An experimental investigation of the optical measurement of microbubbles in a confined radial jet

An experimental shadowgraphy setup and procedure has been designed to investigate microbubble size distribution and production frequency of a mini-tube type microbubble generator as implemented in the Australian Maritime College Cavitation Research Laboratory. To overcome the depth-of-field limitations of traditional shadowgraphy setups, the present study uses a radial diffuser to reduce the depth of the test volume to 1 mm, allowing all bubbles to be imaged within the acceptable plane of focus. Shadowgraphy measurements are made of a microbubble plume, injected into a uniform, low-turbulence dilution flow to homogeneously disperse the microbubbles. Bubble shadows are created with stroboscopic lighting and recorded with a highresolution digital camera and close-range microscope. Results show that the dominant size interval for the microbubble generator used in the current study is 10–15 μm, with a total production frequency of 1454 kHz.