Bed nonhomogeneity in turbulent gas-solid fluidization

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Abstract

Bed dynamic behavior in a gas-solid fluidization system is measured in real time using ECT based on the NNMOIRT recently developed. The ECT results reveal the time-averaged and transient characteristics of the bubble/void phase and the emulsion phase, which is of value to the verification of the 3-D computation codes with real physical systems. In the turbulent regime, the time-averaged solids holdup distribution exhibits radial symmetry, which is not the case for the bubbling regime. The standard deviations of the fluctuations of the cross-sectional, averaged bubble/void phase fraction, and the cross-sectional, averaged solids holdups in the bubble/void phase and in the emulsion phase, all peak at the transition velocity from the bubbling to the turbulent regimes Uc. The addition of 10% fine particles decreases the solids holdup in the emulsion phase due to the breakup of large bubbles. The ECT study indicates that optical fiber probe measurement of the bubble/void phase fraction may yield significantly different results depending on the threshold level selected for the measured solids holdup distribution. The bubble/void phase fraction measured by the optical fiber probe does not vary with bed temperature up to 400°C; the emulsion phase voidage is observed to increase as the bed temperature increases.

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