Study on propagative collapse of a vapor film in film boiling (mechanism of vapor-film collapse at wall temperature above the thermodynamic limit of liquid superheat)

This paper investigates the mechanism of vapor-film collapse by a propagative collapse for film boiling at high wall-superheat. It also reports effects of a local-cold spot on both the minimum-heat-flux (MHF) temperature and the way in which the vapor film would collapse. Experimental results showed that propagation velocity of vapor-film collapse would decrease and MHF temperature would increase when the local-cold spot temperature was decreased. The results also showed that the MHF temperature increased remarkably when the local-cold spot temperature was lower than the thermodynamic limit of liquid superheat, Ttls. It was proved through analytical and numerical models that local temperature at the collapse front of the vapor film, namely the local solid surface temperature at the position of liquid–solid contact, could never exceed the Ttls even if the vapor-film collapse occurred at a high wall-superheat.