Multiscale nature of complex fluid-particle systems

Most multiphase chemical reactors are complex systems. This paper explores the multiscale nature of complex systems in chemical engineering and the intrinsic mechanism of the scale-up effect. Two approaches-multiscale and pseudoparticle-are discussed, which we believe to be effective and promising in revealing underlying mechanisms and extracting simplicity in complex systems. Heterogeneous structure, the most important characteristic of complex systems and a crucial aspect in scaling up reactors, is analyzed as the focus of this paper. The multiscale approach follows the strategy of structure resolution in describing the heterogeneous structure and mechanism compromise in defining the variational criterion. The pseudoparticle approach describes the heterogeneous structure by discretizing the fluid into pseudoparticles with a size much smaller than that of the real particles, that is, the particle-fluid interaction is treated as the interaction between real particles and pseudoparticles. This paper outlines the respective advantages and prospects of these two approaches and explores some concepts in understanding complex systems.