Numerical Study Of Thermal-bubble Actuated MEMS Valveless Micropump

The rapid development of micro-electromechanical systems(MEMS) has promoteda wide research of micro fluidic system. Micro-pump which has the advantages ofminiaturization, low power consumption, easy operation, accuracy and high integrationis a very important driven device of micro fluidic system, and also been widely appliedin various fields, such as the biomedical, aerospace, microelectronics, andenvironmental monitoring. The research of micro-pump has great significance, anddraw pepole’s attention due to its important role in the micro systems.Compare with valve micropump, the valveless micro-pump has simple structure,and reducing the production and bonding processes in the manufacturing process, andthe valveless micro-pump is more efficient than the valve micropump. Most of thecurrent study of valveless micropump is focused on piezoelectric film micro-pump, butthis type of micro-pump requires external high voltage, and has larger error. Valvelessmicro-pumps are driven by thermal bubbles can avoid the above shortcomings. But sofar the research of thermal bubble-driven micro-pump is little, because the bubblegrowth and condensation is a very complex process. So the optimization of geometry ofmicro-pump diffuser/nozzle and the detail flow characteristics variation inner themicro-pump through the numerical simulation will offer some forward-lookingunderstanding for the experiment.In this paper, heat power is supplied at the bottom of the micro-pump chamber togenerate the bubbles, with methanol is used as the working fluid. Based on thermalbubble growth and condensation supply the pumping pressure source and the differentresistance characteristic of diffuser/nozzle caused the mass flow, the workcharacteristics of mirco-pump under different heating model, heating ration, drivenfrequency, diffuser angle and different heating power are numerically studied. TheComputational Fluid Dynamics software Fluent6.3, together with the User DefinedFunctions (UDF), the phase change of mass and energy transfer are added to the sourceterm of control equations, and the simulation results is post-prcocessed by Tecplot360.The results show that the micro-pump pumping flow rate has the trend to increasefirst then decrease with increasing driving frequency trend under the same heating ratio,and the simulation results are consistent with the experimental results of Tsai, themaximum pumping flow rate of simulation and experiment is5.87μL/min and5μL/min, and simulation and experimental results are in good agreement. The micro-pump pumping flow under different heating power also show the trend that increase first thedecrease, this indicates that the micro-pump flow rate do not increase with powerwithout limits. The pumping flow rate also changes with the diverging angle ofdiffuser/nozzle, and maximum pumping flow rate is gotten when the diverging angle is14°. The back flow phenomenon will be caused when the diverging angle is too big,which will reduce the pumping flow rate.The pumping flow rate is different when the micro-pump work under the the singlebubble model and dual bubble model, even they have the same heating area. Thepumping flow rate under the single-bubble pumping mode is smaller than dual-bubblepumping model, which has maximum flow rate of6.57L/min when γ=10%，f=250Hz. The flow rate of the liquid in the pump increase when more heat power is supplied,and the flow rate of the liquid under dual bubble model is larger than the single bubblemodel。During the entire driven cycle, the bubble growth phase is longer than thencondensation phase, and the condensation phase become longer when the supplied heatpower increase. At the same time, the driven pressure under the dual bubble model islarger than the single bubble model, and the pressure drop along the center axis ofdiffuser is larger than the nozzle.Based on the previous numerical study, the operating characteristics of paralleldual-chamber micro-pump is also studied, and the maximum flow rate of the paralleldual-chamber micro-pump can reach to8.16μL/min when the γ=10%，f=100Hz.When the heat ratio is20%, the driving frequency is200Hz, the dual-chambermicro-pump pumping flow rate can achieve maximum flow of13.8μL/min. When theheating power is1.2W, the maximum flow rate of dual-chamber mirco-pump can reachto48.72μL/min, and the single-chamber micro-pump pumping flow rate is8.92μL/min.It is seen that the micro-pump flow rate of the parallel dual-chamber room under thesame conditions significantly improve, thereby improving the work efficiency of themicro-pump.