Microbubble generation for PIV seeding

A new device for microbubble generation using small-scale unsteady cavitation of supersaturated water is presented. Cavitation is created in a radial diffuser with a directed outlet for inlet/saturation pressures ranging from 300 to 1000 kPa. The diffuser is formed using an acrylic plate spaced 100 µm above a 0.5 mm diameter outlet. Optical access is provided via the acrylic plate enabling investigation of the basic flow properties of the cavitation and microbubble trajectories using PIV. The size distribution and production rate of the generated microbubbles are measured using diffused-laser shadowgraphy and long-ranging microscopy within the emerging liquid jet. The size distribution of the microbubble population is suitable for PIV, with all bubbles produced being less than 25 µm. Microbubble production rates in excess of 50 million bubbles per second are achievable. The variation of the generated microbubble population for various operating conditions is presented.