The past 25 years has seen particle technology grow from an under-funded and widely scattered research enterprise to a thriving globally recognized engineering discipline. Despite this change in the research environment, design and analysis of industrial particulate processes remain rooted in empiricism. Scale-up is largely heuristic, and quantitative design methods are non-existent. This is in stark contrast to fluid-phase systems, for which accurate scale-up and design methods have existed for decades.Why is this? One explanation lies in the traditional approaches to studying particle technology operations. Typically, these are studied at two length scales: the macroscale (unit operation level) and the microscale (particle level). Relatively little attention has been directed at an intermediate length scale, the mesoscale, which is characteristic of a "homogeneous" powder. This situation is analogous to ignoring classical thermodynamics and transport properties of fluids in the analysis of fluid-phase operations, instead trying to model unit operation performance directly using statistical mechanics or molecular dynamics.Advances in the design and analysis of particle technology operations requires filling of this "scale gap." This can be accomplished by studying particulate systems in an analogous way to that used to study fluid-phase unit operations. This will require detailed investigation of mass, momentum, and energy transport in existing unit operations; development of experimental systems with well-defined and characterized flow fields; measurement of powder properties (transport properties and transformation kinetics) in these "simple" experimental systems; validation of theory and simulation against these data; and integration of these theories and simulations into system-level models. (C) 2003 Elsevier B.V. All rights reserved.