Three-Dimensional Laminar and Turbulent Natural Convection in a Continuously/Discretely Wall-Heated Enclosure Containing a Thermal Load (original) (raw)
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The SIJ Transactions on Computer Networks & Communication Engineering
This is a numerical study of turbulent natural convection flow in a rectangular enclosure. The flow of heat is one form of Newtonian motion. We consider natural convection in a three dimensional rectangular enclosure in the form of a room with heaters placed on opposite walls and two windows each on the adjacent opposite walls. The study of free convection in the past five decades focused mainly on two different simple geometries, first the single isothermal or constant flux vertical plate in isothermal stagnant surrounding, secondly, the enclosed rectangular cavity with heated floor and cooled walls. There has also been much emphasis on Reyleigh number as opposed to the Reynolds number used in this study. To analyze the flow and heat transfer rates, a complete set of non-dimensionalized equations governing Newtonian fluid and boundary conditions are recast into vector potential to eliminate the need for solving the continuity equations. A Boussinesq fluid motion in a three dimensional cavity is considered. The governing equations with the boundary conditions are descritized using three point central difference approximations for a non-uniform mesh. The resulting finite difference equations are solved using Matlab simulation software. The solutions are presented at the Reynolds number 5500, with Prandtl number 0.71. The results are presented on graphs to show velocity profiles and temperature distribution in the room. The room is divided into a number of regions with those near the heaters having high temperatures as those near the windows have low temperatures. Convective currents caused by buoyancy forces play a major role in determining the velocity profiles in the room.
Energies
This paper proposes an analytical model for natural convection in a closed rectangular enclosure filled by a fluid, with imposed heat fluxes at the vertical walls and adiabatic horizontal walls. The analytical model offers a simplified, but easy to handle, description of the temperature and velocity fields. The predicted temperature, velocity, and pressure fields are shown to be in agreement with those obtained from a reliable numerical model. The Nusselt numbers for both the analytical and numerical solutions are then calculated and compared, varying both the aspect ratio of the enclosure and the Rayleigh number. Based on the comparisons, it is possible to assess the dependence of the reliability of the analytical model on the aspect ratio of the enclosure, showing that the prediction error rapidly decreases with the increase of the enclosure slenderness.
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Thispaper reports the results of numerical investigation on natural convection in a three dimensional rectangular enclosure with heated parallel vertical plates located inside the enclosure. Simulation has been performed used commercial computational fluid dynamics package. The effect of spacing between the heated vertical plates and heat input on the flow and heat transfer characteristics inside the enclosure will be explored and discussed.
Modeling of Natural Turbulent Convection in an Enclosure with Localized Heating
2019
Purpose: The purpose of the study was to model natural turbulent convection in an enclosure with localized heating. Methodology: The study considered the equations governing a free convection. Precisely, the equations governed a Newtonian fluid that experiences transfer of heat or mass. The governing equations were derived from the conservation principles namely the conservation of mass, the conservation of momentum, and the conservation of energy. These equations were decomposed using the Reynolds decomposition then the decomposed equations were non-dimensionalized and reduced using the Boussinesq assumptions. The k-e model was employed in the simulation of flow characteristics. Finally, the equations were solved numerically for the flow quantities. Results: The results were presented in form of isotherms and vector potentials in different sections of the enclosure. The results of the study indicated that the variation of the Rayleigh number affects the flow properties such as the ...
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International Journal of Heat and Mass Transfer, 1992
Convective heat transfer was investigated numerically for rectangular enclosures both undivided and divided in two zones by a vertical partition, and having opposite isothermal walls at different temperatures. The aspect ratio was varied from 0. I to 16 and the Rayleigh number from 3.5 * lo3 to 3.5 * I O7 (non-partitioned enclosures) and from I .O * 10' to 1.6 * 10' (partitioned enclosures). The thickness and conductivity of the partition were varied. The end wall thermal boundary conditions were adiabatic or LTP (Linear Temperature Profile). The continuity, momentum and energy equations for a 2-D laminar steady flow were solved under the Boussinesq approximation by using a finite-difference method and the SIMPLEC pressure-velocity coupling algorithm. Grid-independent results indicate that the reduction in the Nusselt number caused by a thin central partition can be predicted within a few per cent (in the range investigated) by assuming the partition to be isothermal, i.e. infinitely conducting. The finite conductivity of the partition causes a temperature distribution along its length, resulting in an increase in Nu which depends on Rayleigh number, aspect ratio and end wall thermal boundary conditions.
Revista de Engenharia Térmica
In this work, the laminar natural convection in high aspect ratio three-dimensional enclosures has been numerically studied. The enclosures studied here were heated with uniform heat flux on a vertical wall and cooled at constant temperature on the opposite wall. The remaining walls were considered adiabatic. Fluid properties were assumed constant except for the density change with temperature on the buoyancy term. The governing equations were solved using the finite volumes method and the dimensionless form of these equations has the Prandtl number and the modified Rayleigh number as parameters. The influences of the Rayleigh number and of the cavity aspect ratio on the Nusselt number, for a Prandtl number of 0.7, were analyzed. Results were obtained for values of the modified Rayleigh number up to 106 and for aspect ratios ranging from 1 to 20. The results were compared with two-dimensional results available in the literature and the variation of the average Nusselt number with th...
Natural convection in a triangular top wall enclosure with a solid strip
journal of engineering science and technology, 2015
Natural convection inside a two-dimensional rectangular cavity with a triangular roof having an adiabatic solid strip inserted at a middle of the cavity is studied numerically using a finite volume method. Both of the triangular roof and the bottom wall are considered adiabatic while the vertical left side wall is maintained at constant temperature higher than that of inside fluid temperature. The right side wall is considered differentially heated by supplying a constant heat flux. The working fluid is chosen for analysis is air. The Computational Fluid dynamics (CFD) solution commercial package ANSYS FLUENT 14.0 is used for the numerical simulation purpose. The results are presented in the form of isotherms, streamlines, velocity vector and average Nusselt number (Nu) for Rayleigh numbers in the range of 103 to 106.Throughout this study, the aspect ratio is kept equal to 0.5.It is found that the solid adiabatic strip inside the cavity has a significant effect on the flow and therm...
Natural Convection Heat Transfer within Octagonal Enclosure
The problem of steady, laminar and incompressible natural convection flow in an octagonal enclosure was studied. In this investigation, two horizontal walls were maintained at a constant high temperature, two vertical walls were kept at a constant low temperature and all inclined walls were considered adiabatic. The enclosure was assumed to be filled with a Bousinessq fluid. The study includes computations for different Prandtl numbers Pr such as 0.71, 7, 20 and 50 whereas the Rayleigh number Ra was varied from 103 to 106. The pressure-velocity form of Navier-Stokes equations and energy equation were used to represent the mass, momentum and energy conservations of the fluid medium in the enclosure. The governing equations and boundary conditions were converted to dimentionless form and solved numerically by penalty finite element method with discretization by triangular mesh elements. Flow and heat transfer characteristics were presented in terms of streamlines, isotherms and average Nusselt number Nu. Results showed that the effect of Ra on the convection heat transfer phenomenon inside the enclosure was significant for all values of Pr studied (0.71-50). It was also found that, Pr influence natural convection inside the enclosure at high Ra (Ra > 104 ).
CFD-Analysis of Natural Convection in A Triangular Enclosure
Natural convection in enclosed cavities is widely studied because of its importance in many engineering applications. The most commonly used enclosures in the industries are rectangular, cylindrical, trapezoidal, triangular etc. In recent years, natural convection in triangular shaped enclosures have received a considerable attention. The reason for considering this geometry is, it has application in various fields such as building and thermal insulation systems. In the present study natural convection inside a triangular enclosure is analyzed. The analysis is conducted as 3 different cases. For the first case the bottom wall is heated and other two sides are kept at ambient temperature. For the second case, left wall is heated and other two sides are kept at ambient temperature and for the final case right wall is heated and other two sides are kept at ambient temperature. Simulations are carried out for varying Rayleigh number. Heat transfer rate from the hot surface is obtained numerically. The fluid flow characteristics and heat transfer characteristics are analyzed using computational fluid dynamic software ANSYS FLUENT 14.0.