The Numerical Simulation For Flat Membrane Microfiltration

Membrane fouling is one of the most important problems which includes membrane pore blocking,cake forming and concentration polarization.Membrane fouling can induce the increasement of microfiltration resistance,meanwhile transmembrane pressure(TMP) will increase over time,permeation velocity would decay over time at constant TMP.In this study, mechanism models were developed for flat membrane microfiltration.In this study,blocking model was used to simulate and analyze experiments for dead microfiltration suspension containing particles of silicon.First of all,functional relations of four blocking models were derived to obtained model parameters using non-linear regression. This study simulated the TMP increase over time in constant rate.The result of simulation was successfully able to confirm blocking model could simulate the whole microfiltration process to some extent,but the model can't get exact results.It was found that membrane pore blocking occurred at initial time of microfiltration and cake filtration occupies most of the time based on the model parameters analysis.In view of above conclusion,it was found that solidosity increased with the TMP though the analysis of the compressibility of experiment cake which belongs to compressibility cake.This study carried out models of incremental analysis for microfiltration of compressibility cake using TMP as the incremental model. Solidosity of cake was computed by exponential function which was proposed by Grace and Cake resistance was calculated by Kozeny-carman function.The simulation process of incremental model analysis was derived for dead-end and constant rate microfiltration.The simulation results were matched well with experiment results.TMP,cake solidosity and cake resistance were simulated in different Permeation velocity and suspension concentration.For cross-flow microfiltration,this study analyzed the forces of particles of membrane surface.It was found that whether or not particles would deposit on the surface of membrane for micro-size particles dependings on the permeability drag force and inertial lift force determined and the particles settled on the membrane surface would not return to the body(or mother) suspension.The simulation process of particles by force model was derived,and permeation velocity,cake thickness and critical particle size were calculated over time under different TMP,suspension concentration and permeation velocity.Based on diffusion model of cross-flow microfiltration,the two-dimensional CFD model of cross-flow microfiltration was developed with COMSOL(finite element software). viscosity function was reference here by Leighton,and diffusion coefficient was the integrative coefficient which considered the effect of Brownian diffusion and Shear-induced diffusion.The process of concentration polarization layer formation on the surface of membrane was simulated by non-steady.Concentration field of particle on membrane was obtained in different grain diameter,cross-flow velocity and permeation velocity.The resistance of concentration polarization layer was calculated and compared with the results by the experience model of Romero and Davis at the same time;the simulating results are identical with the data obtained from the two models.In this study,the calculation model of flat membrane microfiltration suspension was carried out.The calculation programs were compiled with two operating condition which simulated the change of microfiltration parameters.For sure,the simulations have the ability to guide experiments in some extent which will reduce the amount of unnecessary experience. A CFD model described concentration polarization on surface of membrane was made,which had a great significance for understanding the forming mechanism of concentration polarization layer and concentration profile.