An experimental study on bubble behaviors in forced convective subcooled boiling of high subcoolings

Forced convective subcooled boiling is an effective heat transfer way and used widely in industry. In order to obtain a better understanding of the thermal and hydrodynamic mechanism of the forced convective subcooled nucleate boiling, the characteristics of bubble behaviors of the forced convective nucleate boiling have been studied by many researchers. In this paper, an experimental study was conducted on the bubble behaviors in forced convective subcooled nucleate boiling in an upward annular flow at relatively high subcooling degrees. The images of bubble behaviors during its whole lifetime were captured with high spatial and temporal resolutions by using a high speed video camera and a Cassergrain microscopic lens. The temperature of liquid at the inlet of test section of experimental system was in the range of 50-70degC at atmosphere pressure, so the subcooling of the forced convective boiling was quite high, above 30 K in this study. Some interesting phenomena of the bubble behavior were observed, the bubble shape and behavior were quite different from those of lower subcooling case in forced convective subcooled boiling, the deformation at the bottom of bubble when it is departing and lifting off from the wall was observed, the phenomenon of two consecutive bubbles was also observed, the 2nd bubble grows from the remaining part of the first bubble after it lifts off from the wall. (author)