Generation of Coarse Bubbles and Flow Instability Control by Means of a Bubble Generator

A previously studied bubble generator was tested under new operating conditions to provide for millimeter-sized bubbles. The basic element of the generator is a vortex chamber with water supplied through tangential ducts while gas (air) is introduced in the radial direction. Bubbles with average diameter of 0.5–2.2 mm were produced and registered by high-speed photography. The correlation between the water-air flow rate ratio and the characteristic bubble diameter was established and described by a relationship. Pressure oscillations in the exit section of the device were captured for two-phase flows with fine and coarse bubbles. With a view to applications in membrane filtration and water treatment, the effect of a pin installed in the exit section of the vortex chamber on the pressure oscillations was studied. The pin results in a drastic increase in pressure amplitude, both in the flow without bubbles and in the case of gas supply.