An experimental study of the effect of collision properties on spout fluidized bed dynamics

In this paper we experimentally study the effect of collision properties of different particle systems on the bed dynamics of a spout fluidized bed. This is done in different flow regimes: the spout-fluidization regime (case A), the jet-in-fluidized-bed regime (case B) and the spouting-with-aeration regime (case C). The considered particle systems comprise glass beads, ¿-alumina oxide and zeolite 4A particles, which are all classified as Geldart D. A non-intrusive measurement technique is used, viz. particle image velocimetry (PIV) to measure the particle flow field in a pseudo two-dimensional (2D) spout fluidized bed. Additionally, digital images are analyzed using a newly developed digital image analysis (DIA) algorithm to evaluate the particle volume fraction. It is demonstrated that the new proposed DIA algorithm provides reliable information on the particle volume fraction, showing that it is a powerful tool when combined with PIV. The added value of DIA is confirmed by comparing the particle velocity fields and volumetric particle fluxes. The particle fluxes display only small differences between the particle systems for each of the examined flow regimes, with the largest difference in the jet-in-fluidized bed regime. In this regime, the flow behaviour of the zeolite 4A particles does not show any features of the spout fluidized bed anymore, but behaviour of an ordinary fluidized bed. This is due to the direct bubble formation above the bottom plate, which results in a large disturbance near the spout entrance. It seems that zeolite 4A particles -because of their small restitution coefficient- tend to cluster in a more pronounced way, producing more bubbles compared to glass beads and ¿-alumina oxide particles.