Tomographic measurements of micro- and macromixing using the dual wavelength photometry

The newly developed tomographical dual wavelength photometry enables the me asurement of the local intensity of segregation at a multitude of points in side the stirred vessel. This is done by injecting a mixture of an inert an d a reacting dye into the vessel. The inert dye serves as a tracer for the macromixing, whereas the vanishing of the reacting dye shows the micromixin g. The concentration fields of the dyes are measured simultaneously by tran siluminating the vessel from three directions with superimposed laser beams of different wavelengths. The light absorption by the dyes is measured wit h CCD-cameras and these projections are used for the tomographic reconstruc tion of the concentration fields. Low Reynolds number measurements were per formed with a combination of two Rushton turbines and a combination of two pitched blade impellers. The combination of the pitched blade impellers yie lds a good axial transport but a slow micromixing. The injection in the mid dle between the combination of the two Rushton turbines yields a faster mic romixing, but the macrotransport is limited to the region between the stirr ers. (C)2000 Elsevier Science S.A. All rights reserved.