An Algorithm for Evaluating Overlapping Bubble Images Recorded by Double Pulsed Laser Holography

Article type: Research Article

Authors: Ohta, J. | Mayinger, F. | Feldmann, O. | Gebhard, P.

Affiliations: Department of Mechanical Engineering, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan. | Lehrstuhl A für Thermodynamik, Technische Universität München, Boltzmanstraße 15, Garching 85784, Germany.

Abstract: The present paper describes a method for evaluating images of a bubbly flow in stirred aerated tanks which are typical when pulsed laser holography is applied as the measuring technique. Features of the brightness histograms of reconstructed bubble images are discussed. A procedure is presented to evaluate the bubble images taken from a reconstructed hologram in order to determine the center of gravity of the bubble image. Double pulsed holograms were taken to measure bubble velocities and diameters simultaneously. In this case, overlapping bubble images are sometimes observed in the reconstruction. This significantly impedes the evaluation of the characteristics of the bubbles. Thus, an algorithm is presented in this work to distinguish between single and overlapping bubble images and to separate the overlapping bubble image in a two-dimensional image for a bubbly flow at low void fraction recorded from double pulse holograms. This algorithm was confirmed to be effective if the bubble images are extracted from the entire image.

Keywords: image processing, overlapping bubble image, short time holography

Journal: Journal of Visualization, vol. 4, no. 3, pp. 285-298, 2001