Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Year 2006

K. W. Seo
Pohang University of Science and Technology, Pohang, South Korea

Moo Hwan Kim
Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea

M. Anderson
University of Wisconsin-Madison, Wisconsin, USA

Michael L. Corradini
Engine Research Center and Engineering Physics, University of Wisconsin, Madison, Wisconsin, USA

Our research work seeks to classify the conditions where the existing models are applicable and to better understand these local heat transfer mechanisms. The dramatic variation of thermo-physical properties with a modest change of temperature near the pseudo-critical point make heat transfer correlations such as the Dittus-Boelter correlation unreliable to estimate the heat transfer coefficients in supercritical water. Several other heat transfer correlations have been proposed for these conditions, but none seem able to predict the heat transfer variation over the parameter range needed for reactor thermal-hydraulics design and analyses. The commercially available CFD computer model, FLUENT, was employed to analyze specific supercritical water tests to better understand heat transfer mechanisms in the previous study. The FLUENT simulations showed a surprisingly good agreement under high mass flux conditions, where buoyancy effects could be neglected. The FLUENT model, however, had difficulty predicting the localized low heat transfer seen for high heat flux and low mass flux conditions. We proposed a new parameter, a global Froude number (Fr), dependent on the heat and mass flux, to classify the conditions where this standard FLUENT model was applicable. This global Fr can be used as the parameter to determine under what conditions (1/Fr > 0.01) the buoyancy effect will be dominant and the reduction of the heat transfer rate. This global parameter had similar trends with a local parameter, which used the specific information from specific experimental data for the supercritical fluid. Theoretical modifications to account for variable property effects, which may occur at high heat flux, and buoyancy effects, which could occur at low mass flux should be performed for supercritical fluids due to the previous study. The turbulence model near the wall, the wall function for momentum and energy applicable for a range of supercritical fluid conditions was modified. The modified models deal with buoyancy, acceleration, and the variable property effect for supercritical conditions.

TRB-26 pages DOI: 10.1615/IHTC13.p1.240 Download article

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