BASIC CONCEPTS AND DEFINITIONS C.T. Crowe and E.E. Michaelides GAS-LIQUID TRANSPORT IN DUCTS R.V.A. Oliemans and B.F.M. Pots BOILING AND CONDENSATION S.G. Kandlikar and J.N. Chung FLUID-SOLID TRANSPORT IN DUCTS S. Dhodapkar, K. Jacobs, and S. Hu FLUIDIZED BEDS J.R. Grace, B. Leckner, J. Zhu, and Y. Cheng AEROSOL FLOWS Y. Drossinos and C. Housiadas PARTICLE SEPARATION SYSTEMS C. Kanaoka , H. Yoshida, and H. Makino SPRAY SYSTEMS U. Fritsching DRY POWDER FLOWS G.I. Tardos and P.R. Mort POROUS MEDIA FLOWS M. Dong and F.A.L. Dullien MICROSCALE AND MICROGRAVITY FLOWS A. Serizawa and K.S. Gabriel MULTIPHASE INTERACTIONS G.F. Oweis, S.L. Ceccio, Y. Matsumoto, C. Tropea, I.V. Roisman, Y. Tsuji, R. Lyczkowski, T.R. Troutt, J.K. Eaton, and F. Mashayek MODELING E. Loth, G. Tryggvason, Y. Tsuji, S.E. Elghobashi, C.T. Crowe, A. Berlemont, M. Reeks, O. Simonin, Th. Frank, Y. Onishi, and B. van Wachem ADVANCED EXPERIMENTAL TECHNIQUES E.A. Hammer, G.A. Johansen, T. Dyakowski, E.P.L. Roberts, J.C. Cullivan, R.A. Williams, Y.A. Hassan, and C.S. Claiborn INDEX

Multiphase Flow Handbook

This article reviews the physical processes responsible for the transport and deposition of particles and their theoretical modeling. Both laminar and turbulent processes are considered, emphasizing the physical understanding of the various transport mechanisms. State-of-the-art computational methods for determining particle motion and deposition are discussed, including stochastic Lagrangian particle tracking and a unified Eulerian advection-diffusion approach. The theory presented includes Brownian and turbulent diffusion, turbophoresis, thermophoresis, inertial impaction, gravitational settling, electrical forces, and the effects of surface roughness and particle interception. The article describes two example applications: the deposition of particles in the human respiratory tract and deposition in gas and steam turbines.

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Transport and Deposition of Particles in Turbulent and Laminar Flow

This paper summarizes some applications of ultrasonic vibrations regarding heat transfer enhancement techniques. Research literature is reviewed, with special attention to examples for which ultrasonic technology was used alongside a conventional heat transfer process in order to enhance it. In several industrial applications, the use of ultrasound is often a way to increase productivity in the process itself, but also to take advantage of various subsequent phenomena. The relevant example brought forward here concerns heat exchangers, where it was found that ultrasound not only increases heat transfer rates, but might also be a solution to fouling reduction.

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Enhancement of Heat Transfer by Ultrasound: Review and Recent Advances

We investigate a Boltzmann equation for inelastic scattering in which the relative velocity in the collision frequency is approximated by the thermal speed. The inelasticity is given by a velocity variable restitution coefficient. This equation is the analog to the Boltzmann classical equation for Maxwellian molecules. We study the homogeneous regime using Fourier analysis methods. We analyze the existence and uniqueness questions, the linearized operator around the Dirac delta function, self-similar solutions and moment equations. We clarify the conditions under which self-similar solutions describe the asymptotic behavior of the homogeneous equation. We obtain formally a hydrodynamic description for near elastic particles under the assumption of constant and variable restitution coefficient. We describe the linear long-wave stability/instability for homogeneous cooling states.

On some properties of kinetic and hydrodynamic equations for inelastic interactions

This paper describes computer simulation studies of granular materials under dense conditions where particles are in persistent contact with their neighbours and the elasticity of the material becomes an important rheological parameter. There are two regimes at this limit, one for which the stresses scale with both elastic and inertial properties (called the elastic–inertial regime), and a non-inertial quasi-static regime in which the stresses scale purely elastically (elastic–quasi-static). In these elastic regimes, the forces are generated by internal force chains. Reducing the concentration slightly causes a transition from an elastic to a purely inertial behaviour. This transition occurs so abruptly that a 2% concentration reduction can be accompanied by nearly three orders of magnitude of stress reduction. This indicates that granular flows near this limit are prone to instabilities such as those commonly observed in shear cells. Unexpectedly, there is no path between inertial (rapid) flow and quasi-static flow by varying the shear rate at a fixed concentration; only by reducing the concentration can one cause a transition from quasi-static to inertial flow. The solid concentrations at which this transition occurs as well as the magnitude of the stresses in the elastic regimes are strong functions of the particle surface friction, because the surface friction strongly affects the strength of the force chains. A parametric analysis of the elastic regime generated flowmaps showing the various regimes that might be realized in practice. Many common materials such as sand require such large shear rates to reach the elastic–inertial regime that it is unattainable for all practical purposes; such materials will demonstrate either an elastic–quasi-static behaviour or a pure inertial behaviour depending on the concentration – with many orders of magnitude of stress change between them. Finally, the effects of nonlinear contacts are investigated and an appropriate scaling is proposed that accounts for the nonlinear behaviour in the elastic–quasi-static regime.

Granular shear flows at the elastic limit

Resuspension of particulates from surfaces to turbulent flows : review and analysis

According to numerous experimental observations and theoretical models vibrated layers composed of large granules behave like a solid plastic body. In contrast, in this study experimental data are presented that reveal that, for constant vibration amplitudes A ≥ 1 cm with the frequency ω increasing from zero, all layers pass through three vibrational states, with the respective behaviours being as of (i) a solid plastic body, (ii) a liquid, (iii) a gas. In the liquid-like vibrational state transverse waves propagating along the layer width were observed. These waves were shown to be gravitational resonance waves, with the corresponding frequencies well correlated by the known formula for incompressible liquids. In the gas-like vibrational state compression (shock) and expansion waves propagating across the layer height, were observed.A theoretical model for time-periodic collisional vibrational regimes was developed on the basis of the Euler-like equations of a granular gas composed of inelastic spheres. The model shows that the vibrational granular state (bed porosity, shock wave speed, granular pressure and kinetic energy) is inter alia governed by the dimensionless parameter V = (Aω)/(hmg)1/2, with g, hm being the gravitational acceleration and the height of the resting layer, respectively. This is in contrast with the previous studies, where the behaviour of vibrated granular layers was interpreted in terms of the dimensionless acceleration Δ = (Aω2)/g. The proposed model was tested by processing the data obtained from photographs of the particle distribution within vibrated layers. Theoretical predictions of the particle average concentration compared favourably with the experimental data.Other phenomena observed in vibrated granular layers include the formation of caverns, circulatory motion of granules and synchronized periodic motion of two adjacent vibrated layers of different widths. The importance of the observed phenomena in relation to various technological processes involving bulk materials (vibromixing, vibroseparation, etc.) is discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002211209500098X

M. Fichman

Papers

Resuspension of particulates from surfaces to turbulent flows : review and analysis

Mechanics of collisional motion of granular materials. Part 2. Wave propagation through vibrofluidized granular layers

Adhesion moment model for estimating particle detachment from a surface

A model for turbulent deposition of aerosols

Acoustic enhancement of heat transfer between two parallel plates