A novel 3D Tesla valve micromixer for efficient mixing and chitosan nanoparticle production

Current three-dimensional micromixers for continuous flow reactions and nanoparticle synthesis are complex in structure and difficult to fabricate. This paper investigates the design, fabrication, and characterization of a novel micromixer that uses a simple spatial Tesla valve design to achieve efficient mixing of multiple solutions. The flow characteristics and mixing efficiencies of our Tesla valve micromixer are investigated using a combination of numerical simulations and experiments. The results show that in a wide range of flow rates, viscoelastic solutions with different concentrations can be well mixed in our micromixer. Finally, experiments on the synthesis of chitosan nanoparticles are conducted to verify the practicability of our micromixer. Compared with nanoparticles prepared by conventional magnetic stirring, the size of nanoparticles prepared by micromixing is smaller and the distribution is more uniform. Therefore, our Tesla valve micromixer has significant advantages and implications for mixing chemical and biological reactions.     

基于Fluent的超高压撞击流乳化喷嘴的优化分析

高压液体通过喷嘴加速，形成高速射流，与相反方向的另一股射流相互撞击，发生强烈的相互作用，产生强烈的径向和轴向湍流速度分量以及狭窄的高压高速湍流区，在此区域内，相间或液滴间的碰撞互磨产生的挤压力和剪切力使流体被细化。本文从液体连续相撞击流的两个特征：微观混合和压力波动入手，逐一分析了撞击速度与微观混合、压力波动的关系，得出了压力波动与撞击流速度乱U0成正比关系，微观混合与U^3 0成正比的规律。同时，用流体模拟软件Fluent对喷嘴的结构和尺寸进行优化，并得出最合理的喷嘴结构和尺寸。模拟认为：在相同压力下，采用矩形槽，出口孔径为0．2mm，槽的深度为0．27mm的结构时撞击速度达到最大，并通过实验验证了这一结论。     

Study of Transition States of Melamine for Micromixing with Wax Emulsion+4‐Nonyl Phenol Ethoxylate,Estimated with SEM Technique

Densities (ρ/10³kg m^?3), apparent molar volume (V₂/10^?6m³mol^?1), and viscosities (η/0.1 kg m^?1s^?1) for 5.0 to 60.0 millimol kg^?1 (m mol kg^?1) 1,3,5 triazine (melamine) at interval of 5.0 m mol kg^?1 were determined. The data were regressed and extrapolated to infinite dilution (m→0) and referred to as limiting apparent molal volume (V¯₂ ⁰) and intrinsic viscosity (B) and used to calculate free energy of activation (Δµ₂ ^0*/KJ mol^?1). Such functions illustrate feasibility of micromixing of melamine with paraffin wax emulsifier+4‐nonyl phenol ethoxylate, a nonionic surfactant in aqueous solution. The Δµ₂ ^0* decides micromixing of melamine stabilized by poly(acrylic acid) of 4500 g mol^?1 molecular weight, known as superabsorber for water. Paraffin wax emulsion was stabilized by a nonyl phenol ethoxylate and wax particles observed to adhere to melamine surface due to interactions between poly(acrylic acid) dispersant and ethoxylate group of surfactant, resulting in sedimentation of mixed particles. Thus V¯₂ ⁰, B, and Δµ₂ ^0* values conclude to ‐NH₂ group interactions for micromixing and scanning electron micrograph (SEM) elucidates microstructure and uniformity of micromixing.     

横向电动效应作用下微混合的数值模拟

微流体机械系统中电渗流的雷诺数一般都比较低,微通道内的混合主要通过扩散来完成,因此需要较长的距离和时间才能混合均匀.本文在一个二维微通道内施加横向电场,并讨论了不同横向电场强度、微电极对布置情况、壁面zeta电势等因素对微混合的影响.结果表明此方法可以有效地提高混合效率,增加横向电场强度和电极对密度可以明显提高混合效率,较小的zeta电势可以获得更好的混合效果.     

微团化动态结晶法制备超细HMX炸药

为改善HMX(Cyclotetramethylenetetranitramine,奥克托今)炸药的细化效果,通过分析一般重结晶方法制备超细炸药粒子存在的缺陷,提出了一种基于化学结晶和机械冲击原理的微团化动态结晶超细化技术。分析了该方法的理论基础并探讨了微团化动态结晶超细化机理。应用此方法制备出了亚微米级(D50=0.40m)的超细HMX炸药,其细化产品粒径小且粒度分布范围窄。     

湍流场中物质微元的形态特征及相应的模型

运用高速显微摄影方法对１０￣１…１０￣３ｕｍ尺度上的微观混和过程进行了实验观察，将物质微元的形态特征归结为片状与条状两类。在此基础上，提出了片状结构模型，将微观混和描述为片状微元上的收缩变形与分子扩散。分析表明，由于变形与扩散之间的相互作用，微元上分子扩散区的宽度将趋于某一尺度δ＝１２λＢ，从而使微元体积呈指数增长，ｖ～ｅｘｐ（ｓｆ）．微观混和对化学反应的影响可用Ｄａｍｋ６ｈｌｅｒ数Ｄａ来表征，模型能够正确模拟这种影响。     

Mixing Effects in Continuous Free‐Radical Solution Copolymerization Tank Reactors: II—Investigation of Micromixing Effects

The effect of micromixing on the dynamic behavior of continuous solution copolymerization tank reactors is evaluated both experimentally and theoretically. For this purpose, copolymerization reactions of styrene and divinylbenzene are carried out in a lab‐scale polymerization system, composed of two tank reactors in series, to provide experimental data of conversion and molar masses for analysis of micromixing effects. Besides, a detailed micromixing model, based on a dynamic population balance approach, is developed and solved with the method of characteristics, to investigate the micromixing effects on the dynamic behavior of conversion and molar masses in copolymerization reactions. Particularly, results show for the first time that micromixing effects can be important to explain the dynamic behavior of polymerization reactions performed in bulk, but are not sufficient to explain the whole set of available experimental data, which are much more sensitive to modification of residence time distributions and macromixing.