  This paper investigates experimentally and numerically the dynamics of solid
particles during the layer inversion of binary solid-liquid fluidized beds in
narrow tubes. Layer inversion can happen in solid classifiers and biological
reactors, where different solid particles coexist and segregation by diameter
and density occurs. The fluidized beds were formed in a 25.4 mm-ID pipe and
consisted of alumina and aluminum beads with diameters of 6 and 4.8 mm,
respectively. We placed initially the lighter particles on the bottom in order
to force an inversion of layers, mimicking the layer inversion mechanism. In
the experiments, we filmed the bed with a high-speed camera and tracked
individual beads along images, while in numerical simulations we computed the
bed evolution with a CFD-DEM (computational fluid dynamics - discrete element
method) code. We found the distances traveled by individual particles during
the inversion and the characteristic time for layer inversion.
