Evaluation of mixing profiles for a new micromixer design strategy

The relationship between mixing history and reaction performance in microreactors using computational fluid dynamics (CFD) simulations is identified. In the idealized, simplified mixing model, mixing proceeds linearly and only the mixing time determined the reaction performance. However, in the case of realistic models where mixing proceeds unequally, the partial rapid progression of mixing, more than the mixing time, significantly impacts the reaction. The use of the fluid segment size distribution to capture this effect is proposed. The effective Damköhler number derived from the fluid segment size distribution predicted the reaction yield well. To demonstrate the utility of the mixing profile design strategy, we fabricated a novel micromixer with multiple partial rapid mixing zones. This micromixer achieved excellent results both in a CFD simulation and an experiment. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1154–1161, 2016     

A fluidized bed membrane reactor for the steam reforming of methane

In the present investigation a realistic two-phase model accounting for the change in the total number of moles accompanying the reaction is utilized to explore a novel reactor configuration suggested for the methane steam reforming process. The suggested design is basically a fluidized bed reactor equipped with a bundle of membrane tubes. These tubes remove the main product, hydrogen, from the reacting gas mixture and drive the reaction beyond its thermodynamic equilibrium. The proposed novel design is also equipped with sodium heat pipes which act as a thermal flux transformer to provide the large amount of heat needed by the endothermic reaction through a relatively small heat transfer surface, assuring better reactor compactness. Two options for fluid routing through the membrane tubes are proposed; each is suitable for a certain industrial application. The performance of this novel configuration is compared with that of an industrial fixed bed steam reformer and the comparison shows the potential advantages of the suggested configuration.     

Design and analysis of a dual-cavity coat-hanger die

A method for the design and analysis of a dual-cavity coat-hanger die is presented in this paper. A macroscopic material balance and a microscopic flow analysis using the finite element method are combined to simulate polymeric fluid flow inside the die. Leonard's macroscopic procedure was adopted to include inertial, gravitational, and viscous effects, and the finite element method was then applied to estimate the contributions of inertial and viscous terms. In addition, the flow patterns in the outer cavity were computed by the finite element method so that the appearance of an undesirable vortex could be predicted. The residence time distributions for flow in the die were approximated by a simple, statistical approach. It was found through a case study that a dual-cavity coathanger die can effectively reduce the flow non-uniformities caused by fluid inertia and viscosity variations.     

Integration of on‐the‐fly kinetic reduction with multidimensional CFD

A reduction approach for coupling complex kinetics with engine computational fluid dynamics (CFD) code has been developed. An on‐the‐fly reduction scheme was used to reduce the reaction mechanism dynamically during the reactive flow calculation in order to couple comprehensive chemistry with flow simulations in each computational cell. KIVA‐3V code is used as the CFD framework and CHEMKIN is employed to formulate chemistry, hydrodynamics and transport. Mechanism reduction was achieved by applying element flux analysis on‐the‐fly in the context of the multidimensional CFD calculation. The results show that incorporating the on‐the‐fly reduction approach in CFD code enables the simulation of ignition and combustion process accurately compared with detailed simulations. Both species and time‐dependant information can be provided by the current model with significantly reduced CPU time. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

On‐surface polymerization – a versatile synthetic route to two‐dimensional polymers

Two‐dimensional (2D) polymers are novel covalent sheet materials with promising properties, but also great synthetic challenges. The inadequacy of traditional wet chemical synthesis calls for new synthetic paradigms. In this respect, employing surfaces as inherently 2D reaction venues appears an adequate choice and has recently already yielded encouraging results. Polymerization at air ? liquid and liquid ? liquid interfaces has been reported from time to time over the last decades, whereas recent efforts on solid surfaces are less traditional. In either case, both movement and coupling of monomers are already confined in two dimensions at interfaces or on surfaces. Accordingly, this approach naturally affords low‐dimensional reaction products. To achieve 2D reticulation, monomers are functionalized with multiple reactive groups of the same or a different kind, whereby their number and stereochemical arrangement predefines the ideal structure of the resulting 2D polymer. This perspective article exemplifies different approaches, i.e. types of surfaces, coupling chemistry and activation schemes, to employ surfaces for novel synthetic routes for the bottom‐up synthesis of 2D polymers. © 2015 Society of Chemical Industry     

Pattern‐driven color pattern recognition for printed fabric motif design

Pattern‐driven design method is an important data‐driven design method for printed fabric motif design in textiles and clothing industry. We introduce a novel framework for automatic design of color patterns in real‐world fabric motif images. The novelty of our work is to formulate the recognition of an underlying color pattern element as a spatial, multi‐target tracking, classification, segmentation and similarity association process using a new and efficient color feature encoding method. The proposed design method is based on pattern‐driven color pattern recognition and indexing from the element image database. A series of color pattern recognition algorithms are used for color and pattern feature extraction. The local statistical corner features and Markov random field model are used for motif unit tiling detection and conversion. The color feature encoding problem is modeled in a gray‐scale color difference optimization problem, which can be solved quickly by existing algorithms. Color pattern feature matching, segmentation and indexing techniques are then used to locate and replace the elements in the motif unit image with similar elements in the database. Experiments show that the approach proposed in this study is effective for color pattern recognition and printed fabric motif design.     

Characterization and control of plastic deformation in mesoscale premolded components to realize in‐mold assembled mesoscale revolute joints

This article reports a mold design strategy and a detailed mechanics‐based modeling approach to characterize and control the plastic deformation of premolded components during in‐mold assembly of mesoscale revolute joints. The following new results are reported in this article. First, a mesoscale mold design with varying cavity shape is described to perform in‐mold assembly of the mesoscale revolute joint. Second, a transient computational fluid dynamics (CFD) modeling approach to determine the forces experienced by the mesoscale parts due to injection molding is described. Finally, a mechanics‐based model approach developed using a combination of experimental materials property data and the CFD results as input to a finite element simulation of the deformation response of the mesoscale part is presented for the determination of critical mold design parameters that are necessary for repeatable fabrication of articulating mesoscale revolute joints. Using the advances reported in this article a mesoscale revolute joint has been successfully molded. To the best of our knowledge, this is the first demonstration of in‐mold assembly process using a varying cavity shape mold tocreate an articulating mesoscale revolute joint. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Liquid‐Phase Separation with the Rotational Particle Separator

Recently, the rotational particle separator (RPS) was introduced as a new technique for separating solid and/or liquid particles of 0.1 μm and larger from gases. In this patented technique the principles of centrifugation are exploited to enhance separation of small‐sized phases and particulate matter of density different from the carrier fluid. Practical designs of the RPS available in the market include equipment for purifying gases of industrial processes and portable air cleaners for domestic appliances. New developments are made in the area of the offshore industry. It concerns the separation of oil droplets from water and the separation of condensate, oil, and sand from natural gas. A particular feature of both designs is that the filter element is freely mounted in bearings and rotates, without the need of a motor, by introducing a swirl in the fluid flowing towards the filter element. The design is particularly suited for operation under high pressures as the rotating filter element is fully contained within a cylindrical pipe. The shaft does not pin through the external wall, so no sealing is required. Based on known RPS design principles and fluid flow relations an oil‐water separator is designed and tested.     

Mixing and fast chemical reaction—VII Deforming reaction zone model for the CSTR

Earlier work on batch reactors indicated that the final stage of homogenisation to the molecular scale (micromixing) occurs by molecular diffusion in deforming fluid elements. The product distribution of, for example, consecutive, competitive reactions is sensitive to concentration gradients at the molecular scale (segregation). Such reactions may be used as reactive tracers to throw light on the behaviour of small fluid elements. Moreover an understanding of micromixing allows the selectivity of fast, multiple reactions to be better controlled. This paper describes two ways of applying the unsteady-state equations for diffusion and reaction within a shrinking fluid element to determine the steady-state concentrations in a CSTR. The iterative model is more economical in computer time than the dynamic model and applies to fast reactions (i.e. when the time for diffusion and reaction is a small fraction of the mean residence time). It described well the measured effects on the product distribution of varying the volumetric feed rati the stoichiometric ratio and of changing the operating mode from semicontinuous to continuous. When the initial size of the deformable fluid element is identified with the Kolmogoroff microscale and a reasonable estimate of shear rate is introduced, a highly satisfactory prediction of experimental resu knowing the kinematic viscosity and the power consumption of the stirrer, becomes possible.     

A two-scale model for discrete cell gravure roll coating

A two-dimensional model for predicting the fluid pickout and coated film thickness characteristics of a discrete cell direct gravure roll coater operating in reverse mode is derived. A novel multiscale approach is adopted for this purpose and the resulting equations solved numerically for inertia-less flow conditions. A system of stiff ordinary differential equations is found to be sufficient to capture the major gross flow features, while at the cell level the analysis is based on a finite element solution of the momentum and continuity equations. It represents the first such predictive model of its kind, with particular interest placed on the nature of both the pressure distribution and web-to-roll gap profile spanning the coating bead. The effect of key operating parameters, web-to-roll speed ratio, web-tension, wrap-angle, capillary number and cell-geometry, on the degree of fluid pickout from gravure cells and the coated film thickness is explored. Although an idealised model, the trends observed show qualitative agreement with existing experimental data collected on a small-scale gravure coating rig and point the way forward to the eventual formulation of a full three-dimensional predictive model of the process.     

TIME-SCALE ANALYSIS OF CHEMICAL REACTION SYSTEMS DYNAMICS†

In dynamic simulation and control of chemical reaction systems physical state variables (compositions) are not often defined so as to facilitate the practical use of the system model. This ill-posedness frequently arises due to the presence of hidden time scales in the reaction dynamics. Transformation of variables is then often an efficient manner to facilitate the simulation and control of chemical reactors. In this paper, we emphasize the physical situation by examples and also present a manifold-based analysis which permits to construct a nonsingular transformation for expressing the original model in a explicit form. Using the coordinated-free approach, time scales in kinetic models are interpreted in terms of relaxation and conservation properties. As a whole, the paper provides conceptual fundamentals for a novel and powerful characterization of time-scale reaction variants and invariants     

THE ROLE OF GAS DISTRIBUTION IN FLUIDIZED BED CHEMICAL REACTOR DESIGN†

The design of fluid bed gas distributors may have a marked influence on the performance of a fluid bed reactor. The primary physical reason for this influence is that the distributor design influences the hydrodynamics and thus the gas/solid contacting pattern in the fluidized bed.

In the paper presented here the influence of distributor design on mass transfer and chemical reaction has been investigated systematically in fluid bed reactors with diameters of 0.2 and 1.0 meter. Coefficients of mass transfer between the bubble phase and the suspension phase were determined from chemical conversion and tracer gas residence time distribution measurements. In the experimental program the height of the fluidized bed was varied between 0.3 m and 0.9 m with superficial gas velocities in the range of 0.06 m/s to 0.30 m/s.

The comparison of the experimental results with a suitably modified and extended two-phase model yields quantitative relationships which allow to account for the influence of the gas distributor in the design of fluid bed chemical reactors.     

Optimization‐based design of polymer sheeting dies using generalized Newtonian fluid models

A polymer sheeting die design methodology is presented, which integrates finite element flow simulations, numerical optimization, and design sensitivity analyses to compute die cavity geometries capable of giving a near‐uniform exit velocity. This work extends earlier die design methods to include generalized Newtonian fluid (GNF) models that represent the shear‐thinning behavior of polymer melt. Melt flow computations and design sensitivity analyses are provided using the generalized Hele‐Shaw flow approximation with isothermal power‐law, Carreau‐Yasuda, Cross, Ellis, and Bingham fluid models. The nonlinear equations for die cavity pressure are solved using the Newton‐Raphson iteration method and design sensitivities are derived with the adjoint variable method. The die design method is applied to an industrial coat hanger die, in which a design parameterization is defined that allows for an arbitrary gap height distribution in the manifold of the die. In addition, die performance is assessed and compared for power‐law and Carreau‐Yasuda fluid flow over a range of die operating conditions. Pareto optimal die designs are also considered in this study. POLYM. ENG. SCI., 45:953–965, 2005. © 2005 Society of Plastics Engineers     

A novel simulation approach for particulate flows during filtration

This paper presents a novel approach for simulation of filtration process when velocity gradient within pore space cannot be neglected. The new model is useful for accurate prediction of the filtration performance and particle retention efficiency. Artificial porous media such as filters, by design, have a large surface-to-volume ratio because of an inherent homogeneity present within their structure; the homogenous structure is realized due to organized packing of grains as building blocks, which leads to a significant velocity gradient inner pore space. In this work, the inner-pore flow characteristics of two different homogeneous packing patterns (cubic and oblique hexagonal packing) were examined. The multiple constricted tubes analogy was adopted to model porous media to simplify the inner-pore geometrical structure. A new integrated simulation approach was utilized through implementing the particle trajectory model to every unit bed element of the simulation domain. The accuracy of the numerical simulations used in this study was verified by comparing the particle distribution pattern and penetration depth obtained from simulations to those monitored via a visual experiment. A sensitivity analysis was carried out to study parameters that may affect the particle distribution and penetration length, such as grain-to-particle size ratio, flow rate, and fluid viscosity. The simulation method utilized in this paper provides an in-depth understanding of the fine particle migration during filtration process through artificial porous media, and, thus, provide useful insights for improved filtration design.     

Auslegung von Blasensäulen mithilfe von Compartmentmodellen

In bubble columns, the phenomena of mass and heat transfer as well as the reaction are closely linked to the complex fluid dynamics. Compartment modeling offers the opportunity to integrate these phenomena while enabling an axial and radial distribution with acceptable computing effort. This article includes methods for generating the compartment geometry and fluid dynamic parameters of this modeling approach, facilitating the opportunity to optimize an industrial bubble column.     

Investigation into the Feasibility of Thioditaloside as a Novel Scaffold for Galectin‐3‐Specific Inhibitors

Galectin‐3 is extensively involved in metabolic and disease processes, such as cancer metastasis, thus giving impetus for the design of specific inhibitors targeting this β‐galactose‐binding protein. Thiodigalactoside (TDG) presents a scaffold for construction of galectin inhibitors, and its inhibition of galectin‐1 has already demonstrated beneficial effects as an adjuvant with vaccine immunotherapy, thereby improving the survival outcome of tumour‐challenged mice. A novel approach—replacing galactose with its C2 epimer, talose—offers an alternative framework, as extensions at C2 permit exploitation of a galectin‐3‐specific binding groove, thereby facilitating the design of selective inhibitors. We report the synthesis of thioditaloside (TDT) and crystal structures of the galectin‐3 carbohydrate recognition domain in complexes with TDT and TDG. The different abilities of galactose and talose to anchor to the protein correlate with molecular dynamics studies, likely explaining the relative disaccharide binding affinities. The feasibility of a TDT scaffold to enable access to a particular galectin‐3 binding groove and the need for modifications to optimise such a scaffold for use in the design of potent and selective inhibitors are assessed.     

A novel approach to predict the recovery time of shape memory polymers

In this paper a novel approach is presented for prediction of the recovery time for a shape memory polymer. The Transient Stress Dip Tests of Fotheringham and Cherry are used to determine the two parameters of a Kelvin-Voigt element. The characteristic retardation time of this element can then be calculated to predict the recovery time. It is shown that this approach is successful in predicting the recovery times for a shape memory polymer drawn and recovered under a range of temperatures. Furthermore it is shown that the ratio of the recovery stress to the draw stress is independent of the drawing conditions to a very good approximation.     

颗粒/流体反应的分数维模型

在分形理论的基础上发展了形状不规则颗粒/流体体系的分数维反应模型。在拟稳态条件下求得反应物浓度分布式、反应时间、完全反应时间、相对反应时间、单位时间的反应量和颗粒转化率的分数维表达式。并由此导出膜扩散、灰层扩散和化学反应3个阶段的反应时间等参数,讨论了颗粒的分数维对反应过程的影响。     

Probabilistic reactor design in the framework of elementary process functions

Computational process models in combination with innovative design methodologies provide a powerful reactor design platform. Yet, model-based design is mostly done in a pure deterministic way. Possible uncertainties of the underlying model parameters, prediction errors due to simplifying assumptions regarding the reactor behavior and suboptimal realizations of the design along the reaction coordinate are in general not considered. Here we propose a systematic design approach to directly account for the impact of such variabilities during the design procedure. The three level design approach of Peschel et al. (2010) based on the concept of elementary process functions (EPF) serves as basis. The dynamic optimizations on each level are extended within a probabilistic framework to account for different sources of randomness. The impact of these sources on the performance prediction of a design is quantified and used to robustify the reactor design aiming at a more reliable performance and thus design prediction. The uncertainties of model parameters, non-idealities of the reactor behavior and inaccuracies in the design are included via statistical moments. By means of the sigma point method (Julier and Uhlmann, 1996) random variables are mapped to the design objective space via the nonlinear process model. Importantly, this work introduces a full probabilistic orthogonal collocation approach, i.e. random and stochastic variables can be described. Whereas the former one relates to randomness independent on the reaction time (e.g. kinetic model parameters or initial conditions), the latter one describes stochasticity along the reaction time (e.g. fluctuating pressure or temperature control). As an example process the hydroformylation of 1-dodecene in a thermomorphic solvent system consisting of n-decane and N,N-dimethylformamide is considered.Our probabilistic EPF approach allows designing robust optimal reactors, which operate within an estimated confidence at their expected optimum considering almost any kind of randomness arising in the design procedure. An additional value is that with increased predictive power of the reactor performance its embedding in an overall process is strongly simplified.