Heat transfer coefficient measurement study of several film boiling modes in subcooled HeII

This study was carried out for more detailed information about film boiling heat transfer in subcooled superfluid helium (He II). A number of film boiling modes were experimentally investigated in a wide range of the pressure from the atmospheric pressure down to the saturated vapor pressure. A thin stainless steel foil heater was used to cause film boiling and as a temperature sensor to measure the heater surface temperature. The results drawn from the heat transfer coefficient measurement give a support to the previous conclusion reached by visualization and pressure measurement studies that two film boiling modes appear in subcooled He II, that is the strongly subcooled film boiling mode and the weakly subcooled film boiling mode. It is, however, found that the dependence of the heat transfer coefficient on pressure was much different from those of conventional fluids. The heat transfer coefficient weakly decrease with the pressure in the weakly subcooled film boiling, and on the other hand it is almost independent of the pressure in the strongly film boiling. The peak of heat transfer coefficient appears at about 8 kPa in the transition region between the weakly subcooled and the noisy film boiling modes.