Experimental Study of the Natural-Convection Plume From a Heated Vertical Cylinder

Welling, Irma; Koskela, Hannu; Hautalampi, Timo

doi:10.1080/08916159808946558

Cited by 11 publications

(3 citation statements)

References 12 publications

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“…1 Flow situation considered studies that have further extended this earlier work typical of these being that of Kimura et al [8] and Oosthuizen [9,10]. Typical of the experimental studies of natural convective heat transfer from vertical circular cylinders are those of Jarall and Campo [11], Welling et al [12] and Fukusawa and Iguchi [13]. Cylinders with exposed top inclined at an angle to the vertical have received attention by Oosthuizen [14,15].…”

Section: Introductionmentioning

confidence: 96%

A numerical and experimental study of natural convective heat transfer from an inclined isothermal square cylinder with an exposed top surface

Kalendar

Oosthuizen

2013

Heat Mass Transfer

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Natural convective heat transfer from an isothermal inclined cylinder with a square cross-section which have an exposed top surface and is, in general, inclined at an angle to the vertical has been numerically and experimentally studied. The cylinder is mounted on a flat adiabatic base plate, the cylinder being normal to the base plate. The numerical solution has been obtained by solving the dimensionless governing equations subject to the boundary conditions using the commercial cfd solver, FLUENT. The flow has been assumed to be symmetrical about the vertical center-plane through the cylinder. Results have only been obtained for Prandtl number of 0.7. Values of inclination angle between 0°and 180°and a wide range of Rayleigh number and the dimensionless cylinder width, W = w/h, have been considered. The effects of Dimensionless widths, Rayleigh numbers, and inclination angles on the mean Nusselt number for the entire cylinder and for the mean Nusselt numbers for the various surfaces that make up the cylinder have been examined. Empirical equations for the heat transfer rates from the entire cylinder have been derived.

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Section: Introductionmentioning

confidence: 96%

A numerical and experimental study of natural convective heat transfer from an inclined isothermal square cylinder with an exposed top surface

Kalendar

Oosthuizen

2013

Heat Mass Transfer

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“…Moreover, Goodrich & Marcum (2019) observed that increasing curvature tended to bring forward the transition to turbulence so as to be triggered at a lower rate of heating. While Welling, Koskela & Hautalampi (1998) investigated experimentally the plume motions above the top surface of a vertical heated cylinder, in the present work we neglect the end effects and restrict our attention to the annular wall plume along the cylindrical surface.…”

Section: Introductionmentioning

confidence: 99%

Local linear stability of plumes generated along vertical heated cylinders in stratified environments

Yu,

Hunt

2023

J. Fluid Mech.

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The linear temporal and absolute/convective stability characteristics of a thermal plume generated along a heated vertical cylinder are investigated theoretically under the Boussinesq approximation. Special focus is given to the uniform-wall-buoyancy-flux case whereby the cylinder surface sustains the same linear temperature gradient as the environment. A competition between the axisymmetric and helical modes is a remarkable feature of the instability, distinguishing these ‘annular plumes’ from free plumes/jets for which the helical mode is generally dominant. It is found that higher surface curvature stabilises the temporal axisymmetric mode significantly, but only has moderate effects on the helical mode. The most temporally unstable perturbation mode switches from a helical into an axisymmetric mode when the Prandtl number increases beyond a critical value. Both the roles of shear and buoyancy during the destabilisation are identified through an energy analysis which indicates that, while the shear work is usually a major source of perturbation energy, the buoyancy work manifests for long-wave axisymmetric perturbation modes, and for thin cylinders and high Prandtl numbers. For the specific temperature configuration considered herein, an annular plume is always convectively unstable whereas decreasing the cylinder radius from the planar limiting case first decreases and then increases the tendency of the flow towards being absolutely unstable. The helical mode is especially susceptible to being absolutely unstable on very thin cylinders. Several conditions for the onset of cellular thermal convection and plume detrainment are proposed based on our results and a hypothesis which connects the absolute instability to the detrainment phenomenon.

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“…The effects of wall temperature variations have been studied by, for example [12][13][14]. Typical of the experimental studies of natural convective heat transfer from vertical cylinders are those of [15][16][17]. Some attention has been given to the case where there is a specified heat flux at the surface of the cylinder, e.g., see [18,19].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of Natural Convective Heat Transfer From an Inclined Isothermal Square Cylinder With an Exposed Top Surface Mounted on a Flat Adiabatic Base

Kalendar

Oosthuizen

Alhadhrami

2010

2010 14th International Heat Transfer Conference, Volume 7

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Natural convective heat transfer rates from inclined cylinders with a square cross-section and which has an exposed top surface have been experimentally studied. When relatively small square cylinders with exposed top surfaces inclined at an angle to the vertical are used, the inclination angle to the vertical has, in general, a considerable effect on the magnitude of the mean heat transfer rate and on the nature of the flow over the surfaces that make up the cylinder. In the situation here considered the cylinder is mounted on a large flat essentially adiabatic surface with the other cylinder surfaces exposed to the surrounding air and with the cylinder, in general, inclined to the vertical at angles between vertically upwards and vertically downwards. The situation considered is an approximate model of that which occurs in some electrical and electronic component cooling problems. The cross-sectional size-to-height ratio of the square cylinders used in the present study was comparatively small, i.e. the square cylinders were short, the width, w, of the square cylinders being 25.4 mm and the width-to-height ratios of between 1 and 0.25 being used. One of the main aims of the present work was to determine how the cross-sectional size-to-height ratio of the square cylinder, i.e., w/h, influences the mean heat transfer rate from the cylinder at various angles of inclination between vertically upwards and vertically downwards. The heat transfer rates were determined by the transient method, this basically involving heating the model and then measuring its temperature-time variation while it cooled, the tests being carried out inside a large enclosure. Tests were carried out in air with all models at various angles of inclination to the vertical between vertically upwards and vertically downwards. The effects of w/h, Rayleigh number, Ra, and angle of inclination, φ, on the mean Nusselt number, Nu for the entire cylinder have thus been studied. The Rayleigh number, Ra, based on the cylinder height, h, was between approximately 1E4 and 5E6. The experimental results have been compared with the results obtained in an earlier numerical study.

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Experimental Study of the Natural-Convection Plume From a Heated Vertical Cylinder

Cited by 11 publications

References 12 publications

A numerical and experimental study of natural convective heat transfer from an inclined isothermal square cylinder with an exposed top surface

A numerical and experimental study of natural convective heat transfer from an inclined isothermal square cylinder with an exposed top surface

Local linear stability of plumes generated along vertical heated cylinders in stratified environments

Experimental Study of Natural Convective Heat Transfer From an Inclined Isothermal Square Cylinder With an Exposed Top Surface Mounted on a Flat Adiabatic Base

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