Effect of Fin Height and Rayleigh Number with Small Increments on Convective Heat Transfer in a Horizontal Annulus

This three-dimensional (3D) numerical work based on the volume control method quantifies the convective heat transfer occurring in a hemispherical cavity filled with a ZnO–H2O nanofluid saturated porous medium. Its main objective is to improve the cooling of an electronic component contained in this enclosure. The volume fraction of the considered monophasic nanofluid varies between 0% (pure water) and 10%, while the cupola is maintained isothermal at cold temperature. During operation, the active device generates a heat flux leading to high Rayleigh number reaching [Formula: see text] and may be inclined with respect to the horizontal plane at an angle ranging from 0[Formula: see text] to 180[Formula: see text] (horizontal position with cupola facing upwards and downwards, respectively) by steps of 15[Formula: see text]. The natural convective heat transfer represented by the average Nusselt number has been quantified for many configurations obtained by combining the tilt angle, the Rayleigh number, the nanofluid volume fraction and the ratio between the thermal conductivity of the porous medium’s solid matrix and that of the base fluid. This ratio has a significant influence on the free convective heat transfer and ranges from 0 (without porous media) to 70 in this work. The influence of the four physical parameters is analyzed and commented. An empirical correlation between the Nusselt number and these parameters is proposed, allowing determination of the average natural convective heat transfer occurring in the hemispherical cavity.

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FREE CONVECTIVE HEAT TRANSFER FROM AN OBJECT AT LOW RAYLEIGH NUMBER

Journal of Mechanical Engineering ◽

10.3329/jme.v43i1.15775 ◽

2013 ◽

Vol 43 (1) ◽

pp. 23-28

Author(s):

Md. Golam Kader ◽

Khandkar Aftab Hossain

Keyword(s):

Heat Transfer ◽

Rayleigh Number ◽

Convective Heat Transfer ◽

Convective Heat ◽

Difference Method ◽

Vertical Direction ◽

Large Enclosure ◽

Uniform Grids ◽

Heated Object ◽

Free Convective Heat Transfer

Free convective heat transfer from a heated object in very large enclosure is investigated in thepresent work. Numerical investigation is conducted to explore the fluid flow and heat transfer behavior in thevery large enclosure with heated object at the bottom. Heat is released from the heated object by naturalconvection. Entrainment is coming from the surrounding. The two dimensional Continuity, Navier-Stokesequation and Energy equation have been solved by the finite difference method. Uniform grids are used in theaxial direction and non-uniform grids are specified in the vertical direction. The differential equations arediscretized using Central difference method and Forward difference method. The discritized equations withproper boundary conditions are sought by SUR method. It has been done on the basis of stream function andvorticity formulation. The flow field is investigated for fluid flowing with Rayleigh numbers in the range of 1.0 ?Ra ? 1.0×103 and Pr=0.71. It is observed that the distortion of flow started at Rayleigh number Ra=10. It isobserved that the average heat transfer remains constant for higher values of Reyleigh number and heatingefficiency varies with Ra upto the value of Ra=35 and beyond this value heating efficiency remains constant.DOI: http://dx.doi.org/10.3329/jme.v43i1.15775

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A Numerical Study of the Effect of Triangular Waves on Natural Convective Heat Transfer From an Upward Facing Heated Horizontal Isothermal Surface

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2016-65716 ◽

2016 ◽

Cited By ~ 5

Author(s):

Patrick H. Oosthuizen

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Rayleigh Number ◽

Prandtl Number ◽

Surface Waves ◽

Convective Heat Transfer ◽

Convective Heat ◽

Numerical Study ◽

Heated Surface ◽

Isothermal Surface

A numerical study of natural convective heat transfer from an upward facing, heated horizontal isothermal surface imbedded in a large flat adiabatic surface has been undertaken. On the heated surface is a series of triangular shaped waves. Laminar, transitional, and turbulent flow conditions have been considered. The flow has been assumed to be two-dimensional and steady. The fluid properties have been assumed constant except for the density change with temperature giving rise to the buoyancy forces. This was with treated using the Boussinesq approach. The numerical solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The k-epsilon turbulence model with full account being taken of buoyancy force effects has been employed. The heat transfer rate from the heated surface expressed in terms of a Nusselt number is dependent on the Rayleigh number, the number of waves, the height of the waves relative to the width of the heated surface, and the Prandtl number. This study obtained results for a Prandtl number of 0.74 which is effectively the value for air. An investigation of the effect of the Rayleigh number, the dimensionless height of the surface waves, and the number of surface waves on the Nusselt number has been undertaken.

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Experimental study of free convective heat transfer in a liquid-saturated porous bed at high Rayleigh number

Wärme- und Stoffübertragung ◽

10.1007/bf00997634 ◽

1980 ◽

Vol 13 (1-2) ◽

pp. 61-71 ◽

Cited By ~ 3

Author(s):

N. Seki ◽

S. Fukusako ◽

Y. Ariake

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Rayleigh Number ◽

Convective Heat Transfer ◽

Convective Heat ◽

Porous Bed ◽

Free Convective Heat Transfer

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A Numerical Study of the Simultaneous Natural Convective Heat Transfer From the Upper and Lower Surfaces of a Thin Isothermal Horizontal Circular Plate

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2016-65540 ◽

2016 ◽

Cited By ~ 4

Author(s):

Patrick H. Oosthuizen ◽

Abdulrahim Kalendar

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Rayleigh Number ◽

Prandtl Number ◽

Convective Heat Transfer ◽

Heat Transfer Rate ◽

Convective Heat ◽

Transfer Rate ◽

The Mean ◽

Adiabatic Section

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.

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The Effect of Inclination on Natural Convective Heat Transfer from a Slender Cuboid

Processes ◽

10.3390/pr9091668 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1668

Author(s):

Abdulrahim Kalendar ◽

Yousuf Alhendal ◽

Shafqat Hussain ◽

Patrick Oosthuizen

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Rayleigh Number ◽

Boundary Conditions ◽

Convective Heat Transfer ◽

Convective Heat ◽

Vertical Axis ◽

Surface Boundary ◽

Nusselt Numbers ◽

The Mean

A numerical study was undertaken of the naturally occurring laminar convective heat transfer from a slender cuboid with a relatively narrow cross-section (square) and an exposed top surface. The cuboid was perpendicularly placed on an adiabatic flat base plate and two types of surface boundary conditions were considered. The slender cuboid was inclined relative to the vertical axis at angles ranging from 0 to 180 degrees. The flow was considered symmetrical along the vertical axis of the slender cuboid. The equations governing the system were numerically solved in terms of dimensionless variables using FLUENT software. From the results obtained, mean Nusselt numbers over the slender cuboid were calculated using parameters such as: the Rayleigh number for heat flux, Ra*; the Rayleigh number, Ra; the slender cuboid dimensionless width, i.e., the ratio of the width to the height of the heated slender cuboid, W = w/h; and the position of the slender cuboid relative to the vertical, φ. Simulation results were produced for the boundary conditions of constant temperature, constant heat flux, and for Pr = 0.7. The effects of these parameters on the mean Nusselt number for the combined and for the individual surfaces of the slender cuboid are presented and the mean Nusselt numbers are correlated.

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Numerical Solution of Natural Convective Heat Transfer Under Magnetic Field Effect

Acta Mechanica et Automatica ◽

10.2478/ama-2019-0004 ◽

2019 ◽

Vol 13 (1) ◽

pp. 23-29

Author(s):

Serpil Şahin ◽

Hüseyin Demir

Keyword(s):

Magnetic Field ◽

Heat Transfer ◽

Rayleigh Number ◽

Convective Heat Transfer ◽

Convective Heat ◽

Field Effect ◽

Time Derivative ◽

Magnetic Field Effect ◽

Stability Properties ◽

Chandrasekhar Number

Abstract In this study, non-Newtonian pseudoplastic fluid flow equations for 2-D steady, incompressible, the natural convective heat transfer are solved numerically by pseudo time derivative. The stability properties of natural convective heat transfer in an enclosed cavity region heated from below under magnetic field effect are investigated depending on the Rayleigh and Chandrasekhar numbers. Stability properties are studied, in particular, for the Rayleigh number from 104 to 106 and for the Chandrasekhar number 3, 5 and 10. As a result, when Rayleigh number is bigger than 106 and Chandrasekhar number is bigger than 10, the instability occurs in the flow domain. The results obtained for natural convective heat transfer problem are shown in the figures for Newtonian and pseudoplastic fluids. Finally, the local Nusselt number is evaluated along the bottom wall.

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A Computational Fluid Dynamics Investigation on the Effect of the Angular Velocities of Hot and Cold Turbulator Cylinders on the Heat Transfer Characteristics of Nanofluid Flows Within a Porous Cavity

Journal of Energy Resources Technology ◽

10.1115/1.4047253 ◽

2020 ◽

Vol 142 (11) ◽

Cited By ~ 3

Author(s):

Yan Cao ◽

Yu Bai ◽

Jiang Du ◽

Saman Rashidi

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Natural Convection ◽

Rayleigh Number ◽

Turbulent Flow ◽

Convective Heat Transfer ◽

Convective Heat ◽

Porous Cavity ◽

Cu Nanoparticle ◽

The Impact

Abstract In the present study, turbulent flow of a Cu-water nanofluid through a porous cavity is investigated using a numerical method. Two rotating cylinders with different temperatures are placed inside the porous enclosure to generate turbulent structures. Forced and natural convective heat transfer mechanisms are compared for different Cu nanoparticle concentrations. The natural convection within the enclosure is resulted from buoyancy forces as an effect of temperature differences among hot and cold cylindrical turbulators. To investigate the effect of the cavity geometry on the natural convection heat, the simulations are done for various Rayleigh number values. Accordingly, Rayleigh number increment provides higher Nusselt number values. However, in turbulent flow regimes, forced convection may weaken the natural convection. It is proven that for lower Reynolds numbers, the Nusselt number reaches higher values because of buoyant-driven convective heat transfer deterioration. Moreover, the angular velocity directions of both cylinders slightly affect the Nusselt number. Besides, the impact of porosity on the heat transfer rate is studied for different Darcy numbers. It is concluded that, for lower Ra numbers, as Darcy number rises, the average Nusselt number through the cavity is slightly boosted. In addition, it is shown that for cases with high Ra and Re values, Cu nanoparticle addition adversely affects the heat transfer process. At Ra = 1011, as Cu nanoparticle increases from 0 to 0.02 and 0.04, the average Nu decreases up to 17.65% and 27.48%, respectively.

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Experimental Investigation of Natural Convective Heat Transfer From Horizontal, Inclined and Vertical Cylinder With Constant Heat Flux

Volume 7: Fluid Flow, Heat Transfer and Thermal Systems, Parts A and B ◽

10.1115/imece2010-37903 ◽

2010 ◽

Author(s):

A. Gharehghani ◽

R. Hoseini ◽

M. M. Salahi

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Nusselt Number ◽

Rayleigh Number ◽

Convective Heat Transfer ◽

Convective Heat ◽

Constant Heat Flux ◽

Experimental Results ◽

Constant Heat ◽

Constant Length

In this study, natural convective heat transfer from cylindrical slender rods with different length and diameters and different angles of inclination (from horizontal to vertical) at constant heat flux condition was measured. For each inclination angle, average natural heat transfer coefficient was obtained. The effects of the angle of inclination and that of the diameter and length of cylinders on heat transfer rates were examined. The angles of 0°, 15°, 30°, 45°, 60°, 75° and 90° were studied. Experimental results show that increasing the diameter of the cylinder, with constant length and the Rayleigh number based on length causes the decrease of the Nusselt number. Increasing the length of the cylinders, with constant diameter and Rayleigh number based on diameter causes the decrease of the Nusselt number. Increasing either the angle of inclination or length decreases the effect of diameter on the heat transfer rate. Experimental results in terms of Nusselt number were correlated as a function of modified Rayleigh number and dimensionless parameters containing diameter, length and orientation angle.

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Natural Convection Heat Transfer in Moderate Aspect Ratio Enclosures

Journal of Heat Transfer ◽

10.1115/1.3451052 ◽

1979 ◽

Vol 101 (4) ◽

pp. 655-659 ◽

Cited By ~ 14

Author(s):

B. A. Meyer ◽

J. W. Mitchell ◽

M. M. El-Wakil

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Rayleigh Number ◽

Aspect Ratio ◽

Convective Heat Transfer ◽

Convective Heat ◽

Convection Heat Transfer ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

Aspect Ratios

Local and average heat transfer coefficients for natural convection between parallel plates separated by slats to create enclosures of moderate aspect ratio have been experimentally determined using an interferometric technique. The effects of Rayleigh number, tilt and slat angle, and aspect ratio on the Nusselt number have been determined. The Rayleigh number range tested was up to 7 × 104, and the aspect ratio (ratio of enclosure length to plate spacing) varied between 0.25 and 4. The angles of tilt of the enclosure with respect to the horizontal were 45, 60 and 90 deg. Slat angles of 45, 60, 90 and 135 deg were studied. The results obtained in a previous investigation [1] for aspect ratios of 9 to 36 are included to show continuity. The results indicate that the convective heat transfer is a strong function of the aspect ratio for aspect ratios less than 4. For aspect ratios in the range of 0.5 to 4, spacers between the plates increase, rather than decrease, natural convection heat transfer compared to that for long enclosures. Slat angles less than 90 deg (i.e., oriented downward) reduce convective heat transfer.

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