Boiling heat transfer characteristics for heat inputs with various increasing rates in liquid nitrogen

Abstract

The transition processes from non-boiling (single-phase) to film boiling or nucleate boiling on a horizontal cyclinder of 1.2 mm in diameter in liquid nitrogen caused by exponential, rampwise, and stepwise heat inputs with various increasing rates, were made clear at pressures ranging from 20.7 to 582.4 kPa for the saturated liquid, and at pressures of 1016 and 2047 kPa for the subcooled liquid (the temperature of which is 77.4 K). The direct transition from non-boiling (the heat transfer mechanism of which is quasi-steadily increasing natural convection) to film boiling was observed even for exponential heat input with the long period of around 100 s at atmosphere pressure. The transient heat transfer processes after the vapour film collapse at minimum film boiling in liquid nitrogen were also measured at pressures ranging from 101 to 392 kPa.