声化学微反应器——超声和微反应器协同强化

微反应器和声化学技术都是化工过程强化的重要手段,但都有优缺点。阐释了“声化学微反应器”的理念--微反应器和声化学技术相互集成,利用超声强化微通道内的混合、传质和预防堵塞等,同样借助微反应器实现声场和气泡场的有效调控并解决声空化过程的放大难题,实现协调强化的目的。同时,深入剖析了声化学微反应器内的声空化行为、声场和气泡场调控规律,以及多相流动体系中的混合与传质强化机制。最后展望了该领域的发展方向,并指出超声空化过程中表界面时空尺度现象和理论是实现并优化超声强化的基础。     

声化学微反应器——超声和微反应器协同强化

微反应器和声化学技术都是化工过程强化的重要手段,但都有优缺点。阐释了"声化学微反应器"的理念——微反应器和声化学技术相互集成,利用超声强化微通道内的混合、传质和预防堵塞等,同样借助微反应器实现声场和气泡场的有效调控并解决声空化过程的放大难题,实现协调强化的目的。同时,深入剖析了声化学微反应器内的声空化行为、声场和气泡场调控规律,以及多相流动体系中的混合与传质强化机制。最后展望了该领域的发展方向,并指出超声空化过程中表界面时空尺度现象和理论是实现并优化超声强化的基础。     

微通道内气-液两相传质过程行为及其应用

微通道内气-液两相体系中Taylor流和泡状流具有气泡尺寸均一、停留时间分布窄、可调控性强和比表面积高等优点,具有广泛的应用前景。从Taylor气泡和泡状气泡的传质过程出发,系统综述了微尺度下气泡的溶解规律、传质过程机理和传质/溶解模型等方面的研究进展,并介绍上述流型在反应或过程强化、基础物性及动力学数据测量和微纳材料合成方面的应用。最后总结并展望了技术领域的研究难点与研究方向。     

微通道内气-液弹状流动及传质特性研究进展

气-液弹状流,又称Taylor流,是一种以长气泡和液弹交替形式流动的流动形态。微通道内气-液弹状流因其气泡与液弹尺寸分布均一、停留时间分布窄、径向混合强等优点,是一种适于强化气-液反应的理想流型。本文首先介绍了微通道内气泡的生成机理、气泡和液弹长度,以及气泡生成阶段的传质特征。其次系统综述了主通道中弹状流动及传质过程的研究进展,包括气泡形状与液膜厚度、液弹内循环和泄漏流特征、气-液传质系数的测量与预测,以及物理与化学吸收过程中的传质特性等方面内容。最后阐述了当前研究的不足并展望了气-液弹状流的研究方向。     

声驱动微气泡强化微反应器内高黏体系萃取过程

针对高黏液-液体系中所存在的传质能力弱等问题，开展了在超声微反应器内导入惰性气体以强化高黏液-液萃取体系传质过程的研究。以甲苯萃取水相中香草醛过程为模型体系，研究了超声激发作用下，不同形状、尺寸气泡的振动行为，揭示了声驱动气弹与声驱动微气泡对该体系传质强化机制，为导入气体辅助超声强化高黏液体间的传质过程提供了理论基础。基于液相Reynolds数、气相Reynolds数和声能密度等参数，提出了预测超声微反应器内液-液总体积传质系数的经验关联式，预测值与实验值吻合良好。     

微通道内气-液两相传质过程行为及其应用

微通道内气-液两相体系中Taylor流和泡状流具有气泡尺寸均一、停留时间分布窄、可调控性强和比表面积高等优点,具有广泛的应用前景。从Taylor气泡和泡状气泡的传质过程出发,系统综述了微尺度下气泡的溶解规律、传质过程机理和传质/溶解模型等方面的研究进展,并介绍上述流型在反应或过程强化、基础物性及动力学数据测量和微纳材料合成方面的应用。最后总结并展望了技术领域的研究难点与研究方向。     

微通道内气液两相流行为研究进展

综述了微通道内的气液两相流行为及传质特性。在微通道内流型一般分为泡状流、弹状流、环状流和弹状-环状流,没有分层流。气液传质效率比常规尺度中的提高了2～3个数量级。讨论了气泡对气液两相流的影响及其生成、生长和聚并规律。介绍了微通道内气液两相流的计算机模拟结果。从实验、理论和数值模拟3个方面对微通道内气液两相流的研究和应用前景进行了展望。     

小曲率蛇形微通道弯头处弹状流流动及传质特性的数值研究

采用CLSVOF（coupled level set and volume of fluid）方法,以空气和水为工作流体对小曲率矩形截面蛇形微通道内气液两相流动进行模拟研究。验证模型的合理性后,研究了曲率对弯通道内压降的影响,曲率及气相速度对弹状流气泡及液塞长度的综合影响;同时深入分析了弯管内气液两相流动的传质特性,包括不同曲率下气泡长度的变化,弯管内液侧体积传质系数与液膜体积传质系数的比较,曲率及气相速度对液相体积传质系数的影响。同时,对比了回转弯道与直微通道传质系数的差异,发现弯微通道可以强化传质。     

微尺度过程强化的结晶颗粒制备研究进展

结晶颗粒制备技术在化工、医药、电子、生物等领域具有不可替代的作用。近年来,随着化工过程强化和微化工技术的快速发展,基于微尺度的过程强化方法在晶体颗粒制备过程中得到广泛的应用,成为高端颗粒制备的前沿技术。本文系统综述了该领域的研究进展：围绕微流控组件,简述微结构混合器、微流体技术对提高微观混合效率的原理及其在纳米材料、药物结晶等领域的应用;围绕微尺度力场,综述超重力旋转填充床的结构设计、可视化研究,超声场为代表的声空化效应及外加力场对超细纳米颗粒制备和药物连续结晶过程的应用;进一步,针对新型膜微尺度传质强化过程,分析微孔膜材料强化传质过程以及膜表面的晶体颗粒“黏附-生长-脱落”运动行为,阐明影响微孔膜分散传质强化过程的关键结构和过程参数,系统论述致密膜液层强化传质的表面更新机制和控制结晶颗粒制备的多级膜操作系统。最后,展望微尺度过程传质强化的结晶颗粒制备技术发展趋势。     

微通道内气液两相Taylor流数值模拟

本文采用FLUENT软件对T型微通道内气液两相Taylor流进行模拟,得到了各物理参数对Taylor流的影响规律。在此基础上,采用最小二乘法进行拟合,得到了可以更准确预测T型通道内气液两相Taylor流气泡和液柱长度的经验关联式。     

毛细管中泰勒流液侧传质特性及其强化机理的CFD模拟

采用计算流体力学（CFD）的方法,研究了圆管中泰勒流的液侧传质特性,分析了泰勒气泡上局部传质特性,并研究了气泡上升速度、液膜长度和液栓长度对液膜处和气泡半球帽处平均传质系数的影响。结果表明,泰勒气泡表面局部传质系数存在3个峰值,液膜处的平均传质系数随气泡上升速度增大显著增大,随液膜长度增大而减小,而半球帽处的平均传质系数随气泡速度和液膜长度的增大变化较小,即膜接触时间增加时,液膜处的传质系数降低,而半球帽处传质系数变化较小。另外,引入场协同原则对单元胞内速度场和浓度场进行分析,解释了局部传质特性及强化机理。最后,给出了分别预测短和长膜接触时间下泰勒流液侧体积传质系数的关联式,该式在较宽的管径尺度范围（0.25～3 mm）内的预测误差在±20%以内。     

气液降膜流动中液相速度波动及其传质研究

为了研究降膜流动的动力学性质及其对气液传质过程的影响,在气液逆流的不同气液流动条件下采用激光多普勒(1aser Doppler anemometer,简称LDA)测量了降膜流动的液相速度分布和瞬时速度波动.和以往假定液膜外侧为自由表面,液膜表面处剪切力为零的Nusselt模型进行了比较,LDA测量结果表明气液逆流时降膜流动的最大液相速度出现在液膜表面之内,并且是以近界面区域的速度波动为特征的流动.在相同的降膜装置中进行了乙醇稀溶液的解吸实验,液相传质系数的实验测量值是渗透理论预测值的1～2倍.实验结果表明液相界面区域的速度波动加快了气液界面的表面更新速率,减小了传质阻力,强化了气液界面的传质过程.考虑液膜波动特征对气液接触情况的影响,从气液两相接触时间的角度出发,修正了渗透理论对液相平均传质系数的预测,预测结果和实验结果相吻合.     

蛇形微通道内泄漏流特性

微流体系统通常具备极大的比表面积、易于控制等优势,在气-液相传质、传热、反应等方面具有良好的应用前景。本文考察了6个气液相体系在矩形截面蛇形微通道中的气液两相泰勒流流动情况以及气泡和液弹的动态行为,以气泡截面形状的几何模型为基础,得到了微通道中净泄漏流的量化方程。同时发现在较大的操作区间内,蛇形微通道对泄漏流的可控性优于直形微通道。并且详细分析了不同气液相流量、液相物性（表面张力和黏度）和气泡长度对蛇形微通道主通道净泄漏流的具体影响。     

基于微吸收器的CO2吸收过程研究进展

微化工技术在流体流动、过程强化、传质与反应过程等领域备受关注,本文归纳整理了3种不同类型的微吸收器（微降膜吸收器、微通道吸收器和微网格吸收器）捕集CO₂过程中的水力学性质和传质过程及其机理研究进展,并对3种微吸收器吸收CO₂过程中存在的问题进行分析总结,同时对微吸收器能快速工业化提出展望。其中重点介绍了微通道泰勒流吸收器的水力学流动特性,包括泰勒流气泡的生成机制、气泡和液弹的长度、气泡的输运和运动速度、气泡截面形状及液膜厚度和气液两相流压降;归纳了微通道泰勒流吸收过程的传质过程机理和传质系数的模型以及不同影响因素（通道截面尺寸,通道长度,主通道结构及入口形状,气、液相组成及其流速,吸收剂和系统压力）作用下CO₂吸收效率和传质系数的研究进展。     

Liquid–liquid two‐phase flow in ultrasonic microreactors: Cavitation,emulsification, and mass transfer enhancement

The effects of ultrasound on the hydrodynamic and mass transfer behaviors of immiscible liquid–liquid two‐phase flow was investigated in a domestic ultrasonic microreactor. Under ultrasonic irradiation, cavitation bubble was generated and underwent violent oscillation. Emulsification of immiscible phases was initiated by virtue of oscillating bubbles shuttling through the water/oil interface. The pressure drop was found to decrease with increasing ultrasound power, with a maximum decrement ratio of 12% obtained at power 30 W. The mass transfer behavior was characterized by extraction of Rhodamine B from water to 1‐octanol. An enhancement factor of 1.3–2.2 on the overall mass‐transfer coefficient was achieved under sonication. The mass transfer performance was comparable to passive microreactor at similar energy dissipation rate (61–184 W/kg). The extraction equilibrium was reached under a total flow velocity 0.01 m/s and input power 20 and 30 W, exhibiting its potential use in liquid‐liquid extraction process. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1412–1423, 2018     

Gas-liquid flow mass transfer in a T-shape microreactor stimulated with 1.7 MHz ultrasound waves

This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas-liquid flow in a T-shape microreactor with a diameter of 800 μm.A 1.7 MHz piezoelectric transducer (PZT) was employed to induce the vibration in this microreactor.Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO2 absorption into water and NaOH solution.The approach of absorption of CO2 into a 1 mol· L-1 NaOH solution was used for analysis of interfacial areas.With the help of a photography system,the fluid flow patterns inside the microreactor were analyzed.The effects of superficial liquid velocity,initial concentration of NaOH,superficial CO2 gas velocity and length of microreactor on the mass transfer rate were investigated.The comparison between sonicated and plain microreactors (microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on kLa and interfacial area at various operational conditions.For the microreactor length of 12 cm,ultrasound waves improved kLa and interfacial area about 21％ and 22％,respectively.From this study,it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate.This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors.     

Modeling mass transfer in a Taylor flow regime through microchannels using a three-layer model

The process of convection and diffusion in a Taylor regime of gas–liquid flow through microchannels is modeled based on a three-layer mass transfer model in the axisymmetric formulation. The circulation circuit of Taylor vortices is described in the form of outer and inner layers surrounded by a thin film that does not participate in circulation. Due to the assumption about the predominance of convection over radial diffusion in the inner layer (the Peclet number order of magnitude is nearly 10⁵) and a uniform concentration distribution over the cross sections of each layer, the problem is confined to a quasi-one-dimensional problem with boundary conditions of special type. The obtained numerical solutions allow us to determine the kinetics of mass transfer from a liquid to a channel wall in detail, calculate the average mass-transfer coefficient, and reveal optima in the dependences of the mass-transfer coefficient on the two-phase flow velocity and the capillary diameter; furthermore, there is also an optimum for the length of a liquid slug. The obtained results allow us to understand the pattern of Taylor convection and diffusion fluxes and to reveal the reasons for a decrease in mass fluxes under nonoptimal conditions. This enables the correction of selected geometric and process parameters during the design of microreactor equipment.     

气液界面对流传质的观测与定量分析

采用光学纹影系统对乙醇和水双组分解吸传质过程的对流结构的界面湍动进行了定性观察和定量分析。建立了一套水平非稳态气液传质设备,试验观测了乙醇和水体系中液相组分向气相传质过程的Marangoni界面对流结构。还通过对传统纹影方法的改进,对乙醇解吸传质过程的浓度(本文用质量分数表示)梯度场进行了定量测量。定量分析表明乙醇和水系统解吸过程中,引发界面湍动的原因是局部较大的表面张力梯度。定量分析的结果很好的解释了伴随Marangoni效应的传质过程的混乱的对流结构,为进一步对界面湍动现象的分析提供了帮助。     

多排平直翅片管换热器表面气液降膜流动特性的三维数值模拟

基于VOF模型建立了考虑重力、表面张力及界面摩擦力源项的多排平直翅片管换热器表面气液两相降膜流动三维瞬态CFD模型。不同气流速度下液膜厚度模拟结果与文献中试验值吻合较好,最大偏差小于5%,表明所建立CFD模型是可靠的。通过研究壁面接触角为30°时不同气液Reynolds数下液膜流动特性,结果表明：翅片管表面满膜流的临界Reynolds数Re_l为239,临界喷淋密度为0.06 kg/(m·s);在239 ≤ Re_l ≤ 995内,其平均液膜厚度较Nusselt理论解高16.8%～35.1%;气液逆流和顺流时气相Reynolds数Re_g应分别小于2190.7和3286.0,其主要原因在于过高的Re_g会导致气液界面摩擦力快速增大,从而引发液膜破裂和液滴脱落等现象恶化设备性能。总之,气液顺流更有利于在较高气相Reynolds数下实现翅片管表面的较薄满膜流动。     

整体式床层中液体分布与气-液传质的关系

With a particular focus on the connection between liquid flow distribution and gas-liquid mass transfer in monolithic beds in the Taylor flow regime, hydrodynamic and gas-liquid mass transfer experiments were carried out in a column with a monolithic bed of cell density of 50 cpsi with two different distributors (nozzle and packed bed distributors). Liquid saturation in individual channels was measured by using self-made micro-conductivity probes. A mal-distribution factor was used to evaluate uniform degree of phase distribution in monoliths. Overall bed pressure drop and mass transfer coefficients were measured. For liquid flow distribution and gas-liquid mass transfer, it is found that the superficial liquid velocity is a crucial factor and the packed bed distributor is better than the nozzle distributor. A semi-theoretical analysis using single channel models shows that the packed bed distributor always yields shorter and uniformly distributed liquid slugs compared to the nozzle distributor, which in turn ensures a better mass transfer performance. A bed scale mass transfer model is proposed by employing the single channel models in individual channels and incorporating effects of non-uniform liquid distribution along the bed cross-section. The model predicts the overall gas-liquid mass transfer coefficient with a relative error within ±30%.