CONSIDERATIONS ABOUT CORRELATIONS FOR HEAT TRANSFER TO SUPERCRITICAL PRESSURE FLUIDS SPANNING ALL REGIMES

In this paper an assessment of the performance of existing correlations for heat transfer to supercritical fluids is proposed making use of an approach including the direct observation of experimental trends and the knowledge acquired from the recent development and assessment of a fluid-to-fluid similarity theory. The correlations are revised and discussed in detail on this new basis, trying to highlight the reasons for their failure to predict key regimes as deteriorated heat transfer. As known, though many correlations have been proposed in the past, none can be actually relied upon to predict all the regimes encountered spanning from the liquid like region to the gas-like one in bulk and at the wall of a heated duct, with main reference to the phenomena of deterioration, often occurring when buoyancy or acceleration become dominant on forced convection. Suggestions for the development of more consistent correlations are then proposed on the basis of the new rationale, trying to stimulate interest for new approaches in dealing with the tough problems involved in predicting normal, enhanced and deteriorated heat transfer and to propose new promising modelling techniques. The work is performed in the frame of studies devoted to enable the design of supercritical water cooled light water reactors (SCWRs). The fluid-to-fluid similarity theory provides guidance for devising correlations, having up to now received support from CFD calculations and requesting at least an indirect experimental confirmation in terms of the prediction of heat transfer data to be correlated on the basis of the dimensionless numbers identified by its underlying theor