Experimental study on solids circulation patterns and bubble behavior using Particle Image Velocimetry combined with Digital Image Analysis

The hydrodynamics, viz. the solids circulation patterns and bubble behavior, of a freely bubbling gas-solid fluidized bed has been investigated experimentally using Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA). Coupling of these non-invasive measuring techniques allows us to obtain information on both the bubble behavior and emulsion phase circulation patterns simultaneously, in order to study in detail their intricate interaction. In particular, the combination of DIA with PIV allows correcting for the influence of particle raining through the roof of the bubbles on the time-averaged emulsion phase velocity profiles. Because of the required visual access, this technique can only be applied for pseudo-2D fluidized beds. The bubble rise velocity as a function of the equivalent bubble diameter and the average bubble diameter as a function of the position above the distributor were determined with DIA and compared with literature correlations. Subsequently, the importance was demonstrated of filtering the instantaneous emulsion phase velocity profiles obtained with PIV for particle raining, using DIA, to obtain the time-averaged emulsion phase velocity profiles. The timeaveraged solids circulation patterns have been studied as a function of the superficial gas velocity and bed aspect ratio.