Numerical Analysis on Heat Transfer Characteristics and Buoyancy Effects of Supercritical Pressure Water in Vertical Tube

Abstract Water is widely used in various nuclear power plants as coolant and moderator due to its good thermal conductivity and stability. However, when the pressure and temperature exceed its critical points, the physical properties of water change drastically, especially the specific heat capacity, which makes the heat transfer phenomenon near the critical point more complicated, even deteriorating. On the other hand, the curved geometry of the spiral pipe leads to a special secondary flow phenomenon in the fluid, which will intensify the heat and mass transfer and improve the heat transfer efficiency. At the same time, the flow will be more complicated in the joint influence of gravity, centrifugal force and Coriolis force. This paper studied the heat transfer characteristics of supercritical water in heated vertical tube by numerical simulation and found that changes of physical properties are the main reason for changes of heat transfer characteristics of supercritical water. And as the heat flux in the tube wall increases, heat transfer deterioration is more prone to occur around the pseudo-critical point. Then it verified the relationship between the criterion of buoyancy and heat transfer deterioration. Last, it explained the mechanism of heat transfer deterioration caused by buoyancy effect by calculating shear stress. In the future, works on the relationship between Bo* and shear stress are expected to carried out.