Effects of axial diffusion on laminar heat transfer with low Peclet numbers in the entrance region of thin vertical tubes
- Univ. de Sherbrooke, Quebec (Canada) Faculty of Applied Sciences
- Univ. de Moncton, New Brunswick (Canada). School of Engineering
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. Applications in which this regime of mixed convection occur include shell-tube heat exchangers, and nuclear reactors.
- Sponsoring Organization:
- Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada)
- OSTI ID:
- 624103
- Journal Information:
- Numerical Heat Transfer. Part A, Applications, Journal Name: Numerical Heat Transfer. Part A, Applications Journal Issue: 3 Vol. 33; ISSN NHAAES; ISSN 1040-7782
- Country of Publication:
- United States
- Language:
- English
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