Numerical analysis of natural convection between a heated cube and its spherical enclosure (original) (raw)
Related papers
Three-dimensional natural convection in an enclosure with a sphere at different vertical locations
International Journal of Heat and Mass Transfer, 2010
Numerical calculations are carried out for the three-dimensional natural convection induced by a temperature difference between a cold outer cubic enclosure and a hot inner sphere. The immersedboundary method (IBM) to model a sphere based on the finite volume method is used to study a three-dimensional natural convection for different Rayleigh numbers varying in the range of 10 3-10 6. This study investigates the effect of the inner sphere location on the heat transfer and fluid flow. The flow and thermal fields eventually reach the steady state for all Rayleigh numbers regardless of the sphere location. For Rayleigh numbers of 10 5 and 10 6 , the variation of local Nusselt number of the sphere along the circumferential direction is large, showing the strong three dimensionality of the natural convection in the enclosure unlike to the cases of lower Rayleigh numbers of 10 3 and 10 4. For the highest Rayleigh number, the local peaks of the Nusselt number on the top wall of the enclosure shows the sinusoidal distribution along the circumferential direction. The flow and thermal fields, and the local and surface-averaged Nusselt numbers on the sphere and the enclosure are highlighted in detail.
CFD Analysis of Heat Transfer and Flow Characteristics in A 3D Cubic Enclosure
IJMER
Flow arising “naturally” from the effect of density difference, resulting from temperature or concentration difference in a body force field such as gravity, the process is termed as natural convection. There has been growing interest in buoyancy-induced flows and the associated heat and mass transfer over the past three decades, because of the importance of these flows in many different areas such as cooling of electronic equipment, pollution, materials processing, energy systems and safety in thermal processes. Steady state laminar natural convection in a cubic enclosure with a cold vertical wall and two square heaters with constant temperature on the opposite wall is studied numerically. The enclosure is fitted with various liquids. Three-dimensional Navier Stokes equations are solved by employing SIMPLE algorithm. Computations are performed for a range of Rayleigh number from 104 to 107 while enclosure aspect ratio varies from 0.1 to 1.25. The effects of Rayleigh number, enclosure aspect ratio, and Prandtl number on heat transfer characteristics are studied in detail. The results show that the flow field is very complex and heat transfer from the two heaters is not the same. The effect of Prandtl number is negligible in the range 5 to 100 with other parameters kept constant. This allows the use of liquids such as water for studying other dielectric liquids, provided the flow geometry and other non-dimensional parameters are similar. The overall Nusselt number increased markedly with Rayleigh Number. It is also affected by enclosure aspect ratio.
International Journal of Heat and Fluid Flow, 2008
The effect of radiative heat transfer on the hydromagnetic double-diffusive convection in two-dimensional rectangular enclosure is studied numerically for fixed Prandtl, Rayleigh, and Lewis numbers, Pr = 13.6, Ra = 10 5 , Le = 2. Uniform temperatures and concentrations are imposed along the vertical walls while the horizontal walls are assumed to be adiabatic and impermeable to mass transfer. The influences of the optical thickness and scattering albedo of the semitransparent fluid on heat and mass transfer with and without magnetic damping are depicted. When progressively varying the optical thickness, multiple solutions are obtained which are steady or oscillatory accordingly to the initial conditions. the mechanisms of the transitions between steady compositionally dominated flow and unsteady thermally dominated flow are analyzed.
2013
The three- dimensional numerical study of natural convection in a cubical enclosure, filled with air was carried out in this study. Two heating square sections are placed on the vertical wall of the enclosure. The imposed heating temperatures vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension D/L and the Rayleigh number Ra were fixed respectively at 0,2 and 10 6 . The temperature distribution, the flow pattern and the average heat transfer will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer and flow intensity, by proper choice of the heating mode and the governing parameters.
Numerical analysis of natural convection inside a heat generated fluid was performed for four different spherical geometries that match the experimental vessels used by Asfia et al. [5-7]. The transient calculations were performed with the CFX 5.7 fluid dynamic software. The simulations show that the highest heat flux is just below the rim of the cavity and it can be 50 times higher than at the bottom. Based on the numerical results, the local values of heat transfer coefficient and the distributions of global Nusselt number were calculated. The present, three-dimensional simulation results were compared with the numerical results of Mayinger et al. [3] and Reineke et al. [4], and with the experimental data of Asfia et al. [5-7]. The agreement between the results that is well inside the experimental scatter verifies the selected modeling approach.
Heat and Mass Transfer, 2007
This paper presents and discusses the numerical simulations of transient laminar natural convection cooling of high Prandtl number fluids in cubical cavities, in which the six walls of the cavity are subjected to a step change in temperature. The effect of the fluid Prandtl number on the heat transfer coefficient is studied for three different fluids (Golden Syrup, Glycerin and Glycerin-water solution 50%). The simulations are performed at two different Rayleigh numbers (5 · 10 6 and 5 · 10 7 ) and six different Prandtl numbers (3 · 10 5 ≥Pr≥ 50). Heat conduction through the cavity glass walls is also considered. The propsed correlations of the averaged heat transfer coefficient (Nu) showed that it is dependant on the initial Ra and almost independent on P r. The instantaneous flow patterns, temperature contours and time evolution of volume averaged temperature and heat transfer coefficient are presented and analyzed.
International Journal of Heat and Mass Transfer, 2000
A comprehensive numerical study has been conducted to investigate three-dimensional, steady, conjugate heat transfer of natural convection and conduction in a vertical cubic enclosure within which a centered, cubic, heat-conducting body generates heat. The physical model considered here assumes that a temperature difference exists across the enclosure (right cold wall and left hot wall) and the body generates a constant amount of heat. Under these conditions, the flow inside the enclosure is driven by two temperature differences: a temperature difference across the enclosure and a temperature difference caused by the heat source. A ratio of these two temperatures is a key parameter in this study. The steady, three-dimensional governing equations are written in a dimensionless form with dimensionless parameters that decide the heat transfer and flow characteristics in this system. The analysis is conducted by observing variations of the velocity vectors, pathlines, and isotherms for different Rayleigh numbers and temperature-difference ratios. The details of the three-dimensional flow and isotherms are described in order to investigate the effects of three-dimensionalities on the fluid flow and thermal characteristics in the enclosure. The variations of Nusselt numbers on the hot and cold walls are also presented to show the overall heat transfer characteristics inside the enclosure.
Natural convection in cubical enclosure with hot surface geometry and partial partitions has been analysed. The geometry is a cube with wavy hot surface (three undulations) and three partitions. The investigation has been performed for different partitions lengths and Rayleigh number while the Prandtl number kept constant. This problem is solved by using the partial differential equations which are the equation of mass, momentum, and energy. The results obtained show that the hot wall geometry with partitions affects the flow and the heat transfer rate in the cavity. It has been found also that the mean Nusselt number decreases compared with the heat transfer in the undulated cubical cavity without partitions.
Procedia Engineering, 2014
Heat transfer and flow due to natural convection in air around heated equilateral triangular cylinders of different sizes inside a square enclosure has been analyzed. The triangular cylinder is at higher temperature and the vertical walls of the enclosure are at lower temperature with insulated horizontal walls. The computational model is developed using Ansys Fluent 13 commercial CFD package. The Rayleigh number is varied from 10 4 to 10 6. For a given size of enclosure, cylinders of different size are taken corresponding to aspect ratios of 0.2, 0.3, 0.4 and 0.5. Results are presented in the form of contours of isotherm and stream function.