Showing papers on "Transport phenomena published in 1980"

A comparison of transport algorithms for premixed, laminar steady state flames

Abstract: The effects of different methods of approximating multispecies transport phenomena in models of premixed, laminar, steady state flames were studied. Five approximation methods that span a wide range of computational complexity were developed. Identical data for individual species properties were used for each method. Each approximation method is employed in the numerical solution of a set of five H2-02-N2 flames. For each flame the computed species and temperature profiles, as well as the computed flame speeds, are found to be very nearly independent of the approximation method used. This does not indicate that transport phenomena are unimportant, but rather that the selection of the input values for the individual species transport properties is more important than the selection of the method used to approximate the multispecies transport. Based on these results, a sixth approximation method was developed that is computationally efficient and provides results extremely close to the most sophisticated and precise method used.

Fluid mechanics for chemical engineers

Abstract: 1 Introduction Part I Preliminaries 2 Fluid Statics 3 The Balance Equation and the Mass Balance 4 The First Law of Thermodynamics Part II Flows which are Practically One-Dimensional or can be Treated as Such 5 Bernoulli's Equation 6 Fluid Friction in Steady One-Dimensional Flow 7 The Momentum Balance 8 One-Dimensional High-Velocity Gas Flow Part III Some Other Topics, Which can be Viewed by the Methods of One-Dimensional Fluid Mechanics 9 Model Studies, Dimensional Analysis, and Similitude 10 Pumps, Compressors, and Turbines 11 Flow Through Porous Media 12 Gas-Liquid Flow 13 Non-Newtonian Fluid Flow in Circular Pipes 14 Surface Forces Part IV Two- and Three-Dimensional Fluid Mechanics 15 Two- and Three-Dimensional Fluid Mechanics 16 Potential Flow 17 The Boundary Layer 18 Turbulence 19 Mixing 20 Computational Fluid Dynamics, (CFD) Appendix A Tables and Charts of Fluid Properties, Pipe Dimensions and Flows, and High-Velocity Gas Flows Appendix B Derivations and Proofs Appendix C Equations for Two- and Three-Dimensional Fluid Mechanics Appendix D Answers to Selected Problems

Interfacial transport phenomena invited review

Abstract: Interfacial transport phenomena include all effects associated with momentum, energy, and mass transfer at phase interfaces. I shall begin by examining the nature of the phase interface and associated common lines. I then will develop the general balance equations at each point within a phase, at each point on a dividing surface, and at each point on a common line. Mass conservation, momentum transfer, energy transfer, and mass transfer are treated as special cases.

Transport phenomena in molecular Knudsen gas

Abstract: Transport properties of a collisionless molecular gas between plane-parallel plates are influenced by a magnetic field because of precession of the molecules after polarization by surface collisions. A systematic analysis of phenomena of this kind is attempted by considering mass flow in two directions and heat flow in three directions, together with the five conjugate thermodynamic forces. For the case of diamagnetic linear rigid molecules, the phenomenological coefficients are expressed by matrix elements involving the surface scattering operator. Explicit expressions are derived for a simple model of that operator.

On the theory of fluctuations around non-equilibrium steady states: A generalized time-convolutionless projector formalism

Abstract: A new method of finding nonlinear Langevin type equations of motion for relevant macrovariables and the corresponding master equation for systems far from thermal equilibrium is presented by generalizing the time-convolutionless formalism proposed previously for equilibrium hamiltoian systems by Tokuyama and Mori. The Langevin type equation consists of a fluctuating force, and the nonlinear drift coefficients which are always identical to those of the master equation. A simple formula which relates the drift coefficients to the time correlation of the fluctuating forces is derived. This is a generalization of the fluctuation-dissipation theorem of the second kind in equilibrium systems and is valid not only for transport phenomena due to internal fluctuations but also for transport phenomena due to externally-driven fluctuations. A new cumulant expansion of the master equation is also obtained. The conditions under which a Langevin and a Fokker-Planck equation of a generalized type for non-equilibrium open systems can be derived are clarified. The theory is illustrated by studying hydrodynamic fluctuations near the Rayleigh-Benard instability. The effects of two kinds of fluctuations, internal fluctuations of irrelevant macrovariables and external (thermal) noises, on the convective instability are investigated. A stochastic Ginzburg-Landau type equation for the order parameter and the corresponding nonlinear Fokker-Planck equation are derived.

Transport phenomena in solids with bidispersed pores

Abstract: Existing analyses for transport phenomena in bidisperse porous media assume that the microparticles act as uniformly distributed point sinks. This article provides an analysis which determines under what conditions the point sink approximation is valid. For random packing, the concentration field inside a pellet is described by its ensemble average, i.e., the average over all possible ways in which the microparticles can be packed into the pellet. For these averaged quantities, we formulate the transport equations for a solid with bidisperse pores which provide the criteria of validity of the point sink approximation.

Fluid description of particle transport in HF heated magnetized plasma

Abstract: Particle fluxes averaged over the high frequency oscillations are analyzed. Collisional effects and kinetic mechanisms of energy absorption are included. Spatial dependences of both the high frequency and the (quasi-)steady electromagnetic fields are arbitrary. Equations governing the fluxes are deduced from moments of the averaged kinetic equation. Explicit expressions for steady state fluxes are given in terms of electromagnetic field quantities. The results can also be applied to anomalous transport phenomena in weakly turbulent plasmas.

A simple algebraic method for obtaining the heat or mass transfer coefficients under mixed convection

Abstract: Many processes of practical interest involve mass or heat transfer under the influence of mixed convective flows, such as combined forced and buoyancy-induced flows or magneto-convective flows. In general, the solution of the appropriate transport equations under these conditions is very difficult. In this paper, a simple ‘algebraic’ method based on an order-of-magnitude analysis of the governing transport equation is presented and has been used to obtain the Nusselt and Sherwood numbers for heat and mass transfer from vertical plates, for the heat or mass transfer entrance region in internal flows, for magneto-convective heat transfer from flat plates and for transport from cylinders and spheres in the presence of mixed convective flows. The present method provides expressions that are in excellent agreement with available experimental data and numerical solutions.

Transport phenomena in He3-He4 mixtures near the tricritical point

Abstract: We have made extensive measurements on transport phenomena in He3-He4 mixtures near the tricritical point and along the superfluid transition line at saturated vapor pressure. The He3 mole fraction X ranged from 0.51 to 0.72 and the temperature from 0.8 to 1.5 K. Our measurements were made under steady state conditions using a cell where we measured the vertical He3 concentration gradient ▽X induced by a temperature gradient ▽T produced by a vertical heat flux. The cell included two superposed capacitors and ▽X was determined by means of the dielectric constant method. In this paper, we present a comprehensive report on our results for the thermal diffusion ratio k T and the thermal conductivity κ both in the normal fluid and in the superfluid. In the tricritical region, k T was found to diverge strongly as the tricritical point was approached; no singularity in κ was found. This behavior is consistent with theoretical predictions. In the region near the lambda line, κ remains finite, as expected, but k T appears to have a stronger singularity than predicted by theory. The analysis of our experiment in the normal fluid for mixtures with X>0.51 was complicated by superfluid film flow along the walls of the sample cell. We describe this effect and analyze it with Khalatnikov's theory of superfluidity. However, for the mixture X = 0.51, where there is no such film, the behavior of k T is consistent with predictions. The k T data for the mixtures 0.6 < X < 0.7 could be cast into a tricritical scaling representation, similar to that for the concentration susceptibility. In the superfluid phase we test, for the first time and with fair success, a relation by Khalatnikov between ▽X/▽T and static properties, measured in different experiments. Finally, we discuss the relaxation times that characterize the establishment of steady state conditions. From these data it is possible, under favorable circumstances, to obtain the mass diffusivity D.

Proof of the symmetry of the transport matrix for diffusion and heat flow in fluid systems

Abstract: A phenomenological proof is given of the symmetry of the transport matrix (Bij) of coefficients in the constitutive laws that describe mass and energy transport in a multicomponent fluid for the following choices of frame, forces, and fluxes: the local center of mass frame; the forces ∇(μi/T), where μ0=−1, T is the temperature, and μi for i=1,...K is the chemical potential of the ith component; and the fluxes ji, where j0 is the nonconvective internal energy flux and ji for i=1,...K is the mass flux of the ith component. The proof is based on Onsager’s reciprocity theory and proceeds by using the equations of hydrodynamics and the constitutive equations, postulated to describe mass and energy transport in the fluid, to calculate the time development of a specially selected fluctuation, when that fluctuation is considered to be macrovariation. The resulting dynamical equations are cast into the Onsager form by use of the generalized forces obtained from a thermodynamic calculation of the entropy change ΔS ...

Anomalous transport phenomena in rapid external flows of viscoelastic fluids

Abstract: The concept of an “elastic” boundary layer is proposed to explain certain anomalous transport phenomena which occur during rapid external flows of viscoelastic fluids past immersed objects. Reported experimental observations are interpreted by using models based on this concept. Particularly, data on velocity independent drag and heat transfer coefficients for flow of dilute polymer solutions past tiny cylinders are satisfactorily correlated.

Activation Energies in Isothermal and Non-Isothermal Membrane Transport

Abstract: Transport phenomena induced by temperature difference across a porous partition separating two liquid phases (effect of thermodialysis) has been only recently studied in its general aspects (1–7). Clear-cut differences appear between thermodialysis and the closely related effect of thermoosmosis (8–14), in various quantitative as well as qualitative aspects. On the other hand various significant analogies with non-isothermal matter transport in the bulk liquid (effect of thermal diffusion) have already emerged (3, 6, 7).

Approximate equations for transport coefficients of multicomponent mixtures of neutral gases

Abstract: : Reactive flow systems often consist of multicomponent mixtures of neutral gases. Accurate modelling of reactive flows will, in many cases, require the accurate representation of transport phenomena in the conservation equations. In this paper, we identify and derive accurate, easy-to-evaluate equations for the coefficients of (ordinary) diffusion, viscosity, thermal conductivity, and thermal diffusion. The paper also serves to introduce and supplement the standard references on the subject for readers who are relatively new to the field. (Author)

An application of irreversible thermodynamics to the problem of heat and moisture migration in soil

Abstract: The Equations for the combined transfer of heat and moisture in soil are derived from an application of the principles of irreversible thermodynamics. Unlike previous treatments to the subject, the three phases of soil (water, gas, solids) are considered to constitute distinct thermodynamic systems, described by a set of well defined thermodynamic functions. Separate expressions for the fluxes of heat and matter are thus writen for the separate phases. This allows a more detailed description of soil transport phenomena than was achieved previously. By making use of the derived flux expressions it is shown how the Equations of transport can be written for all cases of practical interest. Although the present treatment refers only to soils containing pure water as the liquid phase, the generalization for the presence of solutes will present no special problem. The derived Equations may apply also to porous bodies other than soil with the liquid phase other than water.

Problems of the Theory of Transport Processes in Systems with Intensive Mass Exchange

Abstract: The principles of the macroscopic theory of processes of convective heat and mass transfer in systems with mass exchange, taking place under conditions of large concentration gradients, have been presented For these systems, the structure of the hydrodynamic fluxes (in particular the velocity profile in the boundary layer next to the wall) shows a marked dependence on the concentration field of the substance being transferred Studies in which the effect of the interaction between the processes of mass transfer and momentum transfer has been analysed quantitatively in relation to problems of chemical and electrochemical technology have been reviewed The bibliography contains 68 references

Flow of a Polymerizing Fluid Between Two Rotating Concentric Cylinders

Abstract: Flow of polymerizing fluids involves a complex interaction between momentum, heat and mass transfer The transport phenomena are interrelated through the dependence of the material parameters (viscosity, specific heat, etc) on the field variables (extent of polymerization, temperature, and the rate of deformation) These “cross” effects tend to obscure measurements of the material properties, and also make the flow analysis quite complex

Analysis of the irreversible thermodynamics model for coupled heat and moisture transport phenomena in unsaturated porous media

Abstract: The irreversible thermodynamics-based model for the description of coupled heat and moisture transfer was analyzed. Transport coefficients appearing in model equations were independently determined, and the equations were numerically integrated to predict temperature and moisture content profiles for a closed system of water unsaturated glass beads. An experimental investigation of the moisture glass beads medium provided measurements of steady-state profiles of local temperatures and moisture content. These data, when compared with model predictions, indicated the validity of the irreversible thermodynamics approach. The coupling coefficient relating thermal gradients to moisture flux was found to be strongly moisture-dependent. The coupling coefficient which relates moisture content gradient to heat flux was found to be extremely small, and the heat flux associated with the moisture content gradient proved to be negligible. 111 references.

Dynamic similarity of transport phenomena

Abstract: The discharges issued by OTEC plants, thermal power plants and other engineering devices, give rise to the transport of "foreign" properties and substances into the natural ocean environment. In order to predict the functioning of such structures and assess their environmental impact, physical modelling has already been utilized. Since the simultaneous fulfillment of both Reynolds and Froude criteria is impossible (in a conventional small scale model operating with the prototype fluid) in the models mentioned the transport phenomenon was reproduced on the basis of the densimetric Froude number (Fr) only, the influence of the Reynolds number (Re) being neglected. On the other hand, the identification of the scale of Fr (viz Apr) with unity can lead to substantial differences between the model and prototype values of Re. (Because AFr = 1 yields AR6 = Ax 3/2 where Xjt is the linear model scale.) Yet many of the pertinent aspects of a turbulent diffusion (energy dissipation, thickness of mixing zones, separation processes, etc.) are strongly dependent on Re, and therefore an appreciable distortion of Re (AJJ3/2 << 1) can lead to some substantial errors with regard to the similarity of these aspects.

Anisotropy of transport phenomena in semiconductors of the tetragonal system

Abstract: An investigation is made into the anisotropy of transport phenomena in semiconductors of the tetragonal system in classical magnetic fields with arbitrary orientation and magnitude. A detailed study is made of the anisotropy of the transport coefficients in the region of weak magnetic fields. A condition is obtained under which semiconductors with anisotropic conductivity are characterized by an isotropic Hall coefficient. It is established that the transport coefficients have qualitatively different asymptotic behaviors in strong magnetic fields of different orientations. The obtained expressions are general in nature and apply to a large class of semiconductors.