, Volume 6, Issue 2, pp 165-173

Quantitative measurements of micro- and macromixing in a stirred vessel using Planar Laser-Induced Fluorescence

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Abstract

The Planar Laser-Induced Fluorescence (PLIF) technique enables measurement of the local degree of deviation in an arbitrary plane inside the mixing vessel. This is achieved by injecting a mixture of an inert dye and a reacting fluorescent into the vessel. The inert dye serves as a tracer for the macromixing. The fluorescent characteristics of the reacting dye change while undergoing a fast chemical reaction with the vessel content and it therefore shows the micromixing indirectly. The concentration fields of the dyes are measured simultaneously. For that a laser beam is expanded into a thin light sheet which illuminates an arbitrary plane in the mixing vessel, exciting the fluorescent dye in this area. The emitted light is detected by a CCD-camera which is positioned vertical to the measurement plane. The fluorescent light passes through two optical filters which are suitable for separating the fluorescent light of the two dyes. The light is then projected on half of the camera chip each so that the same display window is detected twice, and thus the local concentration of the two dyes can be measured simultaneously. Low Reynolds number measurements are performed in a mixing vessel equipped with a Rushton turbine. The lamellar structure is clearly resolved. Areas of micromixing are detected by calculating the local degree of deviation from the concentration fields. These areas are mainly found in the boundary layer of the lamellas.

Kerstin Kling: She received her Diploma in Mechanical Engineering in 1999 from the University of Hannover. She is currently working on her Ph.D. at the Institute of Process Engineering of the University of Hannover under the supervision of Prof. Mewes. Her research interests are optical measurement systems such as Laser-Induced Fluorescence (LIF), Quantitative Visualization and Mixing Processes
Dieter Mewes: He has lead the Institute of Process Engineering of the University of Hannover since 1982. He studied mechanical and process engineering at the Technical University of Berlin. In 1970, he did his Ph.D. and Habilitation at the Institute of Process Engineering in Berlin under the supervision of Prof. Brauer. From 1973 to 1982, he was employed at the Degussa company in different leading positions inside and outside Germany. His research interests are optical and tomographic measurement systems, multiphase flows and heat and mass transfer in various technical applications.