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.
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Abbreviations
- q :
-
angle between two neighboring vectors (see Fig.10)
- q c :
-
critical value forq min(see Section 3.6)
- q min :
-
local minimum ofq-profile (see Section 3.4)
- w1 :
-
occurrence probabilities for the class that has lower values among three classes in the brightness histogram of a bubble image when the histogram is divided into three classes (see Section 3.3)
- wc :
-
critical value for w1 (see Section 3.6)
- Dpixel :
-
ratio of the pixel number of a vector to the total number of pixels for an outline of a bubble image (see Section 3.4)
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Junichi Ohta: He got his Doctor degree in Mechanical Engineering in 1984 from the graduate school of Engineering, Hokkaido University, Japan. He studied as research associate at Kobe University, Japan. Since 1992, he has been associate professor at Fukui University in Japan. His research interests are multi-phase flow, flow visualization and energy conversion.
Franz X. Mayinger: He got his degree (Dipl.-Ing.) in Mechanical Engineering in 1955. In 1961 he obtained his Ph.D. (Dr.-Ing.) in the field of thermodynamics from the Technische Universität München. Having worked in the industry for seven years he then became Professor and Director of the Institut für Verfahrenstechnik of the Universität Hannover in 1969. Since 1981 he has been owner and Professor of the Lehrstuhl A für Thermodynamik of the Technische Universität München. His main research incorporates the field of multi-phase flow, safety of nuclear power plants, heat transfer and the thermodynamic analysis of combustion processes as well as the development and application of optical measurement techniques. His research has been documented in five books and more than 280 publications. Additionally, he has been member of the reactor safety committee of the German Government, the scientific advisory board of the Bavarian government, as well as of international scientific organizations, such as the International Centre of Heat and Mass Transfer. He has been editor of several international journals, e.g. Heat and Mass Transfer. He obtained the Max Jacob Award (1991) for his merits in the field of optical measurement techniques and a honorary doctor (Dr.-Ing. E.h.) from the Universität Hannover in 1994.
Oliver Feldmann: He got his degree (Dipl.-Ing.) in Mechanical Engineering from the Technische Universität München, Germany, in 1996. He currently works on the determination of the bubble-sizes, the bubble-velocities, and the fluid dynamics of the continuous phase in aerated, stirred vessels at the Lehrstuhl A für Thermodynamik of the Technisch Universität München, Germany.
Peter Gebhard: He got his degree (Dipl.-Ing.) in Mechanical Engineering in 1991. In 1996 he obtained his Ph.D. (Dr.-Ing.) degree at Technische Universität München, Germany. His research interests are mainly in the field of analyzing flashing sprays and in describing the mechanisms of the spray-disintegration-process. He developed a Holographic Particle Imaging Velocimetry (HPIV) in order to determine both, the sizes and the velocities of the generated droplets. He currently works in the research department of AUDI.
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Ohta, J., Mayinger, F., Feldmann, O. et al. An algorithm for evaluating overlapping bubble images recorded by double pulsed laser holography. J Vis 4, 285–298 (2001). https://doi.org/10.1007/BF03182589
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DOI: https://doi.org/10.1007/BF03182589