Supercritical water is characterized by a high molecular Prandtl number near the pseudo-critical point, which means that momentum diffuses much quicker compared to heat. Heat transfer at such conditions shows strong non-linear behaviour because of significant changes of the fluid properties. The sudden heat transfer deterioration occures with local reduction of the heat transfer coefficient, what leads to an increase in the heated wall temperature.
For a better understanding of the heat transfer deterioration phenomenon, water flow under supercritical conditions has been studied using the commercial CFD code ANSYS CFX 12.1. Numerical simulations of the turbulent, upward flow in a circular, heated tube were performed using the water properties according to IAPWS IF97. The main objective was to investigate sensitivities of the heated wall temperature and axial velocity distribution predictions on certain model parameters. The model sensitivities were examined on the mesh discretization, boundary conditions (inlet temperature, mass flux, heat flux and pressure), fluid properties and selection of a turbulence model. Selected experiments of Ornatskii (1971) and Shitsman (1963) have been used for validation of the obtained results.