Study Of The Flow Field Characteristics And Filtration Performance In Annulus Of Rotary Tubular Membrane Separator

Rotary tubular membrane filtration is one of the most efficient methods to enhance cross-flow microfiltration. It can resolve the key problem of membrane fouling and concentration polarization that obstruct the development and application of the membrane separation technology for a long time. But its separating mechanism and the flow field characteristics in the annulus have been far from understanding, because the flow field is a combination of circular Couette flow, pressure-driven axial flow, and radial permeating flow at the inner cylinder. The flow field in the meridian plane of the apparatus was measured with Particle Image Velocimetry System (PIV) in 2001. In this paper, the flow field characteristics and filtration performance were investigated based on theoretic analysis and actual measurement.First, on the basis of previous research, transition law of the flow in the annulus and the characteristics of three vortex regimes (wavy vortices, alternating helical vortices and alternating helical wavy vortices) were discussed. When both axial flow and permeating flow existed, the formulae of critical Taylor number were deduced as flow transformed from Couette-Poiseuille flow (CP) into laminar vortices (LV) and from laminar vortices (LV) into wavy vortices (WV) respectively.Then, lots of velocity vector-graphs and streamlines of vortices in the meridian plane of the separator obtained in previous measurement were analyzed. In the absence of axial and permeating flow, when the rotational frequency of inner cylinder was 0.90rps, laminar vortices were observed. Laminar vortices are nearly sauare, and the dimension of vortices approximates to the width of annular gap. Laminar vortices are essentially...