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DEVELOPMENT OF LAMINAR MIXED CONVECTION IN VERTICAL SEMICIRCULAR DUCTS

DOI: 10.1615/ICHMT.2008.CHT.1850
15 pages

N. A. Elsharif
Mechanical Engineering Department, University of Garyounis, Benghazi, Libya

A. A. Busedra
Mechanical Engineering Department, University of Garyounis, Benghazi, Libya

Yousef El Hasadi
Auburn University, 270 Ross Hall Mechanical Engineering Department Auburn, Alabama 36849-5341 USA; and Mechanical Engineering Department, University of Garyounis, Benghazi, Libya

Abstract

The problem of laminar mixed convection in the entrance region of vertical semicircular ducts is investigated. The investigation started with the numerical technique of SIMPLER algorithm to solve the governing equations. Results are obtained for the thermal boundary conditions of uniform heat input axially and uniform peripheral wall temperature at any axial location (H1 boundary condition) with Pr = 7 and 0.7, Re = 500 and a wide range of Gr. These results include development of axial velocity and temperature distributions at different axial locations. At high Gr/Re, the maximum velocity at the entrance region is confined in the center of the duct for both Prandtl numbers up to a critical distance. Beyond that it starts to shift from the center towards the corners of the duct and increases as approaching the fully developed region. The results also include local Nusselt number and local friction factor. The amount of increase along the duct in the friction factor values is found to be much larger than those of Nusselt number values. The effect of Gr/Re is found to increase the local Nusselt number and friction factor in the developing and fully developed regions and shorten the thermal entrance length. However, the effect of Pr is mainly in the entrance region where the local Nusselt number and friction factor that corresponding to air (Pr = 0.7) are found to be higher than those of water (Pr = 7), except in region of the fully developed where the flow is independent of Pr.

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