Transient Performance Study Of The Valveless Piezoelectric Micropump With A Bluff-body Based On Coanda Effect

As the most commonly used driving components and actuators in micro-electro-mechanical systems?MEMS?,the piezoelectric pump has a broad application prospects in micro-chemical analysis,high-precision inkjet printing,chip cooling etc.Although the traditional diffuser/nozzle piezoelectric micropump can avoid the congenital defects of the valve structure,the shortcomings of low pump efficiency and intermittent outflow are hard improved.Therefore,the development of micropump based on other working principle has become one of the hot spots in recent years.In this paper,a novel valveless piezoelectric micropump with a bluff-body based on the Coanda effect is presented.The novel micropump not only has a simple structure,is conductive to miniaturization and fabrication,but also can realize a large outflow and the pump efficiency can be more than 50%.The research contents and conclusions are presented as as the following three points:1.Based on the bluff body flow and the Coanda effect principle,a valveless piezoelectric micropump which is efficient and has a large outflow is designed for the first time by using a bluff-body composed of a semi-cylinder and a triangular prism.The transient characteristic experiments have been carried out to study the variations of the pump efficiency with different pump sizes?Rc?,aspect ratios?L₁/d?and angles???in the ranges of excitation frequency?f??25Hz¹25Hz?and voltage?V??50vpp³00vpp?.When the frequency is fixed,the net flow increases with the increase of the voltage amplitude.When V=200vpp,the net flow increases first and then decrease with the increase of the frequency,but under different sizes of pump chambers,the excitation frequencies corresponding to the optimal net flows are different.In the ranges of aspect ratio?4⁸?and the angle?30°⁴5°?,when f=50Hz and V=300vpp,the maximum net flow is 4.84ml/min and the maximum outlet pressure is 1.75kpa.2.Through a large number of numerical simulations,the influence of driving parameters?Reynolds number 300¹000 and excitation frequency 5Hz⁴00Hz?and structure parameters?bluff-body radius,split structure,angle,aspect ratio and width ratio?on the performance of the micropump are also studied.Compared with the experimental results,the maximum error of numerical simulation results is less than15.5%,which has high reliability.It is found that the pump efficiency increases first and then decreases with the increase of the bluff-body radius,the optimal bluff-body radius is 0.2mm.When the inlet and outlet channels are connected by the wedge or circular split,the pump efficiency is lower than that of the micropump without any split structure.When the angle ranges from 15°to 75°,the pump efficiency increases with the increase of the angle.Moreover,the pump efficiency both first increases and then decreases with the increase of the aspect ratio and the width ratio,it means there is a high efficiency zone in these two variable ranges.Under the condition of?=30°,b₁/b₂=1 and L₁/d?3⁹?,it is found that when the Reynolds number is constant,the pump efficiency first increases and then decreases with the increase of the frequency under different aspect ratios.The frequency corresponding to the optimal efficiency is defined as the optimal frequency.When the Reynolds numbers are 300,600 and 1000respectively,the corresponding optimal frequencies are about 50Hz,150Hz and250Hz.Finally,based on the analysis of the flow fields,it is found the different functions of the vortexes in the suction and pump process determine the performance of the micropump.3.The response surface methodology?RSM?is used to study the pump performance with different aspect ratios and width ratios under the above optimal excitation parameters.The results show that with the increase of the Reynolds number and frequency,the optimal selection range gradually decreases,but the overall performance of the micropump increase gradually.As Re=1000 and f=250Hz,the optimal L₁/d and b₁/b₂ are 8.742 and0.758 respectively,the maximum pump efficiency is 94.93%.