Influence of conjugate thermal boundary on turbulent heat transfer of supercritical CO2 in the horizontal tube

In numerical simulations on horizontal supercritical heat transfer, the tube model excluding or including the solid wall is usually employed. However, a systematic comparison and in-depth elucidation between the non-conjugate and conjugate heat transfer (NCHT, CHT) models are still in absence. To address this critical issue, the present work employs both horizontal models to perform comparative numerical simulations using the shear stress transport (SST) k-ω turbulence model. The results show that the discrepancies in heat transfer between the two modes are negligible under weak buoyancy effect. However, the inconsistencies become more pronounced with intensified buoyancy strength, especially along the top generatrix. Under strong buoyancy effect, the largest deviations in wall temperature and heat flux of the top generatrix between two modes reach up to 396.1°C and 43.5 kW·m-2, respectively, the incorporation of tube wall in CHT computations greatly improved the heat transfer uniformity. The mechanisms that the tube wall acts as a “damper” regulating the heat flow are revealed, which is mainly via the circumferential heat transport and spread from the top where the fluid convection thermal resistance augments; whereas the exclusion of the solid tube wall results in the loss of the surface heat flux adjustment, and the top heat transfer degradation progressively worsens then the wall temperatures sharply rise. As the buoyancy level is within the range of BuP, max