Showing papers on "Transport phenomena published in 1969"

Fundamentals of momentum, heat, and mass transfer

Abstract: Providing a unified treatment of momentum transfer (fluid mechanics), heat transfer and mass transfer. This new edition includes more modern applications of the basic material, and to provide many new homework exercises at the end of each chapter.

Some measurements in the self preserving jet

Abstract: The axisymmetric turbulent incompressible and isothermal jet was investigated by use of linearized constant-temperature hot-wire anemometers. It was established that the jet was truly self-preserving some 70 diameters downstream of the nozzle and most of the measurements were made in excess of this distance. The quantities measured include mean velocity, turbulence stresses, intermittency, skewness and flatness factors, correlations, scales, low-frequency spectra and convection velocity. The r.m.s. values of the various velocity fluctuations differ from those measured previously as a result of lack of self-preservation and insufficient frequency range in the instrumentation of the previous investigations. It appears that Taylor's hypothesis is not applicable to this flow, but the use of convection velocity of the appropriate scale for the transformation from temporal to spatial quantities appears appropriate. The energy balance was calculated from the various measured quantities and the result is quite different from the recent measurements of Sami (1967), which were obtained twenty diameters downstream from the nozzle. In light of these measurements some previous hypotheses about the turbulent structure and the transport phenomena are discussed. Some of the quantities were obtained by two or more different methods, and their relative merits and accuracy are assessed.

Transport phenomena in membranes.

Abstract: The realization that many elementary biological processes occur at membrane-like structures has led to renewed interest in the theory of molecular transport through membranes. Coupling phenomena in membranes, some of which are very complex, can now be rationally described with the aid of the thermodynamics of irreversible processes. The investigation of theoretical membrane models has proved a valuable complement to the thermodynamic method.

Transport Mechanics in Systems of Orientable Particles

Abstract: The phenomenological description of transport processes in a fluid composed of molecules or particles which are orientable is reformulated so as to render it capable of distinguishing between and determining the form of the distribution of orientation. With orientation variables playing the role of continuously distributed parameters suitable for tensorial labeling of multicomponent species, equations for the transport of mass, momentum, energy, and angular momentum in the position‐orientation hyperspace are independently derived by continuum and statistical mechanical arguments. The selection of the point of location of a particle is shown to have an important bearing upon the transport equations of physical space obtained by orientation averaging. Linear constitutive relations are established by means of thermodynamic arguments which suggest anisotropic thermal conductivity and viscosity as well as a coupling tensor each dependent for its anisotropy upon the polyadic (polarization) moments of the distributions. The rotational and translational diffusion fluxes are predicted to be governed by rotational, translational, and coupling multicomponent diffusion tensors, thermal diffusion tensors, and by the analogous shear diffusion tensors. The special case of dilute solution theory is examined and the thermodynamic predictions of generalized transport laws reaffirmed by appeal to component (orientation specific) balances of linear and angular momentum.

Transport phenomena at the wall of agitated vessels

Abstract: This paper deals with an experimental study on the local factors of friction in tangential direction and mass transfer coefficients on the wall of an agitated vessel with paddle type impellers as agitators, and with a discussion of the analogy between momentum and mass transfer phenomena. Experimental results show that the average factor of friction and j factor of mass transfer are correlated the same equation with respect to Reynolds number, and that the vertical distributions of local factors of friction in tangential direction and those of mass transfer coefficients are quite similar. Besides this it is found that the peak of the distribution curve at the height of the impeller is caused by jet flow issuing from the impeller, while the flat part of the curve is attributed to rotating flow. Finally the measured values of the local mass transfer fluctuation intensity were plotted in a diagram.

Cryogenic Heat Transfer

Abstract: Publisher Summary This chapter summarizes some of the available information relating specifically to heat transfer phenomena at low temperatures. The technical presentation includes conduction, insulation, and interfacial processes. Interfacial processes include forced-convection and natural convection processes; pressurized-discharge processes; stratification phenomena in vessels; multiphase processes, including two-phase flow and frost formation, among others ; and radiation and transport phenomena in the superfluid helium. Although most of the material to be presented may be applied to noncryogenic behavior, the chapter emphasizes on applications valid for the cryogens. The use of cryogenic substances has introduced several unique problems in heat transfer. The handling and transporting of these fluids at very low temperatures in the presence of an atmospheric ambient has necessitated the development of specialized insulating methods and design techniques. Where possible or available, cryogenic data has been cited and the uniqueness of low-temperature application has been highlighted.

Transport Phenomena in Heavily Doped Semiconductors

Abstract: Transport Equation. So far we have considered carriers under statistical equilibrium conditions. We shall now deal with the processes taking place under the action of external forces (electric and magnetic fields, temperature, etc.) — processes of great practical and theoretical interest. In these processes, carriers are no longer under equilibrium conditions. We thus have phenomena associated with the ordered motion of carriers and known as transport or transfer phenomena.

Transport Processes in Anisotropic Fluids II. Coupling of Momentum and Energy Transport in a Nematic Mesophase

Abstract: It is a well established fact that transport processes in fluid substances of low molecular weight are adequately described by linear constitutive relations of the form Here, J is the flux of the cntity to be transported and - is the driving force—always the gradient of some potential function—for transport of that entity. The parameter k is the conductivity; it depends on the thermodynamic state of the phase in which transport is occurring, but not on the flux or the driving force. Classical examples of Eq. (1) are Fick's law of diffusion, Fourier's law of heat conduction, Ohm's law of electrical conduction, and Newton's law of momentum transport (viscous friction). In the first three cases cited above, a scalar quantity is transported so that J and cfr are vectors; in the last case cited, a vector quantity is transported so that J and are tensors of second order.

Coupling phenomena as a possible cause of “non-darcian” behaviour of water in soil

Abstract: The “non-Darcian” behaviour of water in soils is discussed considering the coupling that can arise between the different transport phenomena. In general, it is shown that there is a reason to expect that a difference in osmotic pressure will arise when solutions flow through porous media, and that due to that difference the resulting flow be related in a non-linear fashion to the applied pressure difference. Several numerical examples are presented illustrating this behaviour.

Transport Coefficients of van der Waals Fluids and Fluid Mixtures

Abstract: We propose models which are direct extensions to dynamical domains of van Kampen's approach to van der Waals fluids, and are suited for studying transport phenomena near crit­ ical points. Models are described by hydrodynamic equation for hard sphere fluids where long· range interactions are added as semi-macroscopic forces acting among mass elements of the fluids, and are in principle capable of rigorous treatment of critical anomalies. Here we used the models to obtain the lowest order corrections of critical fluctuations to transport coefficients. Denoting the force range by 1 and the reduced temperature distance from the critical point by E, we found the following lowest order corrections: (a) for one-component fluids, shear viscosity 'l},,-,1-1IEI-i/2, bulk viscosity (,,-,1-1IEI-5/2, thermal conductivity A",l-1IEI-1I2, and (b) for binary solutions near critical solution points, diffusion constant D",l-1IEli/2, 'l}'" constant+l-i IEli/2, (",l-1IEI-312, A",l-1IEI-i/2, and thermal diffusion constant DT",l-1IEI-1I2.

Structure of Strong Shock Waves

Abstract: A model is proposed for the structure of strong shock waves which explicitly accounts for the existence of a near molecular beam, hypersonic flow upstream, and of a subsonic, hot continuum flow downstream. This is accomplished by considering the conversion of the beam into the continuum through collisions. Appropriate continuum equations are derived including the input of mass, momentum, and energy from the beam particles. The particles in the molecular beam are assumed to be converted into members of the continuum in a single collision; and the collision transport phenomena associated with the continuum are assumed to be governed by the Chapman‐Enskog expressions. Comparisons with other models for shock structure and with experimental results are given. In view of its simplicity the present model should be applicable to other hypersonic, rarefied flow problems.

Theory of Electron-Phonon Interaction Responsible for Current Saturation Phenomena in Semiconductors

Abstract: A theory applicable over the whole range of ql is presented for electron-phonon int,eraction responsible for the current saturation phenomena in semiconductors. Transport equations are set up by the nonequilibrium Green's function technique. The equations show clearly that phonons play two different physical roles in the description of transport phenomena; one is to act on electrons as waves and the other is to interact with them as quasiparticles. As for amplification of phonons as quasi particles, calculation shows that the radical reduction of amplification factor is not expected even when ql<1. In the case of high-mobility semicon­ ductors, the quasiparticle aspect is applicable in the initial stage of amplification, but the wave aspect is expected to appear in the final stage. The amplification of waves is discussed in . the nonlinear regime. To the second order approximation, it is shown that the amplification factor is decreased with increase of the wave amplitude. The domain problem is studied by using an electronic computer. It is certain that the domain formation is irrelevant to the . Ridley mechanism.

Quantum Corrections to the Thermal Conductivity and Shear Viscosity of a Moderately Dense Gas

Abstract: Using the correlation function approach to transport phenomena, a general formalism is developed for the calculation of the first‐order collisional transfer contributions to the shear viscosity and thermal conductivity of a nondegenerate moderately dense monatomic gas. Applying this formalism to the hardsphere model, quantum corrections to the classical Enskog collisional transfer corrections are obtained and discussed.

The Mercury-Drag Effect, a Demonstration of Transport Phenomena

Abstract: A demonstration of the mercury-drag effect is presented as an example of transport phenomena in dilute gases, in which one gas or vapor diffuses through a second gas, creating a viscous drag on this gas. In the demonstration, mercury vapor from a pool of liquid mercury diffuses through nitrogen gas (pressure 10−5–10−4 Torr), passing through tubes of two different radii (0.69 and 0.33 cm) to liquid nitrogen-cooled cold traps. The pressure changes of the nitrogen gas on the mercury-deficient side of the cold traps is observed and compared with theoretical and experimental values from the literature. Possible reasons for differences are discussed.

Some aspects of linear irreversible thermodynamics and continuum mechanics in the presence of electromagnetic fields

Abstract: Irreversible thermodynamics, conservation principles, andMaxwell relations are used to obtain the constitutive equations for a homogeneous fluid and aKelvin-Voigt viscoelastic solid in a electromagnetic field. Heat conduction equations for aVan der Waals gas and the viscoelastic media are obtained in a natural way and the effects of the electromagnetic fields are investigated.