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Abstract Supercritical heat transfer mechanisms and heat transfer correlations are firstly reviewed in present paper. The heat transfer characteristics of S-CO 2 in circumferentially non-uniform heated vertical upward flow are then numerically studied and the fundamental mechanisms are discussed. The abnormal heat transfer for S-CO 2 is believed to be caused by the comprehensive effect of thermophysical property variations. For S-CO 2 with non-uniform heating and large mass flow rate, the enhanced heat transfer is mainly related to the large specific heat in the near wall region while the deteriorated heat transfer is dominated by the thickening viscous sublayer induced by the viscosity increase. Besides, the buoyancy effect induced by the density variation is still prominent to axial velocity distribution even in the forced convection. Finally a new correlation with higher accuracy is developed for S-CO 2 circumferentially average heat transfer by introducing the correction parameters of viscosity, specific heat, axial flow-acceleration and non-uniform heat flux. Highlights • Supercritical heat transfer mechanisms and correlations are comprehensively reviewed. • Heat transfer of S-CO 2 under non-uniform heating is numerically studied. • The relation between thermophysical property variation and abnormal heat transfer is examined. • An average heat transfer correlation for S-CO 2 under non-uniform heating is proposed and evaluated. [ABSTRACT FROM AUTHOR]

The supercritical-CO 2 (S–CO 2) cooler is one of the main components in S–CO 2 power system. This work aims at revealing the cooling mechanism of S–CO 2 under wide working conditions to assist the S–CO 2 cooler design. The pseudo-condensation is proposed with the analogy between supercritical cooling and subcritical condensation. From the pseudo-condensation and the traditional turbulent field analysis, the specific heat is found to be the dominant parameter for the enhanced heat transfer in S–CO 2 cooling. The disappearing of enhanced cooling heat transfer, in the view of pseudo-condensation, is mainly due to the thickening of pseudo liquid film, which is dominated by the gravity force, inertial force and interfacial force in low mass flux flow while the gravity force effect is negligible in high mass flux flow. However, from the turbulent field analysis, the disappearing of enhanced cooling heat transfer is mainly caused by the thickening boundary layer due to the local increase in density and viscosity in addition to the decrease in specific heat. Finally, based on the S–CO 2 cooling mechanism, two correlations for predicting heat transfer are proposed and evaluated. The present work can significantly enhance in-depth understanding on S–CO 2 cooling and promote engineering application. • The S–CO 2 cooling mechanism is analyzed with pseudo-condensation and turbulent field. • Pseudo-condensation is based on analogy between supercritical cooling and subcritical condensation. • Turbulent field analysis focuses on selection of key influencing thermophysical properties. • Two more accurate correlations are developed based on the obtained cooling mechanism. • The pseudo-condensation for S–CO 2 cooling process is proved to be with high reliability. [ABSTRACT FROM AUTHOR]