Numerical Simulation Of Koch Fractal Passive Micromixer And Study On CO₂ Laser Manufacturing

Lab-on-a-chip is a branch of micro-electromechanical system(MEMS)technology,which is also called Micro Total Analysis System(?-TAS).With the development of micromachining technology,it has been widely used in many fields.Micromixer is an important equipment in the field of biology and chemistry for fast and efficient mixing of fluids in microscale space.In general,due to the influence of the size of the micromixer,the flow in the microchannel is mainly laminar.Especially when the Reynolds number is low,molecular diffusion is the main factor affecting the fluid mixing in the microchannel.However,in general,the diffusion efficiency of molecules is very low,which will increase the mixing time of the fluid in the microchannel,which is not conducive to the practical application of the micromixer in production and life.Therefore,it is of great significance for the development of micromixers to research and design more kinds of micromixers and improve the mixing effect of micromixers.According to the development of passive micromixer at home and abroad in recent years,combined with the research of a large number of researchers,this paper introduces the development status of microfluidic chip field,describes the basic theoretical knowledge of micromixer and the control equation of microchannel in the process of finite element simulation.The mixing mode,molecular diffusion and chaotic convection of fluid in microchannel are summarized.According to whether there is an external driving device,micromixers can be divided into active and passive.The active micromixer mainly drives or disturbs the fluid in the microchannel through an external device,which makes the fluid in the microchannel produce convection effect,so as to promote the mixing of the fluid.The passive micromixer can enhance the molecular diffusion or chaotic convection between fluids by the geometry of the microchannel itself or by adding obstacles in the microchannel,so as to promote the mixing of fluids.Because the Re number is in the range of 0 to 200,the fluid in the micromixer belongs to laminar flow.In order to improve the mixing efficiency of micromixer,Koch fractal principle is applied to the design of passive micromixer,which improves the chaotic convection phenomenon in micromixer and promotes the mixing of fluid in microchannel.In this research,by continuously optimizing the design of baffles in the micromixer,several independent baffles are included in the same baffle group,and the structure of each baffle in the baffle group or baffle group is adjusted,including the number of fractal,the height and angle of baffle,and the distribution of baffle.For example,in the numerical simulation of three separate baffles in each baffle group,six kinds of micromixer structures are arranged according to the baffle height.Through a large number of numerical simulation,the combination with the best mixing efficiency is selected.Then,through a flexible and low-cost CO₂ laser processing system,a micromixer based on PMMA and Koch fractal principle was fabricated.By changing the processing time,processing power,processing speed and other factors,the influence of CO₂ laser processing system parameters on the quality of microchannel was studied.Then,through the thermal bonding machine,the processed PMMA material is bonded,and the fluid is introduced.Finally,the numerical simulation and experimental results are verified,and the results are within the error range,which shows the accuracy of the simulation results.