OUTCOMES OF A SUCCESSFUL FLUID-TO-FLUID SIMILARITY THEORY FOR HEAT TRANSFER AT SUPERCRITICAL PRESSURES

The study of heat transfer characteristics of fluids at supercritical pressures is important for the design and safe operation of the future Supercritical Water Reactors (SCWRs). Several engineering correlations have been developed for predicting heat transfer coefficients at supercritical pressures; nevertheless, their degree of accuracy is not sufficient, especially in cases of deteriorated heat transfer. Therefore, considerable improvements are essential. Thanks to the rationale established by the authors in recent papers and the consequent possibility to define scaled boundary conditions for different simulant fluids, it is presently possible to analyze the problem under a new perspective. Mainly, the relevant dimensionless numbers, which determine the observed phenomena, have been clarified making use of RANS analyses of different fluids flowing upwards in vertical uniformly heated tubes, proving the potential and the capabilities of the proposed similarity theory for heat transfer phenomena. In this paper, the main steps in the application of the similarity theory for reproducing similar physical behavior with different fluids are described, also addressing one of the most important parameters: the operating pressure of the simulant fluid. Two sets of experimental data were used as reference conditions, exhibiting different phenomena ranging from mild to severe deterioration and even followed by heat transfer restoration. The choice of these sets was made to show the behavior of simulant fluids subjected to similar boundary conditions, especially if they are addressing the different regions of liquid-like, trans-pseudocritical and gas-like conditions.