| Summary: | 碩士 === 臺灣大學 === 化學工程學研究所 === 95 === The transition velocities Uc and Uk, discriminated the bubbling, turbulent and fast fluidization, were investigated by the traditional and wavelet analysis on instantaneous pressure fluctuation signals in a circulating fluidized bed (0.108m i.d. × 7m height) for Geldart group B powder (sand: Dp = 204μm, Dp = 344μm). The solid mass flow rate was measured by an impact-line solid flow meter and was controlled by a L-valve.
The results showed that Uc and Uk could be obtained by methods of differential and absolute pressure fluctuations. Both Uc and Uk by methods of differential and absolute pressure fluctuations increased with the particle size. Comparing with other literature data, the value of Uk was significantly influenced by the solid recycle type. Besides the solid recycle system from solid downcomer to riser bed, the solid recycle type could be influenced by the expanded top section on the riser bed. If there was an expanded top section on the riser, the value of Uk was not found by analysis of absolute pressure fluctuations. However, If there was not an expanded top section on the riser, the value of Uk could be found.
By means of the multi-resolution analysis of wavelet transform, the wavelet energy distribution profiles of absolute and differential pressure fluctuations in the three flow regimes were calculated. In bubbling and turbulent fluidization, the energy distribution was dominated by detail signals D6 and D7. Moreover, When the superficial gas velocity reached the value of Uc, the wavelet energy distribution at D6 + D7 was the maximum value. In fast fluidization regime, there were two sections, densely lower section and tenuously upper section. In lower section, the energy distribution was dominated by detail signals D8 and S8; in upper section, the energy distribution was dominated by detail signals D4 and D5. When the superficial gas velocity reached the value of Uk, the value of the wavelet energy distribution at D6 + D7 decreased quickly. When the superficial gas velocity exceeded the value of Uk, the energy distribution was dominated by detail signals D6 + D7 or D8 + S8.
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