Accuracy Evaluation of Image Processing Method for the Measurement of Rising Bubble Volume in Stagnant Fluid

Abstract

The measurement error when calculating the bubble volume by using image analysis was estimated by taking a single bubble of known volume (0.02 × 10^-6-2.00 × 10^-6 m³, or the volume equivalent diameter of 3.37-15.63 mm) and using a stereo visualization system with a high-speed camera. Previous studies calculated the bubble volume from images observed by the one-way photography method using the short-axis rotation of the bubble shape, which was assumed to have short-axis symmetry for approximation of the bubble shape to a spheroid. This study clarified the measurement accuracy for bubble volumes using one- and two-way image analysis methods. The results showed that the one-way method tended to underestimate the bubble volume when using the long-axis rotation, which approximates the bubble depth diameter by using the short-axis diameter, and overestimate the volume when using the short-axis rotation, which approximates the bubble depth diameter by the long-axis diameter. The measurement accuracy of the calculated bubble volume degraded for large bubble volumes. A one-way volume measurement method using a correlation equation was developed, and its accuracy was equivalent to the measurement accuracy of the two-way method using stereo visualization.