| With the rapid development of microelectronics technology,the integration of IC chips is increase constantly,which leads to high heat flux density.The heat flux of per unit increases rapidly which brings great threaten to the reliability of electronic device.High heat flux density has become a bottleneck that impedes the development of integrated circuits.Therefore,the study of heat sink technology of electronic apparatus has become increasingly important.Microchannel heat sink is a promising technique to dissipate high heat flux microelectronic chips in the near future.As a necessary component of microfluidic control system,micropump transforms electric energy,heat energy or mechanical energy into fluid kinetic energy,it can be used as the driving force for microchannel heat sink.Piezoelectric micropump employs piezoelectric actuator to transform electric energy into mechanical deformation.It presents several advantages such as small dimensions,low power consumption,and it is easy to integration.Therefore,piezoelectric micropump receives considerable attentions from researchers for widely applications in biomedicine,chemical analysis,aerospace and microelectronic cooling.According to rectifying mechanism,piezoelectric micropumps can be classified into valve piezoelectric pump and valve-less piezoelectric pump.Even though the valve-less micropump may not completely block the backward flow,valve-less micropump has advantages of high reliabilities,structure simplification,miniaturization compared to valve micropump.In this paper,we study on the performance of diffuser/nozzle based valve-less piezoelectric micropump.The article includes the following sections:1.A dynamic finite element model for investigate the mechanism of valve-less micropump with diffuser/nozzle has been conducted in this paper.The simulation result shows that flow performance of valve-less micropump is not only depend on the diffuser/nozzle but also related to the entire structure.When fluid flows through the nozzle,the chamber which contact with the nozzle end is considered as a diffuser with angle of 180°.This diffuser locates in jet flow region,high velocity fluid will generate turbulence in the interfacial area of nozzle and chamber,the turbulence is equivalent to a “virtual valve”,which can block the reflux,resulting unidirectional flow.2.It is found that the micropump membrane with the higher input voltage leads to a larger fluidic velocity,resulting in higher turbulence degree.Therefore,the turbulence degree is closely related to the input voltage amplitude.When input voltage larger than the threshold voltage(V = 20),the turbulence starts emerging,and the flow rate of micropump increases with input voltage rapidly.3.Experimental results demonstrate that the maximum flow rate of 5.4 ml/min is finally obtained,which is comparable to a typical valve micropump.4.The structure parameters of conical diffuser/nozzle valve-less piezoelectric micropump is studied by the COMSOL Multiphysics.The simulation results are as follows:(1)The curve of flow rate of micropump with the height of the pump chamber showed trend of increase before decrease.(2)The flow rate of micropump increase with the distance of the two diffuser/nozzle,and finally leveled off.(3)The flow rate of micropump increase with the diameter of the inlet/outlet chamber,and finally leveled off.5.The flow rate of planar diffuser/nozzle valve-less piezoelectric micropump is increase the diffuser/nozzle angle within limit ranges,10° seems not the best angle.Therefore,the previously well-adopted optimal “10° rule” should be corrected.6.The cooling performance of microchannel heat sink is simulated by COMSOL Multiphysics.Simulation result shows that the heat source temperature is decrease with the flow rate of micropump,and finally leveled off.Finally,set up experimental devices for the micropumps and microchannel heat sink,the simulation analysis conclusions are verified by experiment results. |
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