Natural-Convection Film- Boiling Heat Transfer. (Experiments of Subcooled Film Boiling with Long Vapor Film).

Abstract

Heat transfer in natural-convection film boiling with a long vapor film was investigated experimentally. Experiments of film boiling on horizontal cylinders of large diameter and long vertical cylinders were conducted to investigate the effect of liquid subcooling on the film-boiling heat transfer. The test liquid was R-113 at atmospheric pressure, and the following results were obtained in the experiments. For cylinders of both types, local heat-transfer coefficients of saturated and subcooled film boiling were much higher than the respective predictions from the two-phase boundary layer theory. In the case of vertical cylinders, the local heat-transfer coefficient did not depend on the distance from the leading edge even if the liquid was subcooled. In the case of horizontal cylinders of large diameter, the local value did not strongly depend on the distance from the stagnation point for saturated film boiling, but it depended on the distance and reached a maximum at a distance from the stagnation point with increasing liquid subcooling. As for the averaged heat-transfer coefficient of horizontal cylinders of large diameter, it increased with increasing liquid subcooling but did not depend on the diameter even under subcooled conditions.