Computational fluid dynamic simulations of regular bubble patterns in pulsed fluidized beds using a two-fluid model

This simulation study explores the two-fluid model's (TFM) capability to reproduce the alternating bubble patterns in a sinusoidal pulsed fluidized bed (PFB). Simulations were performed with frictional limits ranging between 0.58-0.62 with the inlet gas frequency being varied in the range of 3-6 Hz. The preliminary investigations showed that the Johnson and Jackson frictional model with a frictional limit of 0.61 yields a regular bubble pattern. The inference of this regular bubble pattern was based on the discrete Fourier analysis of the temporal pressure signals obtained at different spatial locations inside the PFB. Although the one-dimensional temporal pressure signals characterized a regular bubble pattern behaviour, the staggered bubbles visually observed were highly unstable. Moreover, in-depth insights into the PFB's regime classification showed that the predicted regular bubble patterns are susceptible to uncertainties due to the inherent mathematical limitations of the frictional closures of the TFM. Besides, the combinations of the frictional models/ limits in the TFM simulations could not predict the high stability and intermediate stability regimes of PFB. The present investigations helped identify the limitations of frictional closure models of TFM in predicting the regular bubble patterns and the regime classification for the PFB. It also expresses the need to develop better strategies to model the frictional closure of TFM to accurately account for the ever-evolving dense and dilute particle regions of a PFB.

Automated summary

The study demonstrates that while the simulated bubble patterns show regularity, the actual arrangement of bubbles is unstable. Additionally, the prediction of bubble patterns is affected by the mathematical limitations of frictional closure models.