Heat transfer of supercritical CO2 in vertical round tube: A considerate turbulent Prandtl number modification

In order to predict the heat transfer deterioration (HTD) of supercritical pressure fluids and to provide practical guidance for engineering applications of supercritical pressure CO2 (SC-CO2), a considerate turbulent Prandtl number (Prt) modification was proposed with the use of shear stress transport k−ω turbulent model. The proposed variable Prt model considering the effects of system pressure, fluid properties and tube diameters was validated by comparing with 26 reported experimental data, especially for HTD cases. The comparison results show that the present model not only predicts the HTD but also reproduces the onset of it. The modification of Prt in the buffer layer is the key to predict the wall temperature accurately, since the modified Prt changes in association with the molecular Pr and accommodates the contribution rate of molecular conduction to turbulent mixing on heat transfer. Moreover, the correction factors for tube diameter and system pressure are implemented to adjust the modification of Prt. The applicability of the proposed model to various operating conditions is verified in this paper, therefore the present modification for Prt may be popularized to extensive engineering applications of SC-CO2, especially for the optimization design of SC-CO2 heat exchanger. •Effects of Prt on supercritical CO2 heat transfer in round tubes are studied.•A considerate Prt modification was developed with the use of SST model.•The variable Prt model was validated by a wide range of experimental data.•The significance of Prt in the buffer layer.•The effects of fluid properties and tube diameter are considered in this model.