Effect of flow pattern on power spectral density of pressure fluctuation in various fluidization regimes

Pressure fluctuations were measured in a fluidized bed/circulating fluidized bed along the height of the riser and their power spectral densities (PSD) were obtained by Fast Fourier Transform (FFT) analysis. The research was carried out in a cold flow fluidized bed/circulating fluidized bed under ambient conditions with diameter and height of riser being 0.02 and 0.80 m, respectively. Various fluidization flow regimes including multiple-bubbling regime, slugging regime, turbulent regime, fast fluidized regime and homogeneous dilute transport regime were investigated. PSD was showing different patterns depending on flow regimes and location in the riser. The bubble/slug macro flow structure presented PSD pattern with narrow peak and dominant frequency at about 1.7 Hz. The effect of oscillation of fluidized particles on pressure fluctuation can be observed in this study. The PSD pattern had a broad range frequency from 0 to 4 Hz. The bandwidth of PSD pattern (due to oscillation of solids) decreased with the decreasing of solid concentration in the riser. The different pressure fluctuation sources in the gas-solid fluidization include bubble eruption, oscillation due to bubble/slug passage, and self-excited oscillation of fluidized particles.

The average PSD frequency gradually decreased when increasing Ug/Umf ratio. For gas velocity lower than Uc, the bubbles formation, bubbles eruption and bubbles coalescence are attributed to the pressure fluctuation signal. For gas velocity above Uc, the cluster phenomena are attributed to the pressure fluctuation signal. Therefore, the pressure fluctuation results from the oscillation of clusters.Figure optionsDownload as PowerPoint slideHighlights
► PSD can be used to study the hydrodynamic behavior in all fluidization flow regimes.
► Pressure measurements were made at greater distances above the distributor plate.
► PSD of pressure fluctuation showed different patterns depending on flow regimes.
► PSD pattern was narrower with the increasing of superficial gas velocity.
► The bandwidth of PSD pattern decreased with the decreasing of solid concentration.