Chaotic Behaviour of Gas-Solids Flow in the Riser of a Laboratory-Scale Circulating Fluidized Bed

A cold model of a circulating fluidized bed with a 0.030-m-ID, 2.77-m-high riser was operated in a wide range of operating conditions. Several solids were tested front 57 mu m to 1,830 mu m in size and from 1,100 kg/m(3) to 2,540 kg/m(3) in density. Pressure fluctuations were measured at several points along the riser, and time series were processed to evaluate chaotic invariants (Kolmogorov entropy and correlation dimension). Axial profiles of average values of pressure and voidage were also evaluated. At fixed operating conditions, the Kolmogorov entropy changed along the riser, which appeared to be a function of the local voidage and showed a minimum when voidage decreases from 1.00 until about 0.90. Changes of the Kolmogorov entropy with local voidage were interpreted based on interactions among solids and gas turbulence structures. Three regions were identified in the voidage range investigated: particles-controlled region, clusters-controlled region and bottom-bed-controlled region.