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.

Effect of Transverse Misalignment on Natural Convection From a Pair of Parallel, Vertically Stacked, Horizontal Cylinders

1983 ◽  
Vol 105 (2) ◽  
pp. 241-247 ◽  
Author(s):  
E. M. Sparrow ◽  
D. S. Boessneck
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
The Other ◽  
Natural Convection Heat Transfer ◽  
Vertical Separation ◽  
Heat Transfer Characteristics ◽  
Single Cylinder ◽  
Transverse Misalignment ◽  
Horizontal Cylinders

Experiments were carried out to determine the effects of transverse misalignment on the natural convection heat transfer characteristics of a pair of equitemperature, parallel horizontal cylinders situated one above the other. During the course of the experiments, which were performed in air, the transverse offset was varied systematically at several fixed vertical separation distances, while the Rayleigh number ranged from 2 × 104 to 2 × 105. At small vertical separations, transverse offsetting causes an increase in the upper-cylinder Nusselt number (up to 27 percent) compared with that for the perfectly aligned case (i.e., no offset) and, furthermore, the Nusselt number is responsive to small offsets. On the other hand, at larger vertical separations, the offset-affected upper-cylinder Nusselt number is lower (by up to 20 percent) than the no-offset value but is quite insensitive to small offsets. At large transverse offsets, the upper-cylinder Nusselt number slightly exceeds that for a single cylinder, with the increase being due to a horizontal airflow induced by the acceleration of the lower cylinder’s plume. For all of the cases investigated, the lower-cylinder Nusselt number was virtually identical to that for a single cylinder.

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.

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.

Numerical Simulation of Natural Convection Flow in a Cube With a Horizontal Heated Strip

2008 ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
High Temperature ◽  
Natural Convection ◽  
Vertical Wall ◽  
Convection Flow ◽  
Front Wall ◽  
Natural Convection Flow ◽  
Rayleigh Numbers

Natural convection flow in a cube with a heated strip is solved numerically. The heated strip is attached horizontally to the front wall and maintained at high temperature, while the entire opposite wall is maintained at low temperature. The heated strip simulates an array of electronic chips The Rayleigh numbers of 104, 105, and 106 are considered in the analysis and the heated strip is horizontally attached to the wall. The results indicate that the heat transfer strongly depends on the position of the heated strip. The maximum Nusselt number can be achieved if the heater is placed at the lower half of the vertical wall. Increasing the Rayleigh number significantly promotes heat transfer in the enclosure. Flow streamlines and temperature contours are presented, and the results are validated against published works.

Three Dimensional Numerical Simulation of the Natural Convection in an Annulus With an Internal Slotted Cylinder

2011 ◽  
Author(s):  
Mo Yang ◽  
Jin Wang ◽  
Kun Zhang ◽  
Ling Li ◽  
Yuwen Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Dimensional Model ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Rayleigh Numbers

Detailed numerical analysis is presented for three-dimensional natural convection heat transfer in annulus with an internal concentric slotted cylinder. The internal slotted cylinder and the outer annulus are maintained at uniform but different temperatures. Governing equations are discretized using control volume technique based on staggered grid formulation and solved using SIMPLE algorithm with QUICK scheme. Flow and heat transfer characteristics are investigated for a Rayleigh number range of 10 to 106 while Prandtl number (Pr) is taken to be 0.7. The results indicate, at Rayleigh numbers below 105, the system shows two dimensional flow and heat transfer characteristics. On the other hand, the flow and heat transfer shows three dimensional characteristics while for Rayleigh numbers greater than 5×105. Comparison with experimental results indicated that the numerical solutions by three dimensional model can obtain more accuracy than the numerical solutions by two dimensional model. Besides, Numerical results show that the average equivalent conductivity coefficient of natural convection heat transfer of this problem can be enhanced by as much as 30% while relative slot width is more than 0.1.

scholarly journals Lattice Boltzmann simulation of turbulent natural convection in tall enclosures

2015 ◽  
Vol 19 (1) ◽  
pp. 155-166 ◽  
Author(s):  
Hasan Sajjadi ◽  
Reza Kefayati
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Lattice Boltzmann ◽  
Average Nusselt Number ◽  
Large Eddy Simulations ◽  
Turbulent Natural Convection ◽  
Aspect Ratios ◽  
Lattice Boltzmann Simulation ◽  
Large Eddy ◽  
Rayleigh Numbers

In this paper Lattice Boltzmann simulation of turbulent natural convection with large-eddy simulations (LES) in tall enclosures which is filled by air with Pr=0.71 has been studied. Calculations were performed for high Rayleigh numbers (Ra=107-109) and aspect ratios change between 0.5 to 2 (0.5<AR<2). The present results are validated by finds of an experimental research at Ra=1.58x109. Effects of the aspect ratios in different Rayleigh numbers are displayed on streamlines, isotherm counters, vertical velocity and temperature at the middle of the cavity, local Nusselt number and average Nusselt number. The average Nusselt number increases with the augmentation of Rayleigh numbers. The increment of the aspect ratio causes heat transfer to decline in different Rayleigh numbers.

A Numerical Study of Natural Convection in a Cavity With Two Fins Attached to Its Vertical Walls

2007 ◽  
Author(s):  
G. A. Sheikhzadeh ◽  
M. Pirmohammadi ◽  
M. Ghassemi
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Square Cavity ◽  
Vertical Walls ◽  
The Mean ◽  
Energy Equations ◽  
Rayleigh Numbers

Numerical study natural convection heat transfer inside a differentially heated square cavity with adiabatic horizontal walls and vertical isothermal walls is investigated. Two perfectly conductive thin fins are attached to the isothermal walls. To solve the governing differential mass, momentum and energy equations a finite volume code based on Pantenkar’s simpler method is developed and utilized. The results are presented in form of streamlines, isotherms as well as Nusselt number for Rayleigh number ranging from 104 up to 107. It is shown that the mean Nusselt number is affected by the position of the fins and length of the fins as well as the Rayleigh number. It is also observed that maximum Nusselt number occurs about the middle of the enclosure where Lf is grater the 0.5. In addition the Nusselt number stays constant and does not varies with width of the cavity (lf) when Lf is equal to 0.5 and Rayleigh number is equal to 104 and 107 as well as when Lf is equal to 0.6 and low Rayleigh numbers.

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