Showing papers on "Transport phenomena published in 1997"

Handbook of Physical Quantities

Abstract: Units of Physical Quantities, A.G. Chertov Periodic Table of Elements, K.A. Kikoin Mechanical Properties of Materials, N.V. Kadobnova and A.M. Bratkovski Compressibility, B.V. Vinogradov Density of Substances, A.P. Babichev Friction, I.I. Karasik Acoustics, L.K. Zarembo Thermometry, A.V. Inyushkin Heat Capacity, M.N. Khlopkin Temperature Coefficients of Expansion, E.B. Gel 'man Saturated Vapor Pressure, V.V. Ignatiev, V.A. Krivoruchko and A.I. Migachev Melting and Boiling, E.B. Gel 'man Equation of State and Critical Parameters of Substances, E.B. Gel 'man Surface Tension, B.D. Summ Heat Conduction, A.V. Inyushkin Viscosity, A.V. Eletskii Diffusion, A.V. Eletskii Elementary Processes in Gases and Plasma, A.V. Eletskii Ionization of Atoms and Molecules, A.A. Radzig and V.M. Shustryakov Transport Phenomena in Weakly Ionized Plasma, A.V. Eletskii Electric Characteristics of Metals and Alloys, V.S. Egorov and I.N. Khlyustikov Electrophysical Properties of Semiconductors, E.Z. Meilikhov, S.D. Lazarev, and B.A. Aronzon Insulators, A.P. Geppe Thermoelectric Phenomena, N.A. Babushkina Electron and Ion Emission, T.M. Lifshits and A.L. Musatov Magnetic Properties of DIA-and Paramagnetics, V.Yu. Ivanov and L.I. Vinokurova Magnetic Properties of Ferromagnetic Metals and Alloys, K.G. Gurtovoi Antiferromagnets, V.I. Ozhogin and V.G. Shapiro Ferrites and Other Magnetic Dielectrics, M.V. Bystrov, V.L. Ivashintseva, S.A. Mironov, and R.V. Pisarev Galvanomagnetic and Thermomagnetic Phenomena, N.A. Babushkina and V.S. Egorov Optical Properties of Substances, L.A. Novitskii Atomic and Molecular Spectra, A.A. Radzig Electro-, Magneto-, and Piezooptical and Nonlinear Optical Effects, A.A. Malyutin, M.E. Brodov, and V.P. Yanovskii Lasers, A.A. Malyutin , E. Brodov, and V.P. Yanovskii X-Ray Radiation, R.M. Imamov Fundamental Particles, V.A.P. Nikitin Nuclear Properties of Nuclides, V.M. Kulakov Mossbauer Nuclei, S.S. Yakimov and V.M. Cherepanov Nuclear Reactions, V.P. Rudakov Nuclear Fission, A.I. Obukhov and I.S. Grigoriev Neutron Penetration Through Matter, S.V. Marin Passage of Ionizing Radiation Through Matter, V.P. Rudakov Cosmic Rays, V.S. Ptuskin Geophysics, I.A. Maslov Astronomy and Astrophysics, Yu. E. Lyubarskii and R.A. Syunyaev

Collective Transport: From Superconductors to Earthquakes

Abstract: In these lectures, a variety of non-equilibrium transport phenomena are introduced that all involve, in some way, elastic manifolds being driven through random media. A simple class of models is studied focussing on the behavior near to the critical ``depinning'' force above which persistent motion occurs in these systems. A simple mean field theory and a ``toy'' model of ``avalanche'' processes are analyzed and used to motivate the general scaling picture found in recent renormalization group studies. The general ideas and results are then applied to various systems: sliding charge density waves, critical current behavior of vortices in superconductors, dynamics of cracks, and simple models of a geological fault. The roles of thermal fluctuations, defects, inertia, and elastic wave propagation are all discussed briefly.

Charge distribution and transport in polymers

Abstract: Experimental work on charge distributions and charge transport in polymer films is reviewed. For studying the charge distributions in the thickness dimension, thermal or acoustic techniques are used with resolutions down to /spl sim/1 /spl mu/m. The polymer samples usually are charged with corona, electron beam or thermal methods. Observation of the change of charge and polarization distributions with time allows one to draw conclusions about charge transport and charge injection phenomena. In some cases theoretical models have been established, based on excess-charge drift due to a finite carrier mobility and on charge compensation due to intrinsic or radiation-induced conductivity. Other models are concerned with the interaction of injected or intrinsic space charge with a dipole polarization. Comparisons of measured and calculated charge distributions and their change with time show the applicability of these models and shed new light on charge trapping and charge transport phenomena.

The applicability of the transport-energy concept to various disordered materials

Abstract: It is known that in disordered semiconductors with purely exponential energy distribution of localized band-tail states, as in amorphous semiconductors, all transport phenomena at low temperatures are determined by hopping of electrons in the vicinity of a particular energy level, called the transport energy. We analyse whether such a transport level exists also in materials with densities of localized states (DOSs) different from the purely exponential one. We consider two DOS functions with , typical for polymers, heavily doped semiconductors, and, probably, liquid semiconductors and , typical for mixed crystals. It is shown that in both cases the transport energy exists, implying that it also exists for all intermediate forms of the DOS. Special attention is paid to the dependences of the transport level and of its width on the DOS parameters and temperature.

Momentum Transport Mechanism for Water Flow over Porous Media

Abstract: The momentum transport phenomena at the interface of the porous medium and fluid have been numerically investigated. The single domain approach is used with matching boundary conditions; that is, the Brinkman-Forchheimer-extended Darcy equation is used for the present study. Five typical porous media found in natural and engineered systems are selected in order to cover a wide range of the Darcy number (6.25 × 10−4≤Da≤ 5.90 × 10−11). In addition, six different Reynolds numbers (10 ≤R≤ 1,000) are tested for each case. When Da> 10−7, the results showed the importance of viscous shear in the channel fluid. The viscous shear propagates across the interface into the porous medium and forms a transition region of disturbed flow in the porous medium. The depth of penetration is only dependent on the Darcy number of the porous medium rather than the Reynolds number and the shape of velocity profile. In the vicinity of the interface, it is clear that Darcy's law is inappropriate to describe flow in a permeable wal...

Transport Phenomena in Czochralski Crystal Growth Processes

Abstract: Publisher Summary This chapter reviews the transport phenomena associated with Czochralski (Cz) growth of semiconductor materials. Transport phenomena in crystal growth processes are quite complex due to melt and gas flows that may be oscillatory, or turbulent, or both; coupled convection and radiation; impurities and dopant distributions; unsteady kinetics of the growth process; melt-crystal interface dynamics; free surface and meniscus; stoichiometry in the case of compound materials, and so on. Most of the discussions are restricted to the growth of Si, gallium arsenide (GaAs), and indium phosphide (InP) crystals. The growth of these material spans a pressure range of few millitorrs to about 4 MPa, and thereby reveals a high level of complexity in transport phenomena. These processes form a class of most challenging problems for theoretical, experimental, and industrial research. The chapter presents a description of the theoretical model and the numerical techniques used to solve them. A brief analysis of the melt flow mechanisms is discussed in the chapter. The chapter focuses on low pressure Cz growth of Si crystals and describes the research on high-pressure growth of III-V compounds. The chapter focuses on fluid flow and heat transfer, although their effects on impurity and dopant transport and stresses in the grown crystals have been discussed in some details.

Turbulent Heat Transfer and Fluid Flow in a Porous-Baffled Channel

Abstract: Experiments were conducted to examine the effect of porous-type baffles on heat transfer and friction in a baffled channel. The porous-type baffles are arranged on the bottom and top channel walls in a staggered manner. Flowfield, pressure loss, isotherm pattern, and channel centerline heat transfer coefficients are obtained inside the periodic cell formed between the segmented baffles. Results of the conventional solid-type-baffled channel are also obtained for comparison. The void fraction ν o of porous-type baffle and the baffle spacing S/H are fixed at 0.42, and 1.0, respectively; whereas the baffle height ratio h/H varies from 0.25 to 0.75 and the flow Reynolds number Re ranges from 1 x 10 4 to 5 x 10 4 , respectively. It is disclosed that the flow patterns around the porous- and solid-type baffles are entirely different. These different transport phenomena, in conjunction with the change in baffle effectiveness significantly influence the local heat transfer coefficient distributions but negligibly influence the average heat transfer coefficients. Relative to the solid-type-baffled channel, the porous-type-baffled channel has a lower friction loss.

A new class of particle methods

Abstract: Particle methods are numerical methods designed to solve problems in fluid mechanics and related problems in continuum mechanics. A general approach to the construction of such particle methods is presented in this article. The particles are no mass points but possess a finite extension. They can rotate in space and have a spin. The conservation of mass is automatically guaranteed by the ansatz. The forces of interaction between the particles are derived in a canonical way from the force laws of continuum mechanics and are directly based on a regularized stress tensor. In the absence of external forces and of heat sources and sinks, momentum, angular momentum, and energy are conserved as in the continuum case.

Coupled heat and mass transport phenomena in siliceous aggregate concrete slabs subjected to fire

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 including the effects of evaporation and dehydration processes on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Siliceous 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.

A non-Darcy model for recirculating flow through a fluid-sediment interface in a cylindrical container

Abstract: A numerical investigation has been undertaken to characterize the axisymmetric laminar flow generated by a rotating disk inside a cylinder with an open top, containing a viscous fluid above as layer of fluid-saturated porous medium. The mathematical model is based on a continuum approach for both fluid and porous regions. Attention is focussed on conditions favouring steady, stable, axisymmetric solutions of the Darcy-Brinkman-Lapwood equation. The accuracy of the method is verified by solving some vortex flow problems in disk-cylinder geometries and comparing the results with: (a) existing numerical solutions and, (b) experimental pressure measurements in a similar geometry. Calculations are performed to investigate the fluid exchange between the porous region (porewater) and the overlying water. Results indicate that flow through composite (fluid-sediment) systems can be handled with good accuracy by the method presented here. With our approach the magnitude of advective porewater transport in sediments may be predicted. This finding is important for improved designs of flux chambers and also for understanding advective transport phenomena.

Analysis of transport phenomena during the convective drying in superheated steam

Abstract: This work focused on high-temperature convective drying (superheated steam drying). The process has been investigated both experimentally and numerically. The experimental analysis was carried out in an aerodynamic return-flow wind-tunnel, with very small cylinders of cellular concrete. For the local analysis, the samples were fitted with thermocouples and pressure sensors. The mean moisture content of the cylinders was measured by simple weighing while the temperature and pressure readings were being taken. Global and. local analysis of heat and mass transfer in small cylinders in superheated steam were carried out. The systematical study for several sizes and aerothermal conditions show a similar behavior for moisture content, pressure and temperature values. A numerical model for high temperature drying, using the finite elements method, in a 2-D configuration, was implemented and validated.

Weld metal microstructure calculations from fundamentals of transport phenomena in the arc welding of low-alloy steels

Abstract: In recent years, significant progress has been made toward understanding the development of the weld pool shape and size from the numerical calculations of heat transfer and fluid flow in the weld pool. Although such calculations have provided detailed information about the welding processes, no efforts have been made to understand the development of fusion zone microstructures from the fundamentals of transport phenomena. The aim of this work is to address this. Heat transfer and fluid flow during manual metal arc welding of low-alloy steels containing different concentrations of vanadium and manganese were investigated by solving the equations of conservation of mass, momentum and energy in three-dimensional transient form. The computed microstructures are found to be in good agreement with the experimentally observed microstructures. The agreement indicates significant promise for predicting weld metal microstructure from the fundamentals of transport phenomena.

Dynamical systems theory and transport coefficients: A survey with applications to Lorentz gases

Abstract: Recent developments in the applications of ideas from dynamical systems theory to transport phenomena in non-equilibrium fluids are reviewed. We discuss methods for expressing transport coefficients for fluid systems in terms of dynamical quantities that characterize the chaotic behavior of the phase-space trajectories of such systems. We describe two such methods: the escape rate method of Gaspard and co-workers, and the Gaussian thermostat method of Hoover, Posch and co-workers, and of Evans and Morriss and co-workers. Related issues such as the properties of repellers and attractors and of entropy production in such systems will be discussed. As examples of these formal developments, we describe recent work on Lorentz gases where the escape rate and Gaussian thermostat approaches to transport can be implemented in detail and the results compared with both numerical simulations and with the results of kinetic theory of gases.

Non-darcian surface tension effects on free surface transport in porous media

Abstract: The phenomenological analysis of free surface transport through porous media using the Brinkman-Forchheimer-extended Darcy model is presented. A finite difference scheme using the marker-and-cell (MAC) method is employed to investigate the momentum and energy transport in a porous channel involving free surface transport phenomena. The interfacial tension effect at the free surface is incorporated in the analysis. The present investigation constitutes one of the first numerical investigations of the free surface momentum and energy transport through porous media using the MAC method. Fully developed velocity and temperature fields for saturated as well as unsaturated porous channels, for cases with different Darcy numbers, are compared and verified against existing analytical solutions. Temporal free surface distributions for cases with different Darcy numbers and Reynolds numbers are presented. Also explored is the effect of the free surface transport in porous media on the energy transfer. It is found t...

Modeling Quasi-Steady NAPL Dissolution in Fractured Permeable Media

Abstract: This work explores the rate-limited dissolution of entrapped nonaqueous phase liquids (NAPLs) in a fractured ``permeable`` formation through the use of mathematical models, developed on the basis of a simple conceptual framework. The feasibility of pump-and-treat operations in such formations is assessed through characterization of dimensionless system parameters governing NAPL dissolution and solute transport. These dimensionless parameters include the ratio of permeable block to fracture flow (mobility number), the system dimensionless mass transfer coefficient, and the number of contaminated fracture sections. A closed form analytical solution is developed for the simple case of a single contaminated fracture section. For domains with a large number of contaminated fracture sections, a numerical approach is presented that combines a finite difference scheme for simulation of solute transport in the fracture network together with an analytical solution for solute transport in the permeable block flow. The most favorable conditions for pump-and-treat systems are shown to be systems with large mobility numbers and large mass transfer coefficients. In systems with intermediate and small values of these parameters, effluent solute concentrations may be significantly below equilibrium values, reducing the effectiveness of pump-and-treat remediation. It is also shown that an equivalent continuum approach can be used tomore » model rate-limited NAPL dissolution and transport in the simplified fractured permeable formation. The effective mass transfer coefficient for the representative continuum, however, is nonlinearly related to the local mass transfer coefficient.« less

Mathematical simulation and experimental verification of melting resulting from the coupled effect of natural convection and exothermic heat of mixing

Abstract: When melting processes are associated with an exothermic heat of mixing, unique coupled transport phenomena take place. In this article, a mathematical model has been developed to simulate these unique coupled heat and mass transfer events. The model was based on the control-volume finite difference approach and on an enthalpy method. In order to verify the mathematical model, a low-temperature physical model was established consisting of ice and sulfuric acid solutions. In this physical model, both temperature and velocity measurements were carried out. The model predictions were compared with experimental measurements, and they were found to be in good agreement. The model was also applied to a high-temperature system, namely, the melting of silicon metal in liquid high carbon iron. The predictions distinguished two periods present in the entire melting process. In the first period, the silicon was heated up. The second period, i.e., free melting period, occurred in tandem with the exothermic reaction, and consequently, the melting process was greatly accelerated. As was the case with the low-temperature physical model, as with the high-temperature system, good agreement was obtained between the predicted results and the experimental measurements.