| Membrane micro filtration enhancement by rotary tangential flow is a new enhanced microfiltration technology which working principle is based on the hydro cyclone principle. It improves the structure of membrane separator and the form of suspension entering the separator, so as to increase membrane fluxes and decrease membrane fouling. The author designs rotary tangential flow tubular membrane separator and its test system for the first time. Through theoretical study and actual test, the author studied the flow field characteristics of rotary linear tangential flow and rotary circular tangential flow polypropylene tubular membrane microfiltration systematically, and revealed the mechanism of rotary tangential flow enhancing membrane microfiltration. The results in this paper are not only valuable in theory, but also valuable in practical engineering application. The main contributions of the study are included as follows:1. Under some conditions, the analytical expressions of the three-dimension rotary flow tangential velocity, radial velocity and axial velocity are derived from the Navier-Stokes equations for the first time, and their profile of distribution are analyzed.2. The thickness formula of forming cake layer per unit time of rotary tangential flow is derived. The formula demonstrates that the cake layer thickness is directly proportional to filtration permeation velocity and directly proportional to the density subtracter of suspension and permeating liquid, inversely proportional to the density of cake layer.3. The relation formula of radius ratio of separator with membrane tube, rotary tangential velocity and module annular gap filtration permeating velocity is derived, and the computation formula of membrane maximum length is obtained, these give theoretic fundamentals to design optimally rotary tangential flow tubular membrane separator.4. The non-permeating flow field of rotary linear tangential flow and rotary circular tangential flow and the permeating flow field of polypropylene tubular* Supported by the Natural Science Foundation in China (No. 29976025) and the key scientific research project of Education Committee of Sichuan Provincemembrane microfiltration with the advanced Particle Image Velocimetry (PIV) are tested for the first time. A lot of streamlines and vorticity maps of the meridian plane and tangential section of the separator in different operation conditions are obtained. The distribution characteristics of velocity of the meridian plane and tangential section are analyzed quantitatively.(1) At non-vortex area, no matter how the operation parameters change, the velocity near to rotary tangential flow entrance is higher than far from entrance at the same radial coordinates. At vortex area, generally the flow velocity of inner vortex is lower than the outer vortex. At the vortex center, the velocity is lowest, tangential velocity and radial velocity are equal to zero generally. At the vortex center zone, the tangential velocity and radial velocity are less than the axial velocity.(2) Under test operations, the tangential velocity, radial velocity and axial velocity of vortices borders are 1~2 times of average axial velocity of membrane module annular gap. The maximum tangential velocity, radial velocity and axial velocity of Taylor vortices or ellipse vortices are 2~6 times of average axial velocity of membrane module annular gap.(3) The vortices that are formed on the meridian plane and tangential section, there exists mass transfer between inner and outer parts of fluid. Much fluid of outer vortices gets into the inner ones, which is able to prevent membrane tube from particles blocking up very soon.(4) Testify qualitatively and quantitatively the hydrodynamics classical conclusions: the denser streamlines, the higher its velocity; the looser streamlines, the lower its velocity. At the same time, the velocity of dense streamlines zone is higher than the velocity of loose streamlines.(5) Generally, the membrane microfiltration...
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