Study On Flow And Mixing Performance Of Passive Micromixer

As an important part of microfluidic system,micromixer is widely used in chip laboratory,biomedical detection,chemical reaction and microreactor because of its compact structure,easy integration and little damage to test samples.However,due to the small size of the mixing channel in the passive micromixer,the mixing between fluids mainly occurs in the form of intermolecular free diffusion,resulting in the low mixing efficiency of the passive micromixer,which is difficult to ensure the full mixing and reaction between reactants in the microfluidic system.Therefore,how to reasonably design the passive micromixer is of great significance to improve its flow and mixing performance.Therefore,taking the T-shaped passive micromixer with rectangular section as the research object,this paper studies the flow and mixing performance of the passive micromixer by combining theoretical analysis and numerical simulation.The main research contents are as follows:Firstly,under the constraint of constant total channel volume,the theoretical model of pressure loss and mixing efficiency of symmetrical T-shaped microchannel with rectangular section is deduced,and the mathematical models of pressure loss,mixing efficiency and flow mixing composite performance of T-shaped passive micromixer under different size constraints are established.Then,the numerical simulation method is used to study the effects of the structure and size parameters of the passive micromixer(microchannel section shape,microchannel section length width ratio and inlet and outlet microchannel width ratio)on the pressure loss,mixing efficiency and composite performance of the passive micromixer,and then establish the design criteria of the optimal size of the micromixer to achieve the optimal flow mixing composite performance.Finally,in order to change the problem that the microchannel mixer is dominated by molecular free diffusion and the mixing efficiency is low,the vortex generator of cylindrical flow around flexible flag is introduced into the microchannel mixer.Considering the fluid structure coupling between them,the vortex induced mixing is realized and the mixing efficiency is improved.The influence of cylindrical turbulence flexible flag fluid structure coupling on microchannel fluid mixing performance and energy consumption is studied by the combination of numerical calculation.The results show that:(1)For T-shaped passive micromixers with rectangular,elliptical and isosceles triangular sections,under the constraint of equal volume and equal cross-sectional area,with the increasing of the length width ratio of rectangular section,the biaxial length ratio of elliptical section and the bottom height ratio of isosceles triangular section,the dimensionless pressure loss of the three micromixers first decreases and then increases,while the mixing efficiency gradually improves.At the same time,the flow mixing composite performance first increases and then decreases with the increasing of the length width ratio of rectangular section,the biaxial length ratio of elliptical section and the bottom height ratio of isosceles triangle section.Compared with the three,the elliptical section T-shaped micromixer with a biaxial length ratio of 0.5 is the micromixer with the best flow mixing composite performance.(2)For the T-shaped passive micromixer with rectangular section,the pressure loss first decreases and then increases with the increasing of the length width ratio of rectangular section,and the outlet mixing efficiency decreases with the increasing of the length width ratio of rectangular section.At the same time,the flow mixing composite performance first increases and then decreases with the increasing of the length width ratio of the rectangular section,which means that there is an optimal channel section length width ratio in the micromixer to achieve the optimal flow mixing composite performance.With the increasing of inlet velocity,channel cross-sectional area and channel length,the optimal section length width ratio first decreases and then increases.At the same time,the optimal section aspect ratio to achieve the optimal flow mixing composite performance is not greater than 1.In addition,for the T-shaped passive micromixer with rectangular section,the pressure loss first decreases and then increases with the increasing of the width ratio of inlet and outlet microchannels.Under the condition of inlet flow rate,the outlet mixing efficiency first decreases and then increases with the increasing of inlet and outlet microchannel width ratio,while under the condition of inlet flow rate,the outlet mixing efficiency increases with the increase of inlet and outlet microchannel width ratio.Under both inlet conditions,the outlet mixing efficiency increases with the increase of microchannel height.At the same time,with the increasing of the width ratio of inlet and outlet microchannels,the flow mixing composite performance parameters first increase and then decrease,which means that there is an optimal width ratio of inlet and outlet microchannels,so that the micromixer can achieve the optimal flow mixing composite performance.The optimal width ratio of inlet and outlet microchannels will be affected by inlet conditions,microchannel height and channel length ratio.(3)For the mixer with a cylinder and flexible flag,the simulation show that the mixing in the cylinder flexible flag mixer is mainly carried out by molecular diffusion in the range of medium and small Reynolds numbers,and its pressure loss and mixing degree increase with the increasing of the flag height.In the large Reynolds number range,the mixing degree in the cylinder flexible flag mixer is greatly enhanced by the vortex separated from the vibrating flexible flag.Its pressure loss and mixing efficiency first increase with the increasing of the flag height,and then decrease slightly or reach the quasi stable value.Compared with straight channel mixer and cylinder mixer only,the pressure loss of cylinder flexible body mixer is always greater than the two mixers,but the mixing degree in the channel of cylinder flexible flag mixer is much higher than the two mixers,and the mixing is more uniform.On the one hand,the research of this paper can theoretically improve the research on the geometric parameters of microchannel and its influence on the fluid flow and mixing performance of fluid structure coupling microchannel mixer of cylindrical spoiler flexible flag;On the other hand,in application,it is helpful to effectively improve the mixing efficiency and reduce energy consumption of the micromixer by optimizing the microchannel structure and introducing a flexible vortex generator,and then promote the design of the micro mixer with excellent energy consumption and mixing performance and its application in biomedical testing,microreactor and many other fields while ensuring the performance requirements.