Study on the Flow Field inside the Microfiltration Separator with Rotary Tubular Membrane

Abstract

By using a new type of laser surveying instrument named particle image velocimetry (PIV), the flow field inside a rotary tubular membrane separator with a rotating inner tubular microfiltration membrane and a transparent outer cylinder was measured experimentally, and from which some new observations were resulted. Pairs of stable Taylor vortices with similar dimensions and opposite flowing directions were directly visualized by the measured streamlines and vorticity of flow field in the annular gap of the membrane separator. No matter how the axial Reynolds number, radial Reynolds number and Taylor number changed, the dimensions of the Taylor vortices and the distances between the centers of adjacent Taylor vortices were almost the same, but the shapes of the Taylor vortices at lower Taylor numbers were more regular than those at higher Taylor numbers. The Taylor vortices disappeared because of the turbulence when the Taylor number was too high. The maximum axial velocity near the membrane surface was about 20 times larger than the mean velocity of axial flow inside the annular gap, and the maximum outward radial velocity near the membrane surface was even about 3000 times larger than the average velocity of the radial permeating flow through the tubular microfiltration membrane. The large velocities near the membrane surface, which were due to the Taylor vortices, could prevent solid fine particles from depositing onto the membrane surface and/or entering into the membrane pores and therefore result in reduced concentration polarization and reduced membrane fouling. The results in this study provided some valuable guidelines on the hydrodynamic way to reduce membrane fouling.