Variation of the film boiling mode in He II from the vicinity of the lambda pressure down to the saturated state

The characteristic features of film boiling in both sub-cooled and saturated He II were experimentally investigated. Special emphasis was placed on the film boiling state around the lambda pressure (pλ= 5.04 kPa). It was found that there are two film-boiling modes clearly divided by a line just above pλ. One is a typical sub-cooled boiling mode that is normally found at higher pressures than pλ. The other mode resembles noisy film boiling in saturated He II. The boundary between the two boiling modes lies at the pressure just above pλ, the pressure of which slightly increases as the bath temperature decreases. It was found that noisy film boiling does not occur and the regions of the sub-cooled and silent film boiling modes connect directly in the vicinity of the lambda point. At the same time, the pressure and temperature variation were also measured and the cause of the occurrence of those variations was clarified. The features of each boiling mode were characterized.