AN EXPERIMENTAL STUDY OF NATURAL CONVECTION HEAT TRANSFER FROM A HORIZONTAL CYLINDER IN HIGH RAYLEIGH NUMBER LAMINAR AND TURBULENT REGIONS

This paper reports an experimental study of natural convection heat transfer from a horizontal isothermal cylinder between vertical adiabatic walls. Some of the industrial applications of this problem are cooling and casing design of electronic equipment, nuclear reactor safety, and heat extraction from solar thermal storage devices. Heat transfer from 3.81 cm and 2.54 cm diameter cylinders was determined by measuring the electric power supplied to the heater, which was placed inside the cylinders, and correcting for radiation and end losses. Average Nusselt numbers were determined for a Rayleigh number range of 2 × 103 to 3 × 105 and wall spacing to cylinder diameter ratios of 1.5, 2, 3, 4, 6, 8, 10, 12, and ∞. It was found that the confinement of a heated horizontal cylinder by adiabatic walls enhances the heat transfer from the cylinder continuously. This effect is more pronounced at low Rayleigh numbers. A maximum relative enhancement of 45 percent was obtained over the range of experimental conditions studied. Schlieren and flow visualization studies were conducted at selected values of Rayleigh number and wall spacing to cylinder diameter ratios to further explain the heat transfer characteristics and the associated flow physics of the present problem.

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Natural Convection Heat Transfer Coefficients for a Short Horizontal Cylinder Attached to a Vertical Plate

Journal of Heat Transfer ◽

10.1115/1.3244519 ◽

1981 ◽

Vol 103 (4) ◽

pp. 630-637 ◽

Cited By ~ 10

Author(s):

E. M. Sparrow ◽

G. M. Chrysler

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Natural Convection ◽

Rayleigh Number ◽

Vertical Plate ◽

Convection Heat Transfer ◽

Horizontal Cylinder ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

End Effects

Experiments were performed to investigate the natural convection heat transfer characteristics of a short isothermal horizontal cylinder attached to an equi-temperature vertical plate. The apparatus was designed so that the cylinder could be attached to the plate at any one of three positions along the height of the plate. Two cylinders were employed (one at a time) during the course of the experiments, one of which had a length equal to its diameter while the other had a length that was half the diameter. At each attachment position and for each cylinder, the Rayleigh number (based on the cylinder diameter) ranged from 1.4 × 104 to 1.4 × 105. It was found that the interaction of the flat plate boundary layer with the cylinder brought about a reduction of the cylinder Nusselt number relative to that for the classical case of the long isolated horizontal cylinder without end effects. The respective deviations of the Nusselt numbers for the shorter and longer of the participating cylinders from the literature correlation for the isolated cylinder were twenty percent and ten percent. At a given Rayleigh number, the cylinder Nusselt number was quite insensitive to the position of the cylinder along the plate, with the typical data spread due to height being in the 5–7 percent range. The Nusselt number was also rather insensitive to cylinder length, showing a ten percent increase as the length-diameter ratio was increased from one-half to one.

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Natural Convection Heat Transfer and Entropy Generation From a Horizontal Cylinder With Baffles

Journal of Heat Transfer ◽

10.1115/1.1287501 ◽

2000 ◽

Vol 122 (4) ◽

pp. 679-692 ◽

Cited By ~ 8

Author(s):

B. A/K Abu-Hijleh

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Natural Convection ◽

Rayleigh Number ◽

Entropy Generation ◽

Convection Heat Transfer ◽

Horizontal Cylinder ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

Wide Range

The problem of laminar natural convection heat transfer from a horizontal cylinder with multiple, equally spaced, low conductivity baffles on its outer surface was investigated numerically. The effect of several combinations of number of baffles and baffle height on the average Nusselt number was studied over a wide range of Rayleigh numbers. The computed velocity and temperature fields were also used to calculate the local and global entropy generation for different cylinder diameters. The results showed that there was an optimal combination of a number of baffles and baffle height for minimum Nusselt number for a given value of the Rayleigh number. Short baffles slightly increased the Nusselt number at small values of the Rayleigh number. The global entropy generation increased monotonically with increasing Rayleigh number and decreased with increasing cylinder diameter, baffle height, and number of baffles. [S0022-1481(00)01203-2]

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