Showing papers on "Transport phenomena published in 1995"
TL;DR: In this article, a detailed analysis is presented to demonstrate the capabilities of the lattice Boltzmann method for the two-dimensional, driven cavity flow, and thorough comparisons with other numerical solutions for the 2D cavity flow give accurate results over a wide range of Reynolds numbers.
547 citations
01 Jan 1995
TL;DR: The thermal motion of atoms and molecules is perceived on the macroscopic level as molecular diffusion as discussed by the authors, as the slow but persistent movement "down along the concentration gradient" although the average speed of the atoms is on the order of tens to hundreds of meters per second, because the molecules do not maintain the same direction long enough.
Abstract: Transport phenomena are among the most important processes in natural systems Chemical compounds, the constituents of biogeochemical systems, are in continual motion in all parts of the earth The thermal motion of atoms and molecules is perceived on the macroscopic level as molecular diffusion ie, as the slow but persistent movement “down along the concentration gradient” Although the average speed of the atoms is on the order of tens to hundreds of meters per second, the net transport is small, because the molecules do not maintain the same direction long enough Thus, typical molecular diffusion coefficients of solutes in water are approximately 10-9 m2s - 1 corresponding to characteristic annual transport distances of approximately 20 cm In solids the diffusion coefficients even drop to values as low as 10-14m2s-1 or less
294 citations
TL;DR: In this paper, an aerobic biofilm was characterized using confocal scanning laser microscopy (CSLM), O2 micro-electrodes, particle tracking and microinjection of fluorescent dyes.
164 citations
TL;DR: In this paper, a review of turbulent transport phenomena in flames is presented, where both large-scale turbulent transport and small-scale mixing processes are considered and various mechanisms of interaction between combustion and turbulent flow are identified.
Abstract: A review is presented of turbulent transport phenomena in flames. Both large-scale turbulent transport and small-scale mixing processes are considered and various mechanisms of interaction between combustion and turbulent flow are identified. Flame-surface density descriptions of turbulent combustion at high Damkohler numbers are discussed in detail and some topics are identified which require further attention. Emphasis is placed on problems of premixed turbulent combustion.
146 citations
TL;DR: In this article, three basic equations of fluid mechanics in Lagrange's frame are linearized in terms of three oscillating variables, namely pressure, entropy and displacement or velocity of the fluid element.
140 citations
TL;DR: In this article, the coupled heat and mass transport in a binary isotope mixture of particles interacting with a Lennard-Jones/spline potential has been studied, and four different criteria are used to analyze the concept of local equilibrium in the nonequilibrium system.
Abstract: Nonequilibrium molecular dynamics is used to compute the coupled heat and mass transport in a binary isotope mixture of particles interacting with a Lennard-Jones/spline potential. Two different stationary states are studied, one with a fixed internal energy flux and zero mass flux, and the other with a fixed diffusive mass flux and zero temperature gradient. Computations are made for one overall temperature,T=2, and three overall number densities,n=0.1, 0.2, and 0.4. (All numerical values are given in reduced, Lennard-Jones units unless otherwise stated.) Temperature gradients are up to ∇T=0.09 and weight-fraction gradients up to ∇w1=0.007. The flux-force relationships are found to be linear over the entire range. All four transport coefficients (theL-matrix) are determined and the Onsager reciprocal relationship for the off-diagonal coefficients is verified. Four different criteria are used to analyze the concept of local equilibrium in the nonequilibrium system. The local temperature fluctuation is found to be δT≈0.03T and of the same order as the maximum temperature difference across the control volume, except near the cold boundary. A comparison of the local potential energy, enthalpy, and pressure with the corresponding equilibrium values at the same temperature, density, and composition also verifies that local equilibrium is established, except near the boundaries of the system. The velocity contribution to the BoltzmannH-function agrees with its Maxwellian (equilibrium) value within 1%, except near the boundaries, where the deviation is up to 4%. Our results do not support the Eyring-type transport theory involving jumps across energy barriers; we find that its estimates for the heat and mass fluxes are wrong by at least one order of magnitude.
106 citations
TL;DR: In this paper, 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.
104 citations
TL;DR: In this article, 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.
70 citations
TL;DR: In this article, a review of the contribution of various direct numerical simulation (DNS) methods to understanding and modelling turbulent transport phenomena has been made, and some of them are demonstrated by introducing typical DNS results at the University of Tokyo.
Abstract: With the advances in large scale computers, reliable numerical methods and efficient post-processing environment, direct numerical simulation (DNS) has become a valuable and indispensable resource for fundamental turbulence research, although DNS is possible only when the turbulent Reynolds (or Peclet) number remains small to moderate. This paper reviews the contribution that various DNSS have made to understanding and modelling turbulent transport phenomena. After general remarks are made on the grid requirements and numerical methods of DNS, its novelties as a numerical experiment are summarized and some of them are demonstrated by introducing typical DNS results at the University of Tokyo. Emphasis is laid upon new findings on the turbulence statistics, their budgets and quasi-coherent eddy structures revealed by the simulations of the fully developed channel flow with heat transport at different Prandtl numbers, and also a recent modelling attempt to take into account the new knowledge extracted from these DNSS, i. e. a remarkable change of the destruction mechanism of turbulent scalar flux with the Prandtl number and a low Reynolds number effect on the redistribution process of the Reynolds stress.
62 citations
TL;DR: In this paper, a model building technique involving the investigation of experimental drying data that comprise responses of material moisture content and temperature is presented, based on an iterative procedure in which an initial process mathematical model is tested for inadequacies observed in distributions of residuals produced when predicted state variables are compared to experimental data.
58 citations
TL;DR: In this paper, a velocity-vorticity formulation of the Navier-Stokes equations is adopted, where the kinematic equation is written in its parabolic version.
Abstract: The paper deals with the numerical solution of fluid dynamics (transport phenomena in incompressible fluid flow) using a boundary-domain integral method. A velocity-vorticity formulation of the Navier-Stokes equations is adopted, where the kinematic equation is written in its parabolic version.
TL;DR: In this article, a high resolution computer model based on multizone adaptive grid generation and curvilinear finite volume discretization (MASTRAPP2d) was developed to simulate the crystal growth processes at low and high pressures.
TL;DR: In this paper, a mathematical model for saturated flow of a Newtonian fluid in a thermoelastic, homogeneous, isotropic porous medium domain under nonisothermal conditions is presented.
Abstract: A mathematical model is developed for saturated flow of a Newtonian fluid in a thermoelastic, homogeneous, isotropic porous medium domain under nonisothermal conditions. The model contains mass, momentum and energy balance equations. Both the momentum and energy balance equations have been developed to include a Forchheimer term which represents the interaction at the solid-fluid interface at high Reynolds numbers. The evolution of these equations, following an abrupt change in both fluid pressure and temperature, is presented. Using a dimensional analysis, four evolution periods are distinguished. At the very first instant, pressure, effective stress, and matrix temperature are found to be disturbed with no attenuation. During this stage, the temporal rate of pressure change is linearly proportional to that of the fluid temperature. In the second time period, nonlinear waves are formed in terms of solid deformation, fluid density, and velocities of phases. The equation describing heat transfer becomes parabolic. During the third evolution stage, the inertial and the dissipative terms are of equal order of magnitude. However, during the fourth time period, the fluid's inertial terms subside, reducing the fluid's momentum balance equation to the form of Darcy's law. During this period, we note that the body and surface forces on the solid phase are balanced, while mechanical work and heat conduction of the phases are reduced.
TL;DR: In this paper, the waveform of a thermal pulse in the second sound wave mode lost its dependence on heating time in the case of strong heating and only a limited amount of thermal energy is transported in this mode.
TL;DR: In this article, a new percolation model with long-range correlations was proposed to explain field-scale experimental data for hydrodynamic dispersion in porous media and aquifers.
Abstract: Three different flow and transport phenomena considered here are hydrodynamic dispersion in heterogeneous porous media and aquifers, transport of passive particles in an oscillating flow field, and miscible displacement processes in heterogeneous reservoirs. At microscales all three phenomena are described by the classical convective-diffusion equation (CDE). The presence of long-range correlations at macroscales gives rise to a rich variety of phenomena that cannot be predicted by analyzing the CDE by classical methods. In particular, a new percolation model with long-range correlations provides a rational explanation for the hitherto unexplained field-scale experimental data for hydrodynamic dispersion in porous media and aquifers. Moreover, for transport in oscillating flow in convection cells percolation provides a novel relation between the dispersion coefficient and the Peclet number that cannot be predicted by other methods.
TL;DR: In this paper, the authors proposed a frictionconcentration-polarization model (FCP model) for hollow fiber type reverse osmosis (RO) module systems, which used the Kimura-Sourirajan model for transport phenomena of solute and water transport through a membrane, taking a mass transfer coefficient as local variables and taking a fiber-bore side pressure drop into account.
TL;DR: In this paper, a trajectory-based detection algorithm for coherent motions was proposed and the relationship between coherent motions and scalar (heat) transfer from a structural point of view, i.e. trajectory analysis of the VITA heat transfer events, extraction of key flow modules and relevant heat transport, and the prediction of passive scalar transfer by means of an autoregressive (AR) model.
Abstract: In wall turbulence, it is widely accepted that the coherent motions determine the essential features of turbulent transport phenomena. In the present study, we have refined a trajectory-based detection algorithm for coherent motions and have investigated the relationship between coherent motions and scalar (heat) transfer from a structural point of view, i. e. trajectory analysis of the VITA heat transfer events, extraction of key flow modules and the relevant heat transport, and the prediction of passive scalar transfer by means of an autoregressive (AR) model. As a result, it is shown that the phase relationship of fluctuating velocity components dominates the essential characteristics of the transport processes of heat and momentum in wall turbulence and there exist distinct differences in individual correspondence between the coherent motions and heat transport processes, neither of which can be revealed by the widely used VITA technique. Also, the AR model is shown to provide good time-series predictions for turbulent heat transfer associated with coherent structures near the wall.
TL;DR: The dominant role of carrier\char21{}polar-optical-phonon interaction is shown in determining the nature of the carrier dynamics in the low-density limit, and the miniband width turns out to be a relevant quantity in predicting the existence of Bloch oscillations.
Abstract: The ultrafast dynamics of photoexcited carriers in semiconductor superlattices is studied theoretically on the basis of a Monte Carlo solution of the coupled Boltzmann transport equations for electrons and holes. The approach allows a kinetic description of the relevant interaction mechanisms such as intra- miniband and interminiband carrier-phonon scattering processes. The energy relaxation of photoexcited carriers, as well as their vertical transport, is investigated in detail. The effects of the multiminiband nature of the superlattice spectrum on the energy relaxation process are discussed with particular emphasis on the presence of Bloch oscillations induced by an external electric field. The analysis is performed for different superlattice structures and excitation conditions. It shows the dominant role of carrier\char21{}polar-optical-phonon interaction in determining the nature of the carrier dynamics in the low-density limit. In particular, the miniband width, compared to the phonon energy, turns out to be a relevant quantity in predicting the existence of Bloch oscillations.
TL;DR: In this article, the results of experimental and theoretical studies of the chemical deposition of copper films from metalorganic compounds dissolved in supercritical C 2 F 6 are reported, and the optimal conditions for the growth of highly adherent Cu films with good surface morphology have been determined.
TL;DR: A survey of the various numerical techniques employed to study the transport of ionising particles inside a TEPC is given in this article, where the basic ionisation mechanisms which may occur in a counter are described, and the nonequilibrium phenomena which play an important role mainly for counters that are to be used in measurements at the nanodosemeter level.
Abstract: In this paper a survey is given of the various numerical techniques employed to study the transport of ionising particles inside a TEPC. The first part is devoted to the description of the general concept of particle transport calculations. Thereafter, the different methods available to study transport phenomena and energy deposition in the sensitive volume and in counter walls are described. Finally, the basic ionisation mechanisms which may occur in a counter are described, and the nonequilibrium phenomena which play an important role mainly for counters that are to be used in measurements at the nanodosemeter level are studied.
TL;DR: In this paper, a mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed, taking into account the conservation of mass, momentum, and energy, and the evaporation of free and chemically bound water released by dehydration and their effect on the transport phenomena.
Abstract: A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum, and energy, and the evaporation of free and chemically bound water released by dehydration and their effect on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Carbonate aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions. Language: en
TL;DR: In this article, a methodology is presented for determining the rate constants of elementary surface reactions that can take place in chemical vapor deposition (CVD) processes, where the reactions are divided in transition state structures and determine preexponential factors, and the requirement of thermodynamic consistency is used to estimate activation energies.
Abstract: A methodology is presented for determining the rate constants of elementary surface reactions that can take place in chemical vapor deposition (CVD) processes. The calculations consider well-defined surfaces that can have one or more dangling bonds at a given site and adsorbates that can take up one or more different bonding configurations. Rate constants for each reaction are obtained independently of any process data using statistical mechanics, transition state theory, and bond dissociation energies. Specifically, the reactions are divided in transition state structures and determine preexponential factors, and the requirement of thermodynamic consistency is used to estimate activation energies. The level of sophistication of the calculations is suitable for treating the large number of plausible steps that could take place in a practical CVD system. Incorporation of the calculated rate constants into a reactor model that includes the effects of fluid flow, transport phenomena, and reactions in the gas and at the growing surface enables dominant reaction pathways and rate-limiting steps to be identified. Moreover, the dependence of growth rate and species compositions on operating conditions can be predicted without fitting any parameters. The utility of the approach is illustrated by modeling low pressure deposition of tungsten from tungsten hexafluoridemore » and silane. This model treats 35 reactions in the gas and 213 reactions at the growing surface. Results are compared with available experimental data and sensitivity studies are used to assess the limitations of the approach.« less
TL;DR: The present investigations, based on studies of the toxicology of inhaled reactive gases in the respiratory tract of rodents, provide computer programs for the generation of finite element meshes from serial tissue cross-sections that permit simulation of fluid flow in the complex geometries and local solute mass flux to the vessel walls of biological systems.
TL;DR: In this article, the effect of strong cation-anion and co-ion-membrane interactions have been discussed from the point of view of the composition and state of internal liquid phase.
TL;DR: In this article, the response of Li levels to the power interruption of an inductively coupled plasma (ICP) has been simulated by using a time dependent collisional radiative model of the Li system.
01 Jan 1995
TL;DR: The macroscopic transport of heat, mass, and momentum is important in virtually all materials processing systems and is especially important in crystal growth processes as mentioned in this paper, however, the specific effects often differ dramatically for each system.
Abstract: The macroscopic transport of heat, mass, and momentum is important in virtually all materials processing systems and is especially important in crystal growth processes. Due to this importance, the topic has received much attention; a listing of just a few of the more recent reviews of transport phenomena in melt crystal growth is given by refs. [1]–[10]. The primary goal of this paper is to discuss the effects of macroscopic transport on the growth of crystals from the melt. While transport processes are extremely important in many other types of crystal growth systems, such as vapor growth [11]–[14] and growth from solution [15], it is hoped that those interested in these systems will still find the ensuing discussion valuable. The fundamental nature of continuum transport is similar for all crystal growth processes; however, the specific effects often differ dramatically for each system.
TL;DR: In this paper, the authors consider the response of many-body nonequilibrium systems to thermal perturbations arising out of inhomogenities in the medium and present a general theory of the resulting transport phenomena which is nonlocal in space and memory dependent.
Abstract: In the context of a microscopic approach to phenomenological irreversible thermodynamics, based upon nonequilibrium mechano-statistical foundations, we consider here questions related to the response of many-body nonequilibrium systems to thermal perturbations arising out of inhomogenities in the medium. We present a general theory of the resulting transport phenomena which is nonlocal in space and memory dependent. The limit of the local in space and instantaneous in time approximations is also considered and discussed. Propagation of damped waves is evidenced in equations of the Maxwell-Cattaneo type, which are generalizations of the diffusion-like equations of classical irreversible thermodynamics. A particular example of application of the theory is presented in the follow up article.
TL;DR: In this article, the authors deal with the mass and heat transport phenomena inside the paper sheet and show how to deal with shrinkage during drying, identifying the intrinsic material properties being relevant for internal heat and mass transport.
Abstract: This paper is dealing with the mass and heat transport phenomena inside the paper sheet and shows how to deal with shrinkage during drying. The aim is identifying the intrinsic material properties being relevant for internal mass and heat transport. Two approaches will be followed. The first one is based on the description of microscopic mechanisms for mass and heat transport in a porous material, e.g. Darcy flow for liquid due to capillary forces and vapour diffusion due to a vapour pressure gradient, heat flow as a result of the mass flow and a temperature gradient. The contribution of each mechanism in the overall mass resp. heat fluxes is quantified by means of mechanistic transport parameters, such as vapour diffusivity, Darcy permeability, etc. In the second approach the heat and mass fluxes are related to both temperature and moisture gradients and the contribution of each driving force is weighed by a lump transport parameter. Finally, the coupling between the mechanistic and lump paramet...
01 Jan 1995
TL;DR: In this article, the authors describe a surge of interest in transport phenomena in low-dimensional semiconductor systems, including resonant tunneling through confined states in quantum wells, transport through mini-bands in superlattices, and quantum ballistic transport through quantum point contacts.
Abstract: The science of vacuum electron optics has benefitted tremendously from the close analogy with light optics. This analogy exists on the level of classical motion (geometrical optics), as well as on the level of quantum mechanical motion (wave optics). The last two decades have witnessed a surge of interest in transport phenomena in low-dimensional semiconductor systems. Examples are the study of weak localization and conductance fluctuations in two-dimensional (2D) electron gases, resonant tunneling through confined states in quantum wells, transport through mini-bands in superlattices, and quantum ballistic transport through quantum point contacts. All of these phenomena have an optical analogue, and may be classified as manifestations of solid state electron optics.