Natural Convection Heat Transfer within Octagonal Enclosure (original) (raw)
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NUMERICAL ANALYSIS OF NATURAL CONVECTION IN A RIGHT- ANGLED TRIANGULAR ENCLOSURE
A numerical investigation has been performed for heat transfer analysis in a right-angled triangular enclosure filled with water. The side wall of the enclosure is maintained at high temperature compare to the base wall while hypotenuse is kept thermally insulated. Two-dimensional steady-state continuity, momentum and energy equations along with the boussinesq approximation are solved by finite volume method using commercial available software, FLUENT 6.3. The computational results are shown in terms of isotherms, streamlines and velocity contour for Rayleigh number (10 5 ≤ Ra ≤ 10 7). The heat transfer is presented in terms of local and average Nusselt number. The result encapsulates that both flow field and temperature distributions are affected with Rayleigh number. The simulated results are validated with the experimental and numerical results and it shows a good agreement with the published results. Finally, a correlation for Nusselt number (Nu) with Rayleigh number (Ra) has been developed for vertical hot wall.
Numerical Analysis of Natural Convection in a Right-Angle Triangular Enclosure
Frontiers in Heat and Mass Transfer, 2014
A numerical investigation has been performed for heat transfer analysis in a right-angled triangular enclosure filled with water. The side wall of the enclosure is maintained at high temperature compare to the base wall while hypotenuse is kept thermally insulated. Two-dimensional steady-state continuity, momentum and energy equations along with the boussinesq approximation are solved by finite volume method using commercial available software, FLUENT 6.3. The computational results are shown in terms of isotherms, streamlines and velocity contour for Rayleigh number (10 5 ≤ Ra ≤ 10 7). The heat transfer is presented in terms of local and average Nusselt number. The result encapsulates that both flow field and temperature distributions are affected with Rayleigh number. The simulated results are validated with the experimental and numerical results and it shows a good agreement with the published results. Finally, a correlation for Nusselt number (Nu) with Rayleigh number (Ra) has been developed for vertical hot wall.
Anbar Journal of Engineering Sciences, 2017
Laminar natural convection heat transfer and fluid flow due to the heating from below at variable heat source length inside two dimensional enclosure has been analyzed numerically in this study. The enclosure has filled with air as a working fluid. The vertical inclined walls of the enclosure are maintained at lower temperature while the remaining walls are insulated. The value of Rayleigh number from (1x10 3 ≤ Ra ≤ 4x10 4), the inclination angle at (γ = 0 o , 22.5 o , 45 o) and dimensionless heat source length at (S = 1 and 0.5). The continuity, momentum and energy equations have been applied to the enclosure and solved by using finite difference method. The results showing that the average Nusselt number increases with the increasing of the heating source length and decreases with the increasing in an inclination angle of the vertical walls.
On natural convection in a single and two zone rectangular enclosure
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.
This work numerically investigates the natural convection in an arch enclosure filled with Al2O3-water based nanofluid. The left side wall of the enclosure is maintained at a higher temperature than that of right side wall while the remaining walls are kept adiabatic. Two-dimensional steady-state governing equations are solved using the finite volume method (FVM). The present work is conducted to state the effects of pertinent parameters such as nanoparticles volume faction () = 0 to 9%, curvature ratio (CR) = 1 to 1.5 and Rayleigh number (Ra) = 10 4 to 10 6 on fluid flow and temperature distribution. The numerical results are presented in the form of streamlines, isotherms, local and average Nusselt number. It is observed from the investigation that the variables are exhibiting a significant impact on the heat transfer. The heat transfer rate is enhanced with the increment in the volume fraction of the nanoparticles up to 5% and after that it is decreased gradually. The heat transfer rate is increased with the increase of curvature ratio and it is significantly higher at CR = 1.5. As per the expectation, the heat transfer is increased along with the increment in Rayleigh number. A good agreement is found between the present work and experimental & numerical results from the literature.
2011
Numerical study of natural convection flow in a hexagonal enclosure with a single vertical fin attached to its heated bottom wall has been carried out. Finite element method based Galerkin weighted residual technique is used to solve the governing equation. The horizontal walls of the enclosure are kept at constant high temperature while the inclined walls are kept at constant cold temperature. A vertical heated fin is attached to the hot bottom wall with a length () at a position () from the left surface having thickness (). The Prandlt number for the flow inside the enclosure is 0.71. The results of the problem are presented in graphical and tabular forms and discussed. The fin efficiency and temperature distribution were examined. The numerical results indicate the strong influence of the mentioned parameters on the flow structure and heat transfer as well as temperature. A set of graphical results are presented in terms of streamlines, isotherms contour, temperature profiles, velocity profiles, local Nusselt number and average Nusselt number. The obtained results indicated that the heat transfer rate increases with the increase of Rayleigh number in a hexagonal enclosure. The results are validated comparing with the published works.
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.
International Journal of Heat and Mass Transfer, 2008
A penalty finite element analysis with bi-quadratic elements is carried out to investigate the effects of uniform and non-uniform heating of inclined walls on natural convection flows within a isosceles triangular enclosure. Two cases of thermal boundary conditions are considered; case I: two inclined walls are uniformly heated while the bottom wall is cold isothermal and case II: two inclined walls are non-uniformly heated while the bottom wall is cold isothermal. The numerical solution of the problem is presented for various Rayleigh numbers (Ra), (10 3 6 Ra 6 10 6) and Prandtl numbers (Pr), (0:026 6 Pr 6 1000). It has been found that at small Prandtl numbers, geometry does not have much influence on flow structure while at Pr ¼ 1000, the stream function contours are nearly triangular showing that geometry has considerable effect on the flow pattern. In addition, the presence of multiple circulations are observed for small Pr ðPr ¼ 0:026Þ which causes wavy distribution of local Nusselt number. It is observed that non-uniform heating produces greater heat transfer rates at the center of the walls than the uniform heating; however, average Nusselt numbers show overall lower heat transfer rates for the non-uniform heating case. Critical Rayleigh numbers for conduction dominant heat transfer cases have been obtained and for convection dominant regimes, power law correlations between average Nusselt number and Rayleigh numbers are presented for specific Prandtl numbers.
The present work is aimed to study has been carried out of natural convection in a square enclosure with non-uniformly heated bottom wall and square shape heated block with different Prandtl numbers of 0.71, 1.0 and 1.5 has been investigated numerically. The horizontal bottom wall of the square cavity was non-uniformly heated and inner square shape heated block kept at T h while the side walls of the cavity were maintained at a cold temperature T c with T h >T c and upper wall is adiabatic. Finite element method was employed to solve the dimensionless governing equations of continuity, momentum and energy of the problem. Using the developed code, a parametric study was performed, and the effects of the Rayleigh number and the different Prandtl number on the fluid flow and heat transfer inside the square enclosure were investigated. The obtained results showed that temperature distribution and flow pattern inside the square enclosure depended on both strength of the magnetic field and Rayleigh number. For all cases two counter rotating eddies were formed inside the square enclosure. The magnetic field is decreased with the intensity of natural convection and flow velocity. Also it was found that for higher Rayleigh numbers a relatively stronger field was needed to decrease the heat transfer through natural convection.