Natural Convection Between Two Horizontal Cylinders in an Adiabatic Circular Enclosure

1993 ◽  
Vol 115 (1) ◽  
pp. 158-165 ◽  
Author(s):  
C. J. Ho ◽  
W. S. Chang ◽  
C. C. Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Inclination Angle ◽  
Numerical Study ◽  
Convection Flow ◽  
Vertical Orientation ◽  
Recirculating Flow ◽  
Visualization Experiments ◽  
Horizontal Cylinders ◽  
Gap Width

A numerical study of natural convection flow structure and heat transfer has been undertaken for air around two horizontal, differentially heated cylinders confined to an adiabatic circular enclosure. Parametric simulations were performed to assess the effects of gap width between cylinders as well as the inclination angle of the enclosure with respect to gravity. Results clearly indicate that the fluid flow complexity and heat transfer characteristics of air amid the cylinders and enclosure wall are strongly affected by the Rayleigh number, the inclination angle, and the gap width between the cylinders. With the exception of the vertical orientation, heat exchange between the differentially heated cylinders is predominantly controlled by a counterclockwise recirculating flow enclosing them. In addition, flow visualization experiments were conducted for the physical configuration under consideration, and a generally good agreement for the flow pattern was observed between the predictions and the experiments, further validating the present numerical simulation.

Lattice Boltzmann Computations of Natural Convection Heat Transfer of Nanofluid in a Square Cavity Heated by Protruding Heat Source

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Mustapha Faraji ◽  
El Mehdi Berra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Inclination Angle ◽  
Lattice Boltzmann ◽  
Base Fluid ◽  
Numerical Code ◽  
Convection Flow ◽  
Square Enclosure ◽  
Rayleigh Numbers

Abstract This paper reported the mathematical modeling and numerical simulation of natural convection flow of Cu/water nanofluid in a square enclosure using the lattice Boltzmann method (LBM). The cavity is heated from below by heat source and cooled by the top wall. The vertical walls are adiabatic. After validating the numerical code against the numerical and experimental data, simulations were performed for different Rayleigh numbers (104–0.5 × 107), nanoparticles volume fractions (0–8%), and cavity inclination angle (0 deg–90 deg). The effects of the studied parameters on the streamlines, on isotherms distributions within the enclosure, and on the local and average Nusselt numbers are investigated. It was found that heat transfer and fluid flow structure depend closely on the nanoparticle concentration. Results show differences in stream separation between a base fluid and the nanofluid. Also, adding small nanoparticles fractions, less than 6%, to the base fluid enhances the heat transfer for higher Rayleigh numbers and cavity inclination angle less than 30 deg. It is concluded that the optimal dilute suspension of copper nanoparticles can be applied as a passive way to enhance heat transfer in natural convection engineering applications.

scholarly journals Numerical Investigation of Natural Convection Flow in a Hexagonal Enclosure Having Vertical Fin

2019 ◽  
Vol 11 (2) ◽  
pp. 173-183 ◽  
Author(s):  
M. Fayz -Al- Asad ◽  
M. M. A. Sarker ◽  
M. J. H. Munshi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Transfer Rate ◽  
Numerical Study ◽  
Bottom Wall ◽  
Convection Flow ◽  
Temperature Profiles ◽  
Natural Convection Flow ◽  
Fin Efficiency

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.

ANALYSIS OF NATURAL CONVECTION HEAT TRANSFER BETWEEN TWO HORIZONTAL CYLINDERS AND THEIR ENCLOSURE

1992 ◽  
Vol 16 (1) ◽  
pp. 17-32 ◽  
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Nusselt Numbers ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

A numerical study has been conducted for natural convection heat transfer for air around two horizontal heated cylinders placed inside a rectangular enclosure cooled from the side. Three cylinder spacings were investigated. The local and overall Nusselt numbers were determined over the range of Rayleigh numbers from 104 to 106. It is found that the thermal performance of the unit is strongly influenced by the Rayleigh number and, to a lesser extent, by the cylinder spacing. A correlation is suggested for the overall Nusselt number.

Natural Convection Heat Transfer Between Eccentric Horizontal Cylinders

1983 ◽  
Vol 105 (1) ◽  
pp. 108-116 ◽  
Author(s):  
J. Prusa ◽  
L. S. Yao
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Outer Boundary ◽  
Outer Cylinder ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Flow ◽  
Grashof Number ◽  
Average Heat ◽  
Horizontal Cylinders

Laminar natural convection flow between vertically eccentric horizontal cylinders is studied numerically. The inner and outer cylinders are heated and cooled, respectively, to maintain constant surface temperatures. A physical model is introduced which accounts for the effects of fluid buoyancy as well as the eccentricity of the outer cylinder. A radial transformation is used to map the eccentric outer boundary into a concentric circle. Both eccentricity and buoyancy have a significant influence on the heat transfer and flow field of a fluid between horizontal cylinders. The effect of buoyancy, which enhances average heat transfer, increases with the Grashof number. Eccentricity influences the flow in two ways. First, by decreasing the distance between the two cylinders over part of their surfaces, it increases the local heat transfer due to conduction. Second, the eccentricity influences the connective mode of heat transfer. Results show that moderate positive values of eccentricity, enhance convective heat transfer. Results for a range of Grashof number are given, for varying eccentricity, for a radius ratio of 2.6 and a Prandtl number of 0. 706. Detailed predictions of the temperature and flow fields, and local heat transfer rates are given for representative cases. Also presented is the variation of average heat transfer rate and average shear stress with Grashof number and eccentricity. Comparisons with earlier numerical, experimental and analytic results are made.

scholarly journals Natural Convection in Inclined Porous Square Enclosure

2020 ◽  
Vol 330 ◽  
pp. 01003
Author(s):  
Abdennacer Belazizia ◽  
Smail Benissaad ◽  
Said Abboudi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Inclination Angle ◽  
Fluid Motion ◽  
Darcy Number ◽  
Convection Flow ◽  
Transfer Rates ◽  
Square Enclosure ◽  
Volume Method

Steady, laminar, natural convection flow in porous square enclosure with inclination angle is considered. The enclosure is filled with air and subjected to horizontal temperature gradient. Darcy- Brinkman-Forchheimer model is considered. Finite volume method is used to solve the dimensionless governing equations. The physical problem depends on five parameters: Rayleigh number (Ra =103-106), Prandtl number (Pr=0.71), Darcy number (Da=0.01), inclination angle φ=(0°-227°), porosity of the medium (ε=0.7) and the aspect ratio of the enclosure (A=1). The main focus of the study is on examining the effect of Rayleigh number on fluid flow and heat transfer rates. The effect of inclination angle is also considered. The results including streamlines, isotherm patterns, flow velocity and the average Nusselt number for different values of Ra and φ. The obtained results show that the increase of Ra leads to enhance heat transfer rate. The fluid particles move with greater velocity for higher thermal Rayleigh number. Also φ affects the fluid motion and heat transfer in the enclosure. Velocity and heat transfer are more important when φ takes the value (30°).

Study of Turbulent Natural Convection in Vertical Storage Tubes for Supercritical Thermal Storage System

2013 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
H. Pirouz Kavehpour ◽  
Adrienne S. Lavine ◽  
Gani B. Ganapathi ◽  
Richard E. Wirz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Storage System ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Convection Flow ◽  
Vertical Orientation ◽  
Turbulent Natural Convection ◽  
Aspect Ratios

The effect of turbulent natural convection in vertical storage tubes containing a supercritical fluid is investigated computationally. In a supercritical thermal storage system, thermal energy is transferred to the storage fluid and is stored as the internal energy of the fluid in supercritical state. The heat is conducted from the heat transfer fluid to the storage fluid through the storage tube wall. Unlike phase-change systems, the heat transfer mechanism within the storage tubes of supercritical thermal storage system is dominantly affected by rigorous turbulent natural convection. The natural convection enhances the heat transfer and compensates for the low thermal conductivity of the storage fluid. The turbulent buoyancy-driven flow field in vertical storage tubes with different aspect ratios is investigated in this paper and the effect of vertical orientation of storage tubes on the characteristics of the flow field is explored. A standard k-epsilon method is utilized to model the Reynolds stresses in turbulent natural convection flow. The results of this study show that the turbulent buoyancy-driven flow and natural convection play an important role in charge and discharge of the supercritical thermal storage system. The charge time of the system is a function of Rayleigh number and aspect ratio of the storage tube.

Natural Convection From Two Thermal Sources in a Vertical Porous Layer

2005 ◽  
Vol 128 (1) ◽  
pp. 104-109 ◽  
Author(s):  
Nawaf H. Saeid
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Separation Distance ◽  
Convection Flow ◽  
Thermal Sources ◽  
Heated Element

Numerical study of natural convection flow induced by two isothermally heated elements located on adiabatic vertical plate immersed in a Darcian porous medium is carried out in the present article. The natural convection is affected by the Rayleigh number, the separation distance between the elements, their temperature ratio, and the length of the upper element. The numerical results are presented as average Nusselt number versus Rayleigh number for wide ranges of the governing parameters. It is found that the heat transfer from the lower element is not affected by the presence of the upper element for equal temperatures of the elements. The heat transfer from the lower element can be enhanced by increasing the temperature of the upper element due to the suction effect. The average Nusselt number along the upper heated element is found to increase with the increase of any of the governing parameters.

An Investigation of the Effect of interrupted fin arrangements on the Thermal Performance of a Heat Sink under a Free Convection Condition

2019 ◽  
Vol 7 (1) ◽  
pp. 43-53
Author(s):  
Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins was investigated numerically in a natural convection field, with steady-state heat transfer. A numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of the fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins. The number of fins used on the surface is eight. In this study, the heat input was used as follows: 20, 40, 60, 80, 100, and 120 watts. This study focused on interrupted rectangular fins with a different arrangement and angle of the fins. Results show that the addition of interruption in fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate as an equation can be obtained.

Laminar natural convection about an isothermally heated sphere at small Grashof number

1968 ◽  
Vol 34 (1) ◽  
pp. 163-176 ◽  
Author(s):  
Francis E. Fendell
Keyword(s):  
Natural Convection ◽  
Three Dimensional ◽  
Perturbation Expansion ◽  
Outer Sphere ◽  
Convective Transport ◽  
Convection Flow ◽  
Constant Density ◽  
Boussinesq Model ◽  
Grashof Number ◽  
Recirculating Flow

The flow induced by gravity about a very small heated isothermal sphere introduced into a fluid in hydrostatic equilibrium is studied. The natural-convection flow is taken to be steady and laminar. The conditions under which the Boussinesq model is a good approximation to the full conservation laws are described. For a concentric finite cold outer sphere with radius, in ratio to the heated sphere radius, roughly less than the Grashof number to the minus one-half power, a recirculating flow occurs; fluid rises near the inner sphere and falls near the outer sphere. For a small heated sphere in an unbounded medium an ordinary perturbation expansion essentially in the Grashof number leads to unbounded velocities far from the sphere; this singularity is the natural-convection analogue of the Whitehead paradox arising in three-dimensional low-Reynolds-number forced-convection flows. Inner-and-outer matched asymptotic expansions reveal the importance of convective transport away from the sphere, although diffusive transport is dominant near the sphere. Approximate solution is given to the nonlinear outer equations, first by seeking a similarity solution (in paraboloidal co-ordinates) for a point heat source valid far from the point source, and then by linearization in the manner of Oseen. The Oseen solution is matched to the inner diffusive solution. Both outer solutions describe a paraboloidal wake above the sphere within which the enthalpy decays slowly relative to the rapid decay outside the wake. The updraft above the sphere is reduced from unbounded growth with distance from the sphere to constant magnitude by restoration of the convective accelerations. Finally, the role of vertical stratification of the ambient density in eventually stagnating updrafts predicted on the basis of a constant-density atmosphere is discussed.

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