will be enhanced. This study also shows that imaging technique provides valuable information for investigation of the hydrodynamic properties of MBRs. By analyzing specific properties of the bubbles like the bubble diameter and rising velocity in the recorded images, it is possible to make an estimation of: gas hold-up, bubble size distribution, and etc. Based on the results obtained in this study, it is thought that the performance of the airlift MBR can still be improved.
Available at: http://works.bepress.com/navid_mostoufi/46/