Comparison of bubble growth obtained from pressure fluctuation measurements to optical probing and literature correlations

Pressure fluctuation measurements (PFM) along with optical probing (OP) are conducted in a 145 mm ID glass column fluidized bed with Geldart B particles to evaluate and compare the measured bubble growth with commonly used literature correlations. Bubble growth from PFM is evaluated by spectral data decomposition, while OP is evaluated by a bubble linking algorithm. It is shown that bubble sizes obtained from literature correlations vary widely for the same fluidization condition due to different methods in their determination. Compared to optical probe measurements, the best agreement is found with the correlation of Horio and Nonaka [A generalized bubble diameter correlation for gas-solid fluidized beds. AIChE J. 33 (1987) 1865–1872]. This agreement is in particular good for gas velocities u0/umf>5u0/umf>5 and bed heights below the influence of slugging. Since PFM yield a characteristic length scale only proportional to the actual bubble size, comparison with bubble sizes from OP and literature correlations is not straightforward. However, this proportionality can be assessed by a physical model of Puncochár and Drahos [Origin of pressure fluctuations in fluidized beds. Chem. Eng. Sci. 60 (2005) 1193–1197]. Their physical model yields a proportionality constant of 3 which matches well the PFM data for gas velocities u0/umf>5u0/umf>5.

► Three different methods are used to determine the bubble size in fluidized beds.
► Pressure fluctuation measurement (PFM), optical probing, and literature correlations are compared.
► The proportionality between PFM and other methods is determined experimentally.
► The PFM proportionality is independent of the bed height and gas velocity.