Nuclear Technology / Volume 154 / Number 3 / June 2006 / Pages 335-349
Technical Paper / Thermal Hydraulics
Because of the dramatic variation of physical properties with a modest change of temperature, no existing engineering correlation or models can accurately predict heat transfer of supercritical fluids. This paper seeks to classify the conditions where the existing models are applicable and to better understand these local heat transfer mechanisms. The first objective is the focus of this paper. FLUENT was employed to compute the wall temperatures for various heat flux and mass flux conditions and to be compared with experimental data. Because the model was developed for a wide range of flow conditions, it was necessary to make certain assumptions. The simulations showed a good agreement with high mass flux conditions, where buoyancy effects could be neglected. The FLUENT model, however, had difficulty predicting the localized low heat transfer rates seen in the combined condition of high heat flux and low mass flux. A new generalized parameter, dependent on the heat and mass flux, was developed to classify under which conditions this FLUENT standard model was applicable. This global Froude number can be used as the parameter to predict under which conditions the buoyancy effect will be dominant and lower heat transfer rates will occur.