Natural Convection in a Horizontal Cavity Partially Occupied by a Porous Media Saturated by a Coolant Liquid

2006 ◽  
Author(s):  
Fakhreddine S. Oueslati ◽  
Rachid Bennacer ◽  
Habib Sammouda ◽  
Ali Belghith
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Natural Convection ◽  
Flow Structure ◽  
Boussinesq Approximation ◽  
Density Variation ◽  
Heat Fluxes ◽  
Complex Flow ◽  
Coupled Equations ◽  
Complex Flow Structure

The natural convection is studied in a cavity witch the lower half is filled with a porous media that is saturated with a first fluid (liquid), and the upper is filled with a second fluid (gas). The horizontal borders are heated and cooled by uniform heat fluxes and vertical ones are adiabatic. The formulation of the problem is based on the Darcy-Brinkman model. The density variation is taken into account by the Boussinesq approximation. The system of the coupled equations is resolved by the classic finite volume method. The numerical results show that the variation of the conductivity of the porous media influences strongly the flow structure and the heat transfer as well as in upper that in the lower zones. The effect of conductivity is conditioned by the porosity which plays a very significant roll on the heat transfer. The structures of this flow show that this kind of problem with specific boundary conditions generates a complex flow structure of several contra-rotating two to two cells, in the upper half of the cavity.

Measurements of Flow Modification by Particle Deposition Inside a Packed Bed Using Time-Resolved PIV

2008 ◽  
Author(s):  
Elvis E. Dominguez-Ontiveros ◽  
Carlos Estrada-Perez ◽  
Yassin A. Hassan
Keyword(s):  
Heat Transfer ◽  
Velocity Field ◽  
Flow Structure ◽  
Particle Deposition ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Temperature Fields ◽  
Complex Flow ◽  
Flow Modification ◽  
Complex Flow Structure

In the Advanced Gas Cooled Pebble Bed Reactors for nuclear power generation, the fuel is spherical coated particles. The energy transfer phenomenon requires detailed understanding of the flow and temperature fields around the spherical fuel pebbles. Detailed information of the complex flow structure within the bed is needed. Generally, for computing the flow through a packed bed reactor or column, the porous media approach is usually used with lumped parameters for hydrodynamic calculations and heat transfer. While this approach can be reasonable for calculating integral flow quantities, it may not provide all the detailed information of the heat transfer and complex flow structure within the bed. The present experimental study presents the full velocity field using particle image velocity technique (PTV) in a conjunction with matched refractive index fluid with the pebbles to achieve optical access. Velocity field measurements are presented delineating the complex flow structure.

scholarly journals Iterative Numerical Scheme for Non-Isothermal Two-Phase Flow in Heterogeneous Porous Media

Algorithms ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 117
Author(s):  
Mohamed F. El-Amin
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Energy Equation ◽  
Body Force ◽  
Two Phase Flow ◽  
Boussinesq Approximation ◽  
Heterogeneous Porous Media ◽  
Phase Flow ◽  
Two Phase ◽  
Coupled Equations

In the current paper, an iterative algorithm is developed to simulate the problem of two-phase flow with heat transfer in porous media. The convective body force caused by heat transfer is described by Boussinesq approximation throughout with the governing equations, namely, pressure, saturation, and energy. The two coupled equations of pressure and saturation are solved using the implicit pressure-explicit saturation (IMPES) scheme, while the energy equation is treated implicitly, and the scheme is called iterative implicit pressure, explicit saturation, implicit temperature (I-IMPES-IMT). In order to calculate the pressure implicitly, the equations of pressure and saturation are coupled by linearizing the capillary pressure which is a function of saturation. After that, the equation of saturation is solved explicitly. Then, the velocity is computed which is used in the energy equation to calculate the temperature implicitly. The cell-centered finite difference (CCFD) method is utilized for spatial discretization. Furthermore, a relaxation factor along is used with the Courant–Friedrichs–Lewy (CFL) condition. Finally, in order to illustrate the efficiency of the developed algorithm, error estimates for saturation and temperature for different values of time steps and number of iterations are presented. Moreover, numerical examples of different physical scenarios of heterogamous media are presented.

scholarly journals Flow Structure and Heat Transfer Enhancement in Laminar Flow With Protrusion-Dimple Combinations in a Shallow Rectangular Channel

2009 ◽  
Author(s):  
O. Alshroof ◽  
J. Reizes ◽  
V. Timchenko ◽  
E. Leonardi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Complex Flow ◽  
Wide Face ◽  
Thermal Fields ◽  
Heat Transfer Augmentation ◽  
Smooth Channel ◽  
Complex Flow Structure

The effect of introducing combinations of spherical dimples and protrusions in a shallow rectangular channel on the flow and heat transfer in the laminar regime has been studied numerically. Four different cases were investigated. These consisted of: an isolated dimple, an isolated protrusion both placed on the centerline of one of the wide face of the channel, a combination of a dimple located on the centerline of the wide face of the channel and a protrusion located downstream but shifted to the side, and finally, a combination in which the protrusion and the dimple are reversed. The resultant, very complex flow structure and thermal fields in the channel are presented. The introduction of a single dimple results in a small enhancement of heat transfer and a very small reduction in pressure drop relative to those obtained in a smooth channel. However, a significant enhancement in heat transfer obtained from a single protrusion is associated with marginal increase in pressure drop. The addition of a protrusion downstream of the dimple leads to an increase of 30% in heat transfer augmentation above that which pertains for the isolated protrusion without any increase in the pressure drop. With the reversal of the positions of the protrusion and the dimple no effect on either the pressure drop or the heat transfer has been observed.

Experimental and Computational Analysis of Natural Convection Over Flat Plate

2008 ◽  
Author(s):  
Farhana Afroz ◽  
Chowdhury Md. Feroz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flat Plate ◽  
Convection Heat Transfer ◽  
Boussinesq Approximation ◽  
Heat Fluxes ◽  
Navier Stokes ◽  
Heated Plate ◽  
Wide Range ◽  
Energy Equations

Natural convection heat transfer over a flat plate with a heat source at bottom side of plate is studied experimentally and numerically. We consider the two-dimensional problem of both steady and unsteady natural convection over the flat plate at vertical, horizontal and inclined position. Experimental analysis is done for three different constant heat fluxes for each angle position. The Navier-Stokes and Energy equations with the Boussinesq approximation are written in Cartesian coordinate system. The problem is solved in the physical variables on the basis of a completely implicit Finite element Method order to examine the heat transfer characteristics. To see the effects of different angle position phenomena of natural convection over flat plate, the computational results presented in the form of streamlines for a wide range of Grashof number at different heat fluxes. The average Nusselt number of heated plate for different angle position has been observed.

Natural Convection in Cylindrical Configuration: Effect of the Obstacle on the Unsteadiness

2002 ◽  
Author(s):  
K. Choukairy ◽  
R. Bennacer ◽  
P. D. Matthey ◽  
R. Duval
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Molecular Diffusion ◽  
Control Volume ◽  
Boussinesq Approximation ◽  
Density Variation ◽  
Necessary Condition ◽  
Thermal Transfer ◽  
The One ◽  
Control Volume Approach

The heat transfer by natural convection are frequently used in the various processes and are also met in various situation in nature. In order to improve these kind of heat transfer, it’s possible to disturb the flow of origin by an obstacle along the way of the principal flow. This obstacle modifies on the one hand the structure of the flow and affects the local transfers. On the other hand, it allows the transition towards and obtaining a macroscopic contribution (eddy) in complement of the microscopic transfer (molecular diffusion). The effect of an obstacle on the thermal transfer, was previously studied and we purpose to complete such studies in transitional domain. The obtained non-stationary natural convection is analysed. A study is carried out by considering the transient resolution (DNS) of such problem in two-dimensional configuration. The density variation is taken into account by the boussinesq approximation. The control-volume approach is used for solving the governing equation. The temporal variation of Nusselt and energy is given with and without obstacle. We illustrate the necessary condition in order to improve the transfer in such configuration. The effect of height and width of the inserted body is systematically analysed.

Computational and Experimental Study of Enhanced Laminar Flow Heat Transfer in Three-Dimensional Sinusoidal Wavy-Plate-Fin Channels

2003 ◽  
Author(s):  
Jiehai Zhang ◽  
Arun Muley ◽  
Joseph B. Borghese ◽  
Raj M. Manglik
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Computational Simulation ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Staggered Grid ◽  
Uniform Heat Flux ◽  
Complex Flow ◽  
Constant Property ◽  
Fin Efficiency

Enhanced heat transfer characteristics of low Reynolds number airflows in three-dimensional sinusoidal wavy plate-fin channels are investigated. For the computational simulation, steady state, constant property, periodically developed, laminar forced convection is considered with the channel surface at the uniform heat flux condition; the wavy-fin is modeled by its two asymptotic limits of 100% and zero fin efficiency. The governing equations are solved numerically using finite-volume techniques for a non-orthogonal, non-staggered grid. Computational results for velocity and temperature distribution, isothermal Fanning friction factor f and Colburn factor j are presented for airflow rates in the range of 10 ≤ Re ≤ 1500. The numerical results are further compared with experimental data, with excellent agreement, for two different wavy-fin geometries. The influence of fin density on the flow behavior and the enhanced convection heat transfer are highlighted. Depending on the flow rate, a complex flow structure is observed, which is characterized by the generation, spatial growth and dissipation of vortices in the trough region of the wavy channel. The thermal boundary layers on the fin surface are periodically disrupted, resulting in high local heat fluxes. The overall heat transfer performance is improved considerably, compared to the straight channel with the same cross-section, with a relatively smaller increase in the associated pressure drop penalty.

Effects of Insulated and Isothermal Baffles on Pseudosteady-State Natural Convection Inside Spherical Containers

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Yuping Duan ◽  
S. F. Hosseinizadeh ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Numerical Procedure ◽  
Boussinesq Approximation ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Extended Surface ◽  
Parametric Studies ◽  
Thermal Layer

The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For high Ra number cases, the hot fluid at the bottom of the sphere is also observed to rise along the symmetry axis and encounter the sinking colder fluid, thus causing oscillations in the temperature and flow fields. Due to flow obstruction (blockage or confinement) effect of baffles and also because of the extra heating afforded by the isothermal baffle, multi-cell recirculating vortices are observed. This additional heat is directly linked to creation of another recirculating vortex next to the baffle. In effect, hot fluid is directed into the center of the sphere disrupting thermal stratified layers. For the majority of the baffles investigated, the Nusselt numbers were generally lower than the reference cases with no baffle. The extent of heat transfer modification depends on Ra, length, and location of the extended surface. With an insulated baffle, the lowest amount of absorbed heat corresponds to a baffle positioned horizontally. Placing a baffle near the top of the sphere for high Ra number cases can lead to heat transfer enhancement that is linked to disturbance of the thermal boundary layer. With isothermal baffles, heat transfer enhancement is achieved for a baffle placed near the bottom of the sphere due to interaction of the counterclockwise rotating vortex and the stratified layer. For some high Ra cases, strong fluctuations of the flow and thermal fields indicating departure from the pseudosteady-state were observed.

Fluid Flow Structure in Arterial Bypass Anastomosis

2005 ◽  
Vol 127 (4) ◽  
pp. 611-618 ◽  
Author(s):  
C. M. Su ◽  
D. Lee ◽  
R. Tran-Son-Tay ◽  
W. Shyy
Keyword(s):  
Fluid Flow ◽  
Flow Structure ◽  
Bypass Graft ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Arterial Bypass ◽  
Flow Recirculation ◽  
Area Reduction ◽  
Complex Flow Structure

The fluid flow through a stenosed artery and its bypass graft in an anastomosis can substantially influence the outcome of bypass surgery. To help improve our understanding of this and related issues, the steady Navier-Stokes flows are computed in an idealized arterial bypass system with partially occluded host artery. Both the residual flow issued from the stenosis—which is potentially important at an earlier stage after grafting—and the complex flow structure induced by the bypass graft are investigated. Seven geometric models, including symmetric and asymmetric stenoses in the host artery, and two major aspects of the bypass system, namely, the effects of area reduction and stenosis asymmetry, are considered. By analyzing the flow characteristics in these configurations, it is found that (1) substantial area reduction leads to flow recirculation in both upstream and downstream of the stenosis and in the host artery near the toe, while diminishes the recirculation zone in the bypass graft near the bifurcation junction, (2) the asymmetry and position of the stenosis can affect the location and size of these recirculation zones, and (3) the curvature of the bypass graft can modify the fluid flow structure in the entire bypass system.

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