The paper addresses the observed trends of friction factor and shear stress at the wall as a function of operating conditions in supercritical pressure fluids. Previous literature suggests that the friction factor correlations applicable at supercritical pressures, at which fluids show considerable changes in properties while crossing the pseudocritical threshold, should be mostly the same as those for fluids with relatively constant properties in the liquid-like and gas-like regions, though corrections should be instead applied for conditions in between the two extremes. Basing on a previous work performed in past years at the University of Pisa to address this issue and after a review of selected information proposed in the field, some experimental conditions are here addressed with the aid of a CFD code, aiming to consider the behaviour predicted by the available models and to discuss the possible agreement of this information with experimental evidence. In particular, a circular pipe with supercritical carbon dioxide and a 2 × 2 rod-bundle mock-up with supercritical water are considered; in the latter case, the capability of CFD to provide local data of the shear stress at the heated and the unheated walls of the bundle helps in suggesting with sufficient clarity the different influence that bulk and wall temperatures have on friction parameters. The obtained results support the use of the classical correction factors proposed in previous literature to correct isothermal friction factor correlations with density and/or viscosity ratios to account for an observed decrease across the pseudocritical region. This information supports a meaningful explanation of some of the available experimental data that, at the moment, cannot be so detailed as to highlight such local effects, thus proposing a rationale to explain the role of the different parameters influencing hydraulic resistance at supercritical pressure.
Clarifying the trends of hydraulic resistance parameters for supercritical pressure fluids with the aid of CFD
Kassem S.;Pucciarelli A.;Ambrosini W.
2026-01-01
Abstract
The paper addresses the observed trends of friction factor and shear stress at the wall as a function of operating conditions in supercritical pressure fluids. Previous literature suggests that the friction factor correlations applicable at supercritical pressures, at which fluids show considerable changes in properties while crossing the pseudocritical threshold, should be mostly the same as those for fluids with relatively constant properties in the liquid-like and gas-like regions, though corrections should be instead applied for conditions in between the two extremes. Basing on a previous work performed in past years at the University of Pisa to address this issue and after a review of selected information proposed in the field, some experimental conditions are here addressed with the aid of a CFD code, aiming to consider the behaviour predicted by the available models and to discuss the possible agreement of this information with experimental evidence. In particular, a circular pipe with supercritical carbon dioxide and a 2 × 2 rod-bundle mock-up with supercritical water are considered; in the latter case, the capability of CFD to provide local data of the shear stress at the heated and the unheated walls of the bundle helps in suggesting with sufficient clarity the different influence that bulk and wall temperatures have on friction parameters. The obtained results support the use of the classical correction factors proposed in previous literature to correct isothermal friction factor correlations with density and/or viscosity ratios to account for an observed decrease across the pseudocritical region. This information supports a meaningful explanation of some of the available experimental data that, at the moment, cannot be so detailed as to highlight such local effects, thus proposing a rationale to explain the role of the different parameters influencing hydraulic resistance at supercritical pressure.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
