The dynamic characteristics of a valve-less micropump

The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathematical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to obtain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency.     

Study of laminar separation in the vicinity of the point of piecewise-constant pressure distribution over the wall

A family of two-dimensional divergent channels with piecewise-constant velocity and pressure distributions over the wall is considered. The method of matched asymptotic expansions is applied to study the two-dimensional viscous incompressible flow at high but subcritical Reynolds numbers in the vicinity of a pressure jump point on the channel wall. It is shown that if the pressure difference is of the order O(Re^?1/4), then in the vicinity of this point a classical region of interaction between the viscous boundary layer on the wall and the outer inviscid flow occurs. The problem formulated for the interaction region is solved numerically. The asymptotic values of the pressure difference corresponding to separationless flow are determined and the separation flow patterns are constructed.     

Numerical prediction of turbulent flow in a conical diffuser usingk-ε model

Fully developed incompressible turbulent flow in a conical diffuser having a total divergence angle of 8° and an area ratio of 4∶1 has been simulated by ak-ε turbulence model with high Reynolds number and adverse pressure gradient. The research has been done for pipe entry Reynolds numbers of 1.16×10⁵ and 2.93×10⁵. The mean flow velocity and turbulence energy are predicted successfully and the advantage of Boundary Fit Coordinates approach is discussed. Furthermore, thek-ε turbulence model is applied to a flow in a conical diffuser having a total divergence angle of 30° with a perforated screen. A simplified mathematical model, where only the pressure drop is considered, has been used for describing the effect of the perforated screen. The optimum combination of the resistance coefficient and the location of the perforated screen is predicted for high diffuser efficiency or the uniform velocity distribution.     

大密封压比超音速自由旋气动窗口设计与试验研究

 介绍了横向超音速自由旋气动窗口设计方法，分析了单级气动窗口难以实现大密封压比的原因。针对气动窗口扩压器入口气动参数分布特点，提出了一种扩压器带端壁吹气的气动窗口设计方案并进行了试验验证，气动窗口密封压比达到了85。结果表明：扩压器入口端壁吹气是一种有效提高气动窗口密封压比的技术措施，内端壁吹气对密封压比影响较大，外端壁吹气对密封压比影响较小。     

Design of resolution testing facility for ultraviolet imager

We present a resolution testing system of ultraviolet （UV） imager. In this system, an UV Czerny-Turner monochromator with a small f-number is designed to get more energy as an UV radiation source, and its stray light is rejected effectively by light traps. And UV diffuser is employed in order to get uniform light distribution on the resolving power test target. We also design a novel UV collimator which makes infinite UV testing targets. It can reduce the difficulty of optical design and the machining cost, and utilize UV energy at maximum extent. This facility has been applied in the imaging quality evaluation of the UV instrument, and the results accord with the theoretical analysis.     

NUMERICAL STUDY OF PERIODICAL FLOWS OF PIEZOELECTRIC VALVELESS MICROPUMP FOR BIOCHIPS

IntroductionMicro-pump is one of the most important fluid-driving elements in biochips. Workingprinciple of micropumps is quite different from traditional macro-scale pumps. Currently,valveless piezoelectric micropump is one of the most popular micropumps…     

扩压器入口面积比对自由旋涡气动窗口性能的影响

 针对采用主动式扩压器的自由旋涡气动窗口，实验考察了扩压器入口面积比对扩压器压力恢复性能及自由旋涡气动窗口密封性能的影响。结果表明：入口面积比是影响扩压器压力恢复性能的重要因素；通过优化扩压器入口面积比,可以提高气动窗口密封压比和稳定性。主动式扩压器比传统扩压器具有更小的最佳入口面积比，使气动窗口射流更接近于理想自由旋涡射流；主动式扩压器最佳入口面积比约为2.03。在最佳入口面积比情况下，扩压器内端壁吹气临界驻室压力最低，外端壁吹气压力对密封压力基本没有影响。     

叶片倾角变化对扩压器中非定常流动的影响

本文对离心压气机中扩压器与叶轮匹配时的非定常流动进行了数值研究,主要研究了不同扩压器叶片倾角对扩压器中流场的影响,结果显示,扩压器叶片倾角的改变对扩压器中的流场有很大影响,适当调整扩压器叶片的倾角可以减小扩压器流场的波动,同时,叶片与机匣和轮毂的夹角的变化,对于扩压器中流动的分离的发展有重要影响.因此选择合适的扩压器叶片倾角可以改善离心压气机级的性能.     

Simulation of Random Shock Oscillations in a Duct

The effect of random low-amplitude pressure perturbations on the flow in a variable-cross-section duct in the presence of shocks located downstream of the throat is investigated numerically. Questions relating to the processing and analysis of the results obtained are considered.     

生物芯片无阀压电微流体泵流场数值研究

采用浅水波模型把浅薄形微泵的三维流动近似为二维厚度平均流动，并采用有限元／压强修正法求解水平流场和计算微泵流量．数值结果表明：1)在微泵扩散管的过流截面上流速有时间相位差和回流现象．2)微泵在吸流末期泵腔出现对称旋涡．3)微流体泵的定向净流量来自于Navier-Stokes方程的非线性．还给出微泵流量与扩散管长宽比、厚宽比、液体粘度和进出口反压差的定量关系．通过参数优化可以使微泵得到尽可能大的流量．