P-44 An experimental study of bubble behaviors in subcooled boiling

Abstract

Subcooled boiling is the phenomenon which occurred nucleate boiling and condensation at a time after flowing subcooled water into the heated channel, and becomes instability flow of downstream. Therefore, prediction of void growth in subcooled boiling condition is important in the thermal hydraulic design of two phase flow heat transfer equipments such as boilers, heat exchangers and BWR. Especially, the void behavior in the subcooled boiling has an important consequence for neutron moderation in the BWR core. The subcooled boiling generally has characteristics of a two phase flow region near the heated surface and a single phase flow away from the heated surface. The prediction of void fraction in subcooled boiling is very difficult because of the existence of non-equilibrium conditions and the sensitivity of void behaviour to various parameters. Subcooled boiling is developed the experimental formula and the correlation equation by installing dependent parameter. Studies of subcooled boiling is possible to divide it roughly into two categories, to measure the heat transfer coefficient of the heated surface, and to predict the void fraction by measuring the bubble diameter which is related to the void behavior. This paper reports the experimental research of bubble behavior on the subcooled boiling in water forced convective flow. The result is that it clearly the relationship between the void fractions, which are measured the pressure drop along the heated channel, and the bubble behaviors, which are measureed by using a high speed camera, when the test condition is changed of the heat flux, subcooled degree and flow rate. As a result, the maximum bubble diameter was difficult because of the test condition. And, the bubble condensation rate of bubble which is after confirming the maximum diameter is difficult because of the test condition.