Numerical investigation of particle-scale convective heat transfer in supercritical H2O/CO2 mixture

Heat transfer efficiency critically dictates the performance of energy conversion reactors. In supercritical water gasification systems, extensive decomposition of organic matter releases substantial CO 2 , thereby shifting the reaction medium into a supercritical H 2 O/CO 2 mixture. Despite its practical significance, particle-scale convective heat transfer under such conditions remains poorly understood, particularly the role of the large specific heat capacity zone (LSHCZ) near the pseudo-critical point. In this study, particle-resolved direct numerical simulation (PR-DNS) was employed to investigate convective heat transfer around a fixed spherical particle immersed in flowing supercritical H 2 O/CO 2 mixture. The results reveal that traversing the LSHCZ induces a marked enhancement in heat transfer for the mixture. At identical Reynolds number ( Re ) and applied heat flux, the convective heat transfer coefficient ( h ) of the mixture is 1.04 - 1.24 times that of pure supercritical water. Along the particle circumference, the local h of mixture consistently outperforms that of pure water at all angular positions. The difference between the two fluids gradually decreases from the front stagnation point to the separation point, but subsequently recovers and intensifies toward the rear stagnation region. This trend becomes increasingly pronounced with increasing Re . Such behavior is attributed to the broadened specific heat capacity peak and the enhanced thermal storage capability of mixture. Finally, a new correlation for convective heat transfer of supercritical H 2 O/CO 2 mixture is proposed.