Study On Natural Circulation Characteristics Of Separated Heat Pipe System Based On RELAP5

With the continuous development of heat pipe technology in recent years,its excellent heat transfer and passive characteristics make it an important application in the field of nuclear safety.Its application requires a lot of basic theoretical analysis and key technical demonstration tests.At present,there are few studies on the separated heat pipe system under negative pressure conditions,and there are still many thermal hydraulic problems to be further explored.In this paper,according to the characteristics of low temperature and low pressure of the separated heat pipe system,the flow and heat transfer characteristics of the separated heat pipe system are simulated and analyzed by RELAP5 / MOD4.0 software.Firstly,according to the low temperature and low pressure characteristics of the separated heat pipe,combined with an existing passive residual heat removal test device,the flow and heat transfer characteristics of the passive residual heat removal system using the separated heat pipe technology were simulated.Using RELAP5 / MOD4.0 software,the node division and simulation calculation verification of this system were carried out.For single-phase and twophase experiments,two sets of experimental conditions were selected for simulation verification.Finally,the calculated values of each parameter in the system were compared with the experimental data.The deviation is within 14 %,which proves the applicability of RELAP5 to calculate the separated heat pipe system.The heat transfer characteristics of the separated heat pipe system were obtained by simulation,and the separated heat pipe system was analyzed for three boundary conditions.In the range of simulated working conditions,the heat transfer power of the separated heat pipe heat removal system ranges from 95.40 k W to 772.08 k W,and the influence of the hot end wall temperature on the heat transfer power of the separated heat pipe system is greater than that of the air temperature.By changing the initial non-condensable gas content of the system,the influence of non-condensable gas content on the heat transfer deterioration of the separated heat pipe system and its influencing reasons are proved.By comparing the heat transfer power of the separated heat pipe heat removal system under different liquid filling rates,the optimal liquid filling rate of the system is determined to be between 12.5 % and 37.5 %.Finally,the operating characteristics of the separated heat pipe heat removal system and the causes of its instability are analyzed,and the heat transfer characteristics of the system under the arrangement of various air heat exchangers are analyzed and compared.The phenomenon similar to flash evaporation in the system is determined by the working fluid state at each position of the separated heat pipe.By setting the inlet pressure deviation value of the air heat exchanger,the stable range of the separated heat pipe operation at different cold and hot end boundary temperatures is determined.By analyzing the void fraction of the steam rising section,the liquid carrying phenomenon and the flooding effect of the air heat exchanger are determined,and it is directly related to the stability of the system.By comparing the heat transfer characteristics of the separated heat pipe system under various air heat exchanger arrangements,the optimal arrangement angle of the condensation section of the separated heat pipe is determined to be horizontal arrangement.When the arrangement angle is 30 °,the heat removal power is the worst.The conclusions obtained in this paper can provide reference for the application of separated heat pipe passive residual heat removal system.