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  • 1
    Electronic Resource
    Electronic Resource
    A novel way of computing the Basset term in unsteady multiphase flow computations (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1579-1582 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The inclusion of the Basset (history) term in the equation of motion of a sphere in creeping flow increases substantially the computational time and memory requirements for a numerical solution of the trajectory of the sphere. A transformation of the equation of motion of a sphere in a fluid is obtained, in which the velocity of the sphere does not appear in the history integral. Although the transformed equation is a second-order ordinary differential equation (ODE), it is explicit in the dependent variable and presents considerable advantages in reduced computational time and memory requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858430
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  • 2
    Electronic Resource
    Electronic Resource
    Particle dynamics and mixing in the frequency driven "Kelvin cat eyes" flow (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 11 (2001), S. 351-358 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The "Kelvin cat eyes" stream function is used as a simple fluid flow model to study particle dynamics, mixing and transport in a two-dimensional time-dependent flow field. Lagrangian formulation is used to describe the motion of small spherical particles present in the flow. Individual particle trajectories, under the influence of various flow parameters are studied. The equation describing the motion of these particles constitutes a set of first-order nonlinear differential equations describing a dynamical system. The time-dependent Eulerian flow field is studied as a nonintegrable Hamiltonian system in order to get insight into the underlying nonlinear properties of the system, which directly influence its complicated transport and mixing behavior. Chaotic advection (Lagrangian turbulence) was observed for heavy particles (high Stokes numbers) while no stochastic behavior was observed for light particles. The introduction of perturbation had only a limited effect on individual particle trajectories. However, the introduction of perturbation caused a shrinking of the phase space where bounded stochastic or quasi-periodic motion occurs. This phenomenon can lead to a better understanding of the link between the behavior of the underlying flow in the Hamiltonian formulation and the dynamics of the passive scalars in the Lagrangian description. The Eulerian flow field itself was found to behave chaotically under the influence of a periodic perturbation, because the stable and unstable manifolds associated with neighboring hyperbolic points intersected. This coincides with the better mixing of the fluid. Stochasticity was also discovered close to the periodic points of the system using Poincaré maps. Mixing and transport properties are analyzed as a function of the perturbation frequency. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1366371
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetic theory and molecular dynamics simulations of microscopic flows (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 3915-3925 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This study aims at the understanding of the viscosity distributions near a solid wall in microscopic pores. The pair-correlation function is derived from the density distribution function, which in itself is obtained from molecular dynamics simulations. The revised Enskog equation for the shear flow of strongly inhomogeneous hard-sphere fluids is solved by the Chapman–Enskog method and the viscosity coefficients are obtained by keeping all the high-order derivatives of the density and pair-correlation functions. The molecular dynamics method is used in order to simulate the Couette flow of a Lennard-Jones fluid in a micropore, with weak or strong wall–fluid interactions. Under the weak interaction, slip is observed near the wall and the fluid in the contact layer exhibits higher viscosity than the fluid in other regions. Under the strong interaction, a layer of fluid always adhered to the wall is observed. A low viscosity valley often exists next to the high viscosity region, where apparently the flow commences. It is observed that the molecular dynamics simulations predict higher viscosity than the kinetic theory of the hard-sphere model, as it is expected. However, the distributions obtained from both methods are in qualitative agreement. The present study suggests that, provided the bulk viscosity and appropriate boundary conditions are used, the Navier–Stokes equations are valid at a distance of two to three molecular layers from the wall. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869490
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  • 4
    Electronic Resource
    Electronic Resource
    Motion of a permeable sphere at finite but small Reynolds numbers (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 1375-1383 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of the motion of a porous sphere in a viscous fluid has three pertinent characteristic times: two for the external flow field of the viscous fluid and a third one for the internal flow field, inside the porous material. Because of this, a singular perturbation method must be used to obtain an analytical solution to the governing differential equations and for the determination of the flow field outside the porous sphere. Such a method is used here, and a solution is obtained, by using the so-called Saffman boundary condition at the interface between the porous sphere and the outside fluid. This solution is valid at finite but small Reynolds numbers. Thus, general expressions for the hydrodynamic force acting on the porous sphere and, hence, for the drag coefficient of the sphere are obtained. This general expression yields, as special cases, other known expressions for the drag coefficients, which were derived under more restrictive conditions, such as creeping flow, no-slip boundary conditions or zero permeability (solid) spheres. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869662
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  • 5
    Electronic Resource
    Electronic Resource
    Gravity flow of a viscous liquid down a slope with injection (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2739-2741 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The free-surface lubrication equations are solved numerically for the time-dependent three-dimensional flow down an inclined plane produced by continuous injection through a circular orifice in the plane. The flow pattern ultimately becomes steady with stream depth and width scaling as the − (1)/(7) th power and (3)/(7) th power of the downslope distance from the orifice, in agreement with a known similarity solution. The predicted stream width gives partial agreement with a recent experimental result, even though significant thermal effects were present in the experiment. The physical prototype is flow of lava.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866977
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  • 6
    Electronic Resource
    Electronic Resource
    Interparticle forces and lift on a particle attached to a solid boundary in suspension flow (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 49-60 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lattice Boltzmann method is used to simulate the shear flow field around a stationary particle attached to a solid boundary. One or more freely flowing (suspended) particles are introduced in the flow and are allowed to move, subject to the gravity force and the induced hydrodynamic force. Periodic conditions on the side boundaries assure that the same number of particles always remains in the computational domain. The total force exerted on the stationary particle is computed during the whole simulation process and resolved as the drag and lift components. By comparing these components of the hydrodynamic force before and after the freely flowing particles are introduced in the flow field, we determine the effect of suspended particles on a stationary particle. The results show that, even in the absence of particle collisions, the hydrodynamic force developed on the stationary particle is significant enough to induce the resuspension process if this particle were free to move. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1426389
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  • 7
    Electronic Resource
    Electronic Resource
    Phenomenological model for dispersed bubbly flow in pipes (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 12-22 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An analytical approach to the problem of steady-state, axisymmetrically disperesed, bubbly flow in pipes based on a zero equation turbulence model is discussed. The formulation incorporates recent experimental observations and introduces the effect of bubble size in a rudimentary way. The two-phase mixture is modeled as a variabledensity single fluid assuming an empirical void distribution family. The turbulent shear stress is formed from the contributions of both the velocity and density variation, and the solution of the resulting Reynolds-type equation yields the velocity profile of the flow. Predicted void fraction and velocity distributions agree well with experimental measurements. The main objective of the model is to predict the friction multiplier with minimal computational effort. The velocity profiles of this model agree reasonably well with experiments. Predictions for the friction multiplier are compared to six known and widely used correlations, as well as to experimental data. All the correlations severely underpredict the friction multiplier in the disperesed bubbly flow regime, while the results of our model agree well with the measurements, within the range of its validity.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410103
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  • 8
    Electronic Resource
    Electronic Resource
    Unsteady heat and mass transfer from a spheroid (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 609-614 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The unsteady heat-transfer processes from oblate or prolate spheroids, at the limit of very small Peclet numbers is examined. A perturbation technique for the temperature and the geometry of the particle is used to obtain the rates of heat and mass transfer, first in the Laplace and then in the time domain. A solution to the problem is obtained, including the ∊2 contribution (∊ is the eccentricity). The solution reveals the existence of several history terms, which are analogous to the history terms of the creeping flow equation of motion. One of these terms is solely due to the eccentricity of the spheroid. This is an indication that the shape of the particle is a factor of the existence and from of history terms. In addition, an exact expression for the steady-state heat transfer from a spheroid is obtained using a convenient transformation of the heat-transfer integral.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430306
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  • 9
    Electronic Resource
    Electronic Resource
    A numerical study of heat and momentum transfer for tube bundles in crossflow (1989)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 9 (1989), S. 1381-1394 
    Details
    ISSN: 0271-2091
    Keywords: Heat exchangers ; Crossflow ; Tube bundle ; Nusselt number ; Streamfunction/vorticity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical scheme is developed to predict the heat transfer and pressure drop coefficients in flow through rigid tube bundles. The scheme uses the Galerkin finite element technique. The conservation equations for laminar steady-state flow are cast in the form of streamfunction and vorticity equations. A Picard iteration method is used for the solution of the resulting system of non-linear algebraic equations. Results for the heat transfer and pressure drop coefficients are obtained for tube arrays of pitch ratios of 1·5 and 2·0. Very good agreement of the present results and experimental data obtained in the past is observed up to Reynolds numbers of 1000. It is also observed that the results of the present method show better agreement with the experimental data and that they are applicable for higher Reynolds numbers than results of other studies.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650091107
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  • 10
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    Inclusion of heat transfer computations for particle laden flows (2008)
    American Institute of Physics
    Details
    Publication Date: 2008-04-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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