APPLICATION OF THE HOMOTOPY ANALYSIS METHOD (HAM) TO THIN FILM FLOW OF A GENERALIZED SECOND-GRADE FLUID ON A VERTICALLY MOVING BELT

We formulate and apply the homotopy analysis method (HAM) to determine the solution of the nonlinear differential equation governing thin film flow of a generalized second-grade fluid on a vertically moving belt. This problem is also known as the Landau–Levich or drag-out problem, which is the problem of withdrawal of a plate or fiber from a liquid bath. We make use of a modified model that has shear-dependent viscosity and that can predict normal stress differences. The results obtained exhibit the effectiveness and reliability of HAM.     

A STUDY OF NON-NEWTONIAN FLOW AND HEAT TRANSFER OVER A NON-ISOTHERMAL WEDGE USING THE HOMOTOPY ANALYSIS METHOD

The thermoconvective boundary layer flow of a generalized third-grade viscoelastic power-law non-Newtonian fluid over a porous wedge is studied theoretically. The free stream velocity, the surface temperature variations, and the injection velocity at the surface are assumed variables. A similarity transformation is applied to reduce the governing partial differential equations for mass, momentum, and energy conservation to dimensionless, nonlinear, coupled, ordinary differential equations. The homotopy analysis method (HAM) is employed to generate approximate analytical solutions for the transformed nonlinear equations under the prescribed boundary conditions. The HAM solutions, in comparison with numerical solutions (fourth-order Runge-Kutta shooting quadrature), admit excellent accuracy. The residual errors for dimensionless velocity and dimensionless temperature are also computed. The influence of the “power-law” index on flow characteristics is also studied. The mathematical model finds important applications in polymeric processing and biotechnological manufacture. HAM holds significant promise as an analytical tool for chemical engineering fluid dynamics researchers, providing a robust benchmark for conventional numerical methods.     

Interpolation of probability-driven model to predict hydrodynamic forces and torques in particle-laden flows

The development of hydrodynamic force/torque closure models with physical fidelity is crucial for ensuring reliable Euler–Lagrange simulations in particle-laden flows. Our previous work (Seyed-Ahmadi and Wachs. J Fluid Mech. 2020;900:A21) proposed a microstructure-informed probability-driven point-particle (MPP) method to construct a data-driven particle-position-dependent closure model, incorporating the effect of surrounding particle positions on forces/torques. However, the MPP model is not pluggable in Euler–Lagrange simulations due to the computation of constant coefficients through linear regression and reliance on statistical arguments to obtain the probability map for a pair of values of solid volume fraction (Φ) and Reynolds number (Re). To overcome this limitation, we propose an interpolated MPP (iMPP) method, involving interpolation in the Φ and Re spaces. Our results demonstrate that the iMPP method can capture over 70% of the total fluctuations in hydrodynamic forces/torques in approximately 97.8% of the tested cases. This advancement contributes to a more versatile closure model suitable for integration into E-L simulations.     

DEM study on the discharge characteristics of lognormal particle size distributions from a conical hopper

This study employs the discrete element method (DEM) to investigate the impact of the widths of lognormal particle size distributions (PSDs) with the same mean particle diameter on hopper discharge behaviors, namely, discharge rate, particle velocities, and size‐segregation. Results reveal that (i) the hopper discharge rate decreases as PSD width increases; (ii) the mean discharge rates are constant with time, but the fluctuations increase as the PSD width increases; (iii) the overall size‐segregation increases with PSD width; (iv) the overall mean particle diameters of the narrower PSDs do not exceed the initial mean of 5 mm, whereas that of wider ones do; (v) the relationship between PSD width and particle velocities is non‐monotonic with no consistent trends; and (vi) no direct correlation exists between particle velocity and size‐segregation. The results here provide valuable insights on the behavior of the prevalent polydisperse mixtures in hoppers. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1174–1190, 2018     

Cavity size distributions in high free volume glassy polymers by molecular simulation

Two very permeable polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP) and a random copolymer of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (TFE/BDD), have very similar and large fractional free volumes (FFV), but very different permeabilities. Using atomistic models, cavity size (free volume) distributions determined by a combination of molecular dynamic and Monte Carlo methods are consistent with the observation that PTMSP is more permeable than TFE/BDD. The average spherical cavity size in PTMSP is 11.2 Å whereas it is only 8.2 Å in TFE/BDD. These cavity size distributions determined by simulation are also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy.     

Modelling particle size distributions and secondary particle formation in emulsion polymerisation

An extensive model is given for the particle size distribution (PSD), particle number, particle size and amount of secondary nucleation in emulsion polymerisations. This incorporates what are thought to be all of the complex competing processes: aqueous phase kinetics for all radical species arising from both initiator and from exit (desorption), radical balance inside the particles, particle formation by both micellar and homogeneous nucleation mechanisms, and coagulation (the rate of which is obtained using the Healy–Hogg extension of DLVO theory). The predictions of the model are compared to extensive experimental results on rates, time evolution of the particle size distribution, and relative amounts of secondary nucleation, for styrene initiated by persulfate with sodium dodecyl sulfate and with sodium dihexyl sulfosuccinate as surfactants. For this system values of almost all of the many parameters needed for the model are available from independent measurements, and thus no significant parameter adjustment is plausible. Accord with experiment is imperfect but quite acceptable, supporting the validity of the various mechanisms in the model. Effects such as the experimental variation of particle number with ionic strength, as well as calculated coagulation rate coefficients as functions of particle size, suggest that coagulation of precursor (i.e., newly-formed) particles is a significant effect, even above the cmc. The modelling also suggests why secondary nucleation occurs readily in systems stabilised with polymeric surfactant.     

下行床气粒流动行为的Eulerian-Lagrangian模拟

采用计算流体力学和离散单元方法耦合模型（CFD-DEM）对二维下行床内的气粒流动行为进行了全床数值模拟。模拟结果展示了下行床典型操作条件下特有的气固动态流动结构：沿流动方向存在明显的入口控制区、过渡区和（完全）发展区;颗粒聚团并不是出现在浓度相对较高的入口区,而是在过渡区之后的发展过程中逐渐形成较多的、松散的动态聚团结构。下行床发展段呈现典型的近壁浓环结构,这与实验结果基本一致。考察了颗粒之间以及颗粒与壁面之间的碰撞参数对下行床内气固流动结构的影响,发现完全弹性碰撞颗粒体系在入口区呈现最快速的颗粒分散;而对本文研究的操作条件,颗粒碰撞参数对发展段时均流体力学行为只产生轻微的影响。     

CFD modeling of gas dispersion and bubble size in a double turbine stirred tank

In the present paper, gas dispersion in a double turbine baffled stirred tank is modeled using a commercial computational fluid dynamics (CFD) code FLUENT 6.1 (Fluent Inc., USA). A bubble number density equation is implemented in order to account for the combined effect of bubble break-up and coalescence in the tank. In the proposed work, the impellers are explicitly described in three dimensions using multiple reference frame model. Dispersed gas and bubbles dynamics in the turbulent water are modeled using an Eulerian-Eulerian approach with dispersed k-ε turbulent model and modified standard drag coefficient for the momentum exchange. The model predicts spatial distribution of gas holdup, average local bubble size and flow structure. The results are compared with experimental and numerical finding reported in the literature and good agreement between the present model and measurements of Alves et al. [Gas liquid mass transfer coefficient in stirred tanks interpreted through bubble contamination kinetics. Chemical Engineering Science, 2002, 57, 487-496] is achieved.     

Modeling of the green body drying step to obtain large size transparent magnesium-aluminate spinel samples

Laboratory-scaled transparent samples have already been obtained, but upsizing the samples remains a technological challenge. Indeed, every step of the process can lead to defects that hinder optical properties. Among all of the processing steps, drying is one of the most critical, especially for large samples with complicated shapes. It can induce micro-cracks that enlarge during sintering. Optimizing this step has thus become a necessity to obtain valid samples for industrial applications. We developed a finite element method (FEM) simulation model from a simple drying profile performed on laboratory-scaled cylindrical samples. Then, we applied this model to larger industrial-scaled samples, to optimize their drying process. Finally, we obtained crack-free 75 mm diameter sintered samples, which become highly transparent after the appropriate hot isostatic pressing thermal treatment.     

Partial least squares with outlier detection in spectral analysis: A tool to predict gasoline properties

The aim of this study is to propose a novel partial least squares with outlier detection (PLS_OD) calibration method and show its usefulness in calibration successfully with data containing outlying objects. We apply this method in gasoline spectral analysis to predict gasoline properties. In particular, a comparative study of PLS_OD and other five methods is presented. The performances of the proposed method are illustrated on spectral data set with and without outliers. The obtained results suggest that the proposed method can be used for constructing satisfactory gasoline prediction model whether there are some outliers or not.     

Direct numerical simulation of particle collisions in two-phase flows with a meshless method

The element-free Galerkin (EFG) method was used to simulate particle motion in two-phase flows with a new node distribution arithmetic suitable for meshless methods. The control equations were discretized with the standard Galerkin method in space and a fractional step finite element scheme in time. Regular background cells were used for the quadrature. The forces of the fluid on the particles were obtained by integrating the stress and shear forces on the particle surfaces. Simulation of the movement of a particle in a channel showed the Karman vortex street forming behind the particle with increasing particle velocity. Simulation of the movement of two particles in a channel showed the well-known drafting, kissing and tumbling, which has been obtained experimentally. Multi-particle flows were simulated with the results showing that meshless methods are capable of dealing with real particle collisions, which makes meshless methods superior to all mesh-based methods. Moreover, the theoretical relation of interparticle collision rate derived using kinetic theory was compared with the present numerical results and it is found that the collision rate is much lower than the theoretical estimation based on kinetic theory.     

Transport models in disordered organic semiconductors and their application to the simulation of thin‐film transistors

Relevant organic thin‐film transistor (OTFT) simulation software must account for the main specificities of organic semiconductors (OSCs) in terms of free carrier density of states, transport mechanisms and injection/collection properties from/to the device contacts. Among the parameters impacting the OTFT performance carrier mobility is a key parameter. Usual methods to extract the mobility from current–voltage measurements lead to only an apparent, or effective, mobility. The value of the apparent mobility is different from the intrinsic channel OSC mobility. Although the effective mobility actually determines most of a given device performance, therefore providing a very useful technology benchmark, it does not describe the intrinsic OSC material transport properties, and may even be misleading in the route to improving the OTFT fabrication process. To obtain a better understanding of the transport properties in OSCs using OTFT electrical characterization, implementing an appropriate physical mobility model in OTFT current–voltage simulation software is mandatory. The present paper gives a review of the carrier mobility models which can be implemented in OTFT simulation software. The review is restricted to analytical and semi‐analytical physical models taking into account the temperature, the carrier concentration and the electric field dependence of the carrier mobility in disordered OSCs. © 2019 Society of Chemical Industry     

Model-based object recognition to measure crystal size and shape distributions from in situ video images

To achieve robust control of industrial crystallization processes, it is necessary to measure the sizes, shapes, and polymorphic forms (i.e., internal structures) of the developing crystal population. This paper describes a model-based object recognition algorithm designed to extract crystal size and shape information from noisy, in situ crystallization images. The effectiveness of the algorithm is demonstrated using in situ images obtained at low, medium, and high solids concentrations during an α-glycine cooling crystallization in water. With respect to measurements obtained through manual image analysis by human operators, the algorithm gives reasonably accurate size and shape measurements. The algorithm is sufficiently fast to enable real-time monitoring for typical cooling crystallization processes.     

Link between bubbling and segregation patterns in gas‐fluidized beds with continuous size distributions

Experiments involving a bubbling, gas‐fluidized bed with Gaussian and lognormal particle‐size distributions (PSDs) of Geldart Group B particles have been carried out, with a focus on bubble measurements. Previous work in the same systems indicated the degree of axial species segregation varies non‐monotonically with respect to the width of lognormal distributions. Given the widely accepted view of bubbles as “mixing agents,” the initial expectation was that bubble characteristics would be similarly non‐monotonic. Surprisingly, results show that measured bubble parameters (frequency, velocity, and chord length) increase monotonically with increasing width for all PSDs investigated. Closer inspection reveals a bubble‐less bottom region for the segregated systems, despite the bed being fully fluidized. More specifically, results indicate that, the larger the bubble‐less layer is, the more segregated the system becomes. The direct comparison between bubbling and segregation patterns performed provides a more complete physical picture of the link between the two phenomena. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

X射线荧光光谱仪及其分析技术的发展

按照获得和分辨特征X射线荧光光谱的方式,X射线荧光光谱仪可以分为波长色散X射线荧光光谱仪（WDXRF）和能量色散X射线荧光光谱仪（EDXRF）两大类。依照这一分类,论述了X射线荧光光谱仪在设备装置和配套方法方面的新状况。X射线荧光光谱仪整机现在向着小型化、智能化、多功能方面发展,仪器各部件也随着研究的深入而得到了更进一步地改进,在这一基础上,仪器可分析元素的含量范围得到了拓展,方法也得到了丰富。目前,X荧光光谱仪开发了微区面分布的元素成像分析方法、高级次谱线分析方法、薄膜分析方法等新的方法,对这些新方法作以介绍,同时也对基本参数法（FP法）的新近发展作了说明。     

On the ability of chromatographic mass balance to predict solute diffusivity in drug delivery systems

The ability to predict the drug diffusion coefficient within hydrogel-based drug delivery devices has a pivotal role in the design of these materials. In the last years, many mathematical models have been developed, but they often rely on fitted parameters with a consequent limitation in terms of prediction. Indeed, they are mainly centered on the pure Fickian diffusion together with degradation and swelling contributions. However, especially with a drug concentration typical of pharmacological treatments, several other mechanisms such as drug–polymer and drug–drug interactions cannot be neglected. In this work, we checked the ability of a simple mathematical model to estimate diffusion coefficients of drugs loaded within hydrogel considered as a chromatographic stationary phase. Mathematical modeling satisfactorily matched with different sets of literature data proving that our assumptions are able to describe the key phenomena governing the device's behavior.     

纳米硫化锰在储能装置中的应用

论述了硫化锰电子结构、晶型、形貌、制备方法。通过控制反应温度、浓度、硫源、锰源等参数控制MnS的晶型、形貌等影响储能装置性能的特征。通过各种MnS及其复合物首圈充放电性能、循环圈数、充放电稳定性、比电容、能量密度和功率密度的对比,初步得到现阶段性能优良的用于储能装置中的MnS及其MnS复合材料。     

电镀液中铑含量的不同分析方法

对标准浓度的铑溶液进行了重量法、等离子发射光谱法（ICP）、火焰原子吸收光谱法（FAAS）、改进后的FAAS（引入一个校正因子, 对FAAS测定方法进行了优化、校正）等不同方法的测定,比较了不同测定方法的精密度和准确度.结果表明：对于杂质少的铑电镀液,宜采用重量法测定,其测定偏差在4％以内,而硼氢化钠作为还原剂的重量法的测定偏差可控制在0.2%以内;对于杂质多的铑电镀液,用ICP和改进的FAAS法均能获得满意结果,相对偏差都小于1%.     

Advances in electrochemical Fe(VI) synthesis and analysis

Hexavalent iron species (Fe(VI)) have been known for over a century, and have long-time been investigated as the oxidant for water purification, as the catalysts in organic synthesis and more recently as cathodic charge storage materials. Conventional Fe(VI) syntheses include solution phase oxidation (by hyphchlorite) of Fe(III), and the synthesis of less soluble super-irons by dissolution of FeO₄ ²⁻, and precipitation with alternate cations. This paper reviews a new electrochemical Fe(VI) synthesis route including both in situ and ex situ syntheses of Fe(VI) salts. The optimized electrolysis conditions for electrochemical Fe(VI) synthesis are summarized. Direct electrochemical synthesis of Fe(VI) compounds has several advantages of shorter synthesis time, simplicity, reduced costs (no chemical oxidant is required) and providing a possible pathway towards more electro-active and thermal stable Fe(VI) compounds. Fe(VI) analytical methodologies summarized in this paper are a range of electrochemical techniques. Fe(VI) compounds have been explored as energy storage cathode materials in both aqueous and non-aqueous phase in “super-iron” battery configurations. In this paper, electrochemical synthesis of reversible Fe(VI/III) thin film towards a rechargeable super-iron cathode is also summarized.     

Experimental evaluation and modeling of liquid jet penetration to estimate droplet size in a three-phase riser reactor

In this work,the effects of injecting an evaporating liquid jet into solid–gas flow are experimentally investigated.A new model(SHED model) and a supplementary model(spray model) have also been proposed to investigate some flow-field characteristics in three-phase fluidized bed with the mean relative error 4.3% between model and measured results.Some experiments were conducted to study the influences of flow-field parameters such as liquid volumetric flow rate,injection velocity,jet angle and gas superficial velocity as well as solid mass flux on the jet penetration depth(JPD).In addition,independent variables were experimentally employed to propose two empirical correlations for JPD by using multiple regression method and spray cone angle(SCA) by using dimensional analysis technique.The mean relative errors between the JPD and SCA correlations versus experimental data were 7.5% and 3.9%,respectively.In addition,in order to identify the variable effect,a parametric study was carried out.Applying the proposed model can avoid direct use of expensive devices to measure JPD and to predict droplet size.