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 in trinsic mechanism of the scale-up effect. Two approaches-multiscale and pse udoparticle-are discussed, which we believe to be effective and promising i n revealing underlying mechanisms and extracting simplicity in complex syst ems. Heterogeneous structure, the most important characteristic of complex systems and a crucial aspect in scaling up reactors, is analyzed as the foc us of this paper. The multiscale approach follows the strategy of structure resolution in describing the heterogeneous structure and mechanism comprom ise in defining the variational criterion. The pseudoparticle approach desc ribes the heterogeneous structure by discretizing the fluid into pseudopart icles with a size much smaller than that of the real particles, that is, th e particle-fluid interaction is treated as the interaction between real par ticles and pseudoparticles. This paper outlines the respective advantages a nd prospects of these two approaches and explores some concepts in understa nding complex systems.