Forced Convection Heat Transfer in Superfluid Helium at Pressures up to Supercritical

本研究的主要结果如下：在亚临界和超临界压力下，流速越大，液温越低，He II的临界热通量越大。在超临界压力下，热流密度高于CHF时存在类似于膜沸腾的换热区。超临界压力下，低热流密度范围的传热曲线梯度较大，高热流密度范围的传热曲线梯度较小。本文将上述曲线的峰值热通量作为拟临界热通量处理。在2.3 atm和2.8 atm下，T_< < >=2.2 K时，各流速下的伪chfs几乎相同，约为2.0 atm下相同温度液体的2.2倍。在流速为2.1 m/s时，达到超临界压力（2.0 K, 2.8 atm）下的He II值。在>中，随着T_<的增加，伪chfs显著降低。在亚临界压力下，He I中的CHFs显著依赖于低流速范围内的压力，在较高的压力下CHFs较低。CHFs随流速的增大而增大，使得压力依赖性变小。当流速大于1.2 m/s时，压力依赖性几乎可以忽略不计。

Major Results of this study are as follows.Critical Heat Fluxes (CHFs) in He II under subcritical and supercritical pressures are higher for higher flow velocity and lower liquid temperature. Under supercritical pressures, there exists a heat transfer region similar to film boiling for the heat flux higher than the CHF.In He I under supercritical pressures, the heat transfer curve for lower heat flux range has a steeper gradient and the curve for higher heat flux has a lower gradient. The peak heat fluxes of the former curves are treated as the pseudo-critical heat fluxes in this study. The pseudo-CHFs for T_<in>=2.2 K at 2.3 atm and 2.8 atm are nearly the same for each flow velocity and are about 2.2 times of those for the same temperature liquid at 2.0 atm. At the flow velocity of 2.1 m/s, they reach the value for He II under supercritical pressure (2.0 K, 2.8 atm). The pseudo-CHFs become significantly lower with the increase in T_<in>.CHFs in He I under subcritical pressures are significantly dependent on pressure in the low flow velocity range : they are lower for higher pressures. The CHFs increase with the increase in flow velocity in such a way that the pressure dependence becoming smaller. The pressure dependence is almost negligible for the flow velocities higher than 1.2 m/s.