Comparison Of Cooling Method Of High Temperature Superconducting Maglev And Preliminary Design Of Cryogenic System

High temperature superconducting（HTS）maglev train is one of the main application directions of superconducting maglev technology.It has the merits of achieving stable levitation without external control.Compared with the wheel-rail trains,it has the advantages of energy saving,environmental protection,wide speed application range,and has a huge space of development.Cryogenic system is the core system of HTS levitation.And the selection of cooling method and structural design directly affect the performance of the superconducting bulk and furtherly affect the running performance of the train.In this thesis,conduction cooling method and liquid nitrogen（LN₂）cooling method have been carried out to study their influence of bulk levitation performance,and the optimization scheme of conduction cooling method is proposed.Finally,a cryogenic system of LN₂circulation is designed for the operating environment of the maglev,and a check calculation is performed to make it meet the application requirements.Initially,this article builds a cryogenic platform based on the conventional conduction cooling method,combined with the SCML-02 test system,to test the levitation performance of the bulk at different temperatures and field cooling heights（FCHs）.Simultaneously,being compared with the LN₂immersion cooling experiment,it is found that there is a huge difference in the levitation performance of these two cooling methods at different temperatures and FCHs.On this basis,the influence of the cooling method on the levitation performance is analyzed.And being combined with the theoretical formula,the reasons for the appearance of this difference in levitation performance are clarified.Then,a conductive cooling model of the superconducting bulk material is established using the COMSOL software,and the temperature field distribution of the bulk in the conventional conduction cooling method is calculated,and the uniformity and accuracy of the temperature field of the bulk in the simulation results are optimized.The optimized plan is then implemented based on the cryogenic platform and the effectiveness of the plan with the utilization of the experiments is also determined.After the comparison,it is found that the optimized cooling structure can effectively improve the levitation performance of the bulk,and the optimization suggestions for the application of the conductive cooling method to the levitation unit are given as well.At the same time,compared with the LN₂immersion cooling method,it is found that the levitation performance of the bulk still cannot reach the value under the LN₂cooling,but the difference in the levitation performance between these two levitation performance is relatively small.In terms of increasing the load capacity of the train,some guiding suggestions are given for the applicable cooling methods of the levitation unit under different working conditions.Finally,aiming at the application environment of the HTS maglev train,this thesis aims to avoid the high operation and maintenance cost of the LN₂immersion cooling system and the shortcomings of poor thermal uniformity of the chiller conduction cooling system.Hence,a natural convection circulation system based on the principle of heat pipe is designed,with emphasis on the structure of cryogenic box.Meanwhile,the three-dimensional modeling,key component design and heat transfer calculation,material selection,piping design and heat load distribution calculation have been completed for the cryogenic box.Eventually,by calculating the thermal load distribution of the cryogenic system during the normal operation of the HTS maglev train,the feasibility of the system is verified,which will provide a future reference for the design of the cryogenic system in the engineering of the HTS maglev train.