Pool heat transfer studies of near-critical and supercritical carbon dioxide

Near-critical and supercritical fluid heat transfer exhibits unique heat transfer characteristics. Pool heat transfer experiments circumvent the drawbacks of traditional flow heat transfer experiments, characterized by numerous factors and challenges in observation, and can offer new insights for the study of heat transfer mechanisms. In this paper, the heat transfer characteristics of different horizontal wires immersed in both liquid and supercritical carbon dioxide were studied by visualization experiments with a schlieren system. The study showed that as approaching the critical point, the pool boiling weakened, resulting in a decrease in the peak heat transfer coefficient. In supercritical cases, heat transfer with low heat flux maintained natural convection, while the cases with high heat flux exhibited similar heat transfer laws and near-wall flow field structures with subcritical film boiling. Meanwhile, experiments with various metal wires revealed distinct self-propagating transition phenomena in boiling modes, driven by the axial heat conduction characteristics. Based on the experiments, a pool heat transfer mechanism of the near-critical and supercritical fluids was proposed.