Showing papers on "Transport phenomena published in 1984"

Fundamentals of transport phenomena in porous media

Abstract: This volume contains the lectures presented at the NATO Advanced Study Institute that took place at the University of Delaware, Newark, Delaware, July 18-27, 1982. The purpose of this Institute was to provide an international forum for exchange of ideas and dissemination of knowledge on some selected topics in Mechanics of Fluids in Porous Media. Processes of transport of such extensive quantities as mass of a phase, mass of a component of a phase, momentum and/or heat occur in diversified fields, such as petroleum reservoir engineer ing, groundwater hydraulics, soil mechanics, industrial filtration, water purification, wastewater treatment, soil drainage and irri gation, and geothermal energy production. In all these areas, scientists, engineers and planners make use of mathematical models that describe the relevant transport processes that occur within porous medium domains, and enable the forecasting of the future state of the latter in response to planned activities. The mathe matical models, in turn, are based on the understanding of phenomena, often within the void space, and on theories that re late these phenomena to measurable quantities. Because of the pressing needs in areas of practical interest, such as the develop ment of groundwater resources, the control and abatement of groundwater contamination, underground energy storage and geo thermal energy production, a vast amount of research efforts in all these fields has contributed, especially in the last t o decades, to our understanding and ability to describe transport phenomena."

Problems of Rate Chemistry in the Flight Regimes of Aeroassisted Orbital Transfer Vehicles

Abstract: The dissociating and ionizing nonequilibrium flows behind a normal shock wave are calculated for the density and vehicle regimes appropriate for aeroassisted orbital transfer vehicles; the departure of vibrational and electron temperatures from the gas temperature as well as viscous transport phenomena are accounted for. From the thermodynamic properties so determined, radiative power emission is calculated using an existing code. The resulting radiation characteristics are compared with the available experimental data. Chemical parameters are varied to Investigate their effect on the radiation characteristics. It is concluded that the current knowledge of rate chemistry leads to a factor-of-4 uncertainty In nonequilibrium radiation intensities. The chemical parameters that must be studied to Improve the accuracy are identified.

Transport Phenomena in Porous Media — Basic Equations

Abstract: The objective of this review is to present the methodology of developing the complete description of transport phenomena in a multiphase, deformable porous medium, and to demonstrate this methodology by applying it to the transport of such extensive quantities as volume, mass, component of a phase, momentum and heat

Diffusion of hydrogen in metals

Abstract: The investigation of the diffusion of hydrogen (muons or hydrogen, deuterium or tritium atoms) in metals is aimed on the one hand at understanding the nature of the elementary diffusive step. The extremely large isotope range and the position midway between classical and quantum mechanical transport allows the experimental and theoretical study of a large variety of transport phenomena. On the other hand the spatial and temporal development of hydrogen diffusion processes in metals is of interest, for example, to materials scientists, particularly in view of potential applications. Recent progress in both branches of research is reviewed.

Modeling Organic Contaminant Partitioning in Ground-Water Systems

Abstract: Effective management of a ground-water system requires description and prediction of the transport and fate of contaminants in that system. This can be facilitated by using mathematical models which accurately represent the physical phenomena operative in the system. One of the most significant phenomena impacting the transport of many organic pollutants is partitioning between the solid (soil) and aqueous (ground-water) phases. The tendency of a contaminant to partition may be roughly approximated from measurements of such constitutive properties as the octanol: water partition coefficient of the contaminant and organic carbon content of the soil. Such rough approximations provide a basis for cursory appraisal, but are inadequate for quantitative system descriptions, particularly where nonlinear equilibrium sorption, kinetically dependent partitioning, or irreversible and/or hysteretic phase distribution phenomena are operative. Accurate simulation of solute transport frequently requires the incorporation of kinetic parameters and/or a nonlinear isotherm relationship to define transport phenomena in the fundamental equations governing mass transport. Laboratory measurements may be utilized to assess sorptive factors of importance, kinetic properties of an organic solute and a soil system, and equilibrium partitioning relationships. Such measurements can be utilized to provide more accurate modeling of contaminant transport.

Transport phenomena in a completely ionized gas with large temperature gradients

Abstract: A solution to the Boltzmann equation is found that extends to large gradients and fields the classical Chapman-Enskog approximation developed by Spitzer and collaborators for electron transport in a fully ionized gas. The extended solution is used to calculate correction factors to the classical transport coefficients of a nonuniform plasma that depend on the temperature-gradient scale length as a parameter. These factors lead to inherently flux-limited heat flow with values in close agreement with Monte Carlo and numerical Fokker-Planck calculations.

Heat engineering convection heat transfer

Abstract: A text which shows how to develop an approach to formulating and solving convection problems. For engineering students with an undergraduate background in fluid mechanics, thermodynamics, heat transfer, and advanced calculus. Contents: General formulation. Individual formulation (laminar flows). Solution. Turbulence. Index.

Wall shear measurements by electrochemical probe for gas-liquid two-phase flow in vertical duct

Abstract: For over 40 years, gas-liquid two-phase flows have been very important in the field of industrial sciences as their heat and mass transfer properties, particularly in chemical, oil and nuclear engineering. These flows are usually classified according to the relative configuration of the two phases, mainly by geometrical and visual criteria (bubble, slug, annular flows, etc.). To better understand the transport phenomena in these rather complicated flows, we need more experimental data, among which is the momentum transferred to the wall by the shear stress. Usually this quantity is indirectly obtained from overall measurements (total pressure drop, average void fraction, etc.). In vertical ducts, the pressure loss by friction is small compared with the total pressure drop and the pressure loss by gravity (weight of the fluid column); therefore, a small error concerning these two terms may involve a considerable uncertainty for the friction. This leads to the interest on the direct measurement of the local wall shear stress. The electrochemical technique using probes mounted flush to the wall appeared to be convenient for that purpose.

Onsager symmetries in field-dependent flows of rarefied molecular gases

Abstract: Investigations of field effects upon transport phenomena in molecular gases have recently been extended from the hydrodynamic to trasition and Knudsen regimes. In the steady state of a binary mixture between parallel plates the average flow velocity, diffusive flux aand heat flux linearly depend upon small gradients of pressure, concentration and temperature. The relation is specified by a matrix of field- and pressure-dependent coefficients L αβ , each of which may be a tensor. The Onsager reciprocity, L αβ ( B )= L βα† (- B , is verified by a derivation from the linearized Boltzmann equation, by taking account of the symmetries of intermolecular and gas-surface collision operators. A more detailed analysis is possible at moderate rarefaction, when the fluxes can be split into bulk and boundary-layer parts, the latter involving field-dependent slip coefficients.

Relativistic Boltzmann theory for a plasma: X. Electrical conduction of the cosmological fluid

Abstract: General expressions are derived for the transport coefficients related to the vectorial transport phenomena in a plasma. As an example, the electrical conductivity of the cosmological fluid is calculated.

Numerical solution of a confined laminar diffusion flame

Abstract: Publisher Summary The flame type of most practical combustion devices is the diffusion flame. Although diffusion flames are important in combustion applications, they have received relatively little attention in theoretical flame studies. Part of this neglect is because of the two-dimensional nature of the problem coupled with the complexities associated with the combined effects of transport phenomena and chemical processes. Theoretical models are needed, however, to obtain an understanding of the factors that influence flame structure and chemistry, in particular, pollutant formation during combustion. Many of the numerical studies that attempt to predict the concentration, thermal, and aerodynamic distributions established in diffusion flames employ a time dependent relaxation approach. In such methods, the governing equations are discretized using finite difference techniques and the solution is advanced in time until steady-state profiles are obtained. However, the slow relaxation of time-dependent methods to steady-state can make parameter studies employing complicated nonlinear transport properties and chemical kinetics extremely time consuming. Steady-state methods, on the other hand, have the potential of solving the diffusion flame equations in much less time. This chapter presents the development of a numerical method, which enables to integrate the two-dimensional, time independent equations directly.

Thermohydrodynamic Instabilities: Buoyancy-Thermocapillary Convection

Abstract: Spontaneous, free or natural convection belongs to those physical phenomena that have fascinated people since the time of Archimedes (213 B.C.). Such convection usually arises when some interplay develops between different transport phenomena and external constraints, such as gravitational, electrical, or magnetic fields. Its many varieties provide, however, beautiful examples of problems among the most fertile and difficult in functional analysis, nonequilibrium thermodynamics, and hydrodynamics.

A study of transport phenomena and interface stability during solidification of binary solutions using front tracking finite elements

Abstract: A new numerical method using "front tracking" finite elements was developed to solve the multi-dimensional transient heat and mass transfer equations associated with the solidification of bindary solutions. The energy balance equation at the interface was not treated as a boundary condition, but rather as an independent equation whose solution gave the new position of interface.· A special new method was developed by which the interface was tracked in time by two steps: first the magnitude of displacement and the normal direction were independently obtained for each node on the interface, then they were superimposed to determine the new interface position. The numerical method can incorporate realistic thermodynamic conditions on the interface {including the effects of interfacial tension) and can accommodate the non-isothermal as well as the irregular but smooth interface. A novel meshing system based on a systematic exponential gridding concept was developed to yield accurate temperatures in the solid and liquid phases and concentration distribution in the liquid. This numerical method was then employed to study the transport phenomena as well as the morphological stability of a planar interface

Transverse Ion Diffusion in Gases

Abstract: Transport properties of ions in gases (i.e. ion mobilities and diffusion coefficients) are of intrinsic, fundamental and applied interest /1/. On the one hand they can give information about the ion-neutral interaction potential; on the other hand they can be used to describe quantitatively the behavior of ions moving in a neutral buffer gas and related charge transport phenomena and are required together with ionization cross section data /2/ for a quantitative understanding of electrical discharges.

Convective Gas Mixing in the Airways of the Human Lung - Comparison of Laminar and Turbulent Dispersion

Abstract: A mathematical model of gas transport in the airways of the human lung with numerical solution of the corresponding differential. equation is presented. The model takes into account, along with the summed cross section of. the Weibel lung model, both convection and longitudinal dispersion of helium and sulphur hexafluoride in air. Simulation was performed using two dispersion coefficients corresponding to laminar and disturbed flow. Moreover, since the dispersion coefficients are closely related to the velocity, five constant flow rates were used for each computation and each simulation. Comparison between the model responses to laminar and turbulent dispersion was made in order to determine which plays the preponderant role in gas transport in the human lung. In addition, agreement between the experimental time constant of CO2 elimination during high-frequency ventilation and the predicted mixing time constant was satisfactory. It is concluded that Taylor laminar dispersion cannot play a significant role in the human airways; however, it seems that convective gas mixing with disturbed dispersion-corresponding to a quasi-steady state - can account for most observed gas transport phenomena during spontaneous breathing and high-frequency ventilation.

Mixed Convection in Multicomponent Systems

Abstract: We have been interested in the study of transport phenomena in liquid phase for a long time. These phenomena are rather well understood in the gas phase, and the kinetic theory of gases predicts, more or less correctly, the experimental values of transport coefficients such as the viscosity and the isothermal diffusion coefficient, and even coupled phenomena, such as the thermal diffusion effect. However in the liquid phase the situation is far from being as favourable and usually one has to usephenomenological models. The validity of such phenomenological models must be tested by means of experimental measurements. As far as the thermal diffusion and Soret coefficients are concerned, these measurements are, at the very least, delicate. Intensive research on thermal diffusion in the liquid phase has been conducted between 1940 and 1960. For technical and experimental reasons, many determinations of Soret coefficients since 1950 have been carried out by the so-called flow cell method. In this type of determination, the mixture is forced to flow-between two horizontal and parallel plates maintained at two different temperatures T1 and T2 (Fig. X-l).

On transport phenomena in dense gases

Abstract: The Chapman-Enskog method is generalized for an equation of quasiparticle type; the solution is expanded with respect to the correlation parameter [9]; and the transport coefficients are represented in the form of infinite sums of Boltzmann integral brackets.

chapter 16 – FLUID MECHANICS

Abstract: Publisher Summary A fluid is a substance that cannot support a shearing stress. This characteristic gives fluids the ability to flow or change shapes. Both gases and liquids are fluids. Fluid mechanics is concerned with the behavior of fluids at the macroscopic level—the level at which measurements are made with pressure gauges, thermometers, and flow meters. Fluid mechanics is the analysis of the behavior of fluids. The description of fluid motion relies on Newton's laws of motion that is formulated in terms of measurable properties of the fluid, such as density, pressure, and flow velocity. A fluid has weight and, therefore, exerts a pressure on submerged objects. A fluid in motion transports momentum and energy. This chapter describes fluid statics and also explains the buoyant force exerted by fluids called Archimedes' principle. Fluid statics is concerned with fluids in which the center of mass of each fluid particle has zero velocity and zero acceleration. The chapter describes viscosity also known as unstable fluid motion.

Finite Element Modeling of Density-Driven Recirculating Turbulent Flow

Abstract: For many fluid flows in both natural and man-made settings, density gradients influence the nature, direction, and magnitude of the flow. Differences in fluid density may be the result of differences in fluid temperature, salinity or the presence of suspended solids. In all of these flows the thermal energy or contaminant transport is intimately linked to momentum transport in the determination of the flow pattern. Usually these flows are turbulent, and as a consequence a proper representation of the transport phenomena must correctly characterize the interplay between turbulent fluctuations and density variations in the flow. A two-dimensional steady model of the mean flow then consists of a mass conservation equation, two component momentum conservation equations and one transport equation for conservation of a scalar.

Thermodynamics of Non-Simple Heat-Conducting Interface

Abstract: Following Moeckel's approach, thermodynamics of non-simple, heat-conducting material interface is investigated. In order to obtain field equations for the fields of mass density, motion, and temperature in the interface, specific balance equations are used for mass, momentum, moment of momentum, and energy in the surface, and constitutive equations are stated. The constitutive equations of the bulk material (the three-dimensional non-simple, heat-conducting fluid) were derived by I-Shih Liu. The forms of all of these constitutive equations are restricted by an entropy principle which is adopted from Muller's entropy principle.