Performance Research And Mechanism Analysis Of PVDF Hollow Fiber Membrane Based On CFD

To meet the increasing demand of water resources for economic development,sewage treatment and wastewater reuse have become the focus of global attention.Membrane bioreactor(MBR),as a new wastewater treatment system organically combined with traditional wastewater treatment technology and membrane separation technology,has the characteristics of small floor space,good treatment effect and stable effluent quality,and has been widely used in the field of watertreatment.However,due to the limitations of experimental conditions and equipment costs,there are still some limitations in the in-depth study of membrane mechanism.CFD(Computational Fluid Dynamics)methods and common software as a simulation tool,experiment research method combining with theory,describe the actual flow field in a smaller scale characteristics of hydraulics and real-time observation of flow law and physical parameters of the model,for the research in the field of membrane and optimum setting provides an important basis.This study adopts the method of fluid mechanics to establish the geometric models of MBR single wire membrane through the pretreatment softeare Gambit.The single phase porous media and solid liquid two phase and gas-liquid two phase were numerically simulated.The membrane performances of solid-liquid separation,gas phase and liquid phase velocity,pressure,wall shear stress were studied.The hydrodynamic characteristics of membrane in the process of filtering were analyzed through comparing the experimental data and the simulation results.By studying the gas holdup distribution in a two-dimensional simplified reactor,the influence of the aeration layout height and aeration strength on the internal flow field of MBR film pollution was investigated,which provided a reliable basis and practicle reference for the optimal design of MBR and the setting of optimum process parameters.According to the simulation process and effect,the conclusion is: The simulation results of single phase of two-dimensional and three-dimensional single filaments are basically the same.The single membrane filament exists in the inlet transition section.The central velocity in it is high and the velocity near the wall decreases gradually.The pressure in the membrane decreases gradually along the pipe length direction.The shear stress on the wall decreases rapidly along the pipe length and tends to be stable.The solid-liquid two-phase separation performance of the membrane was good during full-volume filtration and cross-flow filtration,and the viscosity value at the outlet of full-volume filtration was gradually close to that of pure water.The pressure value in the membrane filament under cross-flow filtration decreases steadily and finally approaches zero at the exit.The flow velocity in a single filament-column membrane module simulated by gas-liquid two-phase flow decreases along the radial direction,and the velocity increases at the exit due to the extrusion of the porous area and the resistance formed by the two side walls.The shear stress is related to the velocity of fluid.The higher the velocity is,the greater the shear stress is.Compared with the liquid phase flow rate of 0.3m/s,the membrane wire at the inlet had a large force and a large fluid flow.After membrane filtration resistance,the velocity dropped relatively slowly,the membrane flux was relatively ideal,and the overall pressure inside the membrane was relatively large.At the outlet of the membrane wire,the pressure dropped rapidly due to the high energy loss.There was no significant difference in the velocity distribution between 0.3m/s and 0.15m/s.At 0.3m/s,the gas velocity on the surface of the film wire was relatively large,and the shear stress generated by the bubble group was strong,which was conducive to the cleaning of the membrane surface pollution in the later stage.The simplified model with a distance of50 mm from the aeration stoma and an aeration speed of 0.45m/s as well as the model with a distance of 30 mm from the membrane module and an aeration speed of 0.3m/s had relatively uniform gas holdup distribution inside the reactor,with good gas-liquid mixing effect,which was the optimal design.