Bubble property determination

Abstract

An optical fibre probe was tested in liquids with biotechnologically relevant compounds, to determine if any limits arise in bubble property determination due to these compounds. The data from this fibre probe was compared to the data from a camera for which an image processing algorithm was developed. This algorithm was able to successfully filter objects using configurable parameters. Objects had to be in focus, within a certain size range and elliptical in shape. The filtering was able to work with partially out of focus bubbles, and bubbles at the edges of the image within tolerances specified by the parameters. To provide insight into the relation between the fibre probe data and camera data a control measurement was performed in pure water, after which measurements were performed in a mixture containing 100g/L ethanol and a mixture containing 0.4M NaCl. The data sets from both measurement methods were compared for bubble velocity and bubble size. The velocity would be directly comparable,
the size was however the local height at the point where the fibre probe pierced the bubbles. As such the height directly below the fibre probe of the bubbles was determined from the images to serve as comparable data. The comparison between the probe data and camera data was inconclusive due to a dissimilarity between the distributions. Mainly the overestimation of the comparable size from the camera data was a problem. Which was likely due to the camera showing only a 2D projection of the bubble and as such the entire height would be used for this comparison. For the velocity the camera data had a narrower distribution as compared to the fibre probe data. This could be caused by the camera averaging the speed of bubbles between two or even three frames if a bubble was not detected in the middle frame, the probe might be more sensitive to these variations and as such yield a wider distribution. The image processing algorithm showed a correct processing of the images to yield usable data, the exact comparable data however still needs to be improved for this specific application.