Study On The Flow And Heat Transfer Characteristics Of The Passive Residual Heat Removal System Of The Swimming Pool-type Low-Temperature Heating Reactor

As an essential part of the reactor safety system,the Passive Residual Heat Removal System(PRHRS)of the Swimming Pool-type Low-Temperature Heating Reactor(SPLTHR)requires a lot of basic theoretical analysis and key technology demonstration tests.At present,there are few studies on the PRHRS of SPLTHR,and there are still many thermal-hydraulic issues to be further explored.According to the characteristics of low temperature and low pressure of the SPLTHR,the flow and heat transfer characteristics of the PRHRS of singlephase and separated heat pipe are studied experimentally and theoretically.First,according to the low-temperature and low-pressure characteristics of the SPLTHR,a principled passive residual heat removal test device was designed and built.The test device takes the heat exchanger placed in the heating pool as the hot end,and the air-cooler arranged at the highest point of the test loop as the cold end.The centrifugal fan provides cooling air for the air-cooler.The flow and heat transfer characteristics of the PRHRS using single-phase natural circulation(hereinafter referred to as single-phase heat removal system)and PRHRS using separated heat pipe technology(hereinafter referred to as separated heat pipe heat removal system)were experimentally studied on this test device.The test conditions were designed with reference to the operating parameters and operating conditions of the SPLTHR.The temperature range of the pool water in the test was 50-90°C,the air temperature range was 15-30°C,and the air velocity range was 0.7-1.7 m/s.The heat transfer characteristics of the single-phase heat removal system are obtained through experiments.In the range of experimental conditions,the natural circulation mass flowrate of the system ranges from 2.3 to 4.7 kg/s,and the heat transfer capacity of the system ranges from 61.7 to 312.8 k W.The experimental results of start-up characteristics under different boundary conditions show that the higher the heat transfer power of single-phase heat removal system in the final stable state,the shorter the stability time required by the system.Through theoretical analysis,it is found that the local resistance has greater influence on the natural circulation flow than the friction resistance.With the increase of height difference between cold and hot core,the influence of height difference between cold and hot core on the natural circulation mass flowrate decreases gradually.By comparing different correlations with experimental values,it is determined that under the condition of low heat transfer temperature difference,the correlation suitable for calculating natural convection heat transfer outside the tube is Yang Shiming correlation,and the correlation suitable for calculating convection heat transfer inside the tube is Aicher correlation.For single-phase heat removal system,air-cooler is the main factor limiting heat transfer capacity.In the range of experimental conditions,the heat transfer capacity of the separated heat pipe heat removal system ranges from 103.4 k W to 475.7 k W.By changing the initial noncondensable gas content of the system,the inlet pressure of the air-cooler is determined to be the main factor affecting the distribution length of non-condensable gas in the air-cooler.According to the experimental results,the correlation of non-condensable gas occupying length in the air-cooler is fitted.The calculation results of the relationship are in good agreement with the experimental results.By comparing the heat transfer capacity of separate heat pipe under different filling rate conditions,the optimal filling rate of the system was determined to be between 25% and 30%.When the system can run stably,the air-cooler is the main factor limiting the heat dissipation power of the system.Finally,the heat transfer characteristics of single-phase and separated heat pipe heat removal systems are compared and analyzed.It is found that when the temperature difference between cold and heat sources is less than 50℃,the insufficient heat transfer temperature difference leads to the rapid decrease of the steam flowrate in the loop of the separated heat pipe heat removal system and the total heat transfer coefficient of the heat exchanger,so that the heat transfer capacity of the separated heat pipe heat removal system is lower than that of the single-phase heat removal system.Through the sensitivity analysis of the heat transfer capacity of the system,the sensitivity of the heat transfer capacity of the single-phase heat removal system to the boundary conditions is determined in order from large to small: pool water temperature,air temperature and air velocity.The sensitivity of heat transfer capacity of separated heat pipe heat removal system to boundary conditions is in descending order: pool water temperature,air velocity and air temperature.In this paper,through the combination of experimental research,numerical calculation and theoretical analysis,the operating characteristics and heat removal performance of the singlephase system and the separated heat pipe system are obtained,which lays a foundation for the application of Passive Residual Heat Removal System of Swimming Pool-type LowTemperature Heating Reactor and provides a basis for system design.