Numerical Study on Natural Convection and Radiation From a Square Disk

2005 ◽  
Author(s):  
Arnout Willockx ◽  
Christophe Tjoen ◽  
Hendrik-Jan Steeman ◽  
Michel De Paepe
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Simulations ◽  
Flow Pattern ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Test Case ◽  
Air Velocity ◽  
Closed Cavity ◽  
Small Vortex

In this paper, a numerical study of natural convection from a disk is presented. The disk is placed vertically in a closed cavity (cylinder) and has a constant heat flux. Different numerical simulations of this test case are executed at various gravity accelerations (=g) inside the cavity. The accelerations are varied from 9.81 m/s2 to 53 m/s2. The Rayleigh number changes with these accelerations. The flow pattern and the temperature distribution inside the cavity are visualized. For natural convection inside a cavity, a vortex is expected in the air flow: a plume of warm rising air at the centre of the cylinder above the heated square disk and descending colder air at the walls of the cavity. The air velocity is higher in the central plume. At w = 9.81 m/s2, the maximum air velocity is 0.05 m/s. This velocity increases with increasing acceleration w till 0.6 m/s at w = 53 m/s2. At low w, the flow pattern exists of a stable vortex and thus a steady-state flow. At w = 15 m/s2, the vortex becomes more unstable and is swirling. At w = 27 m/s2, the vortex is even more swirling and the following periodical phenomenon takes place: first the vortex starts to dissolve in a small vortex at the top of the cylinder and a vortex below this around the square disk. Then, the lower vortex starts to increase again and the upper vortex is fading. So there is again one big vortex with a central, unstable plume that reaches the top of the cylinder. After a few seconds, the plume dissolves again. This phenomenon has no constant period. The higher w, the faster this phenomenon happens and thus the shorter the period. At w = 53m/s2, the vortex seems more turbulent than laminar, however the Rayleigh number is still in the laminar range (Ra<106). The numerical simulations are verified with existing correlations. There was a good agreement between correlations and numerical simulation.

scholarly journals Numerical Study of the Double Diffusion Natural Convection inside a Closed Cavity with Heat and Pollutant Sources Placed near the Bottom Wall

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3085
Author(s):  
Juan Serrano-Arellano ◽  
Juan M. Belman-Flores ◽  
Jesús Xamán ◽  
Karla M. Aguilar-Castro ◽  
Edgar V. Macías-Melo
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Double Diffusion ◽  
Heat Sources ◽  
Simple Diffusion ◽  
Closed Cavity ◽  
Average Temperature ◽  
Diffusive Convection ◽  
Pollutant Sources

A study was conducted on the double diffusion by natural convection because of the effects of heat and pollutant sources placed at one third of the closed cavity’s height. The heat and pollution sources were analyzed separately and simultaneously. The study was considered for the Rayleigh number interval 10 4   ≤   R a   ≤   10 10 . Three case studies were analyzed: (1) differentially heated closed cavity with only heat sources; (2) differentially heated closed cavity with only pollutant sources; and (3) differentially heated closed cavity with heat and pollutant sources. The governing equations of the system were solved through the finite volume technique. The turbulence solution was done with the k-ε model. The dominant influence of the buoyancy forces was found due to the pollutant diffusion on the flow pattern, and an internal temperature increase was observed with the simple diffusion. The most critical case was obtained through the double diffusive convection with an average temperature value of 32.57 °C. Finally, the Nusselt number increased as the Rayleigh number increased; however, the Sherwood number either increased or decreased when the Rayleigh number increased. The highest mean concentration recorded was 2808 ppm; this was found with the value R a = 10 6 .

Analysis of entropy generation and natural convection in an inclined partially porous layered cavity filled with a nanofluid

2017 ◽  
Vol 95 (3) ◽  
pp. 238-252 ◽  
Author(s):  
T. Armaghani ◽  
Muneer A. Ismael ◽  
Ali J. Chamkha
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Layer Thickness ◽  
Porous Layer ◽  
Entropy Generation ◽  
Thermal Performance ◽  
Volume Fraction ◽  
Numerical Study ◽  
Nanoparticle Volume Fraction ◽  
Thermodynamic Irreversibility

The present numerical study investigates the analysis of thermodynamic irreversibility generation and the natural convection in inclined partially porous layered cavity filled with a Cu–water nanofluid. The finite difference method with up-wind scheme is used to solve the governing equations. The study is achieved by examining the effects of nanoparticle volume fraction, inclination angle, and the porous layer thickness. Besides, the computations are achieved within the laminar range of the Rayleigh number. The results show that at Ra = 104, a reduction of total entropy generation is recorded with increasing nanoparticle volume fraction when the porous layer thickness is greater than 0.2. Moreover, when Ra is less than 105, the nanoparticle volume fraction increases the heat transfer irreversibility, and improves the overall thermal performance. It is found also that for a low Rayleigh number, the largest porous layer thickness and the highest cavity orientation improve the thermal performance. On the contrary, at high Rayleigh numbers, these parameter ranges give the worst thermal performance.

Natural Convection in a Cylindrical Porous Enclosure With Internal Heat Generation

1989 ◽  
Vol 111 (4) ◽  
pp. 916-925 ◽  
Author(s):  
V. Prasad ◽  
A. Chui
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Vertical Wall ◽  
Internal Heat ◽  
Heat Removal ◽  
Maximum Temperature ◽  
Wall Boundary Conditions

A numerical study is performed on natural convection inside a cylindrical enclosure filled with a volumetrically heated, saturated porous medium for the case when the vertical wall is isothermal and the horizontal walls are either adiabatic or isothermally cooled. When the horizontal walls are insulated, the flow in the cavity is unicellular and the temperature field in upper layers is highly stratified. However, if the top wall is cooled, there may exist a multicellular flow and an unstable thermal stratification in the upper region of the cylinder. Under the influence of weak convection, the maximum temperature in the cavity can be considerably higher than that predicted for pure conduction. The local heat flux on the bounding walls is generally a strong function of the Rayleigh number, the aspect ratio, and the wall boundary conditions. The heat removal on the cold upper surface decreases with the aspect ratio, thereby increasing the Nusselt number on the vertical wall. The effect of Rayleigh number is, however, not straightforward. Several correlations are presented for the maximum cavity temperature and the overall Nusselt number.

Natural Convection in Shallow, Horizontal Air Layers Encountered in Electronic Cooling

1995 ◽  
Vol 117 (4) ◽  
pp. 307-316 ◽  
Author(s):  
Elias Papanicolaou ◽  
Sridhar Gopalakrishna
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Bottom Surface ◽  
Multiple Sources ◽  
Critical Dimensions ◽  
Convection Regime ◽  
Air Layers

A numerical study of natural convection induced in a horizontal, enclosed air layer due to a discrete, constant heat flux source at the bottom surface is carried out in this paper. The nature of the transition from conduction to a cellular convection regime for this discrete-heating case is characterized. Multiple sources are also considered and the results are compared to those for a single source. The governing equations of continuity, momentum, and energy conservation are formulated for a two-dimensional layer. The important parameters are the overall aspect ratio (length/height of the layer), the ratio of source length to total length, and the Rayleigh number. The effect of varying these parameters is investigated, and heat transfer correlations are derived, for both single and multiple sources, in the form Nus ∝ C (Ra)c>, where Nus is the Nusselt number averaged over each source. The value of C is found to depend strongly on the aspect ratio and the source size. Based on the heat transfer results, the tendency of each geometric configuration to fully attain transition to the convection regime is evaluated. This can provide guidelines for maintaining certain critical dimensions that best exploit natural convection effects, in systems where fan-driven cooling is not available.

A Numerical Study of Natural Convection in a Cavity With Two Fins Attached to Its Vertical Walls

2007 ◽  
Author(s):  
G. A. Sheikhzadeh ◽  
M. Pirmohammadi ◽  
M. Ghassemi
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Square Cavity ◽  
Vertical Walls ◽  
The Mean ◽  
Energy Equations ◽  
Rayleigh Numbers

Numerical study natural convection heat transfer inside a differentially heated square cavity with adiabatic horizontal walls and vertical isothermal walls is investigated. Two perfectly conductive thin fins are attached to the isothermal walls. To solve the governing differential mass, momentum and energy equations a finite volume code based on Pantenkar’s simpler method is developed and utilized. The results are presented in form of streamlines, isotherms as well as Nusselt number for Rayleigh number ranging from 104 up to 107. It is shown that the mean Nusselt number is affected by the position of the fins and length of the fins as well as the Rayleigh number. It is also observed that maximum Nusselt number occurs about the middle of the enclosure where Lf is grater the 0.5. In addition the Nusselt number stays constant and does not varies with width of the cavity (lf) when Lf is equal to 0.5 and Rayleigh number is equal to 104 and 107 as well as when Lf is equal to 0.6 and low Rayleigh numbers.

scholarly journals Thermophysical Characterization and Numerical Investigation of Three Paraffin Waxes as Latent Heat Storage Materials

2019 ◽  
Author(s):  
Manel Kraiem ◽  
Mustapha Karkri ◽  
Sassi Ben Nasrallah ◽  
patrick sobolciak ◽  
Magali Fois ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Storage ◽  
Numerical Study ◽  
Melting Process ◽  
Heat Transfer Mode ◽  
Transfer Mode ◽  
Paraffin Waxes ◽  
Thermophysical Characterization

Thermophysical characterization of three paraffin waxes (RT27, RT21 and RT35HC) is carried out in this study using DSC, TGA and transient plane source technics. Then, a numerical study of their melting in a rectangular enclosure is examined. The enthalpy-porosity approach is used to formulate this problem in order to understand the heat transfer mechanism during the melting process. The analysis of the solid-liquid interface shape, the temperature field shows that the conduction is the dominant heat transfer mode in the beginning of the melting process. It is followed by a transition regime and the natural convection becomes the dominant heat transfer mode. The effects of the Rayleigh number and the aspect ratio of the enclosure on the melting phenomenon are studied and it is found that the intensity of the natural convection increases as the Rayleigh number is higher and the aspect ratio is smaller. In the second part of the numerical study, a comparison of the performance of paraffins waxes during the melting process is conducted. Results reveals that from a kinetically RT21 is the most performant but in term of heat storage capacity, it was inferred that RT35HC is the most efficient PCM.

scholarly journals Numerical Simulation of the Natural Convection with Presence of the Nanofluids in Cubical Cavity

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Mohamed Sannad ◽  
Abourida Btissam ◽  
Belarche Lahoucine
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Flow And Heat Transfer ◽  
Heating Section ◽  
The Right

This article consists of a numerical study of natural convection heat transfer in three-dimensional cavity filled with nanofluids. This configuration is heated by a partition maintained at a hot constant and uniform temperature TH. The right and left vertical walls are kept at a cold temperature TC while the rest is adiabatic. The fluid flow and heat transfer in the cavity are studied for different sets of the governing parameters, namely, the nanofluid type, the Rayleigh number Ra = 103, 104, 105, and 106, and the volume fraction Ф varying between Ф = 0 and 0.1. The obtained results show a positive effect of the volume fraction and the Rayleigh number on the heat transfer improvement. The analysis of the results related to the heat transfer shows that the copper-based nanofluid guarantees the best thermal transfer. In addition, the increase of the heating section size and Ra leads to an increased amount of heat. Similarly, increasing the volume fraction improves the intensification of the flow and increases the heat exchange.

Natural Convection in an Externally Heated Vertical or Inclined Square Box Containing Internal Energy Sources

1985 ◽  
Vol 107 (4) ◽  
pp. 855-866 ◽  
Author(s):  
S. Acharya ◽  
R. J. Goldstein
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Flow Pattern ◽  
Internal Energy ◽  
Flux Ratio ◽  
Energy Sources ◽  
Number Range ◽  
Average Heat ◽  
Square Box

A numerical investigation has been made of two-dimensional natural convection of air in an externally heated vertical or inclined square box containing uniformly distributed internal energy sources. Results have been obtained for Rayleigh numbers (both internal and external) up to 107 and inclination angles of 30, 60, and 90 deg from the horizontal. Two distinct flow pattern systems are observed: one, when the external Rayleigh number is larger than the internal Rayleigh number and the other, when the internal Rayleigh number is considerably greater than the external Rayleigh number. The average heat flux ratio (convective heat flux/corresponding conduction heat flux) along the hot surface is observed to undergo large variations in the external Rayleigh number range associated with the transition from one flow pattern to another. The average heat flux ratio along the cold plate is found to increase with increasing external Rayleigh number and decreasing internal Rayleigh number. The local heat flux ratio along a surface attains its maximum value in the vicinity of the region where the heated (or cooled) fluid from the opposite wall or from the interior encounters the surface.

Sign in / Sign up

Export Citation Format

Share Document