Study On The Desalination Effect And Characteristics Of The Micro-Nanochannel Based On Ion Concentration Polarization

In recent years,the study on the micro-nanochannel in the microfluidic technology has been made significant progress for charged inner walls can function similarly as ion permselective membrane.This article constructed one symmetric model with three parallel microchannels connected with two sets of nanochannel arrays and explained the mechanism of desalination within the channel by using numerical simulation method.For example,when the voltage difference,V_cn,across the nanochannel array is equal to 10V_T,the desalting efficiency can have reached nearly 90%;as the V_cn is increased continuously to 20V_T,the desalination rate will definitely exceed 99%and as the V_cn increases the rate increases more slowly.When it comes to the fluid flow,the article gave out the reason for the pressure flow.When the V_cn is equal to 0,the main form of the fluid motion in the channel should be electroosmosisof the first kind?EOF1?;as the V_cn is improved gradually,the pressure will play the leading role,which will compensate positively for the flow in the upper-stream ofthe channel whilehaving the negative effect on the flow in the down-stream.When the value of the V_cn is big enough,there will be a nonlinear vortex in the vicinity of the nanochannel array,namely the pumping effect induced by the enhanced EOF1.Concerning to the velocity of the flow,we got the dependence of the net fluid velocity on the voltage decline between the inlet and outlet,V_LR,together with the V_cn and the EOF2?electroosmosis of the second kind?slip velocity,U_S2,on the V_cn.When the V_cn is relatively small compared to V_LR,the net velocity in the channel increases approximately linearly with V_cn at a small slope,because the whole channel's fluid motion is mainly determined by EOF1.As V_cnis further increased,the system becomes dominated by EOF2,the net velocity increases linearly with V_cn with a large slope.Lastly,the higher V_LR is,the higher V_cn is needed for the fluid to enter the EOF2-dominated regime.Besides,we also study the relationship between U_S2 and V_cn by adding the same voltage to the inlet and outlet of microchannel embedded with membrane or connected by nanochannel array.Then,we compare the differences of the microchannel's characteristics embedded with membrane before and after adding an array of 9 square obstacles to the channel and changing the position of the array.It was found that the net velocity of the channel was decreased after adding obstacles,the desalination efficiency became higher,EOF2 was suppressed obviously and the desalination zone was expanded towards the upper stream of the channel when the array was at some specific positions.The method above helps to improve the efficiency of desalination in the channel.