Yuanzineng kexue jishu (Jun 2023)
Numerical Study on Thermal-hydraulic Characteristics of Lead-bismuth Loop System under Rolling Motion
Abstract
Lead-bismuth reactor has the advantages of high inherent safety, strong natural circulation capacity, long operation life and rapid transient response, and has a good application prospect in special applications such as ocean engineering. The Marine device will be affected by wind and waves in the ocean and produce rolling motion, which has a series of effects on the thermal and hydraulic characteristics of the system. In order to study the thermal-hydraulic characteristics of lead-bismuth loop system under rolling motion, the size and structure of the loop system were determined, the CFD geometric model was established, the calculation mesh was drawn and the calculation model of the natural circulation characteristics under rolling motion was developed. Based on the established rolling motion calculation method, the numerical simulation study of rolling motion was carried out under the design conditions, and the influence of rolling motion on the natural circulation capacity and heat transfer characteristics of the loop system was studied. Afterwards, experiments were carried out to compare the experimental data with the simulated data to verify the correctness of the model and the reliability of the conclusions. The relative deviation between simulated and experimental fluid temperature is generally less than 5.3%, and the average relative deviation is less than 4.2%. The relative deviation of wall temperature is generally below 2.1%, and the average relative deviation is 1.67%. In addition, the maximum deviation between simulation and experiment of the rolling motion flow is within 3%. The comparison results demonstrate that there is a little gap between the simulation results and the experimental results, and the gap is within the acceptable range, which indicates that the calculation results are reliable. The simulation results show that the rolling motion will cause periodic fluctuations in the natural circulation flow of the loop system. The period of the flow fluctuation is consistent with the motion period, and the amplitude of the fluctuation increases with the maximum rolling motion and the decrease of the motion period. When the maximum rolling angle is 20° and the rolling period is 7.5 s, the instantaneous fluctuation of the flow rate reaches a maximum of 140%, and the reverse flow phenomenon occurs at some moments. The rolling motion will also cause periodic instantaneous fluctuations in the flow and heat transfer characteristic parameters of the system. The law of this fluctuation is similar to the fluctuation law of natural circulation flow. The maximum instantaneous fluctuation of Nu number reaches 515%, and the maximum time average volatility can reach 66%. The results obtained in this study have important engineering application value and scientific significance for the design and optimization of lead-bismuth loop system under rolling motion.
