The effect of particle rotation on the motion and rejection of capsular particles in slit pores

The results from a two‐dimensional computational model describing the motion of capsule‐shaped particles in a slit pore under small Re conditions are reported. Average particle velocities and particle rejection coefficients were determined for capsules with aspect ratios of 2 and 4. Two different approaches were used to characterize particle rotation and hydrodynamic particle‐pore wall interactions. In one approach, all sterically allowed particle orientation angles had equal probability, i.e., infinite rotational diffusion was assumed. In the second approach, particles were allowed to freely rotate in the pore; particle orientations were dictated by hydrodynamic forces acting on the particle surface and rotational particle diffusion was neglected. Minimal lateral migration across the pore was observed for the freely rotating particles. Although particle alignment was observed for the freely rotating particles, rejections predicted from the two approaches were found to be in close agreement. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2828–2836, 2018     

A functional subgrid drift velocity model for filtered drag prediction in dense fluidized bed

Due to computational time limitations, fully resolved simulations using the two‐fluid model of the flow inside industrial‐scale fluidized beds are unaffordable. The filtered approach is used to account for the effect of small unresolved scales on the large resolved scales computed with “coarse” realistic meshes. Using a fully resolved simulation, we highlight the need to account for a subgrid drift velocity to obtain the correct bed expansion when using coarse meshes. This velocity, defined as the difference between the filtered gas velocity seen by the particle phase and the resolved filtered gas velocity, modify the effective relative velocity appearing in the drag law. We close it as a correction of the resolved relative velocity depending on the filtered particle concentration and the filter size. A dynamic procedure is used to adjust a tuning parameter. Bed expansion obtained with a posteriori test on coarse‐grid simulations matches well to fully resolved simulations. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

计算流体力学在化学工程中的应用

计算流体力学(CFD)用于求解固定几何形状设备内的流体的动量、热量和质量方程以及相关的其他方程,已成为研究化工领域中流体流动和传质的重要工具。本文概述了CFD的基本原理以及CFD在化学工程领域方面的应用,重点介绍了CFD在搅拌槽、换热器、蒸馏塔、薄膜蒸发器、燃烧等方面的应用。     

Multistream heat exchangers: Equation‐oriented modeling and flowsheet optimization

Multistream heat exchangers (MHEXs), typically of the plate‐fin or spiral‐wound type, are a key enabler of heat integration in cryogenic processes. Equation‐oriented modeling of MHEXs for flowsheet optimization purposes is challenging, especially when streams undergo phase transformations. Boolean variables are typically used to capture the effect of phase changes, adding considerable difficulty to solving the flowsheet optimization problem. A novel optimization‐oriented MHEX modeling approach that uses a pseudo‐transient approach to rapidly compute stream temperatures without requiring Boolean variables is presented. The model also computes an approximate required heat exchange area to determine the optimal tradeoff between operating and capital expenses. Subsequently, this model is seamlessly integrated in a previously‐introduced pseudo‐transient process modeling and flowsheet optimization framework. Our developments are illustrated with two optimal design case studies, an MHEX representative of air separation operation and a natural gas liquefaction process. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1856–1866, 2015     

Theoretical investigation of a water‐gas‐shift catalytic membrane for diesel reformate purification

The novel application of a catalytic water‐gas‐shift membrane reactor for selective removal of CO from H₂‐rich reformate mixtures for achieving gas purification solely via manipulation of reaction and diffusion phenomena, assuming Knudsen diffusion regime and the absence of hydrogen permselective materials, is described. An isothermal, two‐dimensional model is developed to describe a tube‐and‐shell membrane reactor supplied with a typical reformate mixture (9% CO, 3% CO₂, 28% H₂, and 15% H₂O) to the retentate volume and steam supplied to the permeate volume such that the overall H₂O:CO ratio within the system is 9:1. Simulations indicate that apparent CO:H₂ selectivities of 90:1 to >200:1 at H₂ recoveries of 20% to upwards of 40% may be achieved through appropriate design of the catalytic membrane and selection of operating conditions. Under these conditions, simulations predict an apparent hydrogen permeability of 2.3 × 10^?10 mol m^?1 Pa, which compares favorably against that of competing hydrogen‐permselective membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4334–4345, 2013     

Modeling of CO2 mass transport across a hollow fiber membrane reactor filled with immobilized enzyme

The enzyme‐based contained liquid membrane reactor to capture CO₂ from the closed spaces is a very complicated process with large numbers of interdependent variables. A theoretical and experimental analysis of facilitated transport of CO₂ across a hollow fiber membrane reactor filled with immobilized carbonic anhydrase (CA) by nanocomposite hydrogel was presented. CO₂ concentration profiles in the feed gas phase and the membrane wall were achieved by numeric simulation. The effects of CO₂ concentration, CA concentration, and flow rate of feed gas on CO₂ removal performance were studied in detail, and the model solution agrees with the experimental data with a maximum deviation of up to 18.7%. Moreover, the effect of CO₂ concentration on the required membrane areas for the same CO₂ removal target (1 kg/day) was also investigated. This could provide real‐world data and scientific basis for future development toward a final efficient CO₂ removal device. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

混合澄清槽数值模拟与实验研究进展

稀土是不可再生的重要战略资源,在高新技术材料中具有不可替代的战略作用。混合澄清槽具有操作稳定性好、级效率高、结构简单、易放大等优点,是稀土分离工业中使用最为广泛的萃取设备。本文概述并分析了应用于混合澄清槽模拟的数值模型,结果表明Eulerian-Eulerian多相流模型、k-?湍流模型和多参考系模型因使用简便、精度可靠、对计算机性能要求不高而被当前的研究者们大量采用。此外,针对混合澄清槽抽吸性能、混合特性和澄清特性三大重要性能指标,分别总结了影响各性能的主要参数和调控方法,分析表明在抽吸性能和混合时间方面的研究较为成熟,在液滴聚并破碎数值研究、澄清方式和改进等方面的研究相对薄弱,构建高精度网格、采用更细致分析流场时空发展趋势的大涡模拟和引入种群平衡模型等方法将是下一步深入研究混合澄清槽的重要方向。     

A multiscale,biophysical model of flow‐induced red blood cell damage

A new model for mechanically induced red blood cell damage is presented. Incorporating biophysical insight at multiple length scales, the model couples flow‐induced deformation of the cell membrane (～10 µm) to membrane permeabilization and hemoglobin transport (～100 nm). We estimate hemolysis in macroscopic (above ～1 mm) 2‐D inhomogeneous blood flow by computational fluid dynamics (CFD) and compare results with literature models. Simulations predict the effects of local flow field on RBC damage, due to the combined contribution of membrane permeabilization and hemoglobin transport. The multiscale approach developed here lays a foundation for a predictive tool for the optimization of hydrodynamic and hematologic design of cardiovascular prostheses and blood purification devices. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1509–1516, 2014     

Sag in commercial thermoforming

Our previous analytical solution gives sag advancing implicitly as , or for , sag advances with the cube root of time for a thin wide rectangular Newtonian isothermal sheet. This previous analytical work applies to sheets that are pinned along just two edges, and not all the way around. Corresponding sagometer experimental results confirmed this cube root relation. This work compares the prediction with measured commercial thermoforming behavior on rectangular sheets that are, of course, pinned all the way around. Then sag parallel superposition is used to extend for a sheet pinned all the way around. We evaluate sag parallel superposition using a finite element method (FEM) employing ANSYS Polyflow. The equation assumes sagging sheet cylindricity, and from our FEM we find that this assumption is reliable when . We compare sag measured in commercial thermoforming, using high‐impact polystyrene (HIPS) sheets that are pinned all the way around, by extending with parallel superposition. It is found that the time evolution of the commercial sag follows nearly exactly the same shape as the isothermal prediction. We measure sag runaway, and although the isothermal analysis , predicts the sag runaway time accurately, our isothermal theory overpredicts the amount of sag in the nonisothermal commercial operation by as much as a factor of 14. It is also shown how to use sheet sag measurements from commercial thermoforming to deduce the Newtonian viscosity of a thermoforming resin at a temperature that is above its softening point. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1529–1535, 2014     

用大涡模拟结合改进的内外迭代法数值模拟搅拌槽中的液相流动

1 INTRODUCTION Stirred tank reactors are widely encountered in the chemical, pharmaceutical, and hydrometallurgical proc- esses. The fluid motion in stirred tanks is three-dimensional, complex, and covers a wide range of spatial and temporal scales. In the area surrounding the impeller, the flow is highly turbulent and swirling. The numerical simulation of such reactor systems is helpful in quantifying the effects of the impeller type, geometry, and the operational conditions in order to …     

Transient response of two‐layer slot coating flows to periodic disturbances

Coating uniformity requirement is becoming more severe as new products come into the market. Coating processes have to be designed not only based on the steady‐state operation but also taking into account how the flow responds to ongoing disturbances on process conditions. These disturbances may lead to thickness variation on the deposited liquid layers that may be unacceptable for product performance. This study extends available transient analysis of single‐layer slot coating to determine the amplitude of the oscillation of each individual coated layer in two‐layer slot coating process in response to small periodic perturbation on different operating parameters. The predictions were obtained by solving the complete transient Navier–Stokes equations for free surface flows. The results show the most dangerous perturbations and how the deposited film thickness variations of each layer can be minimized by changing the geometry of the die lip and liquid viscosities. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1699–1707, 2015     

自由基聚合反应器中多尺度流场的模拟进展

自由基聚合过程中,由于混合、传递及聚合反应的相互作用使得反应器内部存在复杂的多尺度流场,例如宏观尺度的速度、浓度、温度分布,介观尺度的液滴粒径分布,微观尺度的聚合反应速率、聚合物分子量和多分散性指数分布。这些复杂的多尺度流场分布使得聚合反应器的模型化研究成为难题。本文较为系统地介绍了自由基聚合反应器中存在的多尺度现象;简述了微观尺度聚合物性质流场分布的模型化与模拟研究方法;从悬浮聚合和乳液聚合两个方面介绍了介观尺度液滴粒径分布的模拟研究进展;从非理想混合的角度阐述了宏观尺度多相流流场分布的研究进展。最后,本文分析了多尺度模型的耦合求解方法。本综述也有本文作者对这个领域的初步观点,可为聚合反应器的设计、优化和放大提供参考。     

基于颗粒直径大小对环形空间携屑影响的数值模拟

钻井是开发石油资源一个非常重要的环节和技术手段,井中岩屑易在井眼底部形成岩屑床,导致下钻遇阻、蹩泵甚至卡钻,因此岩屑运移机理的研究对钻井作业来说至关重要。通过对现场实际情况的调研,得到井下上返颗粒的直径范围,进行数值模拟。运用Solid Works对井下环形空间进行建模与装配,得到井下环形空间的三维模型。使用软件建立井下环形空间的简化模型,通过应用FLUENT中动网格部分的UDF编写成功地实现了钻杆的旋转。运用FLUENT数字模拟软件,通过对流体非定常流的数值模拟,对岩屑在环形空间的运移规律进行研究,模拟条件更加接近实际情况,结果更加精确,可以为钻井井眼清洁工作提供科学参考。     

Coupled simulation of the flue gas and process gas side of a steam cracker convection section

A coupled simulation of the flue gas and process gas side of the convection section of a steam cracker is performed, making use of the CFD software package Fluent. A detailed overview of the operating mode of the different heat exchangers suspended in the convection section is obtained. The asymmetric inlet flow field of the flue gas in the convection section, and the radiation from the convection section walls leads to large differences in outlet temperatures of the tubes located in the same row. The flow fields and temperature fields in the tubes of a single heat exchanger differ significantly with e.g., outlet temperatures of the hydrocarbon‐steam mixture ranging from 820 K to 852 K. Moreover, the simulations reveal the presence of hot spots on the lowest tube row, possibly causing fouling. © 2009 American Institute of Chemical Engineers AIChE J, 2009