Maximum and Minimum Heat Flux and Temperature Fluctuation in Film-Boiling States in Superfluid Helium

Abstract

Superfluid liquid helium (helium-II), especially the subcooled helium-II, is said to have special advantages as a coolant of superconducting devices, particularly where there is a possibility of thermal hazard. First of all, helium-II has better cooling characteristics than boiling normal helium, that is, a large peak heat flux Q _max [^1,2] and also a large recovery heat flux Q _min [³]. (At Q _max, film boiling begins and at Q _min, the liquid near the heated metal surface reenters the stable non-film-boiling.) For the stabilization of superconducting magnets, it is important that the mechanism of heat transfer to helium-II is understood. Investigations have been made into the behavior of transitions between the non-film-boiling state and the film-boiling state at critical heat fluxes (Q _max, Q _min) both in the saturated and in the subcooled helium-II, as well as the cooling stability in the film-boiling state. The mechanism of noisy film boiling which emits an audible high-frequency sound in the saturated helium-II [⁴], also was studied. So far, several investigators have observed the noisy film-boiling process by means of high-speed motion picture techniques and microphone techniques [⁶]. In the present research, the frequency of the temperature change was measured with the help of a microthermometer and a clear correlation was determined between the cooling condition and the temperature fluctuation of the metal surface.