Analytical prediction of heat transfer by unsteady natural convection at vertical flat plates in air

The problem of determining the optimum spacings between parallel vertical isothermal flat plates which are dissipating heat by natural convection to the environment is discussed. One optimum, first suggested by experimental data of Elenbaas with air and later derived theoretically by Bodoia, corresponds to the spacing between parallel vertical plates attached to a surface which will permit the maximum rate of heat transfer from that surface. A different optimum is derived in this paper which for a given heat flux gives the minimum plate spacing required to minimize the temperature difference between the plates and the fluid. The minimum temperature difference is shown to occur when the plate spacing is made sufficiently large that the wall boundary layers do not merge. It is shown that Elenbaas’ optimum, although requiring a plate spacing only 54 percent of that for minimum ΔT, produces a temperature difference which is 38 percent higher than the minimum.

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An Experimental Investigation of Natural Convection With Vertical Cylinders in Mercury

Journal of Heat Transfer ◽

10.1115/1.3450226 ◽

1974 ◽

Vol 96 (4) ◽

pp. 455-458 ◽

Cited By ~ 4

Author(s):

L. E. Wiles ◽

J. R. Welty

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Natural Convection ◽

Flat Plate ◽

Convection Heat Transfer ◽

Vertical Cylinder ◽

Local Heat Transfer ◽

Local Heat ◽

Transfer Coefficients ◽

Flat Plates

An experimental investigation of laminar natural convection heat transfer from a uniformly heated vertical cylinder immersed in an effectively infinite pool of mercury is described. A correlation was developed for the local Nusselt number as a function of local modified Grashof number for each cylinder. A single equation incorporating the diameter-to-length ratio was formulated that satisfied the data for all three cylinders. An expression derived by extrapolation of the results to zero curvature (the flat plate condition) was found to agree favorably with others’ work, both analytical and experimental. The influence of curvature upon the heat transfer was found to be small but significant. It was established that the effective thermal resistance through the boundary layer is less for a cylinder of finite curvature than for a flat plate. Consequently, local heat transfer coefficients for cylinders are larger than those for flat plates operating under identical conditions.

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Discussion: “Unsteady Natural Convection in the Vicinity of a Doubly Infinite Vertical Plate” (Schetz, J. A., and Eichhorn, R., 1962, ASME J. Heat Transfer, 84, pp. 334–338)

Journal of Heat Transfer ◽

10.1115/1.3684387 ◽

1962 ◽

Vol 84 (4) ◽

pp. 338-338

Author(s):

Kwang-Tzu Yang

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Vertical Plate ◽

Unsteady Natural Convection ◽

Infinite Vertical Plate

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Analysis of the Time-Dependent Heating on the Natural Convection from a Vertical Open Ended Porous Cylinder

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.273-276.28 ◽

2008 ◽

Vol 273-276 ◽

pp. 28-33 ◽

Cited By ~ 1

Author(s):

Djamel Eddine Ameziani ◽

K. Bouhadef ◽

Rachid Bennacer

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Wall Temperature ◽

Flow Model ◽

Convection Heat Transfer ◽

Lateral Wall ◽

Natural Convection Heat Transfer ◽

Porous Cylinder ◽

Constant Wall Temperature ◽

Unsteady Natural Convection

The problem of unsteady natural convection heat transfer in a vertical opened porous cylinder submitted to a sinusoidal time variation temperature on the lateral wall has been investigated numerically. The widely used Darcy flow model without flow establishment at the cylinder exit has been used. In the case of constant wall temperature, two types of flows were obtained, with and without fluid recirculation, depending on the filtration Rayleigh number (Ra), the aspect ratio (A) and the Biot number (Bi) have been obtained. The obtained heat transfer, in case of low dimensionless oscillations amplitude (XA<0.5), shows a non significant enhancement (less than 5%) in comparison to the constant wall temperature case.

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