ECT Studies of Gas-Solid Fluidized Beds of Different Diameters

The bed dynamic behavior in three gas-solid fluidized beds, 0.05, 0.1, and 0.3 m in diameters, is studied using the electrical capacitance tomography (ECT). The ECT employs the neural network multicriteria optimization image reconstruction technique. The time-averaged solids concentrations obtained by the ECT are generally in good agreement with those obtained by the optical fiber probe. The 0.1 m ID fluidized bed exhibits the spiral motion of rising bubbles in the bubbling regime. However, for the 0.3 m ID fluidized bed, more than one spiral motion of bubble swarms is observed in the bubbling regime. The small fluidized bed exhibits the round-nosed slug motion. The ECT studies reveal a radial symmetry of the timeaveraged solids concentration distribution for the turbulent regime. Furthermore, the ECT provides the time-averaged and transient properties of the bubble/void phase and the emulsion phase. For a large fluidized bed, the standard deviations of the fluctuations of the cross-sectional averaged solids concentration, bubble/void phase fraction, and solids concentration in the emulsion phase all peak at the transition velocity from the bubbling to the turbulent regimes, Uc. For a small fluidized bed, the quantities of these variables peak at the onset to the slugging regime, decrease in the slugging regime, and then level off in the turbulent regime as the gas velocity increases.