Discussion of similarity principles for fluid-to-fluid scaling of heat transfer behaviour at supercritical pressures

In this paper, a rationale for comparing heat transfer behaviour of different fluids at supercritical pres- sures is discussed. The study is performed as an extension to heat transfer of a previous proposal of dimensionless groups suitable for assessing stability in heated channels with supercritical fluids. The additional difficulty to be overcome with respect to the case of stability of channels with imposed heat flux is related to the role played in the present case by thermo-physical properties, whose trends as a function of dimensionless enthalpy are different for different fluids, sharing anyway a general similarity across the pseudo-critical threshold. The proposed considerations are discussed with the aid of results obtained by computational fluid- dynamic codes, contributing to clarify the extent at which the reported considerations can be considered promising for developing a coherent similarity theory for heat transfer to fluids at supercritical pressures.