Study of evaporation from He II free surface induced by thermal shock wave

摘要

Experimental study on evaporation phenomena in superfluid helium (He II, T < 2.17 K) environment was carried out. We took such advantages of He II environment that a practically pure vapor-liquid system could be realized in a experimental cell because all gaseous components except helium were in frozen state and a thermal shock wave could be used as a pulsed heat source to induce evaporation. Evaporation is caused by the incidence of a second sound thermal pulse onto the HE II free surface. The gas-dynamic phenomena were visualized with the laser holographic interferometer (LHI) and were measured with superconductive thermometers and pressure transducers as well as with the newly developed superconductive hot-wire anemometer. The whole gasdynamic field was seen to consist of an evaporation shock wave, a uniform flow region and a Knudsen layer. The condensation coefficient of He II is obtained from the comparison of the experimental data with the slip boundary condition at evaporating interface derived from the kinetic theory of gases. It was demonstrated that a He II environment could offer an ideal situation for experimental gas-dynamic studies, and such experimental techniques as LHI and a hot-wire fully developed in conventional fluid-dynamics were of use even in cryogenic environment.