The Onset of Convection in a Porous Medium Occupying an Enclosure of Variable Width or Height

2007 ◽  
Vol 129 (12) ◽  
pp. 1714-1718 ◽  
Author(s):  
D. A. Nield ◽  
A. V. Kuznetsov
Keyword(s):  
Porous Medium ◽  
Analytical Study ◽  
Saturated Porous Medium ◽  
Two Dimensional ◽  
Onset Of Convection ◽  
Stabilizing Effect

An analytical study is made of the onset of convection in a saturated porous medium occupying a two-dimensional enclosure of uniform height, but whose width is slowly varying in an arbitrary manner, or one of uniform width, but whose height is slowly varying in an arbitrary manner. It is found that the variation of width generally has a stabilizing effect, whereas variation of height generally has a destabilizing effect.

scholarly journals Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

2016 ◽  
Vol 21 (4) ◽  
pp. 785-803 ◽  
Author(s):  
B.S. Bhadauria ◽  
M.K. Singh ◽  
A. Singh ◽  
B.K. Singh ◽  
P. Kiran
Keyword(s):  
Porous Medium ◽  
Stability Analysis ◽  
Viscoelastic Fluid ◽  
Saturated Porous Medium ◽  
Landau Equation ◽  
Power Series Expansion ◽  
Gravity Modulation ◽  
Internal Heating ◽  
Onset Of Convection ◽  
Fluid Saturated Porous Medium

Abstract In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Thermal Convective Instabilities in a Porous Medium

1984 ◽  
Vol 106 (1) ◽  
pp. 137-142 ◽  
Author(s):  
M. Kaviany
Keyword(s):  
Porous Medium ◽  
Steady State ◽  
Temperature Distribution ◽  
Rayleigh Number ◽  
Saturated Porous Medium ◽  
Critical Rayleigh Number ◽  
Linear Stability Theory ◽  
Onset Of Convection ◽  
Long Time ◽  
Nonlinear Temperature

The onset of convection due to a nonlinear and time-dependent temperature stratification in a saturated porous medium with upper and lower free surfaces is considered. The initial parabolic temperature distribution is due to uniform internal heating. The medium is then cooled by decreasing the upper surface temperature linearly with time. Linear stability theory is applied to the more formally developed governing equations. In order to obtain an asymptotic solution for transient problems involving very long time scales, the critical Rayleigh number for steady-state, nonlinear temperature distribution is also obtained. The effects of porosity, permeability, and Prandtl number on the time of the onset of convection are examined. The steady-state results show that the critical Rayleigh number depends only on the ratio of porosity to permeability and when this ratio exceeds a value of one thousand, the critical Rayleigh number is directly proportional to this ratio.

Combined Effect of Temperature Modulation and Magnetic Field on the Onset of Convection in an Electrically Conducting-Fluid-Saturated Porous Medium

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
B. S. Bhadauria
Keyword(s):  
Magnetic Field ◽  
Porous Medium ◽  
Saturated Porous Medium ◽  
Effect Of Temperature ◽  
Temperature Modulation ◽  
Vertical Magnetic Field ◽  
Onset Of Convection ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
Fluid Saturated Porous Medium

The effect of temperature modulation on the onset of thermal convection in an electrically conducting fluid-saturated-porous medium, heated from below, has been studied using linear stability analysis. The amplitudes of temperature modulation at the lower and upper surfaces are considered to be very small. The porous medium is confined between two horizontal walls and subjected to a vertical magnetic field; flow in porous medium is characterized by Brinkman–Darcy model. Considering only infinitesimal disturbances, and using perturbation procedure, the combined effect of temperature modulation and vertical magnetic field on thermal instability has been studied. The correction in the critical Rayleigh number is calculated as a function of frequency of modulation, Darcy number, Darcy Chandrasekhar number, magnetic Prandtl number, and the nondimensional group number χ. The influence of the magnetic field is found to be stabilizing. Furthermore, it is also found that the onset of convection can be advanced or delayed by proper tuning of the frequency of modulation. The results of the present model have been compared with that of Darcy model.

The Modeling of Viscous Dissipation in a Saturated Porous Medium

2007 ◽  
Vol 129 (10) ◽  
pp. 1459-1463 ◽  
Author(s):  
D. A. Nield
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Forced Convection ◽  
Viscous Dissipation ◽  
Critical Review ◽  
Saturated Porous Medium ◽  
Dissipation Function ◽  
Two Dimensional ◽  
Bottom Heating ◽  
Work Done

A critical review is made of recent studies of the modeling of viscous dissipation in a saturated porous medium, with applications to either forced convection or natural convection. Alternative forms of the viscous dissipation function are discussed. Limitations to the concept of fully developed convection are noted. Special attention is focused on the roles of viscous dissipation and work done by pressure forces (flow work) in natural convection in a two-dimensional box with either lateral or bottom heating.

scholarly journals Natural convection and the evolution of a reactive porous medium

2011 ◽  
Vol 673 ◽  
pp. 286-317 ◽  
Author(s):  
LINDSEY T. RITCHIE ◽  
DAVID PRITCHARD
Keyword(s):  
Porous Medium ◽  
Time Scales ◽  
Saturated Porous Medium ◽  
Diffusion Mechanism ◽  
Reaction Diffusion ◽  
Onset Of Convection ◽  
Convective Circulation ◽  
Long Time ◽  
Porosity And Permeability ◽  
Rayleigh Numbers

We describe a mathematical model of buoyancy-driven flow and solute transport in a saturated porous medium, the porosity and permeability of which evolve through precipitation and dissolution as a mineral is lost or gained from the pore fluid. Imposing a vertically varying equilibrium solubility creates a density gradient which can drive convective circulation. We characterise the onset of convection using linear stability analysis, and explore the further development of the coupled reaction–convection system numerically. At low Rayleigh numbers, the effect of the reaction–permeability feedback is shown to be destabilising through a novel reaction–diffusion mechanism; at higher Rayleigh numbers, the precipitation and dissolution have a stabilising effect. Over longer time scales, reaction–permeability feedback triggers secondary instabilities in quasi-steady convective circulation, leading to rapid reversals in the direction of circulation. Over very long time scales, characteristic patterns of porosity emerge, including horizontal layering as well as the development of vertical chimneys of enhanced porosity. We discuss the implications of these findings for more comprehensive models of reactive convection in porous media.

scholarly journals Penetrative convection due to absorption of radiation in a magnetic nanofluid saturated porous layer

2019 ◽  
Vol 41 (3) ◽  
pp. 129-142
Author(s):  
Amit Mahajan ◽  
Mahesh Kumar Sharma
Keyword(s):  
Porous Medium ◽  
Saturated Porous Medium ◽  
Pseudospectral Method ◽  
Lewis Number ◽  
Selective Absorption ◽  
Penetrative Convection ◽  
Onset Of Convection ◽  
Magnetic Nanofluid ◽  
Chebyshev Pseudospectral Method ◽  
Diffusivity Ratio

AbstractThe present study investigates the onset of penetrative convection in- duced by selective absorption of radiation in a magnetic nanofluid saturated porous medium. The influence of Brownian motion, thermophoresis, and magnetophoresis on magnetic nanofluid treatment is taken into consideration. The Darcy’s model is selected for the porous medium. We conduct a linear stability analysis to examine the onset of instability and evaluate the results for two different configurations, namely, when the layer is heated from below and when the layer is heated from above. The numerical investigations are carried out by applying the Chebyshev pseudospectral method. The effect of the porosity parameter E, parameter Y (represents the ratio of internal heating to boundary heating), Lewis number Le, concentration Rayleigh number Rn, Langevin parameter αL, width of nanofluid layer d, diffusivity ratio η, and modified diffusivity ratio NA is examined at the onset of convection. The results indicate that the convection commences easily with an increase in the value of Y, Le, and NA but opposite in the case with a decrease in the value of E, αL, η and d for both the two configurations. The parameter Rn advances the onset of convection when the layer is heated from below, while delays the onset of convection when the layer is heated from above.

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