Affiliations: Institute of Process Engineering, University of
Hannover, Callinstr. 36, D-30167 Hannover, Germany. Tel: +49-511 762 3638;
Fax: +49-511 762 3031; E-mail: [email protected]
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.
Keywords: Micro- and macromixing, LIF, Stirred vessel, Concentration field