Effects of Natural Convection in the Melted Region Around a Heated Horizontal Cylinder

1980 ◽  
Vol 102 (4) ◽  
pp. 667-672 ◽  
Author(s):  
L. S. Yao ◽  
F. F. Chen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Melting Process ◽  
Horizontal Cylinder ◽  
Perturbation Solution ◽  
Regular Perturbation ◽  
Melting Heat ◽  
Melted Region ◽  
Short Period

Two heat transfer modes are involved in the process of melting around a heated horizontal cylinder: conduction and convection. The magnitude of convection is proportional to the Rayleigh number based on the width of the melted region. The importance of natural convection increases with time. For a short period after the beginning of melting, heat transfer is dominated by conduction. A regular perturbation solution is presented to demonstrate the increasing effect of natural convection on the melting process.

Optimizing Laminar Natural Convection for a Heat Generating Cylinder in a Channel

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Corey E. Clifford ◽  
Mark L. Kimber
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Spent Nuclear Fuel ◽  
Reactor Core ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Transfer Program ◽  
Wet Storage

Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for unconfined cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this investigation, a numerical model of a heated horizontal cylinder confined between two vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the “pseudo-unconfined” cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

2003 ◽  
Vol 125 (2) ◽  
pp. 282-288 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Horizontal Cylinder ◽  
High Conductivity ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Wide Range

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.

scholarly journals Thermophysical Characterization and Numerical Investigation of Three Paraffin Waxes as Latent Heat Storage Materials

2019 ◽  
Author(s):  
Manel Kraiem ◽  
Mustapha Karkri ◽  
Sassi Ben Nasrallah ◽  
patrick sobolciak ◽  
Magali Fois ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Storage ◽  
Numerical Study ◽  
Melting Process ◽  
Heat Transfer Mode ◽  
Transfer Mode ◽  
Paraffin Waxes ◽  
Thermophysical Characterization

Thermophysical characterization of three paraffin waxes (RT27, RT21 and RT35HC) is carried out in this study using DSC, TGA and transient plane source technics. Then, a numerical study of their melting in a rectangular enclosure is examined. The enthalpy-porosity approach is used to formulate this problem in order to understand the heat transfer mechanism during the melting process. The analysis of the solid-liquid interface shape, the temperature field shows that the conduction is the dominant heat transfer mode in the beginning of the melting process. It is followed by a transition regime and the natural convection becomes the dominant heat transfer mode. The effects of the Rayleigh number and the aspect ratio of the enclosure on the melting phenomenon are studied and it is found that the intensity of the natural convection increases as the Rayleigh number is higher and the aspect ratio is smaller. In the second part of the numerical study, a comparison of the performance of paraffins waxes during the melting process is conducted. Results reveals that from a kinetically RT21 is the most performant but in term of heat storage capacity, it was inferred that RT35HC is the most efficient PCM.

Natural Convection Heat Transfer From a Horizontal Cylinder Between Vertical Confining Adiabatic Walls

1986 ◽  
Vol 108 (2) ◽  
pp. 291-298 ◽  
Author(s):  
F. Karim ◽  
B. Farouk ◽  
I. Namer
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
Horizontal Cylinder ◽  
Heat Extraction ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Cylinder Diameter ◽  
Wall Spacing

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.

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

1981 ◽  
Vol 103 (4) ◽  
pp. 630-637 ◽  
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.

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

2000 ◽  
Vol 122 (4) ◽  
pp. 679-692 ◽  
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]

Onset of Natural Convection from a Suddenly Heated Horizontal Cylinder

1980 ◽  
Vol 102 (4) ◽  
pp. 636-639 ◽  
Author(s):  
J. R. Parsons ◽  
J. C. Mulligan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Stability ◽  
Heat Capacity ◽  
Natural Convection ◽  
Stability Analysis ◽  
Horizontal Cylinder ◽  
Finite Cylinder ◽  
Global Motion ◽  
Experimental Apparatus

A study of the onset of transient natural convection from a suddenly heated, horizontal cylinder of finite diameter is presented. The termination of the initial conductive and “locally” conuectiue heat transfer regime which precedes the onset of global natural convection is treated as a thermal stability phenomenon. An analysis is presented wherein the effects of finite cylinder diameter, cylinder heat capacity, and cylinder thermal conductivity are included in calculations of the convective delay time. A simple experimental apparatus is described and data presented. The thermal stability analysis is confirmed experimentally and data is presented which indicates localized natural convection prior to global motion.

scholarly journals CuO–Water Nanofluid Magnetohydrodynamic Natural Convection inside a Sinusoidal Annulus in Presence of Melting Heat Transfer

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
M. Sheikholeslami ◽  
R. Ellahi ◽  
C. Fetecau
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Melting Heat ◽  
Melting Heat Transfer ◽  
Limiting Case ◽  
Good Agreement ◽  
Melting Parameter

Impact of nanofluid natural convection due to magnetic field in existence of melting heat transfer is simulated using CVFEM in this research. KKL model is taken into account to obtain properties of CuO–H2O nanofluid. Roles of melting parameter (δ), CuO–H2O volume fraction (ϕ), Hartmann number (Ha), and Rayleigh (Ra) number are depicted in outputs. Results depict that temperature gradient improves with rise of Rayleigh number and melting parameter. Nusselt number detracts with rise of Ha. At the end, a comparison as a limiting case of the considered problem with the existing studies is made and found in good agreement.

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