Numerical Study On Fluid Flow And Mass Transfer Characteristics In Channel For Reverse Electrodialysis

Reverse electrodialysis(RED)is a technology to convert salinity gradient power into electric energy.The flow channels with ion exchange membranes as the key components are important parts of RED stacks.Non-conductive net spacers are usually adapted in RED stacks to separate and control a fix distance between adjacent membranes to provide a channel for solution flow.However,net spacers increase the stack electric resistance and supply high flow resistance within the channel.Profiled membranes with single-side or double-side microstructures can act functions as net spacers to offer flow channel,which can overcome the drawbacks caused by conventional net spacers.In this works,the solution flow and mass transfer behaviors in the channel formed by chevron-profiled membranes were investigated,and the potential of chevron-profiled membranes performance in RED was discussed.Three-dimensional numerical simulations were performed on a periodic unit cell in fully develop region of RED dilute channel.The girds independence was analyzed,and the numerical model was also validated.The influence of chevron pitch to height ratio,corrugation angle and Reynolds number on fluid flow and mass transfer was extensively investigated.Simulation results show that the chevron corrugations can cause a flow shift in transverse direction resulting a complex flow field thus promotes the feed solution mixing even at low velocity.The solution washes against membrane surface will induce mass transfer enhancement and relatively high local wall shear stress.The effect of chevron corrugations on disturbance can be strengthened with Reynolds number increasing gradually,which led to increase local wall shear stress value on the surface of membrane,and the mass transfer will be also strengthened,but the solution flow though channel with high pressure drop means that flow requires additional pump power consumed.The influence of chevron corrugation angle on mass transfer is restricted by chevron pitch to height ratio and Reynolds number,while has a weak effect on the pump power consumption.The distribution of local wall shear stress on the membrane surface becomes uniform when the value of chevron corrugation angle is low.To decrease chevron corrugation angle in the low range of Reynolds number,which can enhance mass transfer,but the corrugation angle causes weak effect of mass transfer enhancement with the increasing of chevron pitch to height ratio.Disturbance offered by chevron corrugations on fluid flow is significant when chevron pitch to height ratio is low.Decreasing chevron pitch to height ratio,there is a positive effect on mass transfer strengthened and local wall shear stress increase,while it will consume more pump power due to pressure drop increased.In the range of low Reynolds number studied here,the chevron corrugations can promote feed solution mixing at low velocity with lower pump power consumption than net spacers.