An interferometric investigation of the effect of separation distance and temperature imbalance on natural convection for two horizontal cylinders at moderate Rayleigh numbers

1985 ◽  
Vol 19 (4) ◽  
pp. 255-262 ◽  
Author(s):  
P. Razelos
Keyword(s):  
Natural Convection ◽  
Separation Distance ◽  
Interferometric Investigation ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

Effect of Vertical Separation Distance and Cylinder-to-Cylinder Temperature Imbalance on Natural Convection for a Pair of Horizontal Cylinders

1981 ◽  
Vol 103 (4) ◽  
pp. 638-644 ◽  
Author(s):  
E. M. Sparrow ◽  
J. E. Niethammer
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Vertical Plane ◽  
Separation Distance ◽  
The Other ◽  
Vertical Separation ◽  
Heat Transfer Characteristics ◽  
Maximum Value ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

Experiments were performed to study the interactive natural convection from a pair of heated horizontal cylinders situated one above the other in a vertical plane. Prime attention was focused on how the heat transfer characteristics of the upper cylinder are affected by the presence of the lower cylinder. The vertical center-to-center separation distance between the cylinders was varied from two to nine cylinder diameters. The cylinder-to-cylinder temperature imbalance was also varied independently and systematically, with the wall-to-ambient temperature difference for the lower cylinder ranging from zero to three times that for the upper cylinder. Experiments were carried out for upper-cylinder Rayleigh numbers from 20,000 to 200,000. It was found that for a given temperature imbalance and upper-cylinder Rayleigh number, the upper-cylinder Nusselt number takes on a maximum value as a function of separation distance. The separation distance for which the maximum occurs is in the range of seven to nine cylinder diameters. The enhancement or degradation of the upper-cylinder Nusselt number relative to that for a single cylinder is strongly dependent on the separation distance, with degradation of the Nusselt number being more common at small separations and enhancement prevailing at larger separations. With regard to the temperature imbalance, its effect on the Nusselt number is of major importance at small separations but not at large separations.

scholarly journals Natural Convection From Isothermal Horizontal Cylinders

2009 ◽  
Author(s):  
Ian M. O. Gorman ◽  
Darina B. Murray ◽  
Gerard Byrne ◽  
Tim Persoons
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Separation Distance ◽  
Thermal Plume ◽  
Number Range ◽  
Vertically Aligned ◽  
Isothermal Cylinders ◽  
Horizontal Cylinders

The research described here is concerned with natural convection from isothermal cylinders, with a particular focus on the interaction between a pair of vertically aligned cylinders. Prime attention was focused on how the local heat transfer characteristics of the upper cylinder are affected due to buoyancy induced fluid flow from the lower cylinder. Tests were performed using internally heated copper cylinders with an outside diameter 30mm and a vertical separation distance between the cylinders ranging from two to three cylinder diameters. Plume interaction between the heated cylinders was investigated within a Rayleigh number range of 2×106 to 6×106. Spectral analysis of the associated heat transfer interaction is presented showing that interaction between the cylinders causes oscillation of the thermal plume. The effect of this oscillation is considered as a possible enhancement mechanism of the heat transfer performance of the upper cylinder.

Natural Convection From Horizontal Helicoidal Pipes

2000 ◽  
Author(s):  
Hamed Al-Ahmadi ◽  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Characteristic Length ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Coil Diameter ◽  
Horizontal Cylinders ◽  
High Degree ◽  
Rayleigh Numbers

Abstract Natural convection heat transfer from a horizontal helicoidal pipe is experimentally investigated for different coil-pitches. A modified characteristic length incorporating the tube diameter, the coil diameter, and the coil spacing, is proposed as the relevant scale for defining Nusselt and Rayleigh numbers. Using the proposed characteristic length, it is shown that the Nusselt number for horizontal helicoidal pipes can be determined using the available Nusselt versus Rayleigh number correlation for straight horizontal cylinders with high degree of accuracy over the range of the experimental data.

Experimental Apparatus for the Determination of Nusselt and Rayleigh Numbers During Natural Convection From a Heated Horizontal Cylinder

2009 ◽  
Author(s):  
S¸evket O¨zgu¨r Atayılmaz ◽  
Ahmet Selim Dalkılıc¸ ◽  
Hakan Demir ◽  
Nuri Alpay Ku¨rekci
Keyword(s):  
Natural Convection ◽  
Convection Heat Transfer ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Nusselt Numbers ◽  
Surface Temperatures ◽  
Experimental Apparatus ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

Determination of Nusselt and Rayleigh numbers during natural convection heat transfer from horizontal cylinders are investigated experimentally and numerically. Experiments are done by means of the test cabin inside a conditioned room at different environmental and surface temperatures. The environmental and cylinder surface temperatures are ranging between 10–40 °C and 20–60 °C respectively. 1 m long horizontal copper cylinder is used and has outer diameters of 4.8 mm including centered silicone covered cylindrical resistant wires inside it. The experimental apparatus is designed to capable of changing the different operating parameters such as heat flux and environmental temperature. The existence of the gap on the closed surfaces in the test cabin which can cause a stack effect, affected temperature and velocity fields, disturbance of the natural convection condition is also checked. The detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure are reported and the study of experimental setups from the available literature survey with the existing one are compared in this paper. The uncertainty analysis method proposed by Kline and McClintock is used and explained elaborately. Detailed information and algorithm of numerical method are given to ease the understanding of the numerical part of study. Alteration of Nusselt numbers with Rayleigh numbers, the temperature distribution on the heated horizontal cylinder surface by means of Fluent CFD program are shown in the paper. In addition to this, Morgan’s correlation is used for the comparison of Nusselt number and is found in good agreement with the experimental results.

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.

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