声场流化床颗粒浓度时间序列分析

在内径140mm，高1600mm的声场流化床中，以FCC颗粒为流化介质，采用光导纤维探针测定不同轴／径向位置的颗粒浓度时间序列，通过统计分析、功率谱分析和小波分析揭示外加声场对颗粒浓度的影响。结果表明：声场的引入降低了颗粒最小流化速度，声压越大最小流化速度越小，声波频率在150HZ时最小流化速度最小。颗粒浓度功率谱呈现宽频且有明显主频的低频信号，声压越大主频的峰值越小，颗粒浓度信号的主频峰值随频率先下降后上升。对颗粒浓度信号进行5尺度离散小波变换，声场流化床中颗粒浓度信号高频部分增加，低频部分减小。

Time-series Analysis of Particle Concentration in an Acoustic Fluidized Bed

The time-series of the FCC particle concentrations were measured by an optical fiber probe under different superficial gas velocities, sound pressure levels and frequencies in an acoustic fluidized bed （Ф140×1600 mm）. The experiments show that the minimum fluidization velocity has a minimum value when the frequency of sound waves was 150 Hz, moreover it decreased as the sound pressure level was increased at the same sound frequency. Local particle concentration fluctuations was analyzed using both traditional statistical analysis and power spectrum analysis. The standard variance of local particle concentration was lower in an acoustic fluidized bed than in a common fluidized bed. In an acoustic fluidized bed, the frequency of power spectra tends to be width. With increasing the sound pressure level, the dominant frequency of the power spectrum was decreased. The dominant frequency of the power spectrum decreased first and then increased with increasing the sound frequency at the same sound pressure level. On basis of discrete wavelet transform, an original signal was resolved into five detailed scale signals （from detailed scale 1 to detailed scale 5）. It demonstrated that high frequency was increased and low frequency was decreased in an acoustic fluidized bed.