Intensification of hollow fiber membrane cross-flow filtration by the combination of helical baffle and oscillatory flow

Separation performance of ultrafiltration has been hindered by membrane fouling and concentration polarization. This study investigated the effect of fluid dynamics induced by the combination of a helical baffle and oscillatory flow on the performance of a hollow fiber membrane module. An external pressure type cross-flow filtration was employed and purification of humic acid aqueous solution was selected as a model case. Normalized permeate flux and rejection were used for evaluation and compared in the following 4 cases; control, oscillatory flow without helical baffle, helical baffle without oscillatory flow and combined condition of helical baffle and oscillatory flow, called oscillatory baffled membrane module (OBMM). As for the OBMM, the normalized permeate flux could be kept at higher level and the rejection also showed much better performance than the others. The OBMM could maintain the clean membrane surface though all the other conditions could not inhibit the humic acid accumulation. These were caused by the vortices and the swirling flow resulting in the high shear stress and the renewal of the concentration polarization layer by their mixing effect. Finally, the oscillation conditions were varied and summarized in the oscillatory Reynolds number, Re_o, and the filtration performance was increased with the rise of Re_o corresponding to the intensity of oscillation.