Variation of subcooled film boiling state in HeII with the pressure

The characteristic feature of subcooled film boiling in He II was experimentally studied. The visual observation and the transient pressure and temperature measurements were performed to investigate the variation of the subcooled film boiling state with the pressure. In the highly subcooled state, the boiling state was relatively stable and little dynamic behavior of the vapor layer was observed. The pressure and temperature oscillations were hardly detected. As the pressure is reduced and consequently the degree of subcooling decreases, the thickness of vapor layer becomes thick and the dynamic behavior gradually becomes violent. The pressure and temperature oscillations appear with a very high frequency around several kHz. As the pressure further decreases to near the lambda pressure, the boiling state changes to much more violent boiling state with a frequency of several hundred Hz. A vapor bubble repeats formation and crush periodically, which apparently resembles noisy film boiling in saturated He II. The boundary between the stable and the unstable boilings seems to be in the pressure higher than the lambda pressure.