Simulation Of Transport Phenomena Research Articles

1514 Zone-melting法を用いたSi/Ge結晶育成中の移動現象に関する数値解析(OS15.電子デバイス・電子材料と計算力学(4),オーガナイズドセッション)

1514 Zone-melting法を用いたSi/Ge結晶育成中の移動現象に関する数値解析(OS15.電子デバイス・電子材料と計算力学(4),オーガナイズドセッション)

Capillary suction and diffusion model for chloride ingress into concrete

A numerical approach, named TransChlor, is proposed to simulate transport phenomena of various substances in concrete. This approach is a theoretical model based on finite elements and finite differences methods. The model consists of coupled nonlinear partial differential equations based on Fick's diffusion law and on kinematics equations. Simulation results from a parametrical study highlight the influence of microclimatic conditions, exposure to deicing salts and concrete cover permeability and thickness on chloride ingress in concrete. The results show that the chloride ion concentration increases quickly in concrete cover when a structure is exposed to deicing salts at a mountainous location; whereas permeability of concrete cover is an insignificant parameter when the concrete is in direct or splash water contact.

Recent Advances in Computational Simulation of Macro-, Meso-, and Micro-Scale Biomimetics Related Fluid Flow Problems

Over the last decade, computational methods have been intensively applied to a variety of scientific researches and engineering designs. Although the computational fluid dynamics (CFD) method has played a dominant role in studying and simulating transport phenomena involving fluid flow and heat and mass transfers, in recent years, other numerical methods for the simulations at meso-and micro-scales have also been actively applied to solve the physics of complex flow and fluid-interface interactions. This paper presents a review of recent advances in multi-scale computational simulation of biomimetics related fluid flow problems. The state-of-the-art numerical techniques, such as lattice Boltzmann method (LBM), molecular dynamics (MD), and conventional CFD, applied to different problems such as fish flow, electro-osmosis effect of earthworm motion, and self-cleaning hydrophobic surface, and the numerical approaches are introduced. The new challenging of modelling biomimetics problems in developing the physical conditions of self-clean hydrophobic surfaces is discussed.

Drying of two‐phase media: Simulation with liquid pressure as driven force

AbstractIn previous works, a model based on volume averaging theory to describe heat and mass transports in two‐phase media has been proposed. The main novelty was to consider both mass and volume conservation of the solid phase in order to avoid the introduction of an arbitrarily law binding the pressure to the volume fraction of the liquid phase. Indeed, this law leads to an equivalent transport coefficient that must be identified numerically by matching experimental and predicted data in such a way that process and internal model become unjustly dependant. Here, the mathematical description is solved. The forecasting of damages and cracks during drying of fully saturated media incites us to simulate transport phenomena which occur in gel (gelatin) during this process. Although the one‐dimensional configuration which is considered leads us to reduce the elastic behavior to an ideal shrinkage, the numerical results and the qualitative comparison to experimental measures provide some confidence in the proposed model. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Simulation of Transport Phenomena during Natural Convection Cooling of Bagged Potatoes in Cold Storage, Part II: Mass Transfer

Moisture loss from potato is one of the most important economically significant parameters for long-term storage. It is a mass transfer phenomenon, which has strong relevance with heat transfer and fluid flow. Therefore, attempt was made in this study to model the moisture loss in a single bag packed with potato kept in cold store under natural convective environment using the computational fluid dynamics technique. It was found that in spite of high specific humidity, maximum moisture loss occurred in the upper half of the bag during the initial cooling period. As the cooling proceeded, the zone of maximum moisture loss shifted towards the bottom of the bag. The average rate of moisture loss in the bag at steady state was found to be 0·091% (w/w) [water] week−1. The contours of rate of moisture loss and specific humidity maintained symmetry about the vertical axis in a vertical plane and about both the horizontal axes in horizontal plane throughout the cooling process. The experimental total moisture loss was found to be 0·82% (w/w) against the simulated total moisture loss of 0·695% (w/w) over a storage period of 25 days.

Simulation of Transport Phenomena during Natural Convection Cooling of Bagged Potatoes in Cold Storage, Part I: Fluid Flow and Heat Transfer

Agricultural produce, such as potato, onion, etc. are packed in permeable gunny bags for cooling in a natural convective environment and subsequent long-term storage. Due to permeable boundaries, the heat and mass transfer within the bag is strongly affected by the flow characteristics, especially during the transient cooling process. Therefore, an attempt was made in this study to simulate the three-dimensional airflow and heat transfer in this system using the computational fluid dynamics technique. The mass transfer phenomenon is being modelled in Part II of this paper. It was found that air mainly penetrated through bottom and side surfaces of the bag and escaped from top surface. The velocity contours maintained symmetry about both the horizontal axes in horizontal plane and only about the vertical axis in the vertical plane. The same patterns were observed for isotherms as well. The average natural convective velocity in the bag at steady state was found to be 0·0016 m s−1. The temperature of the product in the bag decreased at a very fast rate during the initial cooling period and then dropped to comparatively slow rates. In the vertical plane, the zone of maximum temperature was observed below the top surface of the bag at the early stages of cooling and it proceeded towards the centre point as the cooling progressed. Steady-state average temperature in the bag was found to be 0·13 K higher than the surrounding air temperature at 274 K. The experimental product temperature at the centre of the bag was found to be higher than that of the simulated one. The maximum and minimum temperature deviation from the experimental values were 3·4 K at 287·1 K and 0·5 K at 279·1 K on 2nd and 16th day of cooling respectively when the measured initial and final temperatures of potato at the centre were 297·1 and 278·1 K, respectively for a total cooling period of 25 days.

Mesh-Free Simulation of Transport Phenomena in Continuous Castings of Aluminium Alloys

This paper introduces a general numerical scheme for solving convective-diffusive problems that appear in the solution of microscopic and macroscopic transport phenomena in continuous castings and the heat treatment of aluminium alloys. The numerical scheme is based on spatial discretisation that involves pointisation only. The solution is based on diffuse collocation with multi-quadric radial basis functions. The application of the method is demonstrated in a simplified model of a billet DC casting and verified by a comparison with the classical finite volume method.

Simulation of Transport Phenomena in Metallurgy

steel research internationalVolume 76, Issue 1 p. 3-4 EditorialFree Access Simulation of Transport Phenomena in Metallurgy Hans-Jürgen Odenthal, Hans-Jürgen Odenthal Institute for Industrial Furnaces and Heat Engineering at RWTH Aachen UniversitySearch for more papers by this authorHerbert Pfeifer, Herbert Pfeifer Institute for Industrial Furnaces and Heat Engineering at RWTH Aachen UniversitySearch for more papers by this author Hans-Jürgen Odenthal, Hans-Jürgen Odenthal Institute for Industrial Furnaces and Heat Engineering at RWTH Aachen UniversitySearch for more papers by this authorHerbert Pfeifer, Herbert Pfeifer Institute for Industrial Furnaces and Heat Engineering at RWTH Aachen UniversitySearch for more papers by this author First published: 13 December 2016 https://doi.org/10.1002/srin.200505966 Institute for Industrial Furnaces and Heat Engineering Kopernikusstr. 16 52074 Aachen/Germany www.rwth-aachen.de/iob AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume76, Issue1January 2005Pages 3-4 RelatedInformation

Density-Functional Theory and Car-Parinello Study of Electronic, Structural, and Dynamical Properties of the Hexapyrrole Molecule

Electronic and structural properties of the ground state of the neutral and singly ionized hexapyrrole molecule are studied using density functional theory implemented with plane waves and pseudopotentials to include the effects of the core electrons. The calculated properties are compared with those of an infinite pyrrole chain in a regular 3D lattice of polypyrroles. The dynamical evolution of a charged defect along the chain of an isolated hexapyrrole created with a structural defect on a terminal ring is simulated using Car -Parrinello molecular dynamics. Information is obtained on coherence, time scale, and general features of the motion of the charge along the chain. The aim of this paper is, first, to compare the electronic and structural properties of an isolated, finite chain of pyrrole rings with those of the corresponding infinite chain in a regular 3D lattice of polypyrroles, thus identifying the differences that can be attributed mainly to environment effects. Second, using CarParrinello (CP) molecular dynamics, 1 we shall study the time evolution of a charged defect along the chain of an isolated hexapyrrole created with a structural defect on a terminal ring. The aim is to obtain information on coherence, time scale, and general features of the motion of a charge suddenly produced inside the distorted chain of a conjugated heterocycle polymer. In a previous paper, 2 hereafter referred to as I, we have performed a density functional theory (DFT) study of neutral and doped polypyrroles, each of which is represented as a 3D lattice of infinite chains of pyrrole rings defined in terms of a fixed unit cell with internal degrees of freedom. The polypyrrole has been chosen as a prototype of the organic conjugated polymers that become conducting when properly doped and, thus, have attracted much interest both from a theoretical and an experimental point of view. 3,4,5 It is well-known from several sets of data that real polypyrroles are materials with low degrees of crystallinity, being mixtures of chains with large weight dispersion and different morphology. The presence of several chemical and structural defects makes it difficult to understand whether a property is intrinsically associated with the polymer or caused by defects. For these reasons, a crystalline lattice of infinite regular chains represents a model that contains only some of the peculiar features of the real systems and should be complemented by studying the properties of isolated pyrrole oligomers. Moreover, regular ( R-R ′)-trans-dipyrrole oligomers, with up to seven pyrrole rings, have recently been synthesized and unambiguously characterized. 6 These compounds represent ideal systems for a theoretical study based on ab initio methods because their properties are intrinsically associated with those of an isolated chain and are affected only slightly by the environment. In this paper, we investigate electronic, structural, and dynamical properties of an isolated hexapyrrole both neutral and singly ionized, and perform CP molecular dynamics in order to simulate transport phenomena inside a small chain and obtain information useful for polymers. We have chosen this oligomer because its structure is large enough to exhibit a conformational behavior resembling that of a typical polypyrrole chain, and the electronic properties are sufficiently similar to those of the polymer, as shown by our test calculations. 7,8

Generation of an anatomically based three-dimensional model of the conducting airways.

An anatomically accurate model of the conducting airways is essential for adequately simulating gas mixing, particle deposition, heat and water transfer, and fluid distribution. We have extended a two-dimensional tree-growing algorithm to three dimensions for generation of a host-shape dependent three-dimensional conducting airway model. Terminal branches in the model are both length limited and volume-supplied limited. A limit is imposed on the maximum possible branch angle between a daughter and parent branch. Comparison of the resulting model with morphometric data shows that the algorithm produces branching and length ratios, path lengths, numbers of branches, and branching angles very close to those from the experimental data. The correlation between statistics from the generated model and those from morphometric studies suggests that the conducting airway structure can be described adequately using a "supply and demand" algorithm. The resulting model is a computational mesh that can be used for simulating transport phenomena.

Simulation of Transport Phenomena in Shallow Aquatic Environment

In the framework of the present study, 2D and 3D finite-difference procedures have been developed and applied with regard to flow, heat, and contaminant transport in the marine environment, where a shallow aquatic environment can be assumed. The common characteristic of such a type of environment is that the water depth is much smaller than a typical length in the horizontal direction. Conditions of this environment allow 2D or shallow water 3D numerical models to be applied instead of a more expensive and time consuming full 3D solution. Such an approach is almost obtained without loss of accuracy. By reference to a practical case of a wind dominated environment, the requirements and possible use of the 2D or 3D numerical codes are identified and analyzed. It is shown that the applicability of the 2D model mainly depends on the wind direction. Considerations are made with regard to recirculation of thermal effluent into the inlet of a power station. It is shown that, even in an extremely complicated geometry of the simulated domain, the 2D and 3D simulations can provide the same order of magnitude of results for some wind directions, particularly in the case of wind blowing parallel to the shoreline. On the other hand, for a wind direction nearly perpendicular to the shoreline, the 2D model produces unreliable or simply nonphysical results, whereas the 3D model provides reliable results. These conjectures are of great practical importance because most of the previous thermal effluent studies have been carried out by using the 2D modeling. It is considered that the performance of the 2D and shallow water 3D simulations provide an adequate description and understanding of basic transport phenomena in the simulated domain

639 微小重力環境下での化合物半導体材料プロセッシングにおける諸移動現象の数値解析

639 微小重力環境下での化合物半導体材料プロセッシングにおける諸移動現象の数値解析

A two-dimensional analysis of mass transport in proton exchange membrane fuel cells

A theoretical model is developed to simulate transport phenomena in a proton exchange membrane fuel cell (PEMFC). The primary focus of this paper is the modelling and assessment of two-dimensional effects neglected in previous studies. The work is motivated by the need to understand the transport processes in fuel cells in order to improve heat and water management, and to alleviate mass transport limitations. The model takes into account diffusion of the humidified fuel (H 2, CO 2 and H 2O (v)) and oxidant gases (O 2, N 2 and H 2O (v)) through the porous electrodes, and convective and electro-osmotic transport of liquid water in the electrodes and the membrane. The thermodynamic equilibrium potential is calculated using the Nernst equation, and reaction kinetics are determined using the Butler–Volmer equation. A finite volume procedure is developed to solve the system of differential equations. The model is validated against available experimental data, and numerical simulations are presented for various one- and two-dimensional isothermal cases. The results indicate that the cathode potential loss, associated with the slow O 2 reaction rate, is dominant at all practical current densities. The simulations also show that two-dimensionality has a significant effect on water management and on some aspects of fuel cell performance. In particular, the anode and cathode water fluxes are found to vary considerably along the oxidant and fuel flow channels, and two new transitional water transport regimes are revealed by the two-dimensional simulations. The influences of flow configuration and electrode porosity on predicted cell performance are also discussed.

Applications of laser Doppler anemometry in understanding food processing operations

The measurement of local fluid velocities in food processing equipment is needed for the validation of mathematical models that are used to simulate transport phenomena, and for the estimation of process parameters such as local shear rates and residence time distributions. Laser Doppler anemometry (LDA), a non-invasive technique for measuring fluid velocities, can be used to measure two- or three-dimensional flow fields in food processing equipment. In this article, the application of LDA to facilitate the understanding of fluid flow in extruders, mixers, fermenters and jet impingement ovens with the view to improving equipment performance is described.

Numerical simulation of transport phenomena by using the double porosity/diffusivity continuum model

Numerical simulation of transport phenomena by using the double porosity/diffusivity continuum model

Extension of the continuum model for transport phenomena occurring during metal alloy solidification-II. Microscopic considerations

In a companion paper, a continuum model for simulating transport phenomena occurring during solidification of a binary metal alloy is extended to allow for treatment of effects such as solutal undercooling and solid transport in the form of floating and settling crystals. However, inclusion of such features requires auxiliary models which, in large part, depend on microscopic considerations. Such models are developed in this study and specifically deal with relations for solid and liquid velocities under conditions involving solid motion, as well as determination of solutal undercooling as a function of the solidification rate and stereological characteristics of the solid/liquid interface. The models also permit determination of final grain density and size.

Extension of the continuum model for transport phenomena occurring during metal alloy solidification—I. The conservation equations

In this study, models for simulating transport phenomena occurring during solidification of a binary metal alloy are reviewed, with emphasis placed on the benefits and shortcomings of existing continuum and two-phase approaches. Linkages between the two approaches are discussed, and volume-averaging procedures inherent in the two-phase model are used to develop an extension of the continuum model which retains its computational convenience, while eliminating its inability to treat important features such as solutal undercooling, nucleation, stereological characteristics of the solid/liquid interface, solid movement in the form of floating or settling crystals, and shrinkage. Two approaches to development of a mixture momentum equation are considered, one involving evolution from the liquid momentum conservation equation and the other involving summation of the liquid and solid momentum equations. Special features of both approaches are discussed. In a companion paper, additional models are developed to account for the transport (floating and settling) of solid crystals in the melt, solutal undercooling, and nucleation.

Simulation of transport phenomena in ultrafiltration

A full three-dimensional simulation of ultrafiltration in a rectangular channel has been performed with a steady-state finite element scheme. The flow through the semipermeable membrane has been coupled to the concentration field by the use of a concentration-dependent osmotic pressure. The velocity field is furthermore coupled to the concentration field through the Martin equation, which states that the viscosity varies exponentially with the solute concentration. With a concentration-independent viscosity the simulations show good agreement with a Levêque-type boundary layer solution. With a concentration-dependent viscosity a decreased membrane flux is found. However, as the Reynolds number increases, concentration variations in the transverse direction develop. These variations improve the membrane flux; however, the simulated effect is small. The secondary flow field outside the high-viscosity boundary layer is shown to have a component away from the membrane. This component may be related to an improved transport of solute back from the membrane out into the mainstream.

Food Extrusion Science and Technology

This book melds recent advances in the simulation of transport phenomena during single- and twin-screw extrusion with chemistry pertaining to food material transformation during extrusion. Forty-four chapters in five parts cover transport phenomena during extrusion, rheological properties of cereals

Simulation of Transport Phenomena around the Raceway Zone in the Blast Furnace with and without Pulverized Coal Injection.

A two-dimensional mathematical model is developed to describe transport phenomena in a packed bed of coke in front of blast furnace tuyere with and without pulverized coal injection (PCI). The model consists of two sub-models, one is pulverized coal (PC) combustion model in the blowpipe where the turbulent fluctuation in the gas phase is considered and the other is combustion model in the packed bed of coke. In this model coke particles in the raceway are treated as a continuous phase and both phases of gas and coke particles are calculated by using the Eulerian approach.This model is applied to practical operating conditions. When PC is injected into tuyere, more oxygen is consumed and higher temperature rise appears at the region closer to tuyere tip in the raceway and lower temperature is represented in the coke bed than those of all coke operation. Residence time of PC particles in the blowpipe is quite short, so its burn-off in the blowpipe is very low and the PC particles mainly burn in the raceway cavity. The burn-off of PC particle increases with the volatile matter content, but some particles reach to inner wall of tuyere when high volatile coal is used.