Analysis of heat transfer deterioration mechanism of supercritical fluid based on VOF two-phase method and pseudo-boiling theory

•VOF multiphase model was established to simulate the heat transfer of supercritical fluid.•Compared with the traditional single-phase approach, two-phase method can reasonably predict the HTD of supercritical fluids.•Based on the pseudo-boiling theory, the relationship between the space-time evolution of vapor-like film thickness and heat transfer is studied.•A new supercritical heat transfer correlation reflecting the interaction mechanism of the phase interface is proposed The heat transfer deterioration (HTD) in supercritical fluids is very important for the safe operation and efficiency of supercritical cycle system. For a long time, supercritical heat transfer is based on the assumption of single-phase fluid and emphasizes the effect of buoyancy and flow acceleration, which are difficult to explain its unique phenomenon and predict the HTD accurately. In the present study, the single-phase fluid assumption is abandoned, and the supercritical heat transfer is studied using VOF two-phase method, and the HTD mechanism is revealed based on the pseudo-boiling theory. Firstly, a VOF multiphase model was established to simulate the heat transfer of supercritical fluid flow and compared with the experimental results. The simulation results show that the two-phase method can reasonably predict the HTD of supercritical fluids. The effects of saturation temperature Tsat, pseudo-boiling enthalpy ΔH and evaporation frequency fe on the simulation results are also discussed. Then, based on the pseudo-boiling theory, the relationship between the space-time evolution of vapor-like film thickness and heat transfer is studied. It is found that the peak of vapor-like film thickness corresponds to the wall temperature peak, indicating that the local thickening of vapor-like film is the main reason for the deterioration of heat transfer. Finally, based on the supercritical K number controlling the thickness of the vapor-like film, a new supercritical heat transfer correlation reflecting the interaction mechanism of the phase interface is proposed. This study provides theoretical guidance for re-understanding the mechanism of supercritical heat transfer and heat transfer design of ultra-high parameter power plants.