| Superconducting electrodynamic suspension(EDS)train has a large suspension air gap and can achieve self-stable suspension.Its speed has exceeded 600 km/h,and it has broad application prospects in the field of rail transportation.As a key component of the EDS train suspension frame,the on-board cryostat provides a reliable cryogenic environment for the operation of superconducting magnets,and is an important guarantee for superconducting magnet operating.At present,there are two cooling methods for superconducting magnets in on-board cryostat: the liquid helium zero-evaporation cooling method and the cryocooler conduction cooling method.Neither of the two methods can operate independently from external power supply and cooling source,and the former requires liquid helium as an intermediate cryogen,which is a scarce strategic resource and expensive.In order to improve the portability and stability of on-board cryostat,realize the lightweight of the suspension frame,and reduce the operating cost,this paper proposes a solid nitrogen cryostat with a fully detachable cryocooler structure.In this paper,the structural design,heat leakage,cooling and heat preservation performance of the cryostat are studied by means of analytical calculation,finite element simulation calculation and experimental verification.First of all,in order to improve the portability of the cryostat and realize the lightweight of the EDS suspension frame,the cryocooler can be completely separated from the cryostat by the fully detachable cryocooler structure when it stops working,thereby removing the weight of the cryocooler and its auxiliary equipment.From the perspective of economy and stability,solid nitrogen replaces liquid helium as the intermediate cryogen.Solid nitrogen as a satisfying cryogen with the advantages of wide operating temperature area,large heat capacity,lower density and price,can effectively reduce operating cost and improve the movement stability of superconducting magnet.In addition,the cryostat adopts a doublestage radiation shield,binary current leads and detachable support rods to reduce the heat leakage of the system.The thermal resistance of the contact interface on the cooling path was reduced by using cooling medium and the thermal stability of the cryostat was improved.Finally,according to the cryostat structure and working temperature requirements,Sumitomo RDK-415 D double-stage G–M cryocooler was selected as the cooling source.Secondly,the conduction and radiation heat leakage of the cryostat were analyzed analytically.According to the cooling efficiency of the cryocooler and the solid nitrogen solid-solid phase transition point(35.61 K),the solid nitrogen working temperature range is34～40 K.Combined with the operating time of the cryostat,it is calculated that the solid nitrogen volume in the chamber is 39.4 L.The simplified model of the cryostat was analyzed with the help of multi-physics finite element simulation software.The simulation calculation of the strength and deformation of the outer cavity,the solid nitrogen chamber and the support rod was carried out.Also,the temperature distribution the double-stage radiation shield was simulated.At the same time,the phase transition process of solid nitrogen was calculated by the equivalent heat capacity method,and the temperature rise time of solid nitrogen in the working temperature range of 34～40 K was simulated.The results show that the strength,deformation,temperature distribution of the key components and heat preservation time of the cryostat all meet the design requirements.Finally,according to the structural design and simulation analysis results,the assembly and experimental test of the cryostat was carried out.In the 90-minute cooling test of different cooling mediums on the contact interface of the cooling path of the cryocooler,the results show that the selected thermal grease TFX is the best choice.Then,the cooling and heating performance tests of solid nitrogen were carried out.The results showed that after185 h of cooling,the maximum temperature of solid nitrogen dropped to 34 K.At the same time,the temperature rise time is 6.2 h when the excitation loss is 5 W without cryocooler. |
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