2123 壁近傍を移動する気泡と粒子の挙動  [in Japanese] Behaviors of a bubble and a particle migrating near a wall  [in Japanese]

Behaviors of both clean and contaminated spherical gas bubbles rising near a vertical wall were investigated experimentally below Reynolds number (Re) of 60. We developed an experimental apparatus in which a CCD camera with a microscope follows the rising bubble. We used it to precisely measure the bubble radius, the rising speed and the distance between the bubble and the wall and then estimate the lift force for Re<60. The results show the lift coefficient of the fully contaminated bubble is always positive due to the viscous effect. On the other hand, the lift coefficient of the clean bubble is positive for Re<30. However, the coefficient becomes negative for Re>45 and the attractive force acts on the bubble due to the inertia effect. Consequently, it is found that the surface condition affects on the lift force acting on the bubble rising near the vertical wall.