Bubble characterstics in a 3-D gas-solid fluidized bed: predictions from ultra-fast x-ray tomography and twofluid model

The bubble characteristics in a 3-D cylindrical fluidized bed have been investigated both experimentally and numerically. Experiments were performed on a 0.1 m diameter fluidized bed, with alumina oxide particles (diameter ~1 mm) as a fluidizing material. Measurements were done at a spatial resolution of 1 mm and a temporal resolution of 1000 cross-sectional images per second, using an ultrafast electron beam X-ray computed tomography (XRT) setup (Fischer and Hampel 2010). A two-fluid model using kinetic theory of granular flow (Verma et al., 2013) was used to predict the bed dynamics numerically. The equivalent bubble diameter as a function of height is in close agreement with Darton et al. (1977) and Werther (1975) correlations. The bubble size distribution predicted from simulations is broader compared to experiments. Both the bubble rise velocity and the bubble size increase with increase in excess gas velocity. The experimental measurements and simulation predictions are in fair agreement with the Hilligardt and Werther (1986) correlation.