流体静态混合器的应用和新发展

对航空航天领域中常用的3种流体静态混合器的工作原理、性能及优缺点进行了概述,在论述静态混合器的广泛应用和发展概况的基础上,简要介绍了层板混合器、微混合器2种新型的静态混合器.     

液-液混合过程中混合器的研究进展

混合器是一种应用于物料混合过程的重要工具,具有适用范围广、混合均匀、成本较低等优点.混合元件的结构、微通道以及外加动力对混合效果具有重要的影响作用,已经得到了国内外学者的研究与关注.介绍混合器在液-液混合中的应用.首先,根据是否含有活动元件将混合器分为动态混合器和静态混合器,微混合器分为被动式微混合器和主动式微混合器;然后,分析不同类型混合器的混合效果以及适用范围,阐述当前技术存在的优势与不足;最后,提出了高效化、连续化、节能化是未来混合器的发展方向.     

3种被动式微混合器的性能对比及压损分析

通过数值模拟的方法对3种不同结构的被动式微混合器进行了研究,同时对3种被动式微混合器的混合性能进行了对比,并进一步研究了微混合器的压力损失。结果显示,内肋形微混合器在5种速度条件下的混合性能要优于其他两种微混合器,而且随着流量越来越大,其压力损失也越来越大;内肋形微混合器的压力损失最大,Z形微混合器的次之,Y形微混合器的最小。     

交叉导流式微型混沌混合器

针对微尺度混合的特点,提出了一种以玻璃湿法刻蚀加工技术为基础,基于混沌对流混合机理的三维静态微混合器.微通道内,周期排列的导流块在轴向的压力梯度作用下产生了横向的速度分量,可以诱发混沌对流,同时实现微通道内流体的快速混合.运用流场可视化实验和计算流体动力学（CFD）方法研究了微混合器的混沌混合行为.混合试验表明,SOR微混合器在低Reynolds数和高Reynolds数条件下都可以获得好的混合效果.     

错位碰撞型微混合器混合性能的模拟分析与优化设计

微混合器作为微流控设备的重要组成部分,广泛应用于生化领域,由于在微通道下流体流动为层流,混合较差,对于快速反应,混合是影响效率的主要因素。本文对影响混合效率的3种微混合器结构进行了数值模拟,通过变化微混合器的通道宽高比、发散处最大宽度、碰撞处错位高度3个结构参数,模拟研究其在层流下的混合性能。结果表明,流体碰撞处错位高度对混合性能影响最明显。对模拟结果最佳的微混合器（MST）进一步优化其结构得到新的微混合器（MTT）,将MTT与MST及普通T型微混合器（MT）进行比较。MTT微混合器出口处的混合指数达到81%,而普通T型微混合器在相同的条件下只有5.3%。通过模拟分析混合过程,有效改善了错位碰撞型微混合器的结构,有利于提高流体混合效率,提高反应速度。     

微混合技术的原理与应用

介绍了微混合技术的发展现状;以微混合器内的混合机制为主线,探讨了不同的微混合器结构型式及其在微反应系统中的应用;展望了微混合技术的应用前景。     

一种基于特斯拉阀结构的微混合器设计、模拟及其试验研究

微混合器是常见的用于流体混合的设备,由于特斯拉阀结构简单稳定,流动方式特殊,具有开发微混合器的潜质。本文通过数值模拟的方法,在特斯拉阀结构以及前期研究的基础上,改进并优化了一种特斯拉型的微混合器,利用流体力学软件（Fluent）研究了不同θ角度以及不同雷诺数下的混合程度,并对该结构的混合效果进行了流场分析以及试验验证。结果表明,该新型微混合器的最佳几何参数为θ=30°。两股流体在Re=52.5、混合长度为50mm时,混合程度η=0.9647,体系压降为330.45Pa。该微混合器的操作压降较低,相对于先前结构,混合性能更好,混合长度更短。     

带扩张-收缩型通道的脉动式微混合器的研究

微混合器作为微流控系统中的重要元件,在生物医学、化学分析等领域具有非常多的应用。在分析提高微混合器混合效果途径的基础上,设计了一种带扩张-收缩型通道的脉动式微混合器,通过Fluent-UDF二次开发程序对混合机理及影响混合效果的各种参数进行数值模拟分析,得出在相位差为180°、速度比为2、St数在0.2—0.4时混合效果最好。另外,对其实物模型进行了微混合实验研究,将实验结果与数值模拟结果定性地对比分析,结果吻合较好。     

脉动流动强化微混合的研究

在微尺度下,由于流动处于层流状态,因此混合是一个巨大的难题.针对微尺度混合的特点,提出了一种新型微混合器.这种微混合器利用入口速度方波型脉动实现微通道内流体的有效混合.针对物理问题建立了通用的无量纲方程和边界条件,利用计算流体动力学(CFD)方法研究了微混合器的特性和脉动参数的影响.结果表明在脉动方波占空比为0.5,相位差为180度时,能达到较好的混合效果.当雷诺数为1.0,脉动频率为2Hz时,混合度能达到79%.研究表明:微混合器中流动具有混沌对流特征,脉动流动可极大地增加界面面积,从而实现快速混合.综合各参数的影响建立了参数-脉动体积,当其未超过混合通道体积时,其值越大,混合效果越好.     

微旋流混合器中液体混合特性CFD-PBM数值模拟

微旋流混合器是一种由微旋流气浮演化而来的设备，可以强化物料的混合与传质。文中研究利用CFD-PBM计算模型，研究微旋流混合器内气液两相分布，考察微旋流混合器内流体颗粒粒径分布及变化特性。分别以空气和液相作为气液两相，研究不同气、液相入口流速下的流场形态与相关流体力学参数。结果表明：通入气相会诱导设备内部产生新的循环流动形态，增强宏观混合，直径大于4.0 mm的气泡无法在内筒中的旋流环境中稳定存在，并随着旋流速度逐渐减小，气泡发生聚并，最终演化为4.0—10 mm直径的气泡流出。增加液相入口速度可以增加整体流动速度，同时增加气相体积分数，气相体积分数最高可达到18%。随着气相流速增加，在微旋流混合器内筒下端形成连续空腔。     

Dimensionless number for identification of flow patterns inside a T-micromixer

Results are presented from a numerical study examining the flow dynamics of the liquid phase inside T-type micromixers. The main aim of the study was to determine an identification number for the differentiation of the different flow regimes in the liquid phase in T-type micromixers. The critical value for the identification number at which the transition from vortex flow to engulfment flow occurs was obtained. The results were used to optimize the geometrical parameters and the operating conditions to achieve high mixing performance for the liquid phase in T-type micromixers. The model results were found to be consistent with experimental data for different T-mixers available in the literature.     

微混合设备及其性能研究进展

对近年来微混合设备的加工方法、微混合方式及其在反应、分离及传热方面的应用研究进行了全面综述。分析了微混合设备具有混合效率高 ,停留时间短 ,能耗低 ,操作条件易于控制 ,设备简单 ,内在安全性能好等特点。指出微混合过程在物质的均匀混合、快速转化、物质和能量的快速传递等方面的优势明显 ,但也存在加工成本高、处理量小、同时只适用于干净体系等不足。据此 ,指明了在微混合设备和过程中要着力发展微设备的加工技术 ,开发具有高清洁能力、可处理含固体物料体系和大处理量的微混合设备     

Villermaux-Dushman protocol for experimental characterization of micromixers

The iodide/iodate chemical test reaction (named Villermaux-Dushman method) initially proposed to characterize micromixing in conventional stirred tank reactors has become an extensive method to characterize continuous micromixers. Several protocols have been proposed and adapted to very efficient devices, but misunderstanding makes the use of this chemical test somewhat difficult which can lead to erroneous results. Furthermore, many papers only present the segregation index which is very dependent of the concentration set when mixing time, a concentration-free feature, should be preferred to compare micromixers. This paper presents the detailed protocol of the iodide/iodate test method, with different concentration sets and a general protocol to determine mixing times in micromixers.     

微混合器内流体混合的研究进展

Microreaction technology is one of the most innovative and rapid developing fields in chemical engineering, synthesis and process technology. Many expectations toward enhanced product selectivity, yield and purity, improved safety, and access to new products and processes are directed to the microreaction technology. Microfluidic mixer is the most important component in microfluidic devices. Based on various principles, active and passive micromixers have been designed and investigated. This review is focused on the recent developments in microfluidic mixers. An overview of the flow phenomena and mixing characteristics in active and passive micromixers is presented, including the types of physical phenomena and their utilization in micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, T-micromixer is highlighted as an example to illustrate the effect of design and operating parameters on mixing efficiency and fuid flow inside microfluidic mixers.     

Numerical and Experimental Study on Mixing in Chaotic Micromixers with Crossing Structures

Two chaotic micromixers (Models A and B) based on the split-and-recombine principle using multilayer microchannels are proposed and the mixing performance was analyzed numerically and experimentally for a wide range of Reynolds numbers. The fluid flow and mixing performance were numerically analyzed by solving Navier-Stokes equations. Micromixers were fabricated using a soft-lithography technique. As working fluids, water and a dye/water mixture were used. Quantitative and qualitative analyses were performed using confocal scanning microscopy and image processing techniques. The micromixers could enhance the mixing performance by expanding the interfaces between the working fluids to be mixed. The results confirm the superior mixing index of Model B compared to that of Model A.     

Effect of Channel Aspect Ratio and Inclination Angle on Flow and Mixing Performance of a Microdevice—A CFD Study

Theoretical Foundations of Chemical Engineering - This work includes a 3D computational fluid dynamics study on rectangular-shaped micromixers. Initially, T-shaped micromixer types are considered...     

Simulation of Droplet Generation by Mixing Nozzles

In various chemical processes thorough homogeneous mixing is of great importance. Due to their small characteristic dimensions, micromixers have a great potential to achieve fast and uniform mixing. However, in the field of powder synthesis from precipitation processes the use of standard micromixers is severely limited because of rapid clogging of the microchannels. As an alternative, mixing nozzles which are less susceptible to fouling can provide a sufficient mixing quality. The flow field and fluid distribution inside multi‐fluid droplets during droplet formation is simulated. Depending on the geometry and flow rates, complex velocity fields and flow distributions are found and the impact on the mixing efficiency is qualitatively deduced. Furthermore, we point out how the tendency of fouling can be further reduced with the help of improved nozzle geometries.     

Gas/liquid dispersion in a sequential split micromixer

Two different types of split–recombine micromixers have been tested for a gas/liquid dispersion. Mixing performances of two micromixers have been compared in terms of a mixing efficiency. The effects of liquid flow rates, the ratio of gas/liquid flow rate, bubble sizes, and bubble size distributions have been investigated. The sequential split micromixer and the caterpillar micromixer showed a consistent mixing performance at various flow rates. The sequential split micromixer has shown the smaller and narrower bubble size distribution than that of the caterpillar micromixer at a higher flow rate of 1.8 L/h.