NATURAL CONVECTION HEAT TRANSFER BETWEEN VERTICAL FLAT PLATES WITH UNIFORM HEAT FLUX

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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Experimental study of natural convection heat transfer from horizontal cam tubes in a vertical array under constant heat flux

Journal of Thermal Analysis and Calorimetry ◽

10.1007/s10973-021-11119-0 ◽

2021 ◽

Author(s):

Ally Javadpour ◽

Mohammad Najafi ◽

Sam Lowrey

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Heat Flux ◽

Natural Convection ◽

Convection Heat Transfer ◽

Constant Heat Flux ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

Vertical Array ◽

Constant Heat

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Applicability of Uniform Heat Flux Nusselt Number Correlations to Thermosyphon Heat Exchangers for Solar Water Heaters

Journal of Solar Energy Engineering ◽

10.1115/1.2888151 ◽

1999 ◽

Vol 121 (2) ◽

pp. 85-90 ◽

Cited By ~ 4

Author(s):

S. Dahl ◽

J. Davidson

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Mixed Convection ◽

Heat Exchangers ◽

Convection Heat Transfer ◽

Uniform Heat Flux ◽

Convection Heat ◽

Solar Water ◽

Nusselt Numbers ◽

Uniform Heat

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under morerealistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.

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