scholarly journals Free convection in a vertical cylindrical annulus filled with anisotropic porous medium

2009 ◽  
Vol 13 (1) ◽  
pp. 37-45 ◽  
Author(s):  
Rathinam Thansekhar ◽  
Babu Mahesh ◽  
Sekhar Chandra
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Temperature Distribution ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Free Convection ◽  
Numerical Study ◽  
Radius Ratio ◽  
Permeability Ratio ◽  
Cylindrical Annulus

A numerical study has been carried out for free convection in a vertical cylindrical annulus filled with a porous medium and whose inner wall is isothermally heated and the outer wall is isothermally cooled, the horizontal walls being insulated. The porous medium is assumed to be both hydrodynamically and thermally anisotropic. Numerical results are reported for 0.1 ? K*? 10, 0.1 ? ? ? 10,1 ? A ? 20,2 ? Rr ? 20, and Ra*? 10000. Anisotropy of the porous medium is found to affect fluid flow, temperature distribution and heat transfer significantly. Higher permeability in the vertical direction enhances convective flow intensity and heat transfer inside the annulus. Average Nusselt number on the inner hot wall increases with increase in Rayleigh number or radius ratio, while it decreases with increase in aspect ratio or permeability ratio. The influence of thermal anisotropy is not so significant as that of hydrodynamic anisotropy. The numerically predicted temperature distribution at various locations inside the annulus shows reasonable agreement with experimental results available for isotropic porous medium. Based on a parametric study, correlation for heat transfer is presented in terms of Rayleigh number, aspect ratio, radius ratio, and permeability ratio.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

Effect of Wall Conduction on Combined Free and Forced Laminar Convection in Horizontal Rectangular Channels

1987 ◽  
Vol 109 (4) ◽  
pp. 936-942 ◽  
Author(s):  
G. J. Hwang ◽  
F. C. Chou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Distribution ◽  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Numerical Study ◽  
Fully Developed Flow ◽  
Rectangular Channels ◽  
Laminar Convection

This paper presents a numerical study of the effect of peripheral wall conduction on combined free and forced laminar convection in hydrodynamically and thermally fully developed flow in horizontal rectangular channels with uniform heat input axially, In addition to the Prandtl number, the Grashof number Gr+, and the aspect ratio γ, a parameter Kp indicating the significance of wall conduction plays an important role in heat transfer. A finite-difference method utilizing a power-law scheme is employed to solve the system of governing partial differential equations coupled with the equation for wall conduction. The numerical solution covers the parameters: Pr = 7.2 and 0.73, γ = 0.5, 1, and 2, Kp = 10−4–104, and Gr+ = 0–1.37×105. The flow patterns and isotherms, the wall temperature distribution, the friction factor, and the Nusselt number are presented. The results show a significant effect of the conduction parameter Kp.

Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium

2001 ◽  
Vol 124 (1) ◽  
pp. 203-207 ◽  
Author(s):  
M. R. Dhanasekaran ◽  
Sarit Kumar Das ◽  
S. P. Venkateshan
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Critical Value ◽  
Permeability Ratio ◽  
Anisotropic Permeability ◽  
Anisotropic Porous Medium ◽  
Diffusivity Ratio

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.

Thermal Convection in an Infinite Porous Medium Induced by a Heated Sphere

1997 ◽  
Vol 119 (3) ◽  
pp. 647-650 ◽  
Author(s):  
R. Ganapathy
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Rayleigh Number ◽  
Free Convection ◽  
Wall Temperature ◽  
Transient Behavior ◽  
Temperature Fields ◽  
Series Expansions ◽  
Medium Permeability ◽  
Velocity And Temperature Fields

This paper investigates the transient behavior of the free convection motion and heat transfer induced by a heated sphere with prescribed wall temperature embedded instantaneously in an infinite porous medium. Solutions for the velocity and temperature fields have been obtained in the form of series expansions in Rayleigh number which is based on the medium permeability and the temperature of the sphere. All discussions are based on the assumption that the flow is governed by Darcy's law and the thermal Rayleigh number is small.

scholarly journals Numerical study of natural melt convection in cylindrical cavity with hot walls and cold bottom sink

2013 ◽  
Vol 17 (3) ◽  
pp. 853-864 ◽  
Author(s):  
Abdennacer Ahmanache ◽  
Noureddine Zeraibi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Cylindrical Cavity ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Bulk Temperature ◽  
Flow And Heat Transfer

Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot walls and cold sink is conducted. Calculations are performed in terms of the cavity aspect ratio, the heat exchanger length and the thermo physical properties expressed via the Prandtl number and the Rayleigh number. Results are presented in the form of isotherms, streamlines, average Nusselt number and average bulk temperature for a range of Rayleigh number up to 106. It is observed that Rayleigh number and heat exchanger length influences fluid flow and heat transfer, whereas the cavity aspect ratio has no significant effects.

Experimental Study of Free Convection from a Vertical Flat Plate in Porous Media

2008 ◽  
Vol 273-276 ◽  
pp. 796-801
Author(s):  
L.B.Y. Aldabbagh ◽  
Mohsen Sharifpur ◽  
Mahdi Zamani
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Rayleigh Number ◽  
Free Convection ◽  
Flat Plate ◽  
Saturated Porous Medium ◽  
Convection Heat Transfer ◽  
Steady State Condition ◽  
Free Convection Heat ◽  
Vertical Flat Plate

A set of experiments is done to study the phenomenon of free convection heat transfer from an isothermal vertical flat plate embedded in a saturated porous medium in steady state condition. The porous medium consisting of 0.8 cm spheres. The aspect ratio of the isothermal flat plate, H/W, is equal to 2. Where H is the height and W is the width of the vertical plate. The investigations were cared out for Darcy modified Rayleigh number between 100 and 500. The results indicate that heat transfer increases linearly with increasing the Darcy modified Rayleigh number. In addition, the present results are in good agreement with the higher-order boundary layer theory obtained by Cheng and Hsu [1].

Numerical Investigation of Coupled Surface Radiation and Natural Convection in a Triangular Shaped Roof (Gabel Roof) under Winter Conditions

2019 ◽  
Vol 392 ◽  
pp. 200-217
Author(s):  
Abdel Illah Amrani ◽  
Nadia Dihmani ◽  
Samir Amraqui ◽  
Ahmed Mezrhab
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Climatic Conditions ◽  
Surface Radiation ◽  
Working Fluid ◽  
Building Roof ◽  
Simpler Algorithm

In the building, roof is a major element contributing to the space thermal load. Due to its importance, this component has been widely studies in the literature and under various climatic conditions. In this paper, a numerical study was carried out for the coupling of natural convection and surface radiation heat transfer in a triangular shaped roof with eave (Gabel roof) for cold climates. The numerical solution is obtained using a finite volume method based on the SIMPLER algorithm for the treatment of velocity-pressure coupling. Concerning the radiation exchange, the working fluid (air) is assumed to be transparent, so only the solid surfaces (assumed diffuse-grey) give a contribute to such exchange. Governing parameters on heat transfer and flow fields are Rayleigh number (Ra), aspect ratio (A) and eave lengths (e*). Numerical results are obtained to display the isotherms, streamlines and the heat transfer rate in terms of local and average Nusselt numbers. We found that the production of several circular cells is proportional to the decrease of aspect ratio and the increase of Rayleigh number. In addition, the heat transfer is much more pronounced in the presence of thermal radiation.

scholarly journals Effect of Al2O3/water nanofluid on Conjugate Free Convection in a Baffle Attached Square Enclosure

Mechanika ◽  
2020 ◽  
Vol 26 (2) ◽  
pp. 126-133
Author(s):  
Thansekhar M.Rathinam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rayleigh Number ◽  
Free Convection ◽  
Conjugate Heat Transfer ◽  
Volume Fraction ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure

A numerical study of conjugate free convection heat transfer of Al2O3/water nanofluid inside a differentially heated square enclosure with a baffle attached to its hot wall has been carried out. A detailed parametric study has been carried out to analyze the effect of Rayleigh number (104 < Ra < 106), length, thickness and position of baffle, conductivity ratio and volume fraction of the nanoparticle (0<<0.2) on heat transfer. The thermal conductivity ratio of the baffle plays a major role on the conjugate heat transfer inside the enclosure. Higher the baffle length better is the effectiveness of the baffle. The average Nusselt number is found to be an increasing function of both thermal conductivity ratio and volume fraction of the nanofluid. The minimum enhancement of conjugate heat transfer is 30% when Al2O3/water nanofluid of 0.1 volume fraction is used for the entire range of Rayleigh number considered.

Natural Convection Heat and Mass Transfer in the Vertical Cylindrical Porous Channel Under the Effects of Time-Periodic Boundary Condition

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Hayder I. Mohammed ◽  
Donald Giddings
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Boundary Condition ◽  
Porous Medium ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Heat And Mass Transfer ◽  
Vertical Wall

Abstract Heat and mass transfer are investigated numerically with steady-state laminar natural convection through a vertical cylindrical enclosure filled with a liquid-saturated porous medium. The vertical wall is under a constant magnetic field and various durations of periodic heating boundary condition; the top and bottom surfaces are kept at a constant cold temperature. Continuity, momentum, and energy equations are transformed to dimensionless equations. The finite difference approach with the line successive over-relaxation (LSOR) method is used to obtain the computational results. This study covers the heat transfer, the temperature distribution, and the velocity field in the domain under the variation of different parameters. The code used is validated by modifying it to analyze the Nusselt number in the existing experimental literature of Izadpanah et al. (1998, “Experimental and Theoretical Studies of Convective Heat Transfer in a Cylindrical Porous Medium,” Int. J. Heat Fluid Flow, 19(6), pp. 629–635). This work shows that Nusselt number decreases (with varying gradient) as the aspect ratio increases, and that it increases as the Rayleigh number increases. The centerline temperature has a proportional relationship with the heating amplitude and the heating period (as the system receives more heat) and is inversely proportional with Rayleigh number. Increasing the Rayleigh number causes increased convective velocity, which affects the position of the hot region, and causes a decrease in the temperature field. Increasing the aspect ratio results in a warm stream at the center of the cylinder, and when the time period of the heating increases, the circulation becomes faster and the intensity of the temperature contour layers decreases. In this work, a correlation for Nu as a function of the mentioned parameters is developed.

Quantification of free convection within a hemispherical annulus through a porous medium saturated by water-copper nanofluid

2019 ◽  
Vol 29 (3) ◽  
pp. 1153-1166 ◽  
Author(s):  
Abderrahmane Baïri ◽  
Nagaraj Suresh ◽  
Palanisamy Gayathri ◽  
Nagarajan Nithyadevi ◽  
Purusothaman Abimanyu
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Rayleigh Number ◽  
Electronic Device ◽  
Numerical Study ◽  
Control Volume ◽  
Saturated Porous Medium ◽  
Pure Water ◽  
Thermal Design ◽  
Content Type

Purpose A porous medium saturated with a nanofluid based on pure water and copper nanoparticles is used for cooling a hemispherical electronic device contained in an annulus space. The disc of the cavity could be inclined at an angle ranging from 0 ° (horizontal disc with dome facing upwards) to 180° (horizontal disc with dome facing downwards). The important surface heat flux generated by the dome leads to high Rayleigh number values reaching 7.29 × 10^10. The purpose of this work is to examine the influence of the nanofluid saturated porous medium on the free convective heat transfer. Design/methodology/approach Heat transfer occurring between this active component and the isothermal passive cupola is quantified by means of a three-dimensional numerical study using the control volume method associated to the SIMPLE algorithm. Findings The work shows that heat transfer in the annulus space is improved by interposing a porous medium saturated with the water-copper nanofluid. Originality/value New correlation is proposed to calculate the Nusselt number for any combination of the inclination angle, the fraction volume, the Rayleigh number and the ratio between the thermal conductivities of the porous medium and the fluid. The wide ranges corresponding to these parameters allow the thermal design of this electronic equipment for various configurations.

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