Bubble confinement and deformation during flow boiling in microchannel

The bubble dynamics during subcooled flow boiling were investigated in a single rectangular cross-section (0.5 mm × 1 mm) microchannel. Degassed deionized water was used as the working fluid with the confined bubble behavior observed using a high-speed CCD camera. The microchannel wall confines the bubble growth in the bubble height direction when the bubble departure diameter was larger than the microchannel cross section, resulting in strong deformation of the bubble top interface even before the liquid–vapor interface touched the microchannel wall. The microchannel confinement effect works by exerting a wall confining force on the top interface of the growing bubble. The negative feedback between the velocity of the top interface and the wall confining force is the main reason for the fluctuations in the increasing maximum local void fraction and the bubble aspect ratio during the confined bubble growth period.