Study On The Key Technologies And Working Characteristics Of Large Helium Cryogenic System

China spallation neutron source is a scientific research device used to research the neutron characteristics and detect the micro structure and movement of the material.Its cryogenic system has a total refrigerating capacity of 2000 W/20 K and is mainly used to cooling two hydrogen neutron moderators.It is the largest-scale major national science and technology infrastructure in China.The whole cryogenic system is mainly consists of the cooling unit of helium expansion turbine and the cycle unit of supercritical liquid hydrogen,and in this paper,the working characteristics of the cooling system of the cryogenic helium expansion turbine is studied.Based on the above research background,this paper centers on the research of the working characteristics of the spallation neutron source helium cryogenic system,taking the key equipment and the cooling process of the cryogenic system as the research object,the dynamic simulation model of the key equipment is established,and the convective heat transfer characteristics of the supercritical helium at a low temperature is analyzed based on the simulation and experiment.The purpose of this paper is provided design guarantee and theoretical basis for the safe and efficient operation of the helium cryogenic system at a low temperature,and the main research contents are as follows:(1)Based on the requirement of the spallation neutron source on helium cryogenic system,the process design and dynamic simulation of the cryogenic system is carried out.After the research on the thermodynamic characteristics of the screw compressor,turbine expander,low temperature heat exchanger and low temperature regulating valve of the cryogenic system,the dynamic simulation model of the cooling process of the system is established,and dynamic simulation of the cooling process of the helium cryogenic system is carried out.Finally,experiment is constructed to validate the accuracy of the simulation model.(2)Considering the requirement of the helium cryogenic system on refrigerants,the influence of the velocity,temperature,filter parameter and adsorbing properties of activated carbon on the purification performance of the system is researched.A helium purification system with a high purification performance is developed,and it could make the helium of the cryogenic system reach the requirement of booting within 2 hours.(3)An electric heating load with a temperature zone of 20 K is developed to research the refrigerating capacity and refrigeration temperature of the helium cryogenic system.The simulation to research the influence of the fin material,fin number,porosity and the number of heating rods on the heat transfer characteristics of the load at a low temperature is carried out.The matching method for the solution of the forced convective heat transfer in tube and finite space cross swept cylinder heat transfer is proposed,and it could be used to solute the problem of convective heat transfer of the complex flow field in the fin.A thermal loading rate of 0.2 W/s is proposed for the cryogenic system after the dynamic simulation.