Experimental Study on Sub-cooled Boiling of Natural Circulation in Narrow Rectangular Channels

Sub-cooled boiling of natural circulation has been experimentally investigated based on a natural circulation device with narrow rectangular channels. When the heating power is increased to a certain level, the phenomenon of sub-cooled boiling and bubbles movement can be observed through the visual channel. The results show that the heat transfer coefficient of sub-cooled boiling increases with the increasing of heating power and decreases with the increasing of inlet sub-cooling and size of narrow rectangular channels. The heat transfer process of sub-cooled boiling is mainly affected by the generation and departure of bubbles, accompanied with flow oscillation. It is discovered that there are 3 stages of sub-cooled boiling in the narrow rectangular channels. Finally, an empirical correlation has been proposed for the heat transfer coefficient of natural circulation sub-cooled boiling in narrow rectangular channels, based on dimensionless analysis method and the errors fall in the range of +/- 15 %.