A review of heat transfer deterioration of supercritical carbon dioxide flowing in vertical tubes: Heat transfer behaviors, identification methods, critical heat fluxes, and heat transfer correlations

The knowledge of heat transfer deterioration is of great significance for the application of supercritical fluids in nuclear reactors, solar power systems, and other industrial fields. In order to better understand the current status, the goal of this paper is to conduct a systemic and comprehensive research review on heat transfer deterioration of supercritical carbon dioxide in vertical tubes. First, recent experiments of supercritical carbon dioxide in vertical flows are reviewed. The effect of boundary conditions such as mass flux, heat flux, tube diameter, operating pressure, and inlet temperature are compared and analyzed. Results show that the heat transfer behaviors are complex and inconsistent in different experiments. The sharp variation of the thermal properties and the induced buoyancy and acceleration effects are typically accepted explanations in existing studies. Further studies from a microscopic perspective using molecular dynamics may help to reveal the essence of the heat transfer mechanisms. Then, the identification methods to distinguish deteriorated heat transfer and normal heat transfer are summarized and assessed. A simple method with higher accuracy is also proposed, but no approach can discern the location and magnitude of heat transfer deterioration clearly. Next, the criteria of the onset of heat transfer deterioration in existing studies are reviewed. It is noticeable that the critical heat flux depends not only on mass flux, but also on tube diameter, operating pressure, and inlet temperature. Finally, an exhaustive summary of heat transfer correlations of supercritical carbon dioxide is carried out.