磁共振成像低温超导磁体冷却系统设计及数值分析

为了减小冷却磁共振成像（MRI）低温超导磁体的资源消耗和经济成本，设计可快速冷却室温磁体至60 K以下的系统，并通过建立数学物理模型进行数值模拟，对系统进行优化设计和深入分析. 系统以自主研发的大冷量单级斯特林制冷机为冷源，包括低温风机、低温调控阀和氦气罐等组成部分. 研究表明，优化系统运行参数可以显著提高冷却性能，其中系统内氦气的压力和流速尤为关键，因为两者能够显著影响压降与换热，进而影响冷却时间以及磁体最终所能达到的冷却温度. 此外，当前斯特林制冷机的冷端换热器性能尚有提升空间. 通过参数优化，系统在氦气压力为0.3 MPa、流速为13 m/s时能够达到较快的冷却速率，可在73.5 h内将质量为2 t的室温超导磁体冷却至60 K以下，有潜力在实际应用中实现MRI低温超导磁体的低能耗高效冷却.

Design and numerical analysis of a cooling system for low temperature superconducting magnet of magnetic resonance imaging

A system capable of rapidly cooling magnets from room temperature to below 60 K was designed, in order to reduce the resource consumption and economic cost of cooling the low temperature superconducting magnet of magnetic resonance imaging (MRI). Furthermore, the design optimization and in-depth analysis were carried out by numerical simulation based on its mathematical physics model. A self-developed single-stage Stirling cryocooler with large cooling capacity was used as the cold source of this system, comprising a cryogenic fan, control valves and one helium gas cylinder. Results showed that the cooling performance can be improved by optimizing the operating parameters of system, of which the pressure and flow rate of helium gas were particularly critical, because they can significantly affect the pressure drop and heat transfer and further affect the cooling time and temperature that the magnet could ultimately attain. Moreover, the current cold end heat exchanger performance of Stirling cryocooler still had space for promotion. This system can achieve a fast cooling rate at helium pressure of 0.3 MPa and flow rate of 13 m/s through parameter optimization. A superconducting magnet weighing 2 tons can be cooled to below 60 K from room temperature within 73.5 h based on the above condition, which showed that it had the potential to achieve low energy consumption and high efficiency of cooling MRI low temperature superconducting magnet in practical applications.