Visualization of Bubble Growth and Departure in a Vertical Narrow Rectangular Channel

It is very important to study bubble growth and departure from the nucleation site for better understanding of boiling heat transfer in a narrow channel. Bubble growth and departure in a narrow rectangular under atmosphere pressure is visually observed by the wide and narrow side of the narrow rectangular channel using high speed digital camera. There is a small bubble contact diameter between the bubble base and heating surface when the bubble is growing at the nucleation site, and the growing bubble shape is almost spherical. The bubble growth law at the different nucleation sites is almost uniform under the condition of the same thermal parameters, but bubble departure diameters are obvious distinct because of different sizes of nucleation sites. In the current study, the bubble growth rate in a narrow rectangular channel is small, and the bubble departure time is long, the bubble growth diameter can be predicted by using the amendatory Zuber expression. The effect of thermal parameters on the mean bubble departure diameters is statistical analysed in the view window, the mean bubble departure diameters decrease with increasing heat flux, the mean bubble departure diameters decrease with increasing inlet subcooling, the mean bubble departure diameters decrease with increasing bulk flow velocity.