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ISSN Online: 2377-424X

ISBN Print: 0-89116-130-9

International Heat Transfer Conference 6
August, 7-11, 1978, Toronto, Canada

HEAT TRANSFER IN VERTICAL TUBES UNDER CONDITIONS OF MIXED FREE AND FORCED CONVECTION

Get access (open in a dialog) DOI: 10.1615/IHTC6.3030
pages 43-48

Abstract

Heat transfer rates to upward flowing fluids in vertical tubes under conditions of combined free and forced convection have been observed to display marked decreases from accepted forced convection values. This paper shows that experimental observations in mixed convection flows are in general agreement with the predictions of a theoretical analysis proposed by Hall (1). On the basis of this analysis, variations in heat transfer rates are related to alterations in the flow structure brought about by changes in the relative importance of free and forced convection forces. A plot of Nu/NuT versus GrA/Re2 is used to compare heat transfer data for fluids of widely differing Prandtl numbers. These data are divided into two groups, one for flows where the point of maximum velocity remains at the centre of the tube, and the other for flows where free convection forces are large enough to displace the point of maximum velocity from the tube centre. Data in the latter group are correlated by the relation Nu/NuT = 8.84[GrA/Re2]0·263