| Microfluidic system refers to a system that uses microchannels to manipulate or process microfluidics,and is an important part of MEMS（Micro-Electro-Mechanical System）.The micropump,as a key executive device,marks the level of development of microfluidic systems.Among different kinds of micropumps,the magnetic fluiddriven micropump has the characteristics of simple pumping process,rapid response,strong controllability,and has a wide range of application prospects in the fields of microfluidic transport network,liquid chromatography analysis,polymerase chain reaction,etc.In order to give full play to the advantages of the magnetic fluid-driven micropump,this article focuses on improving the performance of the magnetic fluiddriven micropump and reducing the complexity of the micropump composition system in view of its shortcomings such as low pumping flow,numerous components,and complex manufacturing processes.Research has been carried out.The main research contents of the thesis are as follows:The first chapter studies the development status of micropumps.The current common micropumps are divided into valved micropumps and valveless micropumps according to whether they contain movable valve plates in their structure.Among them,valve-type micropumps mainly include piezoelectric drive,electrostatic drive,electromagnetic drive and pneumatic drive micropumps.Valveless micropumps mainly include electroosmotic drive,surface tension drive,magnetic fluid drive and thermal bubble drive micropumps.The driving principle,working characteristics,advantages and disadvantages of each driving mode of the micropump are summarized,and the working principle,structure composition and performance parameters of the representative micropumps proposed at home and abroad in recent years are summarized and compared.The focus is on the system composition,structural scheme and working characteristics of the magnetic fluid-driven micropump,and the advantages and disadvantages of the magnetic fluid-driven micropump and the direction of improvement are summarized.The second chapter explores the composition of magnetic fluid.The physicochemical properties of commonly used solid magnetic particles,base fluids and surfactants are summarized and classified according to their composition and application fields.Based on the above investigation and analysis,the most suitable magnetic fluid for this topic is selected.In addition,the magnetization characteristics,stability characteristics,viscosity characteristics and thermodynamic characteristics of the magnetic fluid are studied,the control principle of the magnetic fluid micropump is analyzed,and a model of the pressure difference between the two ends of the magnetic fluid under a changing magnetic field is established.In the third chapter,a new type of valveless magnetic fluid driven micropump with a baffle in the pump cavity is proposed based on the characteristics and driving principle of the magnetic fluid.The structure of the micropump was designed,and two baffle shape schemes were proposed.The flow field in the cavity of the two schemes was numerically modeled and simulated by the finite element simulation software,and the optimal scheme was selected.The baffle was further optimized,the end of the baffle was changed to a droplet-like structure,and the influence of the radius of the dropletlike structure on the flow field in the pump cavity was studied through simulation,and the optimal structure radius was selected according to the simulation results.Finally,the optimized structure is simulated for the stability of the flow rate.The simulation results show that the stability of the flow rate is high during the whole pumping process,and the pumping flow of the micropump can be controlled more accurately by controlling the rotation speed of the magnetic fluid.The fourth chapter uses traditional soft lithography process to manufacture micropumps.The layout of the micropump was drawn on the graphic design software,and the mold of the micropump was made through the steps of homogenization,prebaking,exposure,post-baking,development,and hard-baking,and the PDMS mixture was poured onto the mold to make the PDMS chip.Finally,the PDMS chip is bonded to the glass substrate to make a prototype.In addition,the experimental work platform and control system of the micropump were designed and built,and the control scheme and control program were written.The working platform is made of epoxy resin glue to glue the cut PMMA board,and the control system is composed of stepper motor,reducer,motor driver and PLC.In Chapter 5,the flow rate,back pressure and bidirectional pumping test device of the magnetic fluid micropump are designed.The influence of parameters such as motor speed（ω）,pumping back pressure（p）,permanent magnet superimposed number（n）,permanent magnet rotation radius（r）and other parameters on the pumping performance of the micropump are successively measured.Experiments show that the greater the magnetic field strength and the lower the motor speed,the single pumping capacity of the micropump is larger.When the number of magnets stacked is 4,the pumping back pressure is 0,and the magnet rotation radius is 5 mm,the maximum pumping flow rate of the micropump prototype is about 256.83 μl/min,and the maximum back pressure is about 4195.04 Pa.The micropump has no dead volume in the working process,and has a high flow rate and back pressure.The symmetrical structure of the pump cavity allows the micropump to be pumped in both directions.It has a wide range of application prospects in microfluidic systems with high flow requirements. |
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