Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
6
3
2003
Temperature-Dependent Viscosity Effects on the Thermohydraulics of Heated Porous-Medium Channel Flows
Using numerical simulation results, the evolution of the Modified Hazen-Dupuit-Darcy (M-HDD) model, which incorporates temperature-dependent viscosity effects in the prediction of global pressure drop across a heated porous medium channel, is discussed. New flow regimes that owe their existence entirely to variable viscosity effects (thereby explained only by the M-HDD model) are exposited. Temperature-dependent viscosity effects on the departure from Darcy flow to nonlinear (form-drag dominant) flow regime is analyzed in detail. The transition, from linear Darcy flow of a fluid with viscosity decreasing with temperature, is shown to happen at an earlier global velocity than for the constant-viscosity counterpart. Finally, experimental appraisals that support the validity of the M-HDD model are also discussed.
Arunn
Narasimhan
Indian Institute of Technology Madras
Jose
Lage
Southern Methodist University
10
Natural Convection in Domed Porous Enclosures: Non-Darcian Flow
The natural-convection flow and associated heat transfer in a fluid-saturated porous medium have been investigated using the generalized porous medium approach for a dome-shaped enclosure. Many new features have been predicted with the connective heat transfer and the shape of the top dome cover. The solutions are obtained for a wide range of Darcy and Rayleigh numbers for different offsets and eccentricities of the top dome covers. The detailed parametric study reveals that there is a significant change in heat transfer rate when the offset is between 0.2 and 0.4. Different shapes of conic section, such as circular, elliptical, parabolic, and hyperbolic are used for the top dome cover, and their effects on natural convection and heat transfer rates are studied.
Subrat
Das
Modeling and Process Simulation Research Group, Industrial Research Institute Swinburne, Swinburne University of Technology Hawthorn,
Yos
Morsi
Modeling and Process Simulation Research Group, Industrial Research Institute Swinburne, Swinburne University of Technology
17
On Stationary and Oscillatory Modes of Flow Instability in a Rotating Porous Layer during Alloy Solidification
Linear flow instability due to either stationary (nonoscillatory) or oscillatory modes of disturbances in a horizontal porous layer during alloy solidification is investigated under an external constraint of rotation. The porous layer, which is referred to as a mushy layer in the solidification literature, is assumed to rotate about the vertical axis at a constant angular velocity. The investigation is based on the model of Amberg and Homsy (1993) and under the limit of large Stefan number as treated by Anderson and Worster {1996) in the absence of the rotational constraint. An oscillatory mode was found for the first time to dominate over the stationary mode and over several other detected oscillatory modes at the onset of motion. In contrast to the stationary mode, the most critical oscillatory mode was uncovered to reduce the tendency for chimney formation in the rotating porous layer. In engineering applications, presence of these chimneys is undesirable since their presence can produce imperfections that reduce the quality of the solidified material. Results of the stability analyses indicate both stabilizing and destabilizing effects of the Coriolis force on the flow in the porous layer. For example, the effects of the Coriolis force can be stabilizing in the sense that the critical value of the Rayleigh number at the onset of motion increases with the rotation rate, while the effects of the Coriolis force can be destabilizing in the sense that the oscillatory instability is enhanced in the presence of rotation.
Daniel N.
Riahi
School of Mathematical and Statistical Sciences,
One West University Boulevard, University of Texas Rio Grande Valley, Brownsville, Texas 78520 USA
11
Nonlinear Peristaltic Transport through a Porous Medium in an Inclined Planar Channel
In order to determine the characteristics of the peristaltic transport of the gravity flow through a porous medium, the motion of an incompressible, viscous fluid in an inclined planar channel filled with a homogenous porous medium and having walls that are transversely displaced by an infinite, harmonic traveling wave of large wavelength was analyzed using a perturbation expansion in terms of a variant wave number. We obtain an explicit form for the velocity field and a relation between the pressure rise and flow rate in terms of Reynolds number, wave number, permeability parameter, inclined angle, and the occlusion. The effects of the various parameters entering into the problem are discussed numerically and with the help of graphs.
Kh. S.
Mekheimer
Department of Mathematics, Faculty of Science Al-Azhar University, Nasr City 11884, Cairo, Egypt
13
Thermally Developing Forced Convection in a Porous Medium: Parallel-Plate Channel or Circular Tube with Walls at Constant Heat Flux
An adaptation of the classical Graetz methodology is applied to investigate the thermal development of forced convection in a parallel-plate channel or a circular tube filled by a saturated porous medium, with walls held at constant heat flux. The Brinkman model is employed. The analysis leads to expressions for the local Nusselt number and average Nusselt number, as functions of the dimensionless longitudinal coordinate and the Darcy number.
Ming
Xiong
Department of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Rayleigh, North Carolina 27695-7910, USA
10
Effects of Temperature-Dependent Viscosity in Forced Convection in a Porous Medium: Layered-Medium Analysis
The effects of variation of the viscosity with temperature, on quasi-fully developed forced convection in a parallel-plate channel with a saturated porous medium, is investigated analytically on the basis of a Darcy or Hazen-Dupuit-Darcy model, for the case of isoflux boundaries, using a three-layer approximation. For the case of a fluid whose viscosity decreases with temperature, it is found that the effect of the variation is to reduce/increase the Nusselt number for cooled/heated walls. For the case of small Darcy number the effect of viscosity variation is almost independent of the Forchheimer number, while for the case of large Darcy number the effect of viscosity variation is reduced as the Forchheimer number increases.
10