Microfiltration Membrane Channel Flow Field And Enhanced Mass Transfer Research

Membrane separation technology has been paid more attention because of its advantages such as no phase change,no secondary pollution and high separation efficiency.However, in membrane separation process,the particles,colloidal particles and macromolecule will cause the adsorption,seal lock and concentration polarization in membrane surface,which lead to the fluX depression and the decrease of separation efficiency,and severely restricted the industrialization of membrane technology.In this paper,a method of arranging turbulence promoters in membrane channels were proposed in order to reduce membrane fouling and increase mass transfer fluX.Turbulence promoters can improve hydrodynamic conditions in the membrane assembly,significantly improve wall velocity or shear rate and helpful to restrain the deposition of particles on the membrane surface and reducing membrane fouling in microfiltration process,so as to improve the fluX of microfiltration.The enhancement of mass transfer efficiency of turbulence promoters depends mainly on the hydrodynamic effects of the membrane surface.However,the hydrodynamic mechanism of mass transfer enhancement by turbulence promoters is not clear.In this paper,turbulence promoters was used to enhance the crossflow microfiltration process.CFD(Computational fluid dynamics)was used to simulate the flow field with different turbulence promoters in the flat plate membrane channel.The influence of the location and structure parameters of turbulence promoters on the enhancement of mass transfer efficiency was investigated,the structure of the original turbulence promoter was optimized,and a new turbulence promoter with small energy consumption and better mass transfer effect was acquired.The mechanism of enhanced mass transfer in the microfiltration process was improved,which could provide guidance for the application of turbulence promoter.First of all,by means of the turbulent promoters,the influence of the type and location of the parallel arrangement turbulence promoters on the enhancement of mass transfer efficiency was investigated.The results show that the turbulence promoters which were arranged in the middle of membrane channel obtained higher wall shear stress based on the same turbulence promoters and the channel structure parameters.The four prism turbulence promoters can provide highest wall shear stress.In order to reveal the hydrodynamic mechanism of mass transfer enhancement caused by turbulence promoters,CFD was used to simulate the flow field with turbulent promoters in the membrane channels.Numerical analysis of flow field shows that the turbulence promoters induced the formation of vorteX in membrane channels and wall velocity fluctuation and increased wall shear stress,and enhanced the turbulence intensity of the fluid,which can destroy the development of the boundary layer and inhibit the deposition of the particles in the liquid,so as to improve the fluX of microfiltration membrane.Secondly,according to the structural characteristics of the four prism turbulence promoter,a new kind of turbulence promoter was designed,CFD was used to simulate the flow field with new turbulent promoters in the membrane channels.The hydrodynamic mechanism of mass transfer enhancement was analyzed,and the effects of the structure parameters of turbulence promoters,the height of the channel and the inlet velocity on the flow field characteristics were investigated.The analysis of the flow field shows that the new turbulence promoters can reduce the pressure drop while obtaining high wall shear stress.That means the mass transfer effect is better and the energy consumption is smaller than the original model.Finally,the turbulence promoters model which added temperature field to enhance the mass transfer was established,The enhanced mass transfer effect of turbulence promoter with different feed flow angle and inlet velocity was investigated.The numerical simulation results show that the higher inlet velocity is favorable for increasing the transmembrane pressure difference,the wall shear stress and the temperature polarization coefficient,and increasing the driving force of mass transfer and heat transfer.The model of feed angle?f =45° has the best mass transfer and heat transfer effect,and requires the minimum energy consumption.When the inlet velocity was 0.14m/s,the mass transfer fluX reached 111.3kg/m2 h,which was 15.7 times of the model with no turbulence promoter.The effects of feed temperature and particle mass flow rate on membrane fluX were analyzed,and provide guidance for the application of temperature field used for the enhancement of mass transfer.