Thermal Analysis Of High Temperature Superconducting Magnet Cooling System

Strong magnetic fields change the magnetic distance between the nucleus and the extranuclear electrons,thereby changing the properties of the material.Strong magnet ic fields provide new research directions for basic science and cross science.The magnet ic field generated by the superconducting magnet is not only low in operating cost,high in stability,but also more uniform in magnetic field than water-cooled magnets.From the characteristics of superconducting materials,it can be seen that cooling the HTS magnet to a lower temperature can obtain higher magnetic field strength and gradient,which helps to broaden the scope of the physical experiment of the SWIP linear device.When the HTS magnet is excited,the thermal load of the lead accounts for more than 50% of the total thermal load of the cryogenic system.By reducing the thermal load of the lead,the total thermal load of the cryogenic system can be reduced.The factors that affect the thermal load of the current lead are the cooling method of the leads,the thermal conductivity of the leads,the resistivity,and the geometry of the leads.The cooling method of the leads is determined by the cooling method of the superconducting magnet.The thermal conductivity and electrical resistivity of the leads are determined by the material of the leads.The optimal size factor for the leads is calculated by different design methods.According to the calculation results,the lead processing cost is comprehensively considered,and the geometrical dimensions of the lead are designed.According to the result of lead design,the variation of the temperature and heat flux of the lead along the axial direction of the lead under differe nt excitation currents is analyzed by numerical simulation method,which provides a theoretical basis for selecting the current lead of the SWIP linear device.Considering the size of the superconducting magnet and the mechanical properties of the strip,if the conductive direct cooling superconducting magnet is used,although the cooling cost is low,the magnet is not only subjected to the influence of temperature difference during the cooling process,but also needs to withstand the small cryogenic refrigerator.The effect of mechanical vibration.Therefore,liquid helium(helium)is used as the main cooling medium for the superconducting magnet.Cooling the superconducting magnet with a liquid or gaseous cooling medium not only reduces the temperature difference stress inside the magnet,but also shortens the cooling time and improves the safety of the superconducting magnet.The superconducting magnet is first cooled to liquid nitrogen temperature using liquid nitrogen.The effects of liquid nitrogen with different flow states and differe nt flow rates on the maximum temperature difference and cooling time of superconduct ing magnets during the cooling process of superconducting magnets were analyzed by numerical simulation.According to the numerical analysis results,the best solution for liquid nitrogen precooling superconducting magnet is proposed.After the superconducting magnet is pre-cooled by liquid nitrogen,the low-temperature system needs to be deniturized to prepare for the deep cooling of the superconducting magnet.The influence of the nitrogen removal time of the low temperature system on the temperature of the superconducting magnet was analyzed by numerical simulation.In order to achieve rapid cooling of the superconducting magnet,the superconduct ing magnet was deeply cooled by liquid helium,and the influence of the liquid helium of different mass flow rates on the maximum temperature difference and the cooling time of the superconducting magnet during the cooling process of the superconduct ing magnet was analyzed.According to the numerical analysis results,the best solution for liquid helium deep cooling superconducting magnet is proposed.When only helium does not have liquid helium,the superconducting magnet is deeply cooled by helium gas after the superconducting magnet is precooled by liquid nitrogen and nitrogen is discharged in a low temperature system.The cooling capacity is provided by a small cryogenic refrigerator,and the fin heat exchanger and the helium gas form a thermal bridge,and the superconducting magnet is cooled to a lower temperature by convection heat exchange between the helium gas and the superconducting magnet.In the process of cooling the superconducting magnet deep in the helium gas,the heat transfer effect of the fin heat exchanger is particularly import ant,which directly affects the deep cooling time of the superconducting magnet.The heat transfer effect of the fin heat exchanger is closely related to the material of the fin heat exchanger,the fin spacing,and the high fin height.Through the numerica l simula t io n method,the fin heat exchange of different materials(1050 aluminum,RRR=100 copper,304 stainless steel),different fin spacing(3mm,4mm,5mm),different fin height(25mm,30 mm,35mm)is analyzed.The heat transfer effect of the device.According to the numerical analysis results,the theoretical basis for selecting the fin heat exchanger for the SWIP linear device is provided.