Spout Shape and Stability in a Flat-Base Spouted Bed Using a High Speed X-Ray Tomography

Time-resolved measurements of the shape and position of a spout were done with a high speed X-ray CT scanner. This system contains 3 X-ray sources and detector arrays, which makes it possible to scan the whole cross section of spouted bed of 24cm diameter simultaneously.  We reconstructed the images of the spout in several cross sections. The spout size and position is found from the raw data with a temporal resolution of 2500 fps and spatial resolution of 1 mm.

The time averaged spout size is validated with McNab's prediction. From the spout data we estimated the particle circulation in the bed. It shows good agreement with theoretical predictions. When U/U_ms = 0.96 ~ 1.44 (with U_ms the minimum spout velocity), there is very small fluctuation of the spout diameter, with an amplitude less than 10% of the spout diameter. We analyzed the fluctuation using the Power Spectrum Density. It is shown that the spouts are most stable when U/U_ms = 1.20~1.27. We also analyze the movement of the center of the spouts, and find that there is an oscillation of the spout position when it is close to surface of the bed.

Figure 1.  Experiment setup: (a) Overall; (b) 3 D view; (c) Top view.

Figure 2.  The time-averaged profile of the spouts.

Figure 3. The stability of the spouts' size indicated with average Power Spectrum Density (Red -> Blue: Instable -> Stable).