Energy mode change between second sound thermal pulse and evaporation wave in the vicinity of free surface of superfluid He II

相边界上的能量平衡对于研究超流氦自由表面的蒸发现象是很重要的。作为传热机制的超热传导、二次声热脉冲和阻碍传热的量子化涡旋必须定量考虑。为了阐明这一现象，我们对一些相关的物理现象进行了实验研究。1.热脉冲斜入射He Ⅱ自由表面时的蒸发：据报告，根据入射热脉冲之间的能量平衡进行的理论预测，反射热脉冲和蒸发波与目前的实验结果的误差仅为5%，但没有达到完全一致。这种差异被认为是由反射第一声压缩波和可能的ripron的影响引起的，但目前的实验无法揭示原因。在热脉冲大角度入射的情况下，虽然只在波前处观察到全反射，但在波前后的均匀部分没有观察到全反射，但发生了全反射。2. He II的空化流动：He I和He II的空化流动存在根本的差异。这主要是由于He Ⅱ和He Ⅰ的传热机制不同，即He Ⅱ的超热传导和He Ⅰ的热传导不同。3. He Ⅱ沸腾：在近饱和蒸汽压条件下出现了噪声和无声的膜沸腾模式，在过冷He Ⅱ中出现了大量的膜沸腾模式。4.超流激波管：在He Ⅱ自由表面上入射气体动力学激波后，观察到大规模的蒸发和随后的冷凝。

The energy balance across a phase boundary is important for the consideration of evaporation phenomena from a free surface of superfluid helium. The super thermal conduction as a heat transport mechanism, second sound thermal pulse and quantized vortices that impede the heat transfer must be included into a quantitative consideration. In order to clarify the phenomena, a number of relating physical phenomena are experimentally investigated.1.Evaporation upon an oblique incidence of a thermal pulse on a He II free surface : It had been reported that fairly good agreement had resulted between a theoretical prediction on the basis of the energy balance among an incident thermal pulse, a reflecting thermal pulse and evaporation wave with the present experimental result with an error of only 5%, but a complete agreement had not been attained. The discrepancy was supposed to arise from the effects of reflecting first sound compression wave and presumably a ripron, but the present experiment could not reveil the cause. In the case of thermal pulse incidence with a large incident angle, a total reflection occurred, though the total reflection was observed only at the wave front but was not observed in the uniform portion behind the wave front.2.Cavitation flow of He II : Fundamental differences are found between cavitating flows of He I and He II. It is concluded that these are primarily caused by the difference in the heat transfer mechanisms, the super thermal conduction in He II and the thermal conduction in He I. Even a lambda phase transition is induced because of large temperature drop caused by cavitation.3.He II boiling : There appear a noisy and silent film boiling modes under nearly saturated vapor pressure condition, and a number film boiling modes in subcooled He II.4.Superfluid shock tube : It is observed large scale evaporation and subsequent condensation occur upon an incidence of a gas dynamic shock wave on a He II free surface.