Experimental investigation on bubble confinement and elongation in microchannel flow boiling

Bubble confinement and elongation in flow boiling were investigated experimentally in a rectangular microchannel with 0.5 mm in width and 1.0 mm in height using DI water as the working fluid. Bubble growth under various mass flux, heat flux and inlet subcooling conditions was visualized using a high-speed CCD camera, and the recorded images were analyzed to provide quantitative information of the bubble confinement and elongation in the microchannel. The flow conditions and the underlying mechanisms for bubble confinement to occur were discussed. In addition, the bubble growth characteristics, such as the bubble length and growth rate, in both free and confined growth periods were compared. It was found that the bubble growth rate in free growth period is far less than that in confined growth period, and the bubble growth rate before confinement decreases with the increase of bubble size, while the elongation rate increases with the increase of confined bubble size. What is more, it was noted that the initial shape of nucleated bubble in channel corner had significant influences on bubble confinement and elongation.