| The aim of the research is to reduce the polarization and membrane fouling during the micro-filtration process, and this research was funded by a NSFC project named "Research on Micro-filtration Enhancement Mechanism of Centrifugal Force Field (29976025)". Pressure field of rotary cross-flow and axial flow in annular gap of tubular membrane separators was tested by a online pressure testing system- controlled by computer. The micro-filtration enhancement mechanism of rotary cross-flow was discussed, and the three-dimensional turbulence field in annular gap of the rotary cross-flow tubular membrane separators was numerical simulated also. The main contribution of this paper is as follows.1. The pressure field in annular gap of the separator was systematically studied at the first time with an online pressure testing system. The distribution characteristics of time-average and pulse pressure in the annular gap, and their effects to micro-filtration, altogether with factors such as inlet operating pressure, size of the annular gap, and concentration were uncovered in this paper.The radial pressure (regardless of time-average or pulse pressure) reaches its maximum on the surface of the annular gap, its distribution curve looks like an asymmetric saddle, with fluctuation in its middle part The radial pressure gradient decreases with distance between testing point and the inlet position (the order is from top to bottom). The pulse pressure reaches its maximum on or near the membrane surface, and its value on or near the surface of the separator is a little lower than its maximum. The pulse pressure obtains its minimum in the middle of the annular gap if the inlet pressure is SOkPa with a perturbation of 0.3-0.4kPa. The distribution characteristics of pulse pressure and time-average pressure are the same. Centrifugal inertia! force (produced by the suspension's tangential inlet) and turbulence flow are responsible for the radial pressure gradient variation in annular gap. They also cause the violent pressure perturbation, thus both the radial decreasing pressure gradient and the velocityvariation have relatively large values, and the pressure energy exchange with kinetic energy severely. The centrifugal force and turbulence diffusion make the particles overcome the traction of the permeating flow, and severely perturbation flow appears in area near the surface of the membrane. Therefore, particles sinking to membrane surface will return to the main flow due to the centrifugal force and perturbation flow. Since the suspension blend sufficiently, polarization and membrane fouling are reduced and the micro-filtration is enhanced. By the influence of gravity, the axial pressure in the annular gap increases with distance between the testing point and the inlet. The axial pressure fluctuates greatly on or near the membrane surface and the separator's wall, this is due to the turbulence flow and the variation of velocity. The main reason of the pressure fluctuation is the interaction between rotary flow and separator's wall.2. Comparing with the axial cross-flow, the rotary cross-flow has a lower energy consuming, higher valid energy utilization, and more permeating flux. Analysis and discussion based on these facts provide the theoretic basis to its engineering application.Starting from the energy loss coefficient and valid energy utilization, the author investigated the problem of energy consuming in rotary cross-flow and axial cross-flow separating. Due to the centrifugal force, the pressure in the annular gap of rotary cross-flow is higher than that of axial cross-flow in same operating condition, and there exists radial pressure difference and velocity difference. Therefore, rotary cross-flow separator has a higher permeating flux, lower energy consuming, and higher energy utilization than axial cross-flow.3. The micro-filtration enhancement mechanism was uncovered by the comparing investigation of problems such as forces exerted on particles and pressure field characteristics of rotary cross-flow and...
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