Experimental investigations have been reported on steady state natural convection from the outer surface of horizontal ducts in air. Five ducts have been used with aspect ratios (=duct height/duct width) of 2, 1, and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for transition regime using the axial distance as a characteristic length. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers, the aspect ratio, and area ratio for the laminar and transition regimes. The longitudinal or total averaged heat transfer coefficients are observed to decrease in the laminar region and to increase in the transition region. Laminar regimes are obtained only at very small heat fluxes, otherwise, transitions are observed.
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e-mail: mali@ksu.edu.sa
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September 2007
This article was originally published in
Journal of Heat Transfer
Technical Papers
Natural Convection Heat Transfer From Horizontal Rectangular Ducts
Mohamed E. Ali
Mohamed E. Ali
Mechanical Engineering Department,
e-mail: mali@ksu.edu.sa
King Saud University
, P. O. Box 800, Riyadh 11421, Saudi Arabia
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Mohamed E. Ali
Mechanical Engineering Department,
King Saud University
, P. O. Box 800, Riyadh 11421, Saudi Arabiae-mail: mali@ksu.edu.sa
J. Heat Transfer. Sep 2007, 129(9): 1195-1202 (8 pages)
Published Online: December 2, 2006
Article history
Received:
May 15, 2006
Revised:
December 2, 2006
Citation
Ali, M. E. (December 2, 2006). "Natural Convection Heat Transfer From Horizontal Rectangular Ducts." ASME. J. Heat Transfer. September 2007; 129(9): 1195–1202. https://doi.org/10.1115/1.2739623
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