The SuperCritical Water-cooled Reactor (SCWR) is one of the nuclear power plant concepts proposed for the upcoming GEN IV. Basing on the experiences obtained from PWRs and BWRs, the conception of SCWRs aims at improving the plant efficiency while reducing the capital costs; nevertheless, the development process still requires several challenges to be overcome. From the thermal-hydraulic point of view, one of the most relevant open issues concerns the capabilities of codes and correlations to correctly predict heat transfer to supercritical fluids.Heat transfer to supercritical fluids may in fact involve normal, deteriorated and improved heat transfer, depending on the imposed operating and boundary conditions. To date, no existing correlation is capable to reliably predict heat transfer in a sufficiently wide range of operating conditions. The development of a fluid-to-fluid similarity theory for fluids at supercritical pressure may thus help in highlighting common behaviours and characteristics of different supercritical fluids paving the way for the identification of the most relevant dimensionless groups to be considered for heat transfer correlations.Recently, the University of Pisa proposed a similarity theory that provided interesting results. The methodology was validated against numerical calculations and the obtained results show that similarities of relevant flow and turbulence quantities can be achieved for both axial and radial distributions. Once a reference case is selected, the proposed theory provides the boundary and operating conditions that shall be applied in order to obtain similar behaviours when adopting different fluids; among the other boundary conditions the value of the imposed heat flux is presently identified through a trial and error iterative procedure via CFD RANS calculations, owing to the large sensitivity of heat transfer phenomena at supercritical pressure.In the present paper, the capabilities of the proposed methodology are further investigated with respect to past work, widening the range of the addressed operating conditions. In particular, the experimental data by Watts (Water at 25 MPa) are here considered; several cases were reproduced adopting different fluids (i.e. CO2, NH3 and R23), in order to understand possible dependencies of the proposed rationale on the imposed mass flux and the observed heat transfer conditions. The obtained results confirmed the lessons learned from the recent experiences, also showing similarities in the performed sensitivity analyses.The aim of the present paper is to deepen the knowledge of the capabilities of the proposed theory, which seems sufficiently mature to be considered for validation against experimental data.

Advances in the Development of a Fluid-to-Fluid Similarity Theory for Fluids at Supercritical Pressure: Results From Sensitivity Analyses

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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