TRANSIENT BOILING HEAT-TRANSFER CHARACTERISTICS OF NITROGEN (BUBBLE BEHAVIOR AND HEAT-TRANSFER RATE AT STEPWISE HEAT-GENERATION)

Transient boiling heat transfer characteristics of liquid nitrogen at stepwise heat generation is investigated. A series of heat transfer experiments are carried out using a 0.10 mm diameter horizontal platinum wire as the test heater. Bubble behavior is observed by taking high-speed movie photographs. The history of heat transfer rate corresponds well with the bubble behavior during the transition stage to film boiling. In the case of a low heat generation rate, boiling transition occurs due to the coalescence of nucleate boiling bubbles. In the case of a high heat generation rate, a vapor sheath grows along the heater wire. Boiling transition occurs due to the settling of the vapor sheath around the wire and the heat transfer rate just after the boiling transition becomes much lower than that of stationary film boiling. In the case of an extremely high heat generation rate, a lot of fine bubbles grow rapidly and simultaneously when the heater temperature reaches the homogeneous nucleation temperature. Boiling transition occurs due to the filling of fine bubbles on the heater. © 1990.