Influence of free convection on heat transfer during laminar flow in tubes with twisted tapes

Bandyopadhyay, P. S. ; Gaitonde, U. N. ; Sukhatme, S. P. (1991) Influence of free convection on heat transfer during laminar flow in tubes with twisted tapes Experimental Thermal and Fluid Science, 4 (5). pp. 577-586. ISSN 0894-1777

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Official URL: http://www.sciencedirect.com/science/article/pii/0...

Related URL: http://dx.doi.org/10.1016/0894-1777(91)90036-Q

Abstract

Experiments were carried out with a viscous oil flowing through a horizontal tube containing a twisted tape to understand and quantify heat transfer in the presence of free convection. Data were obtained with the constant wall heat flux boundary conditions for two tube diameters (31.7 mm and 22.8 mm) and for twist ratios varying from about 4 to 8. The Reynolds number (Reb) was varied from 35 to 1756, the Prandtl number (Pr b) from 73 to 404, the Rayleigh number (Rab) from 0.186 × 106 to 33.57 × 106, and the modified Rayleigh number (Rab+) from 5.59 × 106 to 1.96 × 109. The data points are classified into three zones: zone 1, where the secondary flow due to swirl is dominant; zone 2, which is a transition zone; and zone 3, where the secondary flow due to free convection is dominant. Data in zone 1 are found to agree well with the correlation of Hong and Bergles, while data in zone 3 are correlated against the Rayleigh number and the modified Rayleigh number in the forms Nub=C Rab m and Nub=C1(Rab+)m1. In developing these correlations it is shown that the extent of transition zone 2 is small. Hence the simple generalized method recommended for all zones is to calculate the Nusselt number using the Hong and Bergles correlation and either one of the free convection correlations and then use the higher of the two values of Nusselt number obtained.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Free Convection; Laminar Flow; Twisted Tape
ID Code:54219
Deposited On:11 Aug 2011 11:54
Last Modified:11 Aug 2011 11:54

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