Abstract

　　　The behavior of an acrylic sphere falling in water contained in a vertical circular pipe subjected to bottom air injection was observed with a video camera and by eye inspection. The flow patterns of air-water two-phase flows thus generated include the bubbly and slug flow regimes. The wettability of the sphere was changed by coating a water repellent material on its surface. The contact angle of the original acrylic sphere was 71° and that of the poorly wetted one was 143°. The terminal velocity of the sphere was measured to make clear the effects of the flow pattern and the wettability of the sphere on the velocity.