Control of the bubble departure diameter by saw-tooth surfaces

Departure mechanism of bubbles from a flat surface and two saw-tooth surfaces were investigated through visualization in order to control the bubble departure diameter. Consequently, four different departure modes (spontaneous mode on the flat surface, spontaneous mode on the saw-tooth surfaces, double contact mode on the saw-tooth surfaces, and top contact mode on the saw-tooth surfaces) were observed. The bubble life time and the departure diameter were shorter and smaller for the bubbles generated on the saw-tooth surfaces in comparison with those generated on the flat surface. This was induced by a change in force balance between the buoyancy and surface tension, which enabled the bubble to break the pinning effect with less buoyancy. Moreover, some bubbles on the saw-tooth surfaces moved from their nucleation site by the surface tension after they reached to the opposite wall. This motion broke the pinning effect and the bubbles departed from the surfaces immediately after the unpinning. The double contact mode let the bubble departure diameter be independent from the size of the nucleation cavity and enabled to control the bubble departure diameter by the surface geometry.