Simulation Of Ion Transport And Electroconvection Near The Surface Of Ion Selective Membrane Under Electric Field

Electrodialysis technology has been applied in desalination industry for a long time.In recent years,electrodialysis has been gradually applied in pharmacy,effluent treatment and other industries in recent years with the improvement of the properties of ion exchange membranes and device.However,in current industrial systems,limited by the effects of polarization,electrodialysis systems are always running in low-voltage regime,and there also exist some defects in the related traditional electrodialysis theoretical research;this paper will concentrate on the electrodynamic state of ion mass transfer model based on electrodialysis,improving traditional theoretical electrodialysis model,and investigating the feasibility of operation under high voltage regime.Firstly,one ion mass transfer model is established based on the traditional electrodialysis.Different electrodynamic states in the membrane system are divided into three stages in current-voltage curve: ohmic stage regime,limiting current regime and over limiting current regime.Studies show that there exists a linear proportional relationship between the flow velocity of non-equilibrium electroosmosis and the square of applied voltage.The non-ideal membrane boundary conditions are proposed on the basis of the traditional ideal membrane boundary conditions in the membrane system.The results show that there only exist discrepancies in the ion transport process under two boundary conditions in low voltage regime.The increasing number of charges inside the membrane will make electrodynamic state of the two boundary conditions tend to be consistent.Comparing the membrane system with the nano-channel system of the same scale,the nano-channel system is also ion selective and it can be found that there is also ion concentration polarization in the nano-channel system.The enhancement of the surface charge density of the nano-channel and the decrease of the number of nano-channels will result in the intensification of intensity in ion mass transfer.Finally,the changes of the system's electrodynamic state caused by the polarization of ion concentration under the action of shear flow are studied.It is proved that electroconvection is the main mechanism accounting for the instability of system in the over limiting current regime.The numerical solution results show that increasing the applied voltage,reducing the inlet velocity and shortening the channel size can greatly improve the ion transmission efficiency.Meanwhile,there also exist a scaling relationship between the height of vortices induced by electroconvection and these impact parameters,and it can be used to adjust the operation of electrodialysis system in high voltage regime according to the actual situation,and it is instructive for electrochemical system which is based on membrane.