LAUSR

Abstract Subatmospheric pool boiling heat transfer was investigated experimentally. At low vapor pressure, the static head of the liquid column induces a non-negligible pressure gradient. This results in a local pressure-induced subcooling that makes the case of boiling at low vapor pressure with a high level of liquid a particular case of subcooled boiling. The experiments were conducted for variety of working parameters: three vapor pressures (2.4 kPa, 3.1 kPa, 4.1 kPa), four levels of liquid (15 cm, 28 cm, 35 cm, 60 cm) and five applied heat fluxes (3.6 W · cm−2, 4.4 W · cm−2, 5.2 W · cm−2, 6.1 W · cm−2 and 7.1 W · cm−2). Owing to a statistical analysis of the signal of a heat flux sensor coupled with high-speed video recording, four different boiling regimes were identified: the regime of convection or small popping bubbles, the regime of isolated bubbles, the regime of intermittent boiling and the regime of fully developed boiling. The small popping bubbles and the intermittent boiling regimes are specific to the low pressure boiling: they are governed by the phenomenon of condensation driven by the aforementioned static pressure induced subcooling. Finally, to provide a visual representation of the influence of the working parameters on the boiling behavior, a dimensionless boiling regime map was proposed. This type of representation is a tool to predict the boiling regimes from a set of operating conditions but it is also useful to interpret the physical phenomena involved and how they differ from those occurring at higher pressure.