Yuanzineng kexue jishu (Aug 2023)
Study on Sub-cooled Boiling Heat Transfer Model in Inclined Rod Bundle Channel
Abstract
Due to the existence of phase transition, sub-cooled boiling, as an efficient heat exchange mode, is widely used in most heat exchange equipment. Under specific application conditions, the rod bundles will work under inclined conditions. For example, some heat exchangers need a certain inclination angle for installation due to space constraints, different positions in the elbow area of the U-tube steam generator have different inclination angles, and some rod bundles in marine nuclear power floating platforms or ship nuclear power plant also experience long-term inclination under ocean conditions with large-period waves. Therefore, it is crucial to research the sub-cooled flow boiling heat transfer characteristics on the surface of inclined heating rod bundles. In this paper, combining with the content of bubble dynamics and according to the characteristics of inclined bubble detachment, the bubble detachment criterion under inclined conditions was formulated. The force calculation of the bubble was then carried out, and the correlation parameters such as the diameter of the bubble detachment were-obtained. In the calculation process, it is considered that the bubbles detachment judgment condition on the upper surface of the inclined heating rod bundles is that the force balance in the direction of bubble buoyancy is broken. Additionally, under inclined heating rod bundles, a calculation model of the heat flux on the heating wall was also established adopting the wall heat flux partitioning model in conjunction with the bubble dynamics. Traditional wall heat partitioning models are mostly based on vertical or horizontal heating walls, however, the applicability for inclined conditions is still being investigated. In comparison to traditional heating conditions, the bubble behavior on the heating surfaces of the inclined heating rod bundles is different, resulting in a different heating transfer process. Therefore, the traditional wall heat partitioning model was improved to adapt to the working conditions of inclined heating rod bundles. The calculation results of the model show that 81.25% of the data can be captured within ±20% of the error line, and the average relative error is roughly 13.07%. The model has good applicability to calculate the heat flux of inclined heating rod bundles. However, the model is more applicable to low sub-cooled boiling than high sub-cooled boiling. During the high sub-cooled boiling, the heat flux calculated by the model is too low, which is because of the slowly rising wall temperature in high sub-cooled boiling. During low sub-cooled boiling, since the change of wall temperature is relatively smaller, the model is more applicable compared with that under high sub-cooled boiling.
