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..

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.

Entropy Generation in Laminar and Turbulent Natural Convection Heat Transfer From Vertical Cylinder With Annular Fins

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Jnana Ranjan Senapati ◽  
Sukanta Kumar Dash ◽  
Subhransu Roy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Vertical Cylinder ◽  
Turbulent Regime ◽  
Maximum Heat ◽  
Turbulent Natural Convection ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
Annular Fins

Entropy generation due to natural convection has been calculated for a wide range of Rayleigh number (Ra) in both laminar (104 ≤ Ra ≤ 108) and turbulent (1010 ≤ Ra ≤ 1012) flow regimes, for diameter ratio of 2 ≤ D/d ≤ 5, for an isothermal vertical cylinder fitted with annular fins. In the laminar regime, the entropy generation was predominantly caused by heat transfer (conduction and convection) and the viscous contribution was negligible with respect to heat transfer. But in the turbulent regime, entropy generation due to fluid friction is significant enough although heat transfer entropy generation is still dominant. The results demonstrate that the degree of irreversibility is higher in case of finned configuration when compared with unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to delineate the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned. The ratio (I/Q)finned/(I/Q)unfinned gets its minimum value at optimum fin spacing where maximum heat transfer occurs in turbulent flow, whereas in laminar flow the ratio (I/Q)finned/(I/Q)unfinned decreases continuously with the increase in number of fins.

Turbulent natural convection along a vertical plate immersed in a stably stratified fluid

2009 ◽  
Vol 636 ◽  
pp. 41-57 ◽  
Author(s):  
EVGENI FEDOROVICH ◽  
ALAN SHAPIRO
Keyword(s):  
Natural Convection ◽  
Vertical Plate ◽  
Stationary Flow ◽  
Stratified Fluid ◽  
Buoyancy Frequency ◽  
Convection Flow ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Turbulent Natural Convection ◽  
Oscillatory Phase

The paper considers the moderately turbulent natural convection flow of a stably stratified fluid along an infinite vertical plate (wall). Attention is restricted to statistically stationary flow driven by constant surface forcing (heating), with Prandtl number of unity. The flow is controlled by the surface energy production rateFs, molecular viscosity/diffusivity ν and ambient stratification in terms of the Brunt–Väisälä (buoyancy) frequencyN. Following the transition from a laminar to a turbulent regime, the simulated flow enters a quasi-stationary oscillatory phase. In this phase, turbulent fluctuations gradually fade out with distance from the wall, while periodic laminar oscillations persist over much larger distances before they fade out. The scaled mean velocity, scaled mean buoyancy and scaled second-order turbulence statistics display a universal behaviour as functions of distance from the wall for given value of dimensionless combinationFs/(νN2) that may be interpreted as an integral Reynolds number. In the conducted numerical experiments, this number varied in the range from 2000 to 5000.

An Experimental Study of Turbulent Natural Convection Boundary Layers

1969 ◽  
Vol 91 (4) ◽  
pp. 517-531 ◽  
Author(s):  
G. C. Vliet ◽  
C. K. Liu
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Layers ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Physical Structure ◽  
Longitudinal Vortex ◽  
Turbulent Regime ◽  
Turbulent Natural Convection ◽  
Convection Boundary

An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014; i.e., fully developed turbulent flow occurs by Ra* = 104. This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014. For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.

Natural Convection From a Horizontal Cylinder—Turbulent Regime

1982 ◽  
Vol 104 (2) ◽  
pp. 228-235 ◽  
Author(s):  
B. Farouk ◽  
S. I. Gu¨c¸eri
Keyword(s):  
Natural Convection ◽  
Numerical Solutions ◽  
Horizontal Cylinder ◽  
Equation Model ◽  
Turbulence Structure ◽  
Turbulent Regime ◽  
Closed Set ◽  
Number Range ◽  
Turbulent Natural Convection ◽  
Nusselt Numbers

A two-equation model has been adopted in obtaining numerical solutions of turbulent natural convection from an isothermal horizontal circular cylinder. The k-ε model employed in this study characterizes turbulence through the kinetic energy and its volumetric rate of dissipation. The transport equations for these two variables, along with those for time-averaged stream function, vorticity, and temperature, form a closed set of five coupled partial differential equations. These equations are solved for the entire flow domain, without boundary layer approximations. Buoyancy effects on the turbulence structure are also accounted for. Results are presented for a Rayleigh number range of 5×107 to 1010 and the average Nusselt numbers are compared with existing correlations and limited available experimental data.

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.

scholarly journals Effect of Coupling Radiation Convection on Heat Transfer in the air gap of a Solar Collector

2020 ◽  
Vol 330 ◽  
pp. 01018
Author(s):  
Fatima Zohra Ferahta ◽  
Cherifa Abid
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Three Dimensional ◽  
Air Gap ◽  
Turbulent Regime ◽  
Confined Space ◽  
Heat Exchange Coefficient ◽  
Closed Cavity ◽  
First Case ◽  
Solar Thermal Collector

In order to study the effect of convection-radiation coupling occurring in the air gap of a solar thermal collector, numerical simulations were conducted for various thicknesses of the air gap with and without radiation. The studied geometry is a closed cavity which represents the confined space between the absorber and the glass. The cavity is inclined at an angle equal to 45 ° and is uniformly heated from below. The flow is three-dimensional and in unsteady state. First, the simulations were conducted considering only convection in the air gap, in this case the radiation is neglected and in a second time, the coupling between convection and radiation was taken onto account. In the first case the results show that the increase of the air-gap thickness leads to an intensification of the natural convection which develops from laminar, chaotic to turbulent regime. When the radiation is taken into account, the results show that the flow regimes are substantially modified, the convection-radiation coupling reduces the temperature of the hot wall, which contributes to the reduction of the intensity of natural convection in the cavity. This observation is verified by the evolution of the temperature field at the absorber and the heat exchange coefficient. So in conclusion, this study allowed us to see the evolution of heat transfer in the air layer between the glass and the absorber, in the absence and in the presence of radiation. Taking into account the radiation in the cavity is essential for the modeling of flows in a cavity (which is often neglected).

Heat Transfer During Solidification Around a Horizontal Tube With Internal Convective Cooling

1997 ◽  
Vol 119 (1) ◽  
pp. 44-47 ◽  
Author(s):  
Yuwen Zhang ◽  
Zhongqi Chen ◽  
A. Faghri
Keyword(s):  
Volume Fraction ◽  
Horizontal Tube ◽  
Solidification Process ◽  
Transient Temperature ◽  
Liquid Region ◽  
Approximate Integral ◽  
Layer Analysis ◽  
Solid Region ◽  
Convection Cooling ◽  
Internal Convection

Theoretical solution for the solidification process around a horizontal tube with internal convection cooling is described in this paper. Boundary layer analysis and the approximate integral method were applied to obtain the solution for the natural convection in the liquid region and the transient temperature profile in the solid region. Effects of Biot number on the wall temperature and the volume fraction solidified are also discussed in this paper.

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