Non-intrusive determination of bubble size in a gas–solid fluidized bed: An evaluation

Bubble sizes measured in a column of diameter 290 mm with FCC particles utilizing both an intrusive optical probe and non-intrusive pressure analysis are compared. The pressure signals were decoupled by differential pressure analysis and incoherence analysis. It is shown that pressure fluctuations induced by jetting/bubble formation can be effectively filtered out by differential pressure and incoherence analysis. The differential pressure signals measured across a vertical interval less than half the maximum bubble size unreasonably damps the power spectral density intensity, leading to underestimation of bubble size and overestimation of mean frequency. In the present work, the incoherence analysis tends to estimate greater bubble size than differential pressure analysis. Bubble chord lengths are overestimated by optical probe signals because small bubbles are not detected. Bubble sizes calculated by the equation of Horio and Nonaka (1987) agree reasonably well with that estimated by incoherence analysis at relatively high superficial gas velocities.