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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 33, 1998 - Issue 3
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Original Articles

EFFECTS OF AXIAL DIFFUSION ON LAMINAR HEAT TRANSFER WITH LOW PÉ CLET NUMBERS IN THE ENTRANCE REGION OF THIN VERTICAL TUBES

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Pages 247-266 | Received 23 Aug 1997, Accepted 04 Oct 1997, Published online: 15 Mar 2007
 

Abstract

Laminar upward and downward flows with mixed convection in a thin vertical tube with a short uniformly heated section were investigated numerically. Calculations were performed by solving the elliptic Navier-Stokes and energy equations for slow flows of air ( Pr = 0.7) corresponding to low Reynolds numbers from 20 to 500 and a wide range of Grashof numbers. Results reveal that axial diffusion plays a significant role in preheating the fluid upstream from the entrance of the heat transfer region for both aiding and opposing buoyancy, with a stronger effect for the latter, and can lead to flow reversal. By mapping the conditions that correspond to significant preheating and flow reversal on a Grashof-Reynolds plane, it has become possible to establish criteria that determine (1) when the upstream boundary conditions can be applied at the entrance of the heated section and ( 2) when the elliptical formulation is necessary to describe the flow field accurately.

Notes

Address correspondence to Professor Nicolas Galanis, Faculty des Sciences Appliqué es, Dé partement de genie mé canique, Université de Sherbrooke, 2500, Boul. Université, Sherbrooke, Quebec J1K 2R1, Canada. E-mail: [email protected]

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