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

跨相边界的能量平衡对于考虑超流氦自由表面的蒸发现象很重要。超热传导作为一种热传递机制，二次声热脉冲和阻碍热传递的量子化涡流必须纳入定量考虑。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.热脉冲斜入射在He II自由表面上的蒸发：据报道，基于入射热脉冲、反射热脉冲和蒸发波之间能量平衡的理论预测与目前的实验结果吻合较好，误差仅为5%，但并不完全一致。这种差异被认为是由于反射第一声压缩波的影响，并可能是一个里普隆，但目前的实验无法揭示其原因。在大角度热脉冲入射的情况下，虽然只在波前观察到了全反射，但在波前的均匀部分没有观察到全反射。2.He II的空化流动：He I和He II的空化流动有根本的不同，这主要是由于换热机制的不同造成的。He II中的超热传导和He I中的热传导，甚至由于空化引起的大温降而引起波长相变。3.He II沸腾：在接近饱和的蒸汽压条件下，出现有噪声和无声的薄膜沸腾模式，以及过冷的He II中的多种薄膜沸腾模式。4.超流体激波管：观察到气体动力激波入射到He II自由表面时，会发生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.