Local microbubble concentration by defocused volumetric shadowgraphy with a single camera
W.A. Cornel (TU Delft - Multi Phase Systems)
J Westerweel (TU Delft - Fluid Mechanics)
Christian Poelma (TU Delft - Multi Phase Systems)
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Abstract
The challenge presented in this research is to determine the local volumetric bubble concentration (or void fraction) in the center of a microbubble cloud with limited optical access and without disturbing the flow. By applying defocused volumetric shadowgraphy to an aerated water column we were able to measure the characteristics of single microbubbles in the control volume for a void fraction of 0.078 percent. The time-averaged local bubble concentration in the center of the water column was measured over four periods (800 seconds each) to investigate the repeatability. Two reference methods, based on differential pressure (ΦV = 0.081 percent ± 0.011) and direct observation of the bubble's in-depth z-position, both validate the results independently.