The temperature of liquid helium (LHe) is 4.2 K, high-performance thermal insulation schemes such as the variable density (VD) and self-evaporation vapor-cooled shield (VCS) are required for LHe tank. However, the working parameters of the VD and VCS in LHe tank have not been investigated. However, the related researches on liquid hydrogen tank neglected the heat transfer of the tank wall and the gap; The VD configuration may less than the optimal because the maximum number of spacers for each layer was pre-set artificially. Meanwhile, the recovery rate of sensible heat cannot be obtained by the existing model. In this work, these limitations are taken into account to establish the thermodynamic model of composite multilayer insulation (FMLI), VD and VCS, respectively. The results show that the correction coefficient of FMLI model is 0.1875; The layer densities of composite variable density MLI (FVD-MLI) with four segments are 3.31, 6.62, 13.23, and 19.98 layer/cm, with a 9.6% reduction in heat leakage compared to that of FMLI. The optimal position of the VCS in VCS-composited MLI (FMLI + VCS) and VCS-composited variable density MLI (FVD-MLI + VCS) is approximately 30% and 25% near the cold boundary respectively, and 36.2% and 40.7% reduction in heat leakage compared to that of FMLI and FVD-MLI respectively. The VD and VCS promote each other in improving thermal insulation performance, while the VCS plays a greater role than VD.

液氦 (LHe) 的温度为 4.2 K，LHe 储罐需要变密度 (VD) 和自蒸发汽冷屏蔽 (VCS) 等高性能绝热方案。然而，尚未研究 LHe 罐中 VD 和 VCS 的工作参数。然而，液氢罐的相关研究忽略了罐壁和间隙的传热；VD 配置可能低于最佳配置，因为每层的最大间隔数是人为预设的。同时，现有模型无法获得显热回收率。在这项工作中，考虑到这些限制，分别建立复合多层绝缘（FMLI）、VD 和 VCS 的热力学模型。结果表明，FMLI模型的修正系数为0.1875；四段复合变密度MLI（FVD-MLI）的层密度分别为3.31、6.62、13.23和19.98层/厘米，与FMLI相比，热泄漏减少了9.6%。VCS-composited MLI（FMLI+VCS）和VCS-composited可变密度MLI（FVD-MLI+VCS）中VCS的最佳位置分别在冷边界附近约30%和25%，减少36.2%和40.7%与 FMLI 和 FVD-MLI 的热泄漏相比。VD和VCS在提高隔热性能方面相互促进，而VCS的作用比VD更大。VCS-composited MLI（FMLI+VCS）和VCS-composited可变密度MLI（FVD-MLI+VCS）中VCS的最佳位置分别在冷边界附近约30%和25%，减少36.2%和40.7%与 FMLI 和 FVD-MLI 的热泄漏相比。VD和VCS在提高隔热性能方面相互促进，而VCS的作用比VD更大。VCS-composited MLI（FMLI+VCS）和VCS-composited可变密度MLI（FVD-MLI+VCS）中VCS的最佳位置分别接近冷边界约30%和25%，减少36.2%和40.7%与 FMLI 和 FVD-MLI 的热泄漏相比。VD和VCS在提高隔热性能方面相互促进，而VCS的作用比VD更大。