变截面通道内流动聚焦微液滴生成数值研究

化学分析研究的不断深入,对液滴微流控精度提出了更高的要求。设计了不同孔径尺寸的流动聚焦通道模型,模拟油-水两相流动剪切微液滴生成过程。采用Level Set方法处理两相流动界面,研究了流动聚焦模型下通道尺寸和油-水两相流量比对生成液滴尺寸的影响。研究结果对实现微液滴生成过程的精准操控具有一定的参考意义。     

CFD数值模拟技术在液滴微流控多相流特性研究的应用进展

高集成化的微流控系统具有界面面积大、传递距离短、混合速度快等优势,已被广泛应用于许多科学领域。然而,微通道内多相流间的相互作用及动力学行为受多方面的影响,仅依靠试验观测技术和理论预测方法难以全面了解多相流传质传热过程、获取流场特性参数、揭示多相流相互作用规律。当下CFD数值模拟技术的快速发展为预测和分析微流控通道内的多相流问题提供了更为直观、有效、准确的帮助。本文对数值模拟技术在液滴微流控多相流特性研究的应用进展进行全面综述,涵盖液滴微流控装置结构及演变、液滴微流控模拟方法及优化以及微通道内多相流作用过程及原理。     

同轴环管微流控设备内液-液两相黏性流体的流动规律

进行了同轴环管微流控设备内黏性聚合物溶液的流动行为研究。研究发现通过调节两相流体黏度与流量,可以得到滴流和射流两种稳定流型,并且可以进一步实现液滴尺寸的调控。同时,还分别针对不同流型建立了数学模型用于液滴尺寸预测。所得结果可以用做利用微流控技术制备聚合物微球的理论指导。     

微通道内纳米颗粒对液滴聚并的影响规律

Pickering 乳液是纳米颗粒稳定的液液两相体系,微流控技术是制备单分散Pickering 乳液的有效方法,而含有纳米颗粒体系在微通道内的液滴聚并规律是该实施方法的关键科学问题之一。以正辛醇为连续相,水为分散相,研究了六边形扩大微通道内液滴碰撞过程,发现了液滴聚并、碰撞不聚并和不相互接触3 种流动状态,研究了流量、颗粒浓度和颗粒亲疏水性对于液滴聚并率的影响规律,分析了颗粒在液膜排空过程中的作用机理。     

微通道内液-液两相流研究进展

从流型、传质和应用3个方面,介绍了近年来微通道内液-液两相流的研究进展。液-液两相流型研究内容主要有两部分,即流型的观察、流型谱图的绘制以及考察多种因素对流型的影响,但是具有普适性的流型谱图和流型转变线仍未提出。液-液两相传质研究方法包括实验研究和数值模拟两种,主要研究在液滴流、弹状流和平行流3种稳定流型下的传质过程;且相对于定性研究,定量的传质研究较少。对于微通道内液-液两相流应用研究,主要体现在萃取、材料合成、生物结晶等方面。此外,对今后微通道内液-液两相的流型、传质和应用研究进行了展望,指出需从实验与模拟计算相结合以及拓展微通道内液-液两相流的应用研究两个方面进行深入研究,推进其工业化进程。     

微流控法构建微尺度相界面及制备新型功能材料研究进展

微流控技术由于具有优异的流体微尺度相界面调控能力,是实现微结构精确可控的新型功能材料的设计制备与性能调控的重要新兴手段。本文介绍了微流控技术可控构建稳定相界面结构的两大体系：一是具有封闭液-液相界面的乳液液滴体系;二是具有非封闭层状和环状液-液相界面的层流体系。回顾了利用微流控技术构建的这两类稳定相界面结构体系制备三大类功能材料的研究进展：一是利用乳液液滴体系制备微球微囊材料;二是利用层状层流体系制备微通道膜材料;三是利用环状层流体系制备超细纤维材料。指出微流控技术为实现功能材料的小尺度化、薄膜化、纤维化、多功能化、材料元件一体化等带来了新的机遇,提出应进一步深入系统地认识液-液相界面设计与调控以及功能材料合成过程的基本规律和机理。     

微通道内液-液两相流流型及传质的研究进展

微通道内液-液两相流流动在微化工系统中占有重要的地位,了解微通道内液-液两相流体流动和传质规律对推动其工业化应用有重要作用。本文以微通道内液-液两相流系统为研究对象,简述了不同工况下微通道内液-液两相流流型和混合传质效率,分析了微通道特征、流体性质和流体流动速度等对流型形成和传质效率的影响。指出目前对于微通道内液-液两相流的研究多处于定性研究,定量研究仅针对某一体系展开,所得结果具有一定的局限性。关于微通道内液-液两相流传质研究实验较多而数值模拟方法相对较少,接下来的研究工作中应该考虑建立微通道内液-液两相流基础研究的数据库,通过分析大量的数据获得有效的流型划分准则和相关经验式以此推动微通道内液-液两相流的工业化应用。同时在传质研究过程中应研究开发相应的数值模拟模型,保证实验和数值模拟相结合,提出有效的传质效率评价机制。     

液滴微流控的集成化放大方法研究进展

相比于传统乳化方法,液滴微流控技术可以在微通道内可控制备单分散液滴模板用于合成各种功能微球,被广泛应用于生物、医疗、制药、环境等领域。由于单个液滴制备微流控单元的产量低,液滴微流控的集成化放大成为了液滴微流控技术面向工业应用的技术难点。本文综述了近年来液滴微流控集成化放大方法的研究进展,重点介绍了不同类型液滴制备微流控单元集成化放大的研究进展,包括基于剪切力形成液滴、基于界面张力形成液滴和基于被动分裂形成液滴的液滴制备微流控单元的集成化放大方法。     

微流控双水相贴壁液滴流动强化酶促反应研究

以微流控双水相液滴流技术为基础,开发了一种酶促反应平台,将微流控贴壁液滴流快速传递、高效混合的特点与双水相反应分离耦合过程优化结合。本体系克服了传统宏观双水相体系传质传热慢以及耗时耗能的问题,并建立了贴壁液滴微反应器,产生更大的内环流,进一步增强传质效果。探究了双水相液滴界面的分子限域能力、对酶和产物的选择性分配能力。通过比较贴微通道壁和未贴微通道壁两类液滴微反应器的酶促反应效果,发现贴微通道壁液滴微反应器仅6 min转化率即可达到40%,其反应速率可达未贴微通道壁液滴微反应器9.4倍。本文通过微流控双水相贴壁液滴流实现了酶促反应的强化,为微尺度下的酶催化反应过程强化提供了一种新的思路。     

微细圆管及扁平管内液-液Taylor流动特性的数值研究

微细通道内Taylor流动广泛应用于能源化工领域,为分析其相界面及阻力特性,利用相对坐标系的方法,研究了竖直圆管及扁平管内的液-液Taylor流动,讨论了通道宽高比、Reynolds数（Re）及分散相体积分数对液膜厚度和两相压降的影响。结果表明：圆管内液滴头部和尾部可以膨胀至近似球形,而扁平管内壁面的限制作用较强,液滴呈现扁平状。随Reynolds数增大,两相界面逐渐收缩,液膜厚度逐渐上升。圆管内液膜厚度比较均匀,扁平管内液膜在通道顶部较薄,而圆弧部分较厚。两相压降随Re和宽高比的增大而增大,随分散相体积分数的增大而降低。相比连续相和分散相压降,界面压降所占的比重最高,并依据模拟结果,提出了圆管及扁平管内液-液Taylor流动的压降预测公式。     

微通道内屈服应力型流体的流变特性及多相流研究进展

屈服应力型流体（YSFs）是一种典型的非牛顿流体,因其丰富的流变特性被广泛关注。屈服应力是高浓度的粒子分散系统和凝胶状物质（多相乳液、微胶囊、3D打印复杂结构、药物输送凝胶等）的基本特征。本文对微通道内简单屈服应力型流体的流动特征和流变行为,及其流变性对多相流系统的影响进行了综述,剖析了受限空间内流体流动与流体流变性,及多相流动力学和界面现象的耦合机制,并对亟需推进的研究方向进行了展望。为微通道内屈服应力型流体的数值模拟、实验研究和应用提供参考。     

微通道内液滴/气泡破裂动力学分析

微化学工程与技术是现代化学工程学科的前沿领域。微通道内液滴及气泡破裂动力学是决定多相过程并行微通道数目放大的基础与难点。破裂流型转换条件、界面动力学和尺寸调控等三方面是微通道内液滴与气泡破裂动力学的主要研究对象。讨论了对称微通道、非对称微通道、多级微通道、旁路微通道、含有障碍物的微通道内气泡和液滴破裂行为及影响因素,指出了目前微尺度下气泡与液滴破裂行为相关研究工作存在的不足,并对该领域未来的发展进行了展望。     

On the CFD modelling of Taylor flow in microchannels

With the increasing interest in multiphase flow in microchannels and advancement in interface capturing techniques, there have recently been a number of attempts to apply computational fluid dynamics (CFD) to model Taylor flow in microchannels. The liquid film around the Taylor bubble is very thin at low Capillary number (Ca) and requires careful modelling to capture it. In this work, a methodology has been developed to model Taylor flow in microchannel using the ANSYS Fluent software package and a criterion for having a sufficiently fine mesh to capture the film is suggested. The results are shown to be in good agreement with existing correlations and previous valid modelling studies. The role played by the wall contact angle in Taylor bubble simulations is clarified.     

Advanced simulation of transient multiphase flow & flow assurance in the oil & gas industry

We discuss here current computational trends (beyond Mechanistic 1D Models) related to transient multiphase flow and flow assurance problems in the oil and gas sector. The developments needed to bring advanced Computational fluid & Multiphase‐fluid dynamics (CFD & CMFD) techniques and models to a mature stage will also be discussed. The contribution presents the possibilities offered today by these simulation technologies to treat complex, multiphase, multicomponent flow problems occurring in the gas and petroleum engineering in general. Examples of various degrees of sophistication will be presented, without focusing on the validation aspect as such. The models are briefly introduced (phase averages, N‐phase, interface tracking, Lagrangian particle tracking and granular flow model). © 2013 Canadian Society for Chemical Engineering     

Gas-liquid two-phase flow in serpentine microchannel with different wall wettability

Gas-liquid flow in serpentine microchannel with different surface properties exhibits drastically different flow behavior.With water and air as working fluids,the method of numerical simulation was adopted in this paper based on CLSVOF (coupled level set and volume of fluid method) multiphase model.After verifing the reasonability of the model through experiment,by changing wall properties and Re number (Re ＜ 1500),the influences of contact angle and surface roughness on flow regime and Po number were discussed.Moreover,the difference of pressure drop between curve and straight microchannel was also calculated.Beyond that,the combined effect of curve channel and wall properties on flow resistance was analyzed.This paper finds that wall properties have great influence on gasliquid flow in microchannels not only on flow regime but also flow characteristics.Meanwhile,the pressure drop in curve microchannels is larger than straight.It is more beneficial for fluid flowing when the straight part of microchannel is hydrophilic smooth wall and curve part is hydrophobic with large roughness.     

Wax deposition modeling of oil/water stratified channel flow

Wax deposition modeling becomes complicated when multiphase flow is involved. Empirical heat and mass transfer correlations are unreliable for multiphase deposition modeling and full scale computational fluid dynamics calculations require expensive computational intensity. In this work, numerical methods are used to study wax deposition in oil/water stratified flow through a channel. A unidirectional flow analysis is used to calculate the nonisothermal hydrodynamics and mass transfer. It was found that the change in the position of the oil/water interface throughout the channel must be taken into accounted for the mass balance to be valid. Unfortunately, this change has not been accounted for in all previous studies. In addition, the growth of the wax deposit as a function of time along with the effect of oil/water flow rate ratio is discussed. The presence of water significantly reduces the severity of wax deposition by altering the heat and mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

Trickle‐bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas–liquid–solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non‐ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non‐ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three‐phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state‐of‐the‐art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.     

Multiphase CFD Simulation of a Solid Bowl Centrifuge

This study presents some results from the numerical simulation of the flow in an industrial solid bowl centrifuge used for particle separation in industrial fluid processing. The computational fluid dynamics (CFD) software Fluent was used to simulate this multiphase flow. Simplified two‐dimensional and three‐dimensional geometries were built and meshed from the real centrifuge geometry. The CFD results show a boundary layer of axially fast moving fluid at the gas‐liquid interface. Below this layer there is a thin recirculation. The obtained tangential velocity values are lower than the ones for the rigid‐body motion. Also, the trajectories of the solid particles are evaluated.     

微通道内CO2吸收与传质及资源化利用的研究进展

由于在流体流动、传质、传热及反应等方面良好的调控能力,微化工技术成为化工学科重要的发展领域。综述了近年来以CO₂应用为背景的微化工系统中的多相流与传质的研究进展。从流体流动和传质机理出发,分别介绍了物理吸收和化学吸收过程的传质规律。总结了二氧化碳资源化利用的应用进展。展望了微化工技术在二氧化碳吸收与传质方面的发展前景。