Techniques of two-phase flow under natural circulation have been used in reactor safety equipment. Bubble velocity is a necessary parameter to describe bubble behaviors and to establish profound bubble heat exchanger models. However

there are rare investigations of bubble velocity in subcooled flow boiling under natural circulation. Subcooled flow boiling under natural circulation was studied for bubble velocity characteristics in a narrow channel with water as working media

which a high speed camera was used to record bubble images in a visualization section of cross area 40 mm×2 mm. The analysis of change in velocity profile of single bubble and bubble cluster

their influencing factors

and velocity characteristics at rolling motion showed that bubble velocity was closely related to bubble size and mass flow rate. The velocity probability density of bubble cluster fitted well to normal distribution. Under rolling motion

bubble velocity exhibited periodic wavelike increase and decrease. The local liquid velocity at bubble center was comparable to bubble velocity at vertical steady state or rolling dynamic state.