INFLUENCE OF PRESSURE ON STABLE FILM BOILING OF SUBCOOLED LIQUID

Film boiling of subcooled liquids is an integral part of the hardening process. Understanding of the mechanisms underlying fi lm boiling is important for modeling processes in atomic power engineering and cryogenic technology.
Stationary processes of fi lm boiling of subcooled liquids under conditions of their free motion near cylindrical heaters, just as subcooled liquid turbulent fl ow past high-temperature surfaces, represent quite a different type of
process. In cooling metal spheres heated to a high temperature by a subcooled water, a special regime of fi lm boiling is observed (microbubble boiling) distinguished by high intensity of heat transfer. Such a regime has not been revealed up to now for nonaqueous liquids. The paper presents new experimental data on heat transfer regimes in cooling nickel spheres in subcooled isopropanol and perfl uorohexane at pressures of up to 1 MPa. It
has been established that stable fi lm boiling is the main regime of heat transfer that accounts for the larger part
of the total time of cooling. The regimes of highly intensive fi lm boiling heat transfer were not observed in the
entire range of operational parameters even in the case of extreme subcoolings of liquid below their saturation
temperature (to 170 K). The intensity of heat transfer in stable fi lm boiling increases noticeably with subcooling
of a chilling liquid.
Film boiling of subcooled liquids is an integral part of the hardening process. Understanding of the mechanisms underlying fi lm boiling is important for modeling processes in atomic power engineering and cryogenic technology.
Stationary processes of fi lm boiling of subcooled liquids under conditions of their free motion near cylindrical heaters, just as subcooled liquid turbulent fl ow past high-temperature surfaces, represent quite a different type of
process. In cooling metal spheres heated to a high temperature by a subcooled water, a special regime of fi lm boiling is observed (microbubble boiling) distinguished by high intensity of heat transfer. Such a regime has not been revealed up to now for nonaqueous liquids. The paper presents new experimental data on heat transfer regimes in cooling nickel spheres in subcooled isopropanol and perfl uorohexane at pressures of up to 1 MPa. It
has been established that stable fi lm boiling is the main regime of heat transfer that accounts for the larger part
of the total time of cooling. The regimes of highly intensive fi lm boiling heat transfer were not observed in the
entire range of operational parameters even in the case of extreme subcoolings of liquid below their saturation
temperature (to 170 K). The intensity of heat transfer in stable fi lm boiling increases noticeably with subcooling
of a chilling liquid.
Author:  A. R. Zabirov, V. V. Yagov, O. N. Kaban′kov M. A. Leksin, and P. K. Kanin
Keywords:  fi lm boiling, subcooled liquid, cooling, microbubble boiling, stable regime, heat transfer coeffi cient
Page:  1466