Discussion and perspectives for improvements of heat transfer correlation capabilities for fluids at supercritical pressures

The paper addresses the present engineering predictive capabilities for heat transfer at supercritical pressures, with main reference to the studies in support to the design of supercritical water nuclear reactors. The work that was made in the frame of the EU ECC-SMART Project by participants, in assessing existing correlations in front of different experimental data sets by a variety of means, is taken as a basis for discussing the adequacy of some of the available formulations. In particular, previously proposed correlations have been assessed in a stand-alone fashion or by the use of in-house and existing system codes. Specific computer programs have been also set up to try optimising the parameters of classical correlation forms when applied to selected experimental data sets. The obtained results show the present difficulties in predicting specific heat transfer regimes of interest for supercritical reactors, with main reference to deteriorated heat transfer, though some correlations have been found to represent at least qualitatively the increase of wall temperature observed in some tube or rod bundle experiments, providing hope of a reasonable quantitative description. A reflection on the different forms in which deteriorated heat transfer is observed in experiments and suggestions for possible improvements of the adopted modelling strategy are also provided in the paper, trying to investigate possibly promising lines of future research.