Chapter 186 - Film Boiling Modes in Weakly Subcooled He II around Lambda Pressure

Abstract

This chapter experimentally investigates film boiling modes in both subcooled and saturated He II. It is found that there are two film boiling modes clearly bounded by a line just above the lambda pressure (pλ). The one is a typical subcooled film boiling mode that normally appears at still higher pressure than pλ. The other film boiling mode resembles noisy film boiling in saturated He II. It is found that in the vicinity of the region of the lambda point or the lower heat flux, noisy film boiling does not occur and subcooled region directly connects with silent film boiling one. The subcooled and the silent film boiling are the same boiling mode and these film boiling modes are identical to the normal film boiling that occurs in common fluids. And the noisy film boiling is a kind of large-scale unstable phenomenon that generates the large oscillation in the heater temperature and the heat transfer coefficient, and it is the characteristic boiling mode in He II. In the regions very close to the λ-point and of the small heat flux which gives the onset condition for film boiling, the noisy film boiling does not occur. The boundary between the weakly subcooled and the noisy film boiling in He II exists just above pλ. This boundary increases as the He II temperature decreases or the heat flux increases.