Three Dimensional Numerical Simulation Of Flow Characteristics And Optimization Of Balde Geometry In An Enzymatic Membrane Reactor

Membrane filtration has been widely applied in many industrial separation treatments, such as wastewater treatment, biological separation and desalination of sea water. Membrane fouling phenomena have well been known to reduce the flux and shorten the lifespan of membrane significantly, which can weaken the filtration efficiency and increase costs seriously. A large number of studies have shown that enhanceing the shear stress on membrane surface by using rotating parts can significantly control membrane fouling.This paper focuses on the widely used magnetic agitator enzyme membrane reactor(Amicon 8050, Millipore), using the method of computational fluid dynamics for numerical modeling. Firstly, we simulate and analysise the flow characteristics in the reactor with single-phase flow, and studied the effect of rotation on that. Due to the flow with high curvature and high Reynolds number, we appl y the RNG k–? model for turbulent coupled with the Multiple Reference Frame approach for the rotation and a porous medium for membrane. Compared with the experimental results, results show that the numerical model has better accuracy and reliability. Then, membrane fouling behavior involves the pollutant transportation, convection, diffusion, deposition and with complex interphase interactions, is a complex problem of multi-phase flow. Polllutant transportation or convection diffusion and membrane fouling behavior is discussed by using Eulerian ?two fluid? model on the basis of single phase flow. Finally, we conduct an optimization of blade shape structure for the enhancement and uniformity of shear stress with single-phase flow. A total of three groups of blade shapes or structure are studied in the paper.The numerical results with single-phase flow show that, due to the mixing effects of rotation there exit several groups of recirculation loops in the reactor, which may affect the transportation and diffusion process of pollutants directly. Vortexes generate on membrane surface due to rotation effect, intensity and distribution of vortexes is closely related to the rotation speed. Velocity or shear stress can be strengthened by the rotation speed, but their distributions are uneven. The low velocity and shear stress area near the center of membrane reduce the utilization of membrane area. Increasing the rotation speed can enlarge the recirculation loops and enhance shear strength, but was unable to improve its distributio n uniformity. The numerical results with multi-phase flow show that, pollutant concentration distribution in the reactor can be divided into three regions, and concentration near the region near the membrane surface is the lowest. Increasing the rotation s peed can accelerate the transportation and diffusion process of pollutants and reduce membrane fouling significantly. The results of optimization of blade shape or structure shows that, the ?T-shape? blade can not only get stronger shear stress but can obtain good uniformity on membrane surface than straight blade limitedly. It performs the best while ?T-reverse? blade performs the worst. Therefore, increasing the cap width of ?T-shape? blade is a good choice for shear stress.