Natural Convection of a Liquid Metal in Vertical Circular Cylinders Heated Locally From the Side

1998 ◽  
Vol 120 (1) ◽  
pp. 108-114 ◽  
Author(s):  
R. Selver ◽  
Y. Kamotani ◽  
S. Ostrach
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Numerical Analysis ◽  
Rayleigh Number ◽  
Thermal Instability ◽  
Experimental Information ◽  
Diameter Ratio ◽  
Circular Cylinders ◽  
Oscillation Frequencies ◽  
Axial Band

An experimental study is made of natural convection in gallium melts enclosed by vertical circular cylinders with localized circumferential heating. Heating is done in an axial band at the mid-height, and both ends of the cylinder are cooled. In the present study, the cylinder aspect (Ar = height/diameter) ratio ranges from 2 to 10, and the Rayleigh number (Ra) ranges from 9.0 × 104 to 3.0 × 107. The Prandtl number is 0.021. Temperature measurements are made at six axial levels around the circumference of the cylinder to study thermal convection in the melt. A numerical analysis is also conducted to supplement the experimental information. When Ra is small, the melt is in steady toroidal motion. Above a certain Ra, the flow becomes nonaxisymmetric as a result of a thermal instability, in the case of Ar larger than 3. With increasing Ra, the motion becomes oscillatory, mainly in the upper half. When Ar is smaller than 3, the toroidal flow becomes nonaxisymmetric and oscillatory at the same time beyond a certain Ra. The conditions for the appearance of oscillations and the oscillation frequencies are investigated in detail.

Oscillatory Natural Convection of a Liquid Metal in Circular Cylinders

1994 ◽  
Vol 116 (3) ◽  
pp. 627-632 ◽  
Author(s):  
Y. Kamotani ◽  
F.-B. Weng ◽  
S. Ostrach ◽  
J. Platt
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Liquid Metal ◽  
Oscillatory Flow ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Supercritical Flow ◽  
Aspect Ratios ◽  
Oscillation Frequencies ◽  
Rayleigh Numbers

An experimental study is made of natural convection oscillations in gallium melts enclosed by right circular cylinders with differentially heated end walls. Cases heated from below are examined for angles of inclination (φ) ranging from 0 deg (vertical) to 75 deg with aspect ratios Ar (height/diameter) of 2, 3, and 4. Temperature measurements are made along the circumference of the cylinder to detect the oscillations, from which the oscillatory flow structures are inferred. The critical Rayleigh numbers and oscillation frequencies are determined. For Ar=3 and φ = 0 deg, 30 deg the supercritical flow structures are discussed in detail.

Heat Transfer by Natural Convection of Helium Between Horizontal Isothermal Concentric Cylinders at Cryogenic Temperature

1988 ◽  
Vol 110 (1) ◽  
pp. 109-115 ◽  
Author(s):  
E. H. Bishop
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Transfer Rate ◽  
Correlation Equation ◽  
Diameter Ratio ◽  
Temperature Profiles ◽  
Cryogenic Temperatures ◽  
Transfer Rates ◽  
Concentric Cylinders

An experimental study was performed of the heat transfer by natural convection of helium between horizontal isothermal concentric cylinders at cryogenic temperatures. Time-averaged temperature profiles at various locations in the annulus and overall heat transfer rates were measured as the Rayleigh number was varied from 6 × 106 to 2 × 109 and the expansion number from 0.20 to 1.0 for a constant Prandtl number of 0.688 and diameter ratio of 3.36. It was found that the heat transfer rate depends on the magnitude of the expansion number as well as on the magnitude of the Rayleigh number. With gas properties evaluated at a volume-weighted reference temperature, a correlation equation is presented that correlates the heat transfer data with maximum deviations of −8.2 and +8.5 percent. The results of this study are compared with previously published studies of other investigators.

Heat Transfer by Natural Convection From an Array of Short, Wall-Attached Horizontal Cylinders

1982 ◽  
Vol 104 (1) ◽  
pp. 125-131 ◽  
Author(s):  
E. M. Sparrow ◽  
D. S. Cook ◽  
G. M. Chrysler
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Vertical Plate ◽  
Diameter Ratio ◽  
Nusselt Numbers ◽  
Cylinder Length ◽  
Horizontal Cylinders ◽  
Length To Diameter Ratio

Per-cylinder natural convection Nusselt numbers were measured for an in-line array of short horizontal cylinders that were affixed to a convectively participating vertical plate. The effect of cylinder length-to-diameter ratio, intercylinder spacing, position at which the cylinder is attached to the vertical plate, and Rayleigh number were investigated. The experiments were performed in air. It was found that the extent to which a given cylinder in the array was affected by cylinders situated below it depended on the Rayleigh number, with enhanced heat transfer coefficients being more likely at higher Rayleigh numbers. Greater enhancement occurred at larger intercylinder spacings. The qualitative characteristics of the Nusselt number results were insensitive to the cylinder length-to-diameter ratio, but the longer cylinders exhibited higher values of the Nusselt number. For the most part, the Nusselt numbers for the wall-attached horizontal cylinders fell below those for the classical horizontal cylinder of infinite length.

Numerical analysis of laminar natural convection in isosceles triangular enclosures

2009 ◽  
Vol 223 (5) ◽  
pp. 1157-1169 ◽  
Author(s):  
E F Kent
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Analysis ◽  
Rayleigh Number ◽  
Flow Field ◽  
Water Heaters ◽  
Thermal Boundary Conditions ◽  
Laminar Natural Convection ◽  
Solar Water Heaters ◽  
Rayleigh Numbers

In this work, a numerical analysis of laminar natural convection in an isosceles triangular enclosure has been performed for two different thermal boundary conditions. In case 1, the base is heated and the two inclined walls are symmetrically cooled, and in case 2, the base is cooled and the two top inclined walls are symmetrically heated. This configuration is encountered in solar engineering applications such as: solar stills that usually have triangular cavities and triangular built-in-storage-type solar water heaters; and heat transfer in attic spaces in both wintertime and summertime conditions. To perform the computational analysis, the finite-volume method is used for the discretization of the governing equations. Base angles varying from 15 to 75° have been used for different Rayleigh numbers ranging from 103 to 105. The effects of the Rayleigh number and aspect ratio on the flow field and heat transfer are analysed. The detailed streamline patterns and temperature distributions are presented. The variation of the mean Nusselt numbers versus Rayleigh numbers for different base angles is given. It is found that the base angle has a drastic influence on the flow field and isotherms for the two cases. For case 1, at small base angles, as the Rayleigh number increases, a multi-cellular flow structure developed inside the enclosure enhances the heat transfer. For case 2, the temperature profiles are always stable and stratified for all Rayleigh numbers and base angles.

Numerical Analysis of Natural Convection in a Cavity at High Rayleigh Number

2000 ◽  
Vol 2000.1 (0) ◽  
pp. 901-902
Author(s):  
Ichiro MIYOSHI ◽  
Takafumi MAKIHARA ◽  
Takahiko TANAHASHI
Keyword(s):  
Natural Convection ◽  
Numerical Analysis ◽  
Rayleigh Number
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