热阻对液氮冷屏性能的影响研究

Influence of the thermal resistance on the LN_2 cold shield performance

超导元件需用液氦降温至极低工作温度才能实现超导性能,液氦温区仅靠真空多层绝热方式无法达到理想绝热效果,采用液氮冷屏隔断液氦和环境之间的传热,能够有效降低液氦系统蒸发损失和液氦用量。为研究热阻对液氮冷屏传热特性的影响,建立了液氮冷屏热阻模型,通过理论传热计算得到了不同热阻与冷屏板温度及传热量之间的关系,利用数值模拟软件对不同热导率材料和不同板厚下冷屏板的温度分布进行了分析。结果表明,最不利热阻为接触热阻和导热热阻,采用高导热系数材料及适度增加冷屏板厚度有助于提高冷屏板温度分布的均匀性,减小接触热阻和冷屏板表面发射率有助于提高冷屏隔热性能,为改善冷屏热屏蔽效果提供依据。

Superconducting elements need low temperature with usually LHe as a cooling medium to get its performance. Such a LHe system is hard to defend heat leak only with high vacuum multi - layer insulation. LN2 cold shields can greatly lower the heat leak to the LHe system and reduce the consumption of LHe. In order to research the impact of the thermal resistance to heat transfer characteristics of the LN2 cold shield, the paper established a thermal resistance model, calculated the affect of different thermal resistance to the cold shield plate temperature and the heat transfer quantity by the theory of heat transfer, and analyzed the temperature of cold shield plate under different thermal conductivity materials and different plate thickness by numerical simulation method. The results show that the most negative thermal resistance is contact and conduction, using the high thermal conductivity material and increasing the thickness of the plate can help to improve the temperature distribution uniformity of cold shield plate, reducing the thermal contact resistance and the surface emissivity can also help to improve cold shield thermal insulation properties, which can provide a reliable method for improving the heat shielding affect of cold shield.