Characterization of Fast Fluidization Regime with Geldart Group B Particles by Wavelet Analysis of Pressure Fluctuation Signals
對壓力擾動信號做小波分析後，發現於稀相輸送，主要的能量坐落於D1和D2；於快速流體化，能量以D8與A8為主；於紊流流體化，能量則以D6與D7最重要。且可由E1D+E2D的曲線轉折點找到Uc1值，由E6D+E7D和 E8D+E8A的曲線交點找到Uc2值。但是當量測位置過高 (z=85cm)時，則無法由E6D+E7D和 E8D+E8A的曲線交點找到Uc2值。
The transition velocities Uc1 and Uc2, bounding the turbulent, fast fluidization, and dilute phase convey flow regimes, were investigated by the tranditional and wavelet analysis on instantaneous pressure signals in a circulating fluidized bed (0.108m i.d. × 7m height) for Geldart group B powder (sand; =173μm, =2547kg/m3). The solid mass flow rate was measured by an impact-line solid flow meter and was controlled by a 80.7mm-i.d. L-valve. From the traditional method, the transition velocity Uc2, discriminated the dilute phase convey and fast fluidization, was determined as the velocity at which the pressure gradients measured from the top (z=435-455cm) and the bottom (z=35-55cm) regions of the riser were almost equal. The transition velocity Uc1, discriminated the fast fluidization and turbulent fluidization, was determined as the velocity at which the maximum pressure gradient at the bottom and the saturation carry capacity of solids (Gs*) were approached. By means of the multi-resolution analysis of wavelet tramsform, we obtained the wavelet energy distribution profiles of absolute and differential pressure fluctuations in the three flow regimes. In dilute phase convey regime, the energy distribution was dominated by detail signals D1 and D2; in fast fluidization regime, the detail signals D8 and A8 became relative significant; and in turbulent flow regime, the detail signals D6 and D7 played the important role with relative high energy content. In this case, the Uc1 was easily detected by the corresponding solid circulation flux at which a turning point of the energy curve of (E1D+E2D) was found, while the Uc2 was approximately detected by the intersection point of the energy curves of (E6D+E7D) and (E8D+E8A). Furthermore, the Uc1 and Uc2 were also determined at different heights above the distributor (z=35, 45, 55 and 85cm) in the riser. The result showed that no intersection of (E6D+E7D) and (E8D+E8A) was found at the height z=85cm.
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