核酸检测一体化微流控芯片设计与液滴操纵分析

设计了一种基于磁珠法的两相流液滴微流控芯片,包含样品提纯、扩增和检测一系列连续的生化过程,可用于快速核酸检测.首先建立了磁珠和液滴在两相流体系内的动力学模型,并借助有限元仿真平台对磁珠微团所处环境进行了磁场仿真,得到不同体积磁珠微团所受的磁力.进一步还分析了磁珠微团、液滴体积、永磁体移动速度对液滴运动状态的影响,最终总结出液滴操纵图.     

数字微流控芯片半月形驱动电极的设计

为了降低数字微流控芯片的驱动电压,将传统的方形驱动电极结构设计为半月形,并研究了不同参数的半月形驱动电极降低驱动电压的效果。首先,根据介电湿润的基本原理分析了不同驱动电极形状对降低驱动电压的影响。然后,通过流体体积法(VOF)对液滴的运动过程进行建模和数值仿真;根据数值仿真结果对比分析了不同结构参数的半月形驱动电极随驱动时间的运动过程。最后,设计了4种不同结构参数的半月形驱动电极芯片,并对其驱动液滴的效果进行了试验验证。结果表明:研制的4种半月形驱动电极微流控芯片中,电极圆弧直径等于电极长度结构的芯片其驱动电压比其他3种电极结构的芯片的驱动电压至少降低了15.6%,而且可以在16V的驱动电压下使1μL去离子水液滴的运动速度达到1.6cm/s,是设计为半月形驱动电极中的最优设计。实验数据证明了电极圆弧直径等于电极长度的半月形驱动电极结构可有效降低微流控芯片的驱动电压。     

收缩管型压电式喷头微滴喷射仿真及实验研究

为探究收缩管型压电式喷头微滴喷射过程中内部流场变化规律以及微滴形成过程,利用Gambit软件建立二维轴对称有限元模型,基于Fluent动网格技术,采用VOF两相流模型,对微滴喷射过程进行仿真分析,研究了微滴形成机理。建立微滴喷射系统对微滴喷射过程进行实验,分析收缩管型压电式喷头工作时入口压强对尾滴、附着液滴形成的影响规律。结果表明:储液腔的振动边界运动引起内部压强变化,导致长液带形成,并断裂形成微滴;入口压强影响尾滴与附着液滴的形成;特定振动边界运动存在对应的可用入口压强范围。     

油水乳化液破乳动力学研究进展

综述了油水乳化液的破乳机理和受力分析现状,由于所采用破乳方法的不同,建立了油水乳化液在旋流场和振动场中不同的数学模型,并分析了破乳过程中分散相液滴的变形、破裂的临界条件,认为旋流场中分散相液滴所受到的切应力是导致液滴变形并造成分散相液滴破碎与乳化的重要原因,振动场中分散相的聚集是基于位移效应向波腹和波节运动,结合微粒临界破裂条件,可知振动破乳时存在一个最佳振动强度范围.     

3DP工艺中双液滴渗透数值模拟与仿真研究

为了提高3DP工艺的精度,需预测粘结剂与颗粒材料粘结的形态,而通过实验很难观测到液滴在粉床中的渗透过程。本文通过应用水平集方法建立了双液滴渗透过程的数学模型,运用多物理场仿真软件COMSOL对其进行了数值模拟,分析了主要工艺参数—液滴水平间距和滴落高度对液滴渗透的形态的影响。同时为验证数学模型和仿真结果的一致性,搭建了实验平台,采用高速摄影对液滴的滴落渗透过程进行图像采集,并通过电子显微镜观测最终的凝聚形态。将实验结果与仿真结果进行了对比,验证了数值模拟的准确性,为进一步的实验研究提供了理论依据。     

咽颌运动模式鱼类胸鳍的运动学建模及仿真

针对实际鱼类胸鳍运动的随机性、不确定性和复杂性等问题给胸鳍推进机理和推进性能研究带来的挑战与困难,以及柔性胸鳍仿生研究所存在的问题,在对太阳鱼胸鳍的结构和运动特征进行大量观测研究的基础上,分阶段建立柔性胸鳍推进运动的运动学模型,并对其运动形态的变化过程进行仿真分析。仿真结果表明,所建立的运动学模型能够较好地描述胸鳍推进运动的运动规律和运动形态。此研究可为柔性胸鳍推进机理、推进性能和仿生等方面的深入研究提供理论依据。     

离子迁移(IMS)漂移管的多物理场模拟方法研究

针对离子迁移漂移管的设计优化,本文建立了一种包括气流和电场的多物理场模拟研究方法。对漂移管进行气路仿真,定性研究其中气流的运动,考察是否存在涡流等影响漂移管性能的因素。利用漂移管中气流速率分布,研究常压下离子在电场与气流共同作用下的迁移过程。根据模拟得到的离子迁移谱图,对漂移管的性能进行了分析。结果表明,该方法能够有效地模拟离子在漂移管中的迁移运动,对漂移管的优化设计有着重要的意义。     

驻波场中油包水型乳化液分散相液滴运动LabVIEW仿真分析

在LabVIEW环境下,通过建立水击谐波驻波场中油包水(W/O)型乳化液分散相液滴的运动方程,实现了W/O乳化液中分散相液滴运动的虚拟仿真分析,从而获取液滴运动特性曲线。结果表明,水击驻波场中分散相液滴朝着水击驻波波节处运动,经过一定的时间后发生聚集,且呈对称分布;探讨了水击驻波参数对液滴运动轨迹的影响。     

车用质子交换膜燃料电池动态建模与仿真分析

基于质子交换膜燃料电池（PEMFC）工作机理的分析,考察工作过程中影响其输出特性的5个主要因素（包括理想电动势、欧姆极化电压、活化极化电压、浓度差极化电压和辅助系统电压）,建立了PEMFC的动态数学模型,利用Matlab/Simulink仿真平台对该模型进行了仿真,结果表明,模型输出能有效反映PEMFC的电压输出特性,为PEMFC控制系统的开发奠定了基础。     

悬空零电极介电湿润芯片的设计

针对目前单极板数字微流控芯片驱动液滴的效果多通过数值仿真方法验证而缺乏实验支持,本文提出将单极板结构中的零电极进行悬空设计,并通过实验对比分析了设计的悬空零电极单极板结构的芯片和传统双极板结构的芯片对液滴的驱动效果。首先,基于介电湿润原理,推导出传统双极板结构中液滴所受到的介电驱动力以及每个阻力,接着,对文中设计的悬空零电极结构的单极板数字微流控芯片中液滴的受力情况进行分析。然后,对比分析两种结构的数字微流控芯片中液滴的受力情况。最后,对两种结构的数字微流控芯片驱动去离子水微液滴的效果进行试验验证。实验结果显示:驱动同等体积大小的微液滴时,本文设计制作的悬空零电极单极板芯片比双极板结构的芯片所需的电压更低,液滴的运动速度更快;当有效驱动电压达到44V时,液滴的速度可以达到15cm/s。得到的实验结果证明了在单极板悬空零电极结构的数字微流控芯片上液滴驱动速度更高,驱动电压更低。     

Enhancement of pneumatic nebulization efficiency through application of an electric field

A technique is described for reducing the size of aerosol droplets produced by a pneumatic nebulizer of the kind commonly used in flame or plasma spectrometry. The technique involves the application of an electric field to the tip of the nebulizer, resulting in an induced surface charge on the liquid being nebulized. In turn, the surface charge reduces the liquid's surface tension and results in the generation of a finer aerosol. In this study, the effect of the electric field is quantified in terms of the spatial dispersion and size distribution of aerosol droplets formed in the presence and absence of the field. Droplet size distributions, obtained using the MgO impression technique and analyzed using log-normal and upper-limit functions, reveal a 63% decrease in the volume mean droplet diameter in the field's presence. As a result, this system is expected to be useful in both flame and plasma spectrometry, where reduced droplet size can yield improved precision and freedom from interferences.     

微量润滑平面磨削接触区换热机理的研究

磨削接触区材料去除厚度是不一致的,同时,在微量润滑过程中,雾滴之间的运动特征存在差异且易受其他因素的影响,致使整个接触区的磨削温度分布呈现出非线性,换热机理也异常复杂。从雾化机理出发,对影响换热效果的两个关键因素--雾滴直径和雾滴速度进行了分析。依据雾滴在不同壁温处表现出的不同换热特性,将磨削区划分为无沸腾换热、核态沸腾换热、过渡沸腾换热和稳定膜态沸腾换热四个不同的换热区域,建立了微量润滑磨削区的换热系数数学模型。在此基础上,运用有限元技术对微量润滑磨削表面的温度场进行了仿真分析,采用单级热电偶技术测量了磨削温度,发现磨削区仿真温度值与实验测量值吻合较好,表明通过该理论获得的微量润滑磨削表面换热系数是可信的。     

Simulation of droplet generation through electrostatic forces

This paper represents the multiphysics simulation of droplet generation of ink containing conductive nano-particles through electrostatic forces on substrate. The main focus is to investigate the phenomena by generating the drops through a nozzle with the help of electrostatic forces. The electrostatic based deposition system has vast application in printed electronics and biotechnology. In electrostatic deposition mechanism for droplet generation, a strong electric potential is applied at the tip of the nozzle; due this electric potential, the liquid containing the nano-particles experience strong electrostatic static forces at the interface with the air (at the tip of the nozzle). When these electrostatic forces exceed the internal (viscous forces) and external forces (surface tension), a deformation takes place which results in the flow of the liquid in the form of droplets. The size of the droplet is dependent on different parameters like applied voltage, properties of the ink, dimension of the nozzle. To have better understanding of this, a numerical simulation was performed based on multi-physics approach. Multiple simulations were performed by changing the position of electrode in nozzle and varying the applied voltage. Droplet size with respect to applied voltage was evaluated; electric field with respect to applied voltage and time for the droplet generation was also evaluated through these simulations. This study will help in better understanding the parameters of droplet generation phenomena and optimal design of the nozzle for the electrostatic inkjet system.     

不同润滑液的电润湿性能研究

润湿性是指液体在固体表面铺展的倾向性,可以通过润湿角描述,是评价润滑液渗透性能的一个重要指标。为了研究润滑液的电润湿性,搭建电润湿润湿角测量装置,对施加负高电压的润滑液润湿角进行测量,得到不同电压下不同润滑液的润湿角变化情况,结合仿真分析施加负高压液滴润湿角变化机制。结果表明:润滑液润湿角受外加电场影响,在一定范围内,电压越大,润滑液润湿角越小;在润滑液中加入纳米颗粒可提高润滑液的电润湿性能;在同等电压下,与去离子水、去离子水基纳米流体、蓖麻油、蓖麻油基纳米流体、葵花油相比,葵花油基纳米流体的电润湿性能最好;对润滑液液滴施加电压后,液滴各位置压力场与速度场发生变化,其顶部压力场较大,速度指向液滴内部,边缘压力场较小,速度指向液滴外部,进而导致润湿角减小。     

润湿性梯度表面上液滴运动的数值模拟

建立液滴在具有润湿梯度表面上运动的物理和数学模型,用Fluent软件模拟出液滴在润湿梯度表面上的运动过程,并从能量变化的方法得到液滴在润湿梯度表面上运动的机制.计算结果表明润湿性梯度表面上的液滴具有不同的能量状态,当液滴的接触角较大时,液滴的表面能较大,此时液滴可以自发地向低接触角的方向运动,润湿性梯度的分布状况将决定液滴运动过程的速度和加速度的大小.     

Modeling and simulation of droplet translocation and fission by electrowetting-on-dielectrics (EWOD)

This paper discusses methods of microfluidic droplet actuation by means of electrowetting-on-dielectrics (EWOD) and provides a technique for modeling and simulating a microfluidic device by using the computational fluid dynamics (CFD) program, Flow3D. Digital or droplet microfluidics implies the manipulation of droplets on a scale of nanoliters (10⁻⁹ L) to femtoliters (10⁻¹⁵ L), as opposed to continuous microfluidics that involve the control of continuous fluid within a channel. The two operations in focus here are droplet translocation (moving) and droplet fission (splitting), in which the pressures and velocities within the droplet are analyzed and compared to existing works, both theoretical and experimental. The variation in the pressure of the leading and trailing faces of a droplet indicates the variation in surface energy—an important parameter that explains how a droplet will move toward a region of higher electric potential. The higher voltage on one side of a droplet reduces surface energy, which leads to an induced pressure drop, thus resulting in fluid motion. Flow3D simulations are for both water and blood droplets at voltages between 50 Vand 200 V, and the droplet size, surface properties (Teflon coated), and geometry of the system are kept constant for each operation. Some peculiarities of the simulation are brought to light, such as instabilities of the system to higher voltages and fluids with higher dielectric constants, as well as the creation of a tertiary droplet when the applied voltage causes a large enough force during fission. The force distribution across the droplet provides a general understanding of the electrowetting effect and more specifically allows for a comparison between the effects that different voltages have on the forces at the droplet surface. The droplet position and mean kinetic energy of the droplet are also investigated and compared to other works, proving the dynamics of a droplet motion found here.     

Numerical simulation of metal transfer process in tandem GMAW

A numerical model based on fluid dynamics theory and electromagnetic theory is developed to simulate the dynamic metal transfer process in tandem gas metal arc welding (T-GMAW). The relationship between welding current and surface tension coefficient is modified by analysis of regression in this model. The numerical simulation of the metal transfer process in T-GMAW is compared with that in single-wire gas metal arc welding (SW-GMAW). It is found that a droplet transfers axially in SW-GMAW, but the droplets transfer non-axially in T-GMAW. To verify the accuracy of simulated results, the welding experiments were performed in which the actual metal transfer processes were recorded by high-speed photography. The simulated results are in good agreement with the experimental ones. This transfer behavior in T-GMAW is analyzed by studying the distributions of physical quantities including pressure, velocity, and electric potential of the droplet. The simulated results reveal that the electromagnetic force between two droplets results in the different metal transfer process. With the increase of the welding current, the surface tension coefficient decreases and the electromagnetic force increases. As a consequence, the metal transfer process in T-GMAW is accelerated.     

圆管式压电喷头的液体分配

针对用于喷墨打印的圆管式压电喷头建立了计算模型,并且根据它的驱动特点选择了合适的边界条件。介绍了仿真软件针对自由表面流动问题的计算原理。然后,以乙二醇水溶液为例,计算了压电喷头分配该溶液的分配过程;利用液滴成像系统获取了不同时刻的液滴图像,验证了建立的模型和数值算法的正确性。最后,计算了压电喷头在不同输入位移、不同黏度以及不同表面张力下的液体分配过程。仿真结果显示:液体分配性能与激励位移密切相关,在72.5mN/m的表面张力作用下,10nm的输入位移很难分配黏度为4.0mPa·s的液体,而15nm的输入位移在分配黏度为4.0mPa·s液体时却能够产生卫星液滴。因此,对于某种液体寻找一个合适的激励条件非常重要,过小的激励产生不了液滴,过大的激励则会产生较大甚至多个卫星液滴;增大黏度会延缓或阻滞液滴形成过程,增大表面张力却能加快液滴形成过程。本文的计算方法对于研制新式喷头或者研究喷头的喷射能力均具有指导意义。     

基于微量润滑磨削的双喷口喷嘴雾化仿真分析

为了减小磨削时砂轮表面气障层的影响,提高磨削液润滑和冷却的效果,设计了一种双喷口结构的喷嘴。分析了微量润滑雾化机理,采用二级雾化理论建立了雾化数学模型,对双喷口喷嘴的雾化过程进行了仿真分析,并对仿真结果进行了验证。研究结果表明：双喷口喷嘴能有效减小雾滴直径,提高磨削液的雾化效果;辅助喷口雾滴可以扰乱砂轮表面的空气环流,减小气障层对主喷口雾滴流向的影响,促使主喷口喷出的雾滴能顺利进入磨削区。     

电动汽车涡旋压缩机内油气分离器的研究

通过数值模拟的方法研究了电动汽车涡旋压缩机在不同转速工况下,进口结构对油气分离器的流场和性能的影响。采用RSM模型对油气分离器内的气相流场进行模拟计算,同时利用DPM模型对4种分离器的油滴轨迹进行追踪。研究结果表明:进口结构变窄将促使油气分离器内部流场具有良好的对称性,并随着转速的提高,不同进口结构分离器的压降都呈抛物状上升,分离效率也有所提升。在满足压降经验模型计算的状况下,矩形-1进口分离器相比另外3种不同进口分离器的速度场对称性良好,且在3000 r/min时对小粒径油滴分离效率达到了74.97%,比圆形进口分离器的分离效率提升了19.30%,保证了低功耗下提升小粒径油滴的分离效率。