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.

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.

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..

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.

Turbulent Natural Convection in Enclosures With Clear Fluid and Completely Filled With Porous Material

2002 ◽  
Author(s):  
Edimilson J. Braga ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Porous Media ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Turbulent Flows ◽  
Energy Transport ◽  
Numerical Solutions ◽  
Clear Fluid ◽  
Turbulent Natural Convection ◽  
Onset Of Turbulence ◽  
Volume Method

Steady laminar and turbulent natural convection in a two-dimensional square cavity, isothermally heated from the left side and cooled from the opposing side, is numerically analyzed using the finite volume method. Benchmark results for laminar and turbulent flows are compared with similar numerical solutions in the literature. The cases of clear and porous media are considered. Governing equations are written in terms of primitive variables and are recast into a general form. The effects of Rayleigh number on flow pattern and energy transport are investigated for Ra ranging from 103 to 1010 for clear media and 101 to 106 for porous media. The turbulence model used was the standard k–ε along with the wall function approach. All results presented herein showed reasonable agreement with calculations presented in the literature. Critical values for the Rayleigh number for the onset of turbulence are suggested. The main objective of this work is to validate a numerical tool for simulating turbulent natural convection in both clear and porous media.

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 Assessment of Double-Inlet Collector in Solar Chimney Power Plant Systems

2017 ◽  
Author(s):  
Nima Fathi ◽  
Seyed Sobhan Aleyasin ◽  
Patrick Wayne ◽  
Peter Vorobieff
Keyword(s):  
Power Plant ◽  
Mass Flow ◽  
Flow Rate ◽  
Scale Model ◽  
Solar Chimney ◽  
Rate Improvement ◽  
Mass Flow Rates ◽  
Limited Mass ◽  
Solar Chimney Power Plant ◽  
Volume Method

Solar chimney power plant systems (SCPPS) offer a simple and reliable way to generate electricity using solar radiation to drive a flow of buoyant air. A typical SCPP setup includes a collector, a tower, and a turbine or several turbines. Current SCPP designs have low thermal efficiency: only between 0.5% and 5% of the incident solar energy is converted into electricity. Inefficiencies result partially from limited mass flow rates through the tower. It is therefore desirable to provide a new design for the collector to increase the inlet air mass flow rate. In this paper, we present a double-inlet collector concept and results of numerical analysis to evaluate this design in terms of flow rate improvement. Computational fluid dynamics (CFD) was utilized to perform the numerical modeling and simulation (M&S) by using a finite volume method package. The Manzanares prototype (the only operational solar tower power plant with available published reports) is selected to implement the double-inlet collector design and study its effect on the power plant. Beside this case, we fabricated a 1/1000 scale model of the Manzanares prototype which enables us to measure the filed variables experimentally. Validation analysis was performed to quantify the reliability of our numerical model with respect to the available experimental data. We obtained a significant increase (14%) in the available output power by using the double-inlet collector.

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