Study On The Characteristics Of Flow And Mass Transfer In Profiled Membrane Channel For Reverse Electrodialysis

Reverse Electrodialysis(RED)is a membrane-based technology that converts the salinity gradient energy into electrical energy.In RED stacks,two adjacent ion exchange membranes are typically separated by a non-conducting polymer spacer,thereby forming a channel for solution flow.Although the presence of the spacer can enhance fluid mixing to reduce the concentration polarization,it will also bring some problems: the non-conducting spacer directly covers the membrane surface,reducing the effective area of the membrane;the moving path of the ions in the channel becomes tortuous,resulting in an increased internal ohmic resistance of the stack.If a profiled membrane is used instead of the traditional smooth membrane and spacer combination,it may possible to avoid the problems caused by the use of non-conducting spacers.At this time,the geometrical structures of the profiled membrane have important effects on mass transfer and pressure drop in the RED channel.In the existing surface structures of the profiled membranes,some have poor disturbance to the fluid,some may cause a large flow resistance,and some may cause difficulties in manufacturing and assembly.There is no profiled membrane structure with satisfactory overall performance until now.Therefore,it is necessary to continue to search for new profiled membrane structures and study their effects on the flow and mass transfer performances.In this paper,a new microstructure of profiled membrane is proposed: single-sided straight ridge V-shaped structure,and the flow and mass transfer in that profiled membrane channel is numerically investigated using ANSYS CFX code.Firstly,the independence of the grid is analyzed,and the accuracy of the numerical model is verified.Then the effects of geometric parameters and Reynolds numbers on the flow and mass transfer performances in the V-shaped profiled membrane channel are studied.The simulation results show that the V-shaped microstructure can induce vortices downstream of it,thereby disturbing the fluid and promoting fluid mixing.At the location of the V-shaped structure,the velocity component perpendicular to the wall increases,resulting in greater wall shear stress and better mass transfer.As the Reynolds number increases,the V-shaped structure enhances the mixing of the fluid,so the mass transfer is greatly improved,thus the uniformity of the concentration distribution is increased,and the concentrationpolarization is reduced,but at the same time,the pumping power consumption is also increased.As the height of the V-shaped structure increases,the cross-sectional area of the channel at the location of V-shaped structure decreases,and the velocity component perpendicular to the main flow direction increases,which causes a large flushing force on the wall surface,thereby increasing the wall shear stress and enhancing mass transfer.As the pitch of the V-shaped microstructure decreases,the disturbance to the solution will increase,so the mass transfer will be enhanced,thus the concentration distribution will become more uniform,and the concentration polarization will also be weakened,but the flow resistance will also increase.As the angle of the V-shaped structure increases,the power number will increase,the mass transfer will become weaker,and the uniformity of the concentration distribution will also deteriorate,but in general,the influence of the angle of the V-shaped structure on the flow and mass transfer is relatively small.Summarizing the influence of the geometric parameters of the V-shaped structure,it can be concluded that by reducing the pitch of the V-shaped structure,appropriately increasing the height of the V-shaped structure,reducing the angle of the V-shaped structure,and increasing the Reynolds number,a better mass transfer effect can be obtained at a lower flow resistance.The optimal V-shaped microstructure geometry parameters in this paper are: the pitch of the V-shaped structure is twice the height of the channel,the angle of the V-shaped structure is 60°,and the height of the V-shaped structure is 150 ?m.