在不同温度和压力下，混合物的摩尔质量对其相对对流传热系数的影响。可以看出，温度和压力对相对对流传热系数的影响很小。当 m_He-Xe 为 15 g/mol 时，气体混合物的传热系数比纯 He 高 6.3%。选择传热系数较高的介质可以获得更高的传热效率。因此，选择 15 g/mol 的 He-Xe 作为介质。

The influence of the molar mass of the mixture on its relative convective heat transfer coefficient at different temperatures and pressures. One can see that temperature and pressure have little influence on the relative convective heat transfer coefficient. When m_He-Xe is 15 g/mol, the heat transfer coefficient of the gas mixtures is 6.3% higher than pure He. A higher heat transfer efficiency can be achieved by choosing a medium with a higher heat transfer coefficient. Therefore, we choose He-Xe at 15 g/mol as the medium.