On the mechanisms by which heat transfer is impaired in buoyancy-aided pipeflow
Abstract
When fluid flows upwards through a heated tube the near-wall fluid experiences a buoyancy force which aids the flow. Whereas it might be expected that this would enhance heat transfer, the authors have shown by experiment that serious impairment of heat transfer can result. They were able to reproduce this effect very satisfactorily by computational simulation using a buoyancy-influenced, variable property, developing turbulent wall shear flow formulation. This encouraged them to examine the results with a view to obtaining a better understanding of the mechanisms involved. The velocity profile changed with axial distance, soon becoming almost flat in the core region and then inverted. The viscous sub-layer grew considerably and the turbulent kinetic energy in the core fell significantly. Examination of the profiles of total stress showed that over much of the flow the shear stress was greatly reduced, in spite of the wall value having increased slightly. Using the results from such simulations, the authors have obtained a detailed picture of the mechanisms by which turbulence and heat transfer are modified by the buoyancy.
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 2000
- Bibcode:
- 2000APS..DFD.MK005J