  In this paper, a numerical study is conducted to investigate boiling of a
cryogen on a solid surface as well as on a liquid surface. Both single mode and
multi-mode boiling is reported for boiling on to a solid surface. In case of
boiling on a liquid surface, liquid nitrogen is selected as the cryogen
(boiling fluid) and water is chosen as the base fluid (heating fluid).
Different flow instabilities and their underlying consequences during boiling
of a cryogen are also discussed. For the boiling on a solid surface, in the
single mode, bubble growth, its departure, and area weighted average heat flux
are reported, where they increase linearly with increase in the wall superheat.
Asymmetry in the bubble growth and departure of 2nd batch of the vapor bubbles
have been observed due to local fluctuations and turbulence created just after
the pinch off of the 1st batch of vapor bubbles in case of multi-mode boiling
on the solid surface. Boiling of LN2 on a liquid surface is reported for a base
fluid (Water) temperature of 300 K. Vapor film thickness decreases with time
and the minimum film thickness just before rupture is 7.62 micrometer,
dominance of thermocapillary over vapor thrust causes breaking of the vapor
film at 0.0325s. The difference in evaporation rate and vapor generation,
before and after vapor film collapse is significant.
