Calibrated bubble depth determination using a single camera

Abstract

Current non-intrusive bubble parameter measurement techniques fail to consider bubble depth when extracting parameters from 2-D images, resulting in inaccurate measurements. A bubble depth determination method is therefore proposed here that uses a correlation between depth and image focus to estimate depth using the edge intensity gradient (“blur”) with simultaneous depth calibration. Images of bubbles at various depths in two-phase and three-phase systems were analysed to correlate bubble depth and blur. To increase the reliability of the methodology across various fluids and conditions, an in-situ calibration method is demonstrated. Bubble depth can be correlated from blur with a fair degree of reliability and the calibration procedure was effective in validating the bubble depth model, even across differing fluid opacity, bubble concentration, and fluid conditions. This article outlines a versatile and robust system that requires a single camera and which enables per image calibration to compensate for experimental configurational changes, making the technique suitable for variable applications.