Showing papers on "Transport phenomena published in 1987"

Principles of electrochemistry

Abstract: Part 1 Equilibrium properties of electrolytes: electrolytes - elementary concepts structure of solutions interionic interactions acids and bases special cases of electrolytic systems. Part 2 Transport processes in electrolyte systems: irreversible processes common properties of fluxes of thermodynamic quantities production of entropy, the driving forces of transport phenomena conduction of electricity in electrolytes diffusion and migration in electrolyte solutions the mechanism of ion transport in solutions, solids and polymers melts transport in a flowing liquid. Part 3 Equilibria of charge transfer in heterogeneous electrochemical systems: structure and electrical properties of interfacial regions reversible electrodes potentiometry. Part 4 The electrical double layer: general properties electrocapillarity structure of the electrical double layer methods of the electrical double-layer study the electrical double layer at the electrolyte-non-metallic phase interface. Part 5 Processes in heterogeneous electrochemical systems: basic concepts and definitions elementary outline of simple electrode reactions the theory of electron transfer transport in electrode processes methods and materials chemical reactions in electrode processes adsorption and electrode processes deposition and oxidation of metals organic electrochemistry. Part 6 Membrane electrochemistry and bioelectrochemistry: basic concepts and definitions ion-exchanger membranes ion-selective electrodes biological membranes examples of biological membrane processes. Appendix A: recalculation formulas for concentrations and activity coefficients. Appendix B: list of symbols.

Some new aspects of the shock-wave/boundary-layer interaction in compression-ramp flows

Abstract: The present study of the pressure fluctuations in the interaction region oif a two-dimensionals compression flow established that the frequency of the shock-wave unsteadiness is of the same order as the bursting frequency of the upstream boundary layer and that this frequency is independent of the downstream separated flow. The conditional-sampling technique developed herein is capable of separating phenomena due to shock-wave oscillations from those due to transport phenomena of turbulence. The results show that turbulence as inferred from wall-pressure fluctuations may be significantly amplified approaching the shock.

Transport phenomena in dissipative heavy-ion collisions: the one-body dissipation approach

Abstract: As the study of Brownian movement is the key to the understanding of all dissipative phenomena, the author uses it to introduce the concepts which are then made use of in a specific dissipative model. The author discusses the 'one-body dissipation model' in its richness of phenomena and compares its predictions to measured data. Special attention is paid to the non-equilibrium relation between friction (or mobility) and diffusion.

Advances in transport phenomena in porous media

Abstract: 1. Heat and Mass Transport in Single and Multiphase Systems.- On the Concept and Size of a Representative Elementary Volume (REV).- Advective and Diffusive Fluxes in Porous Media.- Pore Scale Physical Modeling of Transport Phenomena in Porous Media.- Natural Convection in Porous Media.- Heat and Mass Transport in Geothermal Reservoirs.- Thermohydraulics of an Aquifer Thermal Energy Storage System.- Mechanics of Fluids in Layered Soils.- 2. Particle Transport in Porous Media.- Governing Equations for Particle Transport in Porous Media.- Theory of Filtration.- 3. Transport Phenomena in Fractured Rocks.- Transport Equations for Fractured Porous Media.- Chemical Transport in Fractured Rock.- Multiphase Flow in Fractured Reservoirs.- 4. Uncertainty and the Stochastic Approach to Transport in Porous Media.- Non Stationary Geostatistics.- Stochastic Analysis of Solute Transport in Saturated and Unsaturated Porous Media.- Uncertainty Assessment for Fluid Flow and Contaminant Transport Modeling in Heterogeneous Groundwater Systems.- An Overview of the Stochastic Modeling of Dispersion in Fractured Media.- Sensitivity Analysis of Ground-water Models.- 5. Advances in Numerical Methods.- Mathematical Modeling of the Behavior of Hydrocarbon Reservoirs - The Present and the Future.- Numerical Modeling of Multiphase Flow in Porous Media.- Advection-Dispersion with Adaptive Eulerian-Lagrangian Finite Elements.- Moving Point Techniques.- Table of Contents of "Fundamentals of Transport Phenomena in Porous Media, 1984".

Dehumidification: on the correlation of wet and dry transport processes in plate finned-tube heat exchangers

Abstract: The transverse velocity of the condensing phase during dehumidification is analogous to the transverse velocity at the wall when exercising boundary layer control by fluid extraction through a permeable wall. Wet and dry pressure drop and heat transfer rates are analyzed for correlation using boundary layer suction theory. Data are presented for flat-plate finned-tube heat exchangers during air heating and dehumidification operations and the data show a significant effect of transverse velocity correlated by the boundary layer suction formulation. The condensate film is considered isothermal in this analysis and the results indicate that an improved modeling of the condensate film is required. The authors find that the transverse velocity of the condensing phase has an important effect on transport phenomena during dehumidification and that the validity of the Chilton-Colburn heat and mass transfer analogy in describing dehumidification is supported by these results. It should be noted that the dry data form the beginning of a plate fin heat exchanger data base. The present data show the effect of tube diameter and, independently, fin density variation on the Colburn and friction factors with all other geometric parameters held invariant.

Heat and momentum transport far from equilibrium.

Abstract: Explicit expressions for the heat and momentum transport are given for a gas in a stationary state with temperature and velocity gradients. The results are obtained from a formally exact analysis of the normal solution to the Bhatnagar-Gross-Krook model for the nonlinear Boltzmann equation, and are not restricted to small gradients. The irreversible momentum and heat fluxes are found to be nonanalytic functions of the velocity gradients, indicating that the Chapman-Enskog expansion does not converge for this state. However, these fluxes are analytic in the temperature gradients; in particular, the heat flux is simply proportional to the temperature gradient so that Fourier's law applies even for large gradients. The space dependence of the thermodynamic and velocity fields is determined as a function of the interaction potential, and the results for Maxwell molecules and hard spheres are compared.

Theory of high-field transport in semiconductor superlattice structures

Abstract: The authors present a theoretical framework for the transport of charge carriers in semiconductor multiple-quantum-well structures for motion perpendicular to the layers. The formalism is derived on the basis of strong electric fields but they allow the possibility of describing the low-field ohmic region by using a simple scaling argument. Stark localisation in narrow energy bands implies that the transport phenomena are a superposition of phonon-assisted hopping and intra-band tunnelling. The transport equations and transition rates are derived and discussed in relation to experimental results. In addition they also consider the influence of an external magnetic field both parallel and perpendicular to the layers. The influence of disorder is considered and it is found that it can considerably modify the nature of the physical effects predicted on the basis of the 'pure' eigenstates. Recent experiments on magneto-transport perpendicular to the layers are discussed in the light of this theoretical formalism.

Long-time molecular diffusion, sedimentation and Taylor dispersion of a fluctuating cluster of interacting Brownian particles

Abstract: Generalized Taylor dispersion theory, incorporating so-called coupling effects, is used to calculate the transport properties of a single deformable ‘chain’ composed of hydrodynamically interacting rigid Brownian particles bound together by internal potentials and moving through an unbounded quiescent viscous fluid. The individual rigid particles comprising the flexible chain or cluster may each be of arbitrary shape, size and density, and are supposed ‘joined’ together to form the chain by a configuration-dependent internal potential V. Each particle separately undergoes translational and rotational Brownian motions; together, their relative motions give rise to a conformational or vibrational Brownian motion of the chain (in addition to a translational motion of the chain as a whole). Sufficient time is allowed for all accessible chain configurations to be sampled many times in consequence of this internal Brownian motion. As a result, an internal equilibrium Boltzmann probabilistic distribution of conformations derived from V effectively obtains.In contrast with prior analyses of such chain transport phenomena, no ad hoc preaveraging hypotheses are invoked to effect the averaging of the input conformation-specific hydrodynamic mobility data. Rather, the calculation is effected rigorously within the usual (quasi-static) context of configuration-specific Stokes-Einstein equations.Explicit numerical calculations serving to illustrate the general scheme are performed only for the simplest case, namely dumb-bells composed of identically sized spheres connected by a slack tether. In this context it is pointed out that prior calculations of flexible-body transport phenomena have failed to explicitly recognize the existence of a Taylor dispersion contribution to the long-time diffusivity of sedimenting deformable bodies. This fluctuation phenomenon is compounded of shape-sedimentation dispersion (arising as a consequence of the intrinsic geometrical anisotropy of the object) and size-sedimentation dispersion (arising from fluctuations in the instantaneous ‘size’ of the object). Whereas shape dispersion exists even for rigid objects, size dispersion is manifested only by flexible bodies. These two Taylor dispersion mechanisms are relevant to interpreting the non-equilibrium sedimentation-diffusion properties of monodisperse polymer molecules in solutions or suspensions.

Performance analysis of sub-micron gate GaAs MESFETs

Abstract: A novel 2-D numerical model incorporating nonstationary electron dynamics is used to investigate the complex transport phenomena governing the operation of sub-micron gate GaAs MESFET's. A detailed theoretical analysis of different phenomena observed in subhalf micron devices is given. These include velocity overshoot, stationary and travelling domain formation, soft pinch off, excess drain current etc. The small signal parameters g m , g d and C gs and their dependence on bias condition are evaluated. The effects of physical quantities such as mobility and interface barrier on carrier injection and transport and consequently on device performance are presented.

Practical Thermodynamic Tools for Heat Exchanger Design Engineers

Abstract: Physical Laws in Thermal Engineering Inviscid Fluid Mechanics Single-phase Newtonian Fluid Mechanics Overview of Multiphase Fluid Flow Two-phase Fluid Flow Correlations Thermodynamic Generalization of Fluid Flow Data Engineering Heat Transfer and Thermodynamics Practical Applications Non-equilibrium Thermodynamic Considerations Appendixes References Index.

Continuous and discontinuous models for transport phenomena in polymers

Abstract: A model for transport phenomena in polymers accompanied by morphological changes is presented that includes the essential features of a variety of seemingly disparate models available in the literature. The latter are classified as special cases of the model considered, and according to whether discontinuities of the morphology are or are not explicitly described. An ordering analysis is presented that indicates under which conditions one or more of the terms appearing in the differential equations can be neglected. A special subcase, termed surface crystallization, is shown to emerge in a well-defined asymptotic sense from the general model, and is also shown to yield predictions which are closely analogous to those of a model of Astarita and Sarti that has been very successful in correlating experimental data of the type called case II transport. The advantage of the surface crystallization model is that it is not an ad hoc model. The models considered result in hyperbolic differential equations, as is often the case when relaxation phenomena are taken into account. A procedure for numerically solving hyperbolic equations with great ease is presented.

System physics: A uniform approach to the branches of classical physics

Abstract: A systematic frame for the theory of classical physics is presented. The purpose of the modification in structure of the science is to economize the teaching, learning, and application of physics, and the communication with other disciplines. Isomorphic procedures applicable to the branches of physics and to other sciences are recommended. A system is defined as an imagined container; its contents of extensive (substancelike) quantities are used to describe the state of the system; balance equations account for the dynamic change in a system’s state through processes. The procedure, essentially a space integral formulation of macroscopic transport equations, is applied to physics by using the extensive quantity of entropy and the conserved extensive quantities of mass, energy, momentum, angular momentum, and electric charge. Examples are given from the areas of mechanics, electricity, and heat.

Analysis of Transport Phenomena Using Scaling and Physical Models

Abstract: Publisher Summary This chapter discusses some simple approaches that can be employed to obtain information on the rate of heat and mass transfer for both laminar and turbulent motion. One approach is based on dimensional scaling and hence ignores the transport equations. Another approach, while based on the transport equations, does not solve them in the conventional way. Instead, it replaces them by some algebraic expressions, which are obtained by what could be called physical scaling. Conventional dimensional analysis uses single length and time scales to obtain dimensionless groups. The chapter describes a new kind of dimensional analysis, which employs two kinds of such scales, the microscopic scale and the macroscopic scale. Turbulent transport is represented as a succession of simple laminar flows. For a liquid–fluid interface, a roll cell model is employed for turbulent motion as well as for interfacial turbulence. The chapter describes various physical and scaling models that demonstrate transport phenomena, especially heat and mass transfer.

Kinetic properties of two-dimensional metal systems

Abstract: The two-dimensional degenerate Fermi gas of electrons interacting with phonons is considered. The basic mechanisms of momentum relaxation in such a system, associated with electron-phonon, phonon-phonon and electron-electron collisions, are shown to be qualitatively different from similar mechanisms in an ordinary three-dimensional metal. The physical explanation for this is that the two-dimensional system of interacting electrons and phonons breaks down into almost isolated groups, between which momentum transfer occurs through very slow, staged superdiffusion (mixing) processes. With certain structures of the Fermi surface, quasimomentum transfer through electron-electron collisions is insignificant; hence such collisions are not an efficient relaxation mechanism. In this paper an efficient method is suggested for deriving superdiffusion equations, based on the detailed-balance conditions in the electron-phonon system. A theory of low-temperature transport phenomena is developed for pure two-di...

Numerical modeling of hot carriers in submicrometer Silicon BJT's

Abstract: Conventional semiconductor equations do not accurately describe carrier transport phenomena particularly in submicrometer semiconductor devices because of the use of the local field-dependent mobility. In this work, a hot-carrier transport model is used in the numerical simulation of submicrometer silicon bipolar junction transistors (BJT's). The hot-carrier effect, velocity overshoot, is predicted in this model and the results compare favorably with those obtained by the Monte Carlo method, which consumes much more computer time. A heuristic iterative procedure has been developed that proves to be very efficient in solving the five coupled nonlinear semiconductor equations including the energy balance equations.

Transport Phenomena in Mesoscopic Systems

Abstract: Some of the recent results on the transport properties of small disordered (mesoscopic) metal samples are considered from the viewpoint of the exact electron levels in a given realization of random imurity potential. Statistics of random one-electron energy spectra turns out to be close to the one derived by Dyson for the ensembles of random matrix hamiltonians. This fact, which can be verified by direct calculation, is shown to be sufficient to explain qualitatively most of the results in mesoscopic. Mesoscopic fluctuations of the relaxation time scales (of the widths of one-electron levels) are also considered and are shown to give rise to the alternative contribution to the fluctuations of transport properties.

Pore Scale Physical Modeling of Transport Phenomena in Porous Media

Abstract: The flow of fluids through natural reservoir bodies is complicated, particularly for multiphase processes and especially if there is mass transfer. Physical modeling using visual techniques can give some of the necessary descriptions leading to the proper formulation of mathematical models for predicting reservoir performance. This chapter describes the micromodel techniques developed at Imperial College, highlighting particularly those involving pore scale events which depend on network and pore morphology.

Surface Forces in Transport Phenomena

Abstract: Previous chapters have shown how the field of long-range surface forces alters the composition and properties of liquids in the neighborhood of interfaces. Clearly, these changes must also affect mass transfer processes to some extent. Among the better known transport processes due to surface charge are the electrokinetic phenomena. However, these phenomena will not be discussed in this book because they have been thoroughly reviewed in recent monographs [1–3]. We begin this chapter with a treatment of less well-known phenomena, viz., capillary osmosis and diffusiophoresis, first analyzed by Derjaguin [4]. Then we treat the thermo-osmosis and thermocrystallization flow of liquids.

Transport phenomena in laser created plasma with non-Maxwellian electronic distribution

Abstract: We investigate the Fokker–Planck Equation (FPE) in which we retain electron–ion and electron–electron collision terms, as well as the inverse-bremsstrahlung absorption term. We exhibit asymptotic solutions, which are then used in a linear perturbation theory ‘a la Spitzer’, to calculate local transport coefficients. Their values can differ drastically from classical results, which in turn alters hydrocode simulations.

The role of the volume-averaged temperature in the analysis of nonisothermal, multiphase transport phenomena

Abstract: The analysis of nonisothermal transport phenomena in multiphase systems is almost always accompanied by the use of some type of volume-averaged or spatially-smoothed temperature. In such systems one always encounters parameters, such as a reaction rate coefficient or a viscosity, that are temperature dependent. Given the point relation for some generic parameter in the β-phase, i.e., ψβ = ψβ(T β), one can wonder how the volume-averaged form of this parameter depends on the volume-averaged temperature. In this paper we show that the local volume-averaged form of ψβ is given by $ in which A represents a second order tensor that depends on the system parameters. A somewhat more complex form is encountered for area-averaged functions of the temperature. These functions are especially prevalent in reactor design calculations, which are considered both in terms of early intuitive developments and from the perspective of the method of volume averaging.

The Mathematical Modelling of Transport Phenomena in Non-Transferred Plasma Systems: Accomplishments and Unresolved Problems

Abstract: An overview is presented of transport phenomena in non-transferred plasma arc systems. It has been shown that while the modelling of these systems involves the standard application of computational fluid mechanics techniques, numerous pitfalls may be encountered in practice. A detailed discussion of these is presented, with emphasis on the torch inlet conditions, the effect of swirl, the temperature dependence of the system properties and the laminar-turbulent transition in the system. A critical comparison is presented with experimental measurements, and the necessary future work is also outlined.

Some aspects of the transport phenomena near the mobility edge in disordered semiconductors

Abstract: The critical behaviour of transport coefficients in the region near the mobility edge is discussed. It is shown that the temperature dependence of the thermopower and its variation with the Fermi level position can be used to evaluate the critical indices and the role of the correlation effects.