Turbulent Natural Convection in a Composite Enclosure Using the Thermal Non-Equilibrium Model

2016 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Caio B. Masciarelli
Keyword(s):  
Natural Convection ◽  
Solid Phase ◽  
Porous Matrix ◽  
Working Fluid ◽  
Square Cavity ◽  
Turbulent Natural Convection ◽  
Solid Region ◽  
Energy Equations ◽  
Volume Method ◽  
Non Equilibrium

Turbulent natural convection in a two-dimensional horizontal composite square cavity is numerically analyzed using the finite volume method and the thermal non-equilibrium approach. Distinct energy equations for the working fluid and for the porous matrix are proposed reflecting different energy balances for each phase. The composite square cavity is formed by three distinct regions, namely, clear, porous and solid region. It was found that the fluid begins to permeate the porous medium for values of Ra greater than 10^6. Nusselt number values show that for the range of Ra analyzed there are no significant variation between the laminar and turbulent model solution. When comparing the effects of Ra and Da on Nu, results indicate that the solid phase properties have a greater influence in enhancing the overall heat transferred trough the cavity.

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..

Tin Solidification in the Presence of Turbulent Natural Convection

2002 ◽  
Author(s):  
Luis Joaquim Cardoso Rocha ◽  
Angela O. Nieckele
Keyword(s):  
Natural Convection ◽  
Domain Size ◽  
Solidification Process ◽  
Special Treatment ◽  
Liquid Region ◽  
Turbulent Regime ◽  
Closed Cavity ◽  
Turbulent Natural Convection ◽  
Solid Region ◽  
Volume Method

The solidification process of tin, inside a closed cavity, is numerically investigated by the finite volume method. A non-orthogonal system of coordinates is employed to adapt to the irregular geometry, with a moving mesh to account for the changing domain size. The momentum equations are solved for the contravariant velocity components. The SIMPLEC algorithm handles the coupling between velocity and pressure. A special treatment is given at the liquid-solid interface to obtain the momentum and energy balance. The phase change process is strongly influenced by natural convection in the melt. At the beginning of the process, the cavity is full of liquid, and the natural convection slightly influences the interface shape. But as the liquid region diminishes during the process, the influence of natural convection increases. Further, at the same time as the liquid size region is reduced, the intensity of the flow increases, and the flow can became turbulent, affecting the heat flux at the interface and consequently the size of the solid region. Therefore, the purpose of the paper is to analyze the influence of the turbulent regime on the kinetics of the solidification process. The turbulent flow is taken into account by a low Reynolds number model. The influence of the Rayleigh number on the velocity and temperature field is investigated.

scholarly journals Numerical Study of the Turbulent Natural Convection in a Trapezoidal Cavity: Influence of the Inclination of the Lateral Walls

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Boussinesq Approximation ◽  
Governing Equations ◽  
Square Cavity ◽  
Turbulent Natural Convection ◽  
Side Walls ◽  
Volume Method ◽  
Calculation Code

In this paper, we study the heat transfer in turbulent natural convection in a two- dimensional cavity with a trapezoidal section and isoscales filled out of air with as height H =2.5 m. In these conditions, the side walls are differentially heated while the horizontal walls are adiabatic. The k-ε turbulence model with a small Reynolds number was integrated in our calculation code. The governing equations of the problem were solved numerically by the commercial CFD code Fluent; which is based on the finite volume method and the Boussinesq approximation. The elaborated model is validated from the experimental results in the case of the turbulent flow in a square cavity. Then, the study was related primarily to the influence of the slope of the side walls of the cavity on the dynamic behavior and the heat transfer within the cavity.

Conjugate Natural Convection in a Square Cavity Heated From Below

2004 ◽  
Author(s):  
F. Sa´nchez ◽  
F. Solorio ◽  
Ruben A´vila
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Velocity Field ◽  
Two Dimensional ◽  
Square Cavity ◽  
Conjugate Natural Convection ◽  
Natural Convection Problem ◽  
Energy Equations ◽  
Volume Method ◽  
Lateral Walls

This paper presents numerical results for two-dimensional steady-state natural convection in a square cavity. The upper and lower walls are kept at different constant temperatures, whereas the lateral walls have certain thickness and thermal conductivity and are externally insulated. Under these conditions we deal with a conjugate natural convection problem in which the heat conduction in the lateral walls is coupled with the internal convection. The continuity, momentum and energy equations were solved by using the finite volume method. The results here presented include: (i) the temperature distribution in the lateral walls and in the fluid, (ii) the velocity field, and (iii) the average Nusselt number at the upper and lower walls. It was found that the steady state fluid flow is strongly dependent on the initial temperature condition, when the fluid is initially at rest. The PIV technique allowed us to get some experimental data by measuring the velocity field in a two-dimensional square cavity. A good agreement between numerical and experimental results was found.

Turbulent Heat Transfer in a Horizontal Enclosure With a Thin Porous Obstruction in the Middle

2003 ◽  
Author(s):  
Edimilson J. Braga ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Porous Matrix ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Square Cavity ◽  
Turbulent Natural Convection ◽  
Nusselt Numbers ◽  
Volume Method ◽  
Generalized Coordinate

Turbulent natural convection in a horizontal two-dimensional square cavity, isothermally heated from below and cooled at the upper surface, is numerically analyzed using the finite volume method and a generalized coordinate system. The enclosure has a thin horizontal porous obstruction located at the cavity mid height. Governing equations are written in terms of primitive variables and are recast into a general from. In general, the porous obstruction decreases the heat transfer across the heated walls showing an overall lower Nusselt numbers when compared with those without the same porous obstruction. However, the presence of a porous obstruction. However, the presence of a porous obstruction in a square cavity seems to force an earlier transition from laminar to turbulent regime due to higher generation rates of turbulent kinetic energy into the porous matrix.

Turbulent Natural Convection Inside a Square Enclosure With Baffles

2010 ◽  
Author(s):  
Khudheyer S. Mushatet
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Staggered Grid ◽  
Algebraic Equations ◽  
Turbulent Natural Convection ◽  
Square Enclosure ◽  
Thermal Fields ◽  
Energy Equations ◽  
Volume Method

In this paper, the turbulent natural convection heat transfer and fluid flow inside a square enclosure having two conducting solid baffles has been numerically investigated. Fully elliptic Navier-Stockes and energy equations are disrectized using finite volume method along with a staggered grid techniques. The resulting algebraic equations were solved by using semi-implicit line by line Guase elimination scheme. The effect of turbulence was incorporated to treat the regions near the walls. The flow and thermal fields are investigated for different parameters such as the relative baffles height, Rayleigh number and the distance between baffles. The conducted results indicated that the resulting vortices are decreased in number and elongated with the decrease of the dimensionless relative baffle heights. Also the results show that the rate of heat transfer is increased with the increase of Ra especially for the region near the baffles.

Computational fluid dynamics for modeling the turbulent natural convection in a double air-channel solar chimney system

2016 ◽  
Vol 27 (08) ◽  
pp. 1650095 ◽  
Author(s):  
I. Zavala-Guillén ◽  
J. Xamán ◽  
G. Álvarez ◽  
J. Arce ◽  
I. Hernández-Pérez ◽  
...  
Keyword(s):  
Natural Convection ◽  
Mexico City ◽  
Mass Flow ◽  
Solar Chimney ◽  
Turbulent Natural Convection ◽  
Air Turbulence ◽  
Warm Summer ◽  
Air Channel ◽  
Arid Desert ◽  
Volume Method

This study reports the modeling of the turbulent natural convection in a double air-channel solar chimney (SC-DC) and its comparison with a single air-channel solar chimney (SC-C). Prediction of the mass flow and the thermal behavior of the SC-DC were obtained under three different climates of Mexico during one summer day. The climates correspond to: tropical savannah (Mérida), arid desert (Hermosillo) and temperate with warm summer (Mexico City). A code based on the Finite Volume Method was developed and a [Formula: see text] turbulence model has been used to model air turbulence in the solar chimney (SC). The code was validated against experimental data. The results indicate that during the day the SC-DC extracts about 50% more mass flow than the SC-C. When the SC-DC is located in Mérida, Hermosillo and Mexico City, the air-changes extracted along the day were 60, 63 and 52, respectively. The air temperature at the outlet of the chimney increased up to 33%, 38% and 61% with respect to the temperature it has at the inlet for Mérida, Hermosillo and Mexico City, respectively.

Numerical Investigation of the Onset of Steady Natural Convection in a Square Cavity Partially Filled With a Single Porous Block

2014 ◽  
Author(s):  
Vinicius Daroz ◽  
Silvio L. M. Junqueira ◽  
Admilson T. Franco ◽  
José L. Lage
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Critical Rayleigh Number ◽  
Contour Plot ◽  
Viscous Effects ◽  
Square Cavity ◽  
Heterogeneous Model ◽  
Porous Block ◽  
Vertical Walls ◽  
Volume Method

The critical Rayleigh number at the onset of natural convection within a square cavity filled with a centralized porous block was investigated. The porous medium is modeled by using the heterogeneous model and the governing equations are solved for each phase separately. The thermal gradient is applied from the bottom to the top horizontal walls while the vertical walls are kept adiabatic. The amount of solid within the cavity was kept constant by fixing both external and internal porosity in 36% and 40%, respectively. The equations are solved using the Finite Volume Method and the interpolation scheme for the convective terms is the Hybrid Scheme. For the pressure-velocity coupling, the SIMPLEC method is used. The effects on the conductive-convective regime transition, reads critical Rayleigh Number, characterized by the average Nusselt number and the heatlines contour plot, was investigated by varying the Rayleigh number and the porous block permeability. The results show that the so called critical Rayleigh number is affected by the block permeability. As the permeability decreases, the flow tends to recirculate around the block being squeezed against the cavity walls and therefore, more susceptible to viscous effects. A correlation to the critical Rayleigh number is presented as a function of the agglomerate permeability showing that the higher the permeability the lower the amount of energy required to trigger the convection.

Turbulent Heat Transfer in an Enclosure With a Horizontal Permeable Plate in the Middle

2006 ◽  
Vol 128 (11) ◽  
pp. 1122-1129 ◽  
Author(s):  
Edimilson J. Braga ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Porous Plate ◽  
Porous Matrix ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Turbulent Natural Convection ◽  
Nusselt Numbers ◽  
Model Solutions ◽  
Volume Method ◽  
Rayleigh Numbers

Turbulent natural convection in a vertical two-dimensional square cavity, isothermally heated from below and cooled at the upper surface, is numerically analyzed using the finite volume method. The enclosure has a thin horizontal porous obstruction, made of a highly porous material and extremely permeable, located at the cavity midheight. Governing equations are written in terms of primitive variables and are recast into a general form. For empty cavities, no discrepancies result for the Nusselt number when laminar and turbulent model solutions are compared for Rayleigh numbers up to 107. Also, in general the porous obstruction decreases the heat transfer across the heated walls showing overall lower Nusselt numbers when compared with those without the porous obstruction. However, the presence of a porous plate in the cavity seems to force an earlier separation from laminar to turbulence model solutions due to higher generation rates of turbulent kinetic energy into the porous matrix.

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