微尺度内液-液传质及反应过程强化的研究进展

微化工技术作为一种高效的过程强化技术获得了广泛应用。本文从流动、传递及反应三者之间的耦合机制出发,系统综述了近十五年以来关于微尺度内液-液两相流动与传质过程特征、强化传质的微反应器、评价标准及其在化学品合成与材料制备中的应用等方面的研究进展,并对其未来发展方向进行了展望。     

流态化模拟:基于介尺度结构的多尺度CFD

介尺度结构是研究气固流态化多尺度行为的关键。传统的基于平均化处理方式的双流体模拟不能准确描述流化床中的多尺度流动和传递行为。相较而言,基于能量最小多尺度(EMMS)方法的结构多流体模型(SFM)基于局部空间(网格)内的非均匀介尺度结构流动特征,其宏观预测结果与网格分辨率基本无关,因而可以大幅降低模拟计算量。基于SFM模拟得到的流动结构,EMMS多尺度传质模型进一步成功解释了传统传质文献中的数据差异。集成上述模型,形成了一整套模拟流化床流动-传递-反应耦合过程的多尺度计算流体力学(CFD)方法,并将其应用于预测循环流化床中典型的S型轴向分布、揭示噎塞转变的机理以及流化床放大困难的原因。多尺度CFD使工业规模循环床的三维、全系统、动态流动-反应耦合过程的准确模拟成为可能,并为实现从模拟向实时虚拟过程转变的目标打下基础。     

微化工系统内多相流动及其传递反应性能研究进展

微化工系统是化学工程学科的研究热点之一,鉴于其良好的传递和反应特性,在多相反应和分离过程中受到了广泛的关注。目前关于微化工系统的研究主要集中在新型微分散技术、微介观尺度混合、多相传递性能以及反应过程调控等方面,近年来取得了显著的进展。本文主要针对微化工系统研究中的关键科学问题进行综述,探讨微化工系统的研究进展,并对其未来的发展方向进行了展望。     

旋转床超重力环境下多相流传递过程研究进展

旋转填充床作为一种高效的传质、分离与反应设备,在化工、环境保护、纳米材料制备、能源、制药等工业过程得到广泛应用。本文对旋转填充床超重力环境下,流体力学特性、传质性能、微观混合、多尺度传递特性等方面的研究进行了总结归纳。近年来,随着计算机科学与多相流传递过程的研究进展,对传递过程的研究也由实验手段为主转变为实验与数值模拟相结合的手段,对有关的数值模拟研究以及相应的多相流模型也予以总结描述。在此基础上,对旋转填充床超重力环境下多相流研究的未来发展提出了有关设想。     

鼓泡床中基于气泡结构的多相反应模型

气固鼓泡床是一个流动、传热/传质和反应多尺度时空耦合的复杂系统。其中介尺度流动结构（如气泡）对于气固相间传递起着关键性的作用。为了准确描述气固流态化系统中的“三传一反”行为,需要在合理物理简化的基础上建立介尺度模型。提出了基于气泡结构的多流体反应模型,考虑了介尺度非均匀结构对于鼓泡床内气固相间反应的影响;定义了基于气泡的反应非均匀因子修正双流体（TFM）传质反应模型,从而使模型更加易用。通过鼓泡床内的臭氧催化分解反应模拟,对模型进行了初步验证,模拟结果与文献结果相符。     

学研结合的《化工传递原理》课程改革与实践——以水净化膜表面特性影响的动量分子传递过程为例

培养具有较强实践和创新能力的新工科复合型人才是本科化工教育的重点。化工传递原理作为化学工程与工艺专业学生必修课,在提升本科教育质量中发挥重要作用。然而,化工传递原理课程存在理论性强、抽象推理多、学科交叉广、实验及理论同步配套程度低等问题,为有的放矢地解决课程难题,提高教学质量和品质,教学团队从教学目标和教学方法等多方面进行深度改革和创新;为重点突出以前沿科学研究为契机的学研结合新范式进行化工传递原理课程改革与实践,本文以水净化膜表面特性影响的动量分子传递过程为例,通过科学研究实验结合化工动量传递理论提升教学质量。将化工传递的科学研究与课堂理论教学相耦合,突出以学生为主体和产出导向的标准提升教学品质。这种新范式将有益于工科学生解决复杂化学工程问题能力的显著提升,为综合型本科化工类专业的改革发展提供重要支撑。     

基于EMMS范式的离散模拟及其化工应用

化工过程通常涉及化学、化工、过程系统工程3个层次,而每个层次又包含微尺度、介尺度和宏尺度,如化工层次的颗粒、颗粒团和反应器尺度。每个层次中的微尺度单元都自然适用离散模型,即通过跟踪每个单元的运动获得整个体系演化的宏观规律。但由于单元数量巨大,工程模拟往往依赖经过统计平均的连续介质模型。由此带来的精度问题,特别是忽略了介尺度结构的问题,随着对化工过程效率和绿色度等要求的提高而日渐突出。介绍了通过问题、模型、软件和硬件结构的一致性提升离散模拟的精度、能力和效率的方法、进展及其在复杂分子体系、颗粒流、气固流态化等方面的应用,展示了通过离散模拟实现虚拟过程工程的可能性。     

限域传递机制初探：以限域状态为切入点描述传递阻力

纳米限域空间中分子的传递是新一代化工过程的共性问题。限域空间引入界面润湿性与限域自由度，导致固体-流体受到的非对称相互作用显著，使得流体状态大幅度偏离均一主体相，经典传递理论不再适用。面向限域的传递理论的缺失，已不能满足现代化工发展的需求。本文综述本团队及前沿的限域传递研究工作，并基于统计力学与非平衡热力学方法进行分析，发现前沿研究分别涵盖三个角度：新自由度下分子间相互作用力决定流体反常状态，反常状态描述流体限域传递物性，反常传递物性描述限域传递阻力实现通量描述。针对三个角度，总结出限域传递阻力雏形，并从三个角度对限域热点工作初探分析，以限域状态为起点，将三个角度贯通是发展限域传递模型的方向，进而为现代化工发展基础数据和模型。     

受限界面处流体分子行为的调控及相关分子热力学模型初探：基于高比表面氧化钛的研究进展

纳米受限界面处的流体由于受到界面性质的影响显著,且存在复杂的传递和反应机制耦合问题,其流体分子行为难以调控,成为了现代化工新技术（如膜过程、多相催化）突破的瓶颈。结合了近几年本课题组的相关工作进展,以化学性质稳定的高比表面氧化钛作为研究平台,对界面处流体分子受限行为进行分析,研究了传递和反应机制分别对界面处流体行为的影响,并探索其调控机制;同时对建立的相应分子热力学模型进行了初步探索,通过原子力显微镜技术将界面摩擦性质和分子间相互作用关联,为分子热力学模型提供分子参数。     

分子模拟在化学工程中的应用

总结了不同尺度分子模拟技术在化工中的发展现状,利用量化计算的方法,可以研究纳微尺度表界面的活性及其对催化反应的影响。采用分子动力学模拟可很方便地研究受限条件下流体行为,采用粗粒化模拟技术可研究介观结构。最后介绍了反应力场模拟这种涵盖反应和传递的模拟新方法。随着模拟理论和并行技术的进步,分子模拟的定量化程度越来越高,必将与化工应用的实验结果越来越有可比性,从而在化工生产和实践中担当更重要的角色。     

基于REDIM方法构建的亚网格燃烧模型及其应用

将近年发展的详细反应机理简化方法:反应-扩散流形(REDIM)方法与假定滤波密度函数相结合,构造了新的亚网格燃烧模型。由于REDIM方法既能描述快速反应状态又能描述扩散过程起主导作用的慢速反应状态,因此新构造的燃烧模型理论上可用于计算扩散和化学反应均起重要作用的湍流部分预混燃烧及分层燃烧模式。为了验证其性能,利用新模型对基准的Darmstadt湍流分层火焰燃烧器进行了大涡模拟(LES)计算:首先分别采用粗、细两种网格对无反应湍流状态进行了计算,以检验网格精度;随后对一个有分层效应的湍流燃烧状态进行了计算。LES计算得到的速度、温度、组分等统计信息与实验结果吻合良好,验证了新亚网格燃烧模型在预测湍流分层火焰方面的能力。     

Catalytic Production of Liquid Fuels from Biomass‐Derived Oxygenated Hydrocarbons: Catalytic Coupling at Multiple Length Scales

The catalytic processing of biomass‐derived feedstocks to liquid fuels and chemical intermediates is complex and expensive. Therefore, conversion processes involving a limited number of reaction, separation, and purification steps are necessary. Coupling of catalytic processes has the potential to lead to the development of new processes, thereby improving the overall economics of biomass conversion. Functional coupling at the molecular scale has the potential to produce novel catalytic materials to replace homogeneous catalysts. Active site coupling of different sites within the same reactor can help reduce operating costs by combining sequential reactions in a single reactor. Chemical reaction coupling of heterogeneous and homogeneous reactions may lead to improvements in overall catalytic performance for liquid phase processes by enhancing surface reactions with liquid phase reactions. Finally, phase coupling leads to improvements in overall yield by improving the equilibrium conversion or by suppressing undesired side reactions.     

Advances in modelling of biomimetic fluid flow at different scales

The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed.     

Coupled transport of fluxes as caused by confined reactions

The effect of confined chemical reaction on the coupling of fluxes has been studied. The confined reactions are found to produce strong coupling between various diffusive fluxes and between diffusive fluxes and chemical reactions. A general mathematical framework has been derived for coupled transport with a single reversible reaction. The reaction is assumed to be near equilibrium so that an analytical solution can be obtained. Some specific cases of coupled transport have been solved using this general mathematical framework. The extension of the theory to more than one reaction is considered. Useful applications might include electrical generation from the CO₂ gradient of power plants or chemical refrigeration. Many other possible processes are suggested.     

Single point electrodeposition of nickel for the dissymmetric decoration of carbon tubes

Dissymmetric micro- and nanoobjects are of enormous interest in many areas ranging from molecular electronics to targeted drug delivery. So far it has been quite difficult to synthesize dissymmetric objects at these scales and most approaches are based on using interfaces to break the symmetry. Only a few bulk procedures are known so far to produce the so-called Janus-type objects. We report here a simple approach for the bulk generation of dissymmetric micro- and nanoobjects, especially carbon tubes (CTs), based on a known, but so far underestimated electrochemical principle, namely bipolar electrodeposition. A suspension of CTs is introduced in a capillary containing an aqueous nickel salt solution and a high electric field is applied to orientate and polarize the individual tubes. During their transport through the capillary under sufficient polarization, each tube is the site of water oxidation at one end, and of Ni²⁺ reduction at the other one. The resulting nickel deposit at one end of the tube allows manipulation of the objects with the help of a magnetic field.     

复杂流体-固体界面相互作用热力学机制

具有复杂结构的纳微界面往往是界面复杂作用和宏观实验现象的主导因素。要准确描述界面处复杂流体的行为,需要引入能描述复杂流体-固体界面相互作用的分子热力学模型。本综述围绕分子热力学模型化方法拓展至纳微界面传递问题,提出“分子热力学建模+分子模拟+纳微实验”三者有机配合新思路。并针对复杂流体-固体界面相互作用的定量研究,着重综述了作者在热力学建模,分子模拟以及采用原子力显微镜 (atomic force microscopy,AFM) 实验方面的研究进展,创新性地提出将AFM定量化分析作为桥梁,用于构建分子模拟模型,描述复杂界面作用,揭示分子热力学机制,为构建纳微界面传递模型以及分子热力学模型由体相拓展至界面提供了可能。     

搅拌釜内固-液悬浮体系的CFD-DEM模拟(英文)

Computational fluid dynamics-discrete element method （CFD-DEM） coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank. Influences of operating conditions and physical properties of particles （i.e., particle diameter and density） on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied. The wide distribution of particle angular velocity ranging from 0 to 105 r·min-1 is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to under-stand the physics of particle movement in micro-to macro-scales in the solid suspension of a stirred tank.     

TAYLOR DISPERSION OF MULTICOMPONENT SOLUTES

Coupled transport of multicomponent solutes in globally continuous systems is considered in the framework of the Generalized Taylor dispersion theory. Coupling between transports of n different species at the local (or micro-) scale, is considered to result from first-order irreversible surface reactions occurring on the local space boundaries, or from the off-diagonal terms of the solute diffusivity matrices.

General expressions are obtained for the global effective (long-time) solute dispersion matrix cofficients: mean global scalar reactivity, velocity vector and dispersivity dyadic.

The effect of surface chemical reactions is to partition the matter between different solute constituents. This is manifested in a coupling of the global transport coefficients, which may be mathematically removed by a linear (canonic) transformation applied to the effective global transport equation. This type of coupling does not exist for inert solutes.

The second type of the global coupling is represented by the off-diagonal terms of the global velocity and dispersivity matrices. It exists for both reactive and inert solutes. This coupling stems from the convective dispersion process (dependence or the global velocity vector on the local space coordinate). Is shown to be irremovable from the global transport equation by any linear transformation via the solute partition matrix. In the canonic form of the global equation the irremovable coupling is manifested by the traceless parts of the global solute velocity matrix and the global solute dispersivity.

The solution scheme is illustrated by calculating the mean global diffusivity of a solute consisting of two components, transport of which is coupled at the microscale via the molecular diffusivity matrix. At the macroscale the coupling is shown to be represented by negative off-diagonal terms of the global diffusivity matrix,     

Non-isothermal reaction-diffusion systems with thermodynamically coupled heat and mass transfer

Non-isothermal reaction-diffusion (RD) systems control the behavior of many transport and rate processes in physical, chemical, and biological systems. A considerable work has been published on mathematically coupled nonlinear differential equations of RD systems by neglecting the possible thermodynamic couplings among heat and mass fluxes, and reaction velocities. Here, the thermodynamic coupling refers that a flux occurs without its primary thermodynamic driving force, which may be gradient of temperature, or chemical potential, or reaction affinity. This study presents the modeling equations of non-isothermal RD systems with coupled heat and mass fluxes excluding the coupling of chemical reactions using the linear non-equilibrium thermodynamic approach. For a slab catalyst pellet, it shows the dynamic behavior of composition and temperature profiles obtained from the numerical solutions of non-linear partial differential equations by Mathematica for two industrial reaction systems of synthesis of vinyl chloride and dissociation of N₂O.