抄録
A new experimental method to generate single small gas bubbles from a submerged orifice using pulsed ultrasound wave in a liquid is presented. Pulsed ultrasound wave having frequency of 15 kHz and maximum pressure amplitude of about 10 kPa is irradiated to a bubble growing from an orifice. Single air bubbles ranging from about 0.05 to 0.2 mm in radius are obtainable in silicone oil (kinematic viscosity : 1 mm2/s) using two orifices (0.02 and 0.04 mm in diameter), and by varying the timing to apply the pulse. Bubble deformation and detaching process was visualized and analyzed using both high-speed photography and direct numerical simulation. Consequently, it is revealed that bubbles are forced to elongate upward due to the oscillatory flow of gas through an orifice with high velocity, and the elongation causes the bubble to detach from an orifice. The sizes of bubbles at detachment can be well estimated with a common spherical bubble formation model.
