Abstract
A bubble cluster formed by the bubble concentration near the wall in bubbly two-phase flow with sub-mm diameter bubbles is experimentally investigated in a rectangular channel for upward flows. The rising velocity and behavior of the cluster are measured by the PIV (Particle Image Velocitimetry). By adding the surfactant, the coalescence of bubbles is prevented and small bubbles about 1mm in diameter are uniformly generated. In the two-phase flow with sub-mm diameter bubbles, the horizontal bubble clusters 20-40mm in length are formed near the wall because bubbles are strongly accumulated by the lift force and they slide up along the wall. Consequently, the cluster shape was changed by the junction of bubble in the center of cluster and by the separation in the both end of cluster. These results are caused by the difference of the rising velocity between the cluster center and the both end.
