79 巻 (2013) 800 号 p. 701-711
This paper presents an experimental investigation of motion characteristics of microbubbles rising close to a vertical plane wall. The study focuses on how microbubble behaviors change with the bubble diameter and along the wall for a constant bubble flow rate. Tap water is used as the working fluid, and hydrogen microbubbles are generated by water electrolysis. A particle tracking velocimetry technique is used to precisely measure the microbubble velocity, with which we found that the mean rise velocity of microbubbles is much faster than theoretically estimated rise velocity of single microbubble in stationary water. The mean bubble rise velocity increases with the bubble diameter and decreases in the downstream direction, and both are related to the balance between accumulation and diffusion of spatial buoyancy distribution near the wall. In particular, in the case of small microbubbles, bubble clouds are generated close to the wall and show intermittent roll-up motion in the wall-perpendicular direction (void burst motion). We discussed on this motion with various waveforms of the bubble rise velocity and bubble-bubble distance.