Numerical Simulation Of Filtration Process Of Ceramic Membrane Filter

Ceramic membrane filtration technology has the advantages of high precision,stable filtration and strong environmental adaptability.It is widely used in many fields such as production of drinking water,medicine and food.It also shows great potential in the production process of separation,clarification,purification,concentration,sterilization and desalination.In this paper,aiming at the existing ceramic membrane filter equipment,the pure water filtration process of ceramic membrane filter is numerically simulated by CFD technology,and the internal flow field of the filter is analyzed.In this paper,ANSYS FLUENT software is used to simulate the pure water filtration process of membrane element and membrane module filter,and the influence of inlet flow rate,membrane aperture and filtration mode on the filtration performance of membrane element and membrane module filter is studied.The results show that the filtration pressure difference increases with the increase of inlet flow rate and presents a linear relationship,and the smaller the membrane pore size is,the faster the filtration pressure difference increases.The filtration pressure difference increases with the decrease of membrane pore size.The main pressure loss occurs in the infiltration process,and other pressure losses are very small,even negligible.The contribution rate of the outermost membrane channel,the middle layer channel and the innermost layer channel to the pure water flux of membrane elements is as follows: the outermost channel > the middle layer channel > the innermost layer channel.When the pore size of the membrane is very small,the permeability of the innermost channel is very small,which can be ignored.The filtration pressure difference of membrane module is much smaller than that of membrane element.When the total filtration mode is adopted,the filtration efficiency of the membrane module filter is much higher than that of the membrane element filter,which can reduce the operation cost of the filter,improve the water production,and extend the service life of the ceramic membrane,so as to improve the economic benefits.Then,fluent was used to simulate the cross flow filtration process of membrane element filter,and the influence of inlet flow rate,operating pressure difference,membrane aperture and filtration mode on the filtration performance was studied.The results show that the increase of inlet flow,the increase of operating pressure difference and the decrease of membrane pore size can improve the membrane permeability flux,and the influence of membrane aperture on the permeability flux is more significant.The increase of inlet flow and operating pressure difference has no obvious effect on the contribution rate of pure water flux of each membrane channel,but the increase of membrane pore size makes the contribution more uniform.The main factors influencing the contribution rate of each membrane channel are the pore size and the configuration of the membrane channel.When the inner pressure filter is adopted,the flow rate in the membrane channel is the largest,the tangential velocity near the channel surface is larger,and the shear stress is larger;if the sewage is filtered,the pollution rate and degree of the inner surface of the membrane channel are relatively small.When the external pressure filter is adopted,the water flow velocity is low because of the large cross-section of the shell cavity,and even the low-speed zone is formed in the middle area of the outlet of the cavity.The tangential velocity of the outer surface of the membrane is low and the shear stress is small.When the sewage is filtered,it is easier to deposit the particles;this causes the uneven distribution of the pollution on the outer surface of the membrane,which shortens the membrane to make it easier to deposit the particles Service life.Under the same operating parameters,the pressure on the inner channel surface of the inner pressure filter is always greater than that of the outer mold surface of the external pressure filtration;when the internal pressure filtration,the permeability flux of the membrane element is always greater than that of the external pressure filter.Finally,the DPM model was used to simulate the particle trajectories in the process of total and cross flow filtration,and the effects of different filtration methods on particle trajectories were studied.The results show that the uniformity of the membrane surface pollution in different filtration modes is compared: internal pressure cross flow mode > internal pressure dead end mode > external pressure cross flow mode > external pressure dead end mode;the comparison of particle capture rate in different filtration methods: internal pressure dead end mode > external pressure dead end mode > external pressure cross mode > internal pressure cross flow mode.The internal pressure cross flow mode is the best filtration method,with uniform pollution and less pollution.