Combined effects of channel curvature and rotor configuration on the performance of two-stage viscous micropumps

The combined effects of channel curvature and rotor configuration on the performance of two-stage viscous micropumps were studied numerically. The Navier-Stokes equations were simulated to investigate the performance of two-stage micropumps. The performance of two-stage micropumps was studied in terms of the dimensionless mass flow rate and dimensionless driving power. Four different rotor configurations were designed by changing placement of two rotors inside a microchannel: Two aligned and two staggered configurations. The aligned rotor configuration of type 1 is to place the two rotors along the convex wall, while type 2 is to place them along the concave wall. Numerical results show that the rotor configuration plays a significant role in the performance of two-stage micropumps. The channel curvature acts in a different way according to the rotor configuration. The mass flow rate of aligned rotor configuration of type 1 is greatly improved by the channel curvature, while it diminishes the mass flow rate of type 2. The maximum mass flow rate for the aligned rotor configuration of type 1 is obtained when the two rotors are placed at the junction of the circular and straight sections of the channel. The performance of staggered configurations is negligibly affected by the channel curvature. This characteristics is found due to rotation direction of the rotors. As the two rotors rotate in the opposite direction for the staggered configurations, the flow characteristics in the circular section is little affected by the channel curvature. The circumferential distance between the two rotors can be optimized in terms of the mass flow rate. The optimal value of the circumferential distance is about L = 1.4 for the staggered rotor configurations, and it is almost independent of the channel curvature. As the channel height increases, the circumferential distance becomes less significant for the staggered rotor configurations while it becomes significant for the aligned rotor configurations.

     

Thermal behavior and entropy generation rate analysis of a viscous flow in MHD micropumps

Studying the effects of various parameters on the behavior of velocity, temperature and thus the entropy generation rate in the microfluidic systems to reduce loss power is very important. Minimization of entropy generation in the flow system enables us for the parametric optimization of the MHD micropumps operation. In the present study, a transient, laminar and fully developed electrically conductive fluid flow in MHD micropumps has been investigated and the temperature distribution and effects of dimensionless influencing parameters on the entropy generation rate has been presented. Pumping operator in MHD micropumps are the Lorentz forces, which is produced as a result of the interaction between magnetic and electric fields. Governing equations have been solved numerically using finite-difference (ADI) method. The results of simulation have shown good agreement with analytical results by ei-genfunction expansion method. In addition, the results are compared with experimental data from literature which confirms the accuracy of the model. The obtained results showed that aspect ratio, Hartman, Prandtl, Eckert numbers and Joule heating parameter have significant influences on the flow and temperature distribution as well as entropy generation rate in MHD micropumps that controlling them can lead us for optimized operation of MHD micropumps.

     

液气复合驱动液压挖掘机动臂运行特性及能效

液压挖掘机作业中,大质量动臂举升储存的势能经液压阀口节流转化为热能耗散,不仅浪费能源,还使液压油温度升高,需附加冷却系统降温,增加了机器的成本和复杂性。为解决上述问题,在原有负载敏感驱动回路的基础上,提出基于三腔液压缸的工作装置自重液气平衡势能回收利用方法,三腔液压缸中一个油腔与液压蓄能器直接连通,存储利用工作装置的势能。研究中,首先根据前期的仿真结果,建立了基于三腔液压缸的液压挖掘机测试样机,通过试验,分析对比了分别采用两腔液压缸和三腔液压缸驱动动臂的运行特性与能效特性,测试结果表明,增加液气储能容腔后,提高了系统运行的平稳性,动臂运行过程中的能耗降低48.5%,峰值功率降低64.7%,节能效果显著。新的方法也同样适用于各类液压缸驱动的重载举升装置。     

利用压电微泵驱动和脉动混合可控合成金纳米粒子

为了合成粒径均一、单分散性好的金纳米粒子,提出一种压电驱动式脉动微混合可控合成金纳米粒子的方法。该方法采用两腔三阀结构的压电微泵作为驱动源,结合Y形微混合器,基于两压电微泵脉动交叉式输出性能来实现多种不同混合模式的可控混合。利用Fluent软件对Y形微混合器内不同流量及频率下的混合效果进行了优化分析,优选出了压电微泵的控制参数。在实验室内设计、制作了用于金纳米粒子可控合成的系统样机,并开展了相应的金纳米粒子可控合成试验。试验结果表明：电压为40 V,频率为300 Hz时,合成的金纳米粒子粒径较为均一,分散性较好,该结果验证了文中所提方法的可行性。此方法亦可应用于其他纳米粒子的可控合成。     

Flow analysis in a return channel of a multi-stage centrifugal pump

Flow recirculation is an unpleasant and even hazardous phenomenon that can cause mechanical damage in turbomachinery and has to be prevented during their operations. We numerically studied the effects of return channel blade curvature on reducing the recirculation of flow inside the return channel vanes of a multi-stage centrifugal pump. Computational fluid dynamics (CFD) analyses were performed for a wide range of volumetric flow rates. The standard k-ε turbulence model was adopted as the turbulence model, and the impeller rotation simulated employing the Multiple reference frames (MRF) method. First, a baseline model together with five different modified geometries for return channel was studied and compared using a two-stage pump framework. The results reveal that decreasing the curvature of the return channel blade makes smooth streamlines and eliminates the flow recirculation inside the return channels. As the second part, two return channels with the highest pump performance were selected to be used in the simulation of a multistage pump. The simulations of the multi-stage pump show that the flow inside the baseline return channel includes considerable areas of flow recirculation, while the modified return channels again have attached flow stream. It is concluded that the return channels with the smooth curvatures and outlet blade angles above 90° remove the flow recirculation inside the return channels, resulting in higher pump efficiencies.     

Algorithm with improved accuracy for real-time measurement of flow rate in open channel systems

Most methods for flow rate measurement in open channels usually have low accuracy over a range of flow rates due to varying fluid properties, flow conditions and channel length. This paper suggests an algorithm to improve on the accuracy of flow rates computed based on hydraulic structure and slope-hydraulic radius methods. A model for determining flow rates in accelerating flows is also developed. In the proposed algorithm, the parameter used for adapting the flow rate models is obtained by comparing the measured fluid depth with the depth simulated based on the one-dimensional Saint Venant equations. The results show that an improvement from ± 2.3% to ± 0.8% accuracy in the flow rate measurement using the Venturi flume method could be achieved. In unsteady state flow in a straight-run channel, the results based on flow simulation also show possibility of achieving accurate computation over a wide range of flow rates.     

钛合金曲面磨粒流加工扰流流道仿真与试验研究

针对具有复杂曲面的钛合金工件磨粒流抛光后表面粗糙度Ra不均匀问题,提出一种具有扰流结构的仿型约束加工流道。借助计算流体动力学（CFD）分析软件,结合SST k-ω湍流模型、离散相模型（DPM）和Oka冲蚀模型,仿真分析原始流道和5种不同扰流角度的扰流流道内磨粒流动力学特性。数值模拟结果表明：扰流流场中的磨粒流相较于原始流场在工件表面具有更大的湍流动能、动压力和冲蚀速率,其中扰流角度为30°时冲蚀均匀性较好。基于仿真条件搭建了磨粒流加工试验平台,使用原始流道和30°扰流流道分别进行了加工试验。试验结果表明：使用原始流道加工5 h后,工件表面曲率不同区域的表面粗糙度Ra值分散,加工效果均匀性较差;使用扰流流道加工5 h后,工件表面各区域表面粗糙度Ra的均匀性明显优于无扰流流场的加工均匀性。     

柔性微型阀对静电驱动振膜微泵压力性能的影响

将最小能量法与均匀压力载荷下圆薄膜大变形半解析解相结合,分析了静电驱动柔性微型阀对静电驱动振膜微泵压升性能的影响。微型阀容积的引入会导致静电驱动振膜微泵的压升出现一定程度的降低,但降低幅度远小于阀门容积对常规定排量泵的影响。微型阀的阀片以柔性薄膜为基片,因此所需的关阀电压远远低于微泵泵腔的驱动电压,从而使静电微泵和微型阀运行的可靠性得到了极大的提高。     

A numerical study on the flow and mixing in a microchannel using magnetic particles

We have numerically investigated the characteristics of the flow and mixing in a microchannel using magnetic particles. The main flow is driven by the pressure gradient along the channel, while the secondary flow for the mixing is induced by the drag forces of the particles. Here, the particles can move in the flow due to the strong attraction under the periodically-varying magnetic field generated by electromagnets. For the study, the fractional step method based on the finite volume method is used to obtain the velocity field of the fluid and the trajectories of the particles. This study aims at achieving good mixing by periodically changing the direction of magnetic actuation force in time to activate the interaction between the particles and the flow. The quality of mixing is estimated by considering the mixing index and Poincaré section. In this study, parameter studies on the switching frequency, the magnetic actuation force, the number of magnetic particles and so on are performed to understand their effects on the flow and mixing. Results show that the clustering of magnetic particles during the magnetic actuation plays an important part in good mixing. It is also found that the magnetic force magnitude and switching frequency are the two main parameters that make a combined influence on the mixing efficiency. Such a mixing technique using magnetic particles would be an alternative, effective application for the flow and mixing in a microchannel.     

考虑流固耦合的压电微小泵的有限元运动分析

采用ADINA对微泵进行有限元运动分析，在统一考虑结构与液体性质的基础上，研究压电泵在实际应用中激励力的频率、大小和液体密度、粘度对微小泵出口流量的影响，在此基础上，给出了在设计微泵时激励和传输液体的选择方法。     

Study of fluid damping effects on resonant frequency of an electromagnetically actuated valveless micropump

As fluid flow effects on the actuation and dynamic response of a vibrating membrane are crucial to micropump design in drug delivery, this paper presents both a mathematical and finite-element analysis (FEA) validation of a solution to fluid damping of a valveless micropump model. To further understand the behavior of the micropump, effects of geometrical dimensions and properties of fluid on the resonant frequency are analyzed to optimize the design of the proposed micropump. The analytical and numerical solutions show that the resonant frequency decreases with the slenderness ratio of the diffuser and increases with the opening angle, high aspect ratio, and thickness ratio between the membrane and the fluid chamber depth. A specific valveless micropump model with a 6-mm diameter and 65-μm thickness polydimethylsiloxane (PDMS) composite elastic membrane was studied and analyzed when subjected to different fluids conditions. The resonant frequency of a clamped circular membrane is found to be 138.11 Hz, neglecting the fluid. For a gas fluid load, the frequency is attenuated by slightly shifting to 104.76 Hz and it is significantly reduced to 5.53 Hz when the liquid fluid is loaded. Resonant frequency remarkably shifts the flow rate of the pump; hence, frequency-dependent characteristics of both single-chamber and dual-chamber configuration micropumps were investigated. It was observed that, although the fluid capacity is doubled for the latter, the maximum flow rate was found to be around 27.73 μl/min under 0.4-A input current with an excitation frequency of 3 Hz. This is less than twice the flow rate of a single chamber of 19.61 μl/min tested under the same current but with an excitation frequency of 4.36 Hz. The proposed double-chamber model analytical solution combined with the optimization of the nozzle/diffuser design and assuming the effects of damping proved to be an effective tool in predicting micropump performance and flow rate delivery.     

液气储能双缸驱动大型液压挖掘机动臂节能特性研究

液压挖掘机工作过程中存在大量的重力势能浪费,严重影响整机能效并造成大的排放污染。针对双液压缸驱动动臂的大型液压挖掘机,提出采用双液气储能液压缸驱动液压挖掘机动臂、集成驱动与势能回收一体化原理,降低机器作业能耗和排放。将原双腔液压缸改为集成有储能腔的三腔液压缸,储能腔与液压蓄能器直接连通,通过液压蓄能器初始充液压力平衡工作装置自重,直接回收利用工作装置重力势能。根据36 t大型液压挖掘机作业特点和重力势能变化情况,设计出液压缸和液压蓄能器的参数。进一步建立数字化样机,通过对液气储能驱动系统进行仿真研究,对液压泵输出流量和控制阀的阀口参数重新匹配,修改了与回转复合动作的合流控制策略,并初步验证了液气储能驱动系统的节能效果。在此基础上构建了试验样机,90°标准装车作业循环测试表明,与同型号液压挖掘机相比,在满足同样挖掘力的情况下,整机工作效率提升20.7%,燃油消耗降低17.1%,如按每天作业8 h计算,单台车每天可节约燃油达47 L,减少二氧化碳排放123.6 kg。     

Theoretical and experimental investigation for developing a gas-liquid two-phase flow meter

Despite the intricacy, inline metering of two-phase flow has a significant impact in multitudinous applications including fusion reactors, oil, nuclear, and other cryogenic systems. Since measurement of individual flow rate is prominent in various systems, it warrants the establishment of a flow meter system that can monitor the mass flow rates of liquid. In this regard, an approach was taken towards the development of a two-phase flow meter system in the present study. The concept involves two-phase flow through narrow parallel rectangular channels resulting in laminar, stratified flow with a slope at the liquid-vapor interface. The height of the liquid column at specific channel locations is measured for determining the flow rate. However, the geometric configurations of the channels and fluid properties are pivotal in ensuring accurate measurement. Consequently, theoretical and experimental studies are performed to investigate the correspondence between flow rate and change in liquid height. Based on the governing equations, a theoretical model is established using MATLAB®. The model investigated the intricate influence of various flow and fluid properties in the estimation of the mass flow rate. The experimental investigation was done with various conditions under different liquid and vapor volume flow rates for validating the proposed supposition and the theoretical model. Both the theoretical and experimental analyses showed fair correspondence. The proposed system estimated the mass flow rate within a tolerance of ±10% and showed potential towards the development of the cryogenic two-phase flow meter.     

聚二甲基硅氧烷气动微型蠕动泵制作工艺的研究

聚二甲基硅氧烷(PDMS)气动微型泵由3个PDMS气动微阀构成,依靠3个微阀的蠕动作用实现输运液体的作用.PDMS气动微泵的关键制作工艺是液体通道的弧形化和PDMS层之间、PDMS层与玻璃基片之间的封接.实验证明AZ4620正性光刻胶所制作的阳模能形成剖面形状呈弧形的液体通道.采用等离子体氧化处理法封接技术实现了PDMS层之间、PDMS层与玻璃基片之间的封接,该工艺易操作,封接速度快,而且封接效果好.     

无阀压电微流体泵工作特性与结构参数

根据平面无阀压电微流体泵的结构特点,采用厚度平均的浅水模型和有限元法,得到微流体泵液体－振动片耦合方程。耦合方程的模态分析给出硅片一阶模态自然频率和振型,以及硅片振幅－频率关系。在模态分析之后,加入压电力考察振动片响应、微泵流动特征和微泵流量。同时研究微泵结构参数(微泵压电片半径、扩散管长度、最小宽度、扩散张角)对微流体泵液—固耦合系统的自然频率、振动片振幅和微泵流量的影响,得出对微流体泵优化设计有重要意义的结果。     

Polymer lab-on-chip systems with integrated electrochemical pumps suitable for large-scale fabrication

A low-cost, polymer-based microfluidic platform is described that not only includes passive microfluidic parts, but also pumps based on an on-chip electrochemical gas generation by electrolysis. A hydrogel is used as electrolyte material, which allows a simple fabrication process by screen printing or stencil printing. Test structures were designed and fabricated to illustrate the feasibility of the approach for batch processing. Microfluidic chips including reservoirs and channel structures were fabricated by microinjection molding and used to demonstrate the movement of liquids inside microchannels by the proposed micropumps. The channel system was furthermore functionalized by a plasma surface treatment to form hydrophobic and hydrophilic areas. For sealing of the channel system, as well as for bonding the microfluidic part to glass-like sensor parts, laser-cut adhesive tapes were applied.     

Modeling and flow analysis of piezoelectric based micropump with various shapes of microneedle

Micropumps have been investigated as drug delivery and disease diagnostic devices. Many of these micropumps have been designed, considering primarily, available micro fabrication technologies rather than appropriate pump performance analysis. Piezoelectric and silicon based micro pumps are more popular as compared to other smart materials being explored. The microneedle is an integral part of these micropumps providing an interface between the drug reservoir and the patient’s body for extracting the blood for investigation. Blood collected in the pump chamber passes through the biosensor and gives the required investigation report. It is aimed to minimize the pain while the microneedle is inserted in the body without having any effect on the flow characteristics. Several factors affect the pain while inserting the needle, out of which shape and size of the microneedle are two important parameters. In this study we have investigated the effect of shape of the microneedle on the flow inside the micropump. A micropump design is based on the required flow at the biosensor point. All computations were carried out with water (Newtonian fluid) as the working fluid after carrying out a comparative analysis with human blood (non-Newtonian fluid). For the pentagonal shaped microneedle, the velocity at the top of the microneedle was minimum, which is beneficial in that fluid should remain in contact with the sensor for longer time.

     

基于数值方法对离心压缩机级两种回流器内部流动的分析与对比

一台C式离心压缩机采用了2种形式的回流器,一种入口处存在突扩,称为回流器A,另外一种和弯道光滑过渡,称为回流器B。本文对上述2种回流器分别进行了数值模拟。计算结果表明,回流器B的性能要优于A。对于回流器A,进口由于存在突扩,导致入口处的流动恶化,进一步导致了冲角的改变,最终导致径向面流道内存在旋涡。对于回流器B,由于和弯道光滑过渡,流动较为均匀,并保持了良好的冲角,径向面内的流动也要优于回流器A。     

Pressure data for various flow channels in proton exchange membrane (PEM) fuel cell

Micro flow channels in flow plates of fuel cells have become much narrower and longer to improve reactant flow distribution leading to increase of pumping power. Therefore it is very important to minimize the pressure drops in the flow channel because increased pumping power reduces overall efficiency. We investigated pressure drops in a micro flow channel at the anode and cathode compared to pressure losses for cold flow in straight, bended and serpentine channels. The results show that friction factors for cold flow channels could be used for parallel and bended flow channel designs for fuel cells. Pressure drop in the serpentine flow channel is the lowest among all flow channels due to bypass flow across the gas diffusion layer under reactive flow condition, although its pressure drop is highest for a cold flow condition. So the effect of bypass flow for serpentine flow channels should be considered when designing flow channels     

基于ICEPAK的液冷冷板散热的性能分析

针对液冷冷板解决电子设备散热问题,在流道区域受限制的情况下,选用3种新型流道形状。利用ICEPAK仿真软件对其进行热仿真分析,探究其散热性能。在限定散热区域内,保持3种流道截面积相等,进口流量相等,从而控制流速相等。均布流道,通过改变流道数目,得到每种形状流道关于温度-流道数目的曲线,对比分析3种不同形状流道的散热性能。同时,对这3种方案进行了试验验证,确保仿真结果与实测数据的一致性。结果表明:双层流道形状方案的散热性能良好,能较好地满足设计要求。