Natural Convection in Vertical Channels with Porous Media and Adiabatic Extensions

2010 ◽  
Vol 297-301 ◽  
pp. 1432-1438
Author(s):  
Assunta Andreozzi ◽  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Natural Convection ◽  
Wall Temperature ◽  
Finite Extension ◽  
Darcy Number ◽  
Geometrical Parameters ◽  
Computational Domain ◽  
Stream Condition ◽  
Diffusive Effects ◽  
Volume Method ◽  
Heated Plates

A numerical investigation on natural convection in air in a vertical heated channel, partially filled with porous medium, with adiabatic extensions downward and collinear the heated plates is accomplished. The fluid flow is assumed two-dimensional, laminar, steady state and incompressible. The porous material is considered as homogeneous and isotropic and the Brinkman-Forchheimer-extended Darcy model is considered. A finite-extension computational domain is employed to simulate the free-stream condition and allows to account for the diffusive effects and the numerical results are obtained using the finite volume method by FLUENT. Results in terms of wall temperature profiles are presented to evaluate the effects of the main thermal and geometrical parameters. The adiabatic extensions determine a wall temperature decrease and wall temperature decreases increasing Darcy number. In full filled heated channels wall temperature presents a significant increase for Darcy number decrease.

scholarly journals Natural Convection over Two Superellipse Shapes with a Porous Cavity Populated by Nanofluid

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6952
Author(s):  
Noura Alsedais
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Darcy Number ◽  
Governing Equations ◽  
Porous Layers ◽  
Porous Cavity ◽  
The Mean ◽  
Volume Method

The influences of superellipse shapes on natural convection in a horizontally subdivided non-Darcy porous cavity populated by Cu-water nanofluid are inspected in this paper. The impacts of the inner geometries (n = 0.5,1,1.5,4) Rayleigh number (103 ≤ Ra ≤ 106), Darcy number (10−5 ≤ Da ≤ 10−2), porosity (0.2 ≤ ϵ ≤ 0.8), and solid volume fraction (0.01 ≤ ∅ ≤ 0.05) on nanofluid heat transport and streamlines were examined. The hot superellipse shapes were placed in the cavity’s bottom and top, while the adiabatic boundaries on the flat walls of the cavity were considered. The governing equations were numerically solved using the finite volume method (FVM). It was found that the movement of the nanofluid upsurged as Ra boosted. The temperature distributions in the cavity’s core had an inverse relationship with increasing Rayleigh number. An extra porous resistance at lower Darcy numbers limited the nanofluid’s movement within the porous layers. The mean Nusselt number decreased as the porous resistance increased (Da ≤ 10−4). The flow and temperature were strongly affected as the shape of the inner superellipse grew larger.

Natural Convection in a Vertical Cavity Partially Filled With Porous Medium: Effect of Aspect Ratio, Darcy and Fluid Rayleigh Numbers

Volume 1 ◽  
2004 ◽  
Author(s):  
Sushant Anand ◽  
R. C. Arora
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Saturated Porous Medium ◽  
Darcy Number ◽  
Medium Effect ◽  
Staggered Grid ◽  
Medium Increase ◽  
Diffusive Fluxes ◽  
Volume Method

Numerical investigation of natural convection in a rectangular cavity partially filled with fluid-saturated porous medium has been carried out. Rayleigh number (104 to 107) and Darcy Number (10−1 to 10−10), Aspect Ratio (0.75, 1.0, and 1.25) are considered parameters. The governing equations have been solved numerically by SIMPLEC, a finite volume method on staggered grid arrangement. Power-law scheme has been used to approximate convective and diffusive fluxes. The results obtained are presented for the streamlines, isotherms and variation of Nusselt number at the walls. For values of Darcy Number above 10−4, a convective regime has been found to exist in which flow is nearly independent of Darcy Number, while at low values (below 10−6) the conduction dominated region occurs in the porous medium. Increase in Aspect Ratio increases intensity of circulation while maintaining the symmetry with respect to diagonals. Increase in aspect ratio increases the region of uniform temperature which covers most of the porous region.

Effect of Wall Conduction on Natural Convection in Symmetrically Heated Vertical Parallel Plates With Discrete Heat Sources

2002 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Vincenzo Naso
Keyword(s):  
Heat Conduction ◽  
Natural Convection ◽  
Wall Temperature ◽  
Channel Wall ◽  
Stokes Equations ◽  
Vertical Channel ◽  
Navier Stokes ◽  
Temperature Profiles ◽  
Computational Domain ◽  
Parallel Plates

The effect of heat conduction on air natural convection in a vertical channel, symmetrically heated, with flush-mounted strips at the walls, was numerically analyzed. Reference was made to laminar two-dimensional steady-state flow and to full elliptic Navier-Stokes equations on a I-shaped computational domain. Solutions were carried out by means of the FLUENT code. Results are presented in terms of wall temperature profiles, air velocity and temperature profiles in the channel. The wall temperature is affected by the location of the strip on the channel wall and maximum wall temperature is far larger when the heater is located in the upper region of the channel. Heat conduction in the channel wall lowers maximum wall temperature below the heater and the thicker the wall the larger the temperature reduction.

Turbulent Natural Convection in Horizontal Composite Cavities

2003 ◽  
Author(s):  
Edimilson J. Braga ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Natural Convection ◽  
Computational Domain ◽  
Turbulent Model ◽  
Governing Equations ◽  
Square Cavity ◽  
Thermal Systems ◽  
Turbulent Natural Convection ◽  
Solid Region ◽  
Treat All ◽  
Volume Method

Turbulent natural convection in a two-dimensional horizontal composite square cavity, isothermally heated at the left side and cooled from the opposing surface, is numerically analyzed using the finite volume method. The composite square cavity is formed by three distinct regions, namely, clear, porous and solid region. Accordingly, the development of a numerical tool able to treat all these regions as one computational domain is of advantage for engineering design of thermal systems. Governing equations are written in terms of primitive variables and are recast into a general form. It was found that the fluid begins to permeate the porous medium for values of Ra greater than 106. Nusselt number values show that for the range of Ra analyzed there are no significant variation between the laminar and turbulent model solution..

Transient Natural Convection in Convergent Vertical Channels With Porous Media

2008 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Porous Medium ◽  
Nusselt Number ◽  
Steady State ◽  
Natural Convection ◽  
Wall Temperature ◽  
Initial Time ◽  
Computational Domain ◽  
Parallel Plates ◽  
Convergent Channel ◽  
Transient Natural Convection

In this paper transient natural convection in a vertical convergent channel with or without saturated porous medium is studied numerically. The investigation is carried out in laminar, two dimensional regime and employing the Brinkman-Forchheimer-extended Darcy model. The physical domain consists of two non-parallel plates which form a convergent channel. Both plates are heated at uniform heat flux. The solutions are achieved using the commercial code FLUENT. A finite-extension computational domain is employed to simulate the free-stream condition. The results are obtained for different convergence angles, for 0° to 5°, and porosity coefficient (0.4, 0.6 and 0.9), a channel aspect ratio equal to 10, a Rayleigh number equal to 104 and a Darcy number equal to 0.01. The dimensionless results are reported in terms of average and maximum wall temperatures, average Nusselt number as a function of time and at steady state wall temperature, local Nusselt number and temperature and stream function fields. The cases with porous medium in the channel shows that in conductive regime dominant, at initial time, average and maximum wall temperatures are lower than the case without porous medium in the channel. For the convective regime dominant, the lowest average and maximum wall temperatures are attained for the case without porour medium in the channel. At steady state, in the inlet zone the cases with porous medium present wall temperature lower than the no porous case. In the other part of the channel the opposite behaviour is detected.

Numerical Investigation of Developing Natural Convection in Vertical Double-Passage Porous Annuli

2018 ◽  
Vol 387 ◽  
pp. 442-460 ◽  
Author(s):  
Girish N. ◽  
Oluwole Daniel Makinde ◽  
M. Sankar
Keyword(s):  
Natural Convection ◽  
Thermal Conditions ◽  
Darcy Number ◽  
Geometrical Parameters ◽  
Cylindrical Wall ◽  
Boundary Layer Equations ◽  
Thermal Fields ◽  
Concentric Cylinders ◽  
Laminar Natural Convection ◽  
Implicit Finite Difference

The present study deals with the numerically investigation of developing laminar natural convection in the vertical double-passage porous annuli formed by three vertical concentric cylinders of which the middle cylinder is a thin and perfectly conductive known as baffle. In this analysis, two thermal conditions are considered namely, either inner or outer cylindrical wall is constantly heated while the opposite wall is insulated. An implicit finite difference technique is employed to solve the boundary layer equations in both the annular passages. The temperature profiles and velocity profiles in axial as well as radial directions have been presented for different values of Grashof number, Darcy number, baffle position and radius ratio. The results reveal that both physical and geometrical parameters have profound influence on the development of velocity and thermal fields as well as heat transfer rate.

scholarly journals Natural Convection in Inclined Porous Square Enclosure

2020 ◽  
Vol 330 ◽  
pp. 01003
Author(s):  
Abdennacer Belazizia ◽  
Smail Benissaad ◽  
Said Abboudi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Inclination Angle ◽  
Fluid Motion ◽  
Darcy Number ◽  
Convection Flow ◽  
Transfer Rates ◽  
Square Enclosure ◽  
Volume Method

Steady, laminar, natural convection flow in porous square enclosure with inclination angle is considered. The enclosure is filled with air and subjected to horizontal temperature gradient. Darcy- Brinkman-Forchheimer model is considered. Finite volume method is used to solve the dimensionless governing equations. The physical problem depends on five parameters: Rayleigh number (Ra =103-106), Prandtl number (Pr=0.71), Darcy number (Da=0.01), inclination angle φ=(0°-227°), porosity of the medium (ε=0.7) and the aspect ratio of the enclosure (A=1). The main focus of the study is on examining the effect of Rayleigh number on fluid flow and heat transfer rates. The effect of inclination angle is also considered. The results including streamlines, isotherm patterns, flow velocity and the average Nusselt number for different values of Ra and φ. The obtained results show that the increase of Ra leads to enhance heat transfer rate. The fluid particles move with greater velocity for higher thermal Rayleigh number. Also φ affects the fluid motion and heat transfer in the enclosure. Velocity and heat transfer are more important when φ takes the value (30°).

Natural Convection and Conduction in Porous Wall, Solar Collector Systems Without Vents

1992 ◽  
Vol 114 (1) ◽  
pp. 40-46 ◽  
Author(s):  
M. Mbaye ◽  
E. Bilgen
Keyword(s):  
Natural Convection ◽  
System Performance ◽  
Solar Collector ◽  
Convection Heat Transfer ◽  
Porous Wall ◽  
Darcy Number ◽  
Geometrical Parameters ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Different Temperatures

Steady natural convection heat transfer has been studied in porous wall, solar collector systems. The boundary conditions were: two isothermal walls at different temperatures, two horizontal bounding adiabatic walls, and either uniform or nonuniform heat generating porous layer without vents. The aspect ratio A was from 0.5 to 1.4. The Rayleigh number varied from 103 to 108. The Darcy number was from 10−8 to 10−2 but the detailed studies were carried out only for 10−4, an optimum value. The results are presented in terms of thermal parameters (θ, θmax, Nu) as a function of Ra and other nondimensional parameters (A=H/L, B=1/L, F=d/L, kr). The isotherms and streamlines within the system are also produced. The overall results indicate that geometrical parameters are the most important parameters affecting the system performance.

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