Analytical Multi-Scale Methodology for Fluidization Systems - Retrospect and Prospect

Understanding the spatio-temporal multi-scale structure of fluidization is a challenging problem. This presentation reviews our 20-year efforts on this subject, showing the roadmap that has gradually evolved from a simple idea to a systematic methodology inclusive of subsidiary, related systems and industrial applications. The strategy of establishing stability conditions through analyses of the compromise between dominant mechanisms is emphasized. The presentation concludes with prospects for further theoretical explorations and industrial applications. 1. Understanding spatio-temporal multi-scale structures is not only a challenge for fluidization engineering, but also an opportunity to contribute to complexity science: Gas-solid fluidization systems are non-linear and non-equilibrium in nature and feature spatio-temporal multi-scale structures, showing alternately a solid-rich dense phase and a gas-rich dilute phase at any local point and the co-existence of these two phases in space at any instance. Globally, however, a dilute region and a dense region co-exist in both the radial and the axial directions, leading to the overall heterogeneity in these systems. In addition, state bifurcation in fluidization systems can occur under certain critical conditions, showing a sudden change in structure with a slight change in operating conditions. This is commonly known as “choking” in engineering. Due to the crucial influence of structural changes on transport properties and reaction processes, quantification of these structural changes has become a core task for our fluidization community. However, theoretical prediction of these changes remains undeveloped, and contradictions continue to exist between different attempts due to insufficient understanding. Particularly, the stability condition for the heterogeneous structures and the critical condition for choking have long been perplexing, since a general and single variational criterion is not available for nonlinear and non-equilibrium systems. Therefore, new concepts need to be introduced. This represents an opportunity for our fluidization community. Our investigations of this problem have shown that any progress on this particular subject of fluidization has provided, at the same time, a paradigm and a driving force for research on complex systems in general. 1 Li et al.: Analytical Multi-Scale Methodology for Fluidization Systems Published by ECI Digital Archives, 2007

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