Cohesive powders are composed of fine particles (particles generally less than 44 microns in size). Interparticle forces are extremely large and cause clumping, sticking, and channeling when attempts are made to fluidize these powders. Although flow problems can be experienced in the transport of free-flowing solids, they pale in comparison to the problems experienced with the flow of cohesive powders. Most process designers have shied away from using cohesive powders. However, cohesive powders are often produced in processes by attrition. Recent research has shown that beneficiation of oil shale and coal is possible after grinding these materials down to the cohesive size range. The purpose of this work is to develop a hydrodynamic model capable of predicting the choking/non-choking flow regime boundary for cohesive solids. There are six tasks in this study: Preparation of a project work plan; Hydrodynamic model development; Determination of solid rheological properties for incorporation into the hydrodynamic model; Small-scale flow tests; Large-scale flow tests; and comparison of model with data and preparation of final report. Consolidation tests to determine the solids modulus of elasticity, G, for various powders were conducted: cohesive oil shale (10 microns in size), 500-micron and 40-micron glass beads, and 6-micron atomic alumina.more » Values of the solids viscosity were calculated from experimental data obtained in the small-scale rise test unit for FCC catalyst. Work was started on modifying the 30-cm-diameter test unit. This unit will be used to obtain large-scale data on cohesive solids in dilute-phase flow. 8 refs., 16 figs., 2 tabs.« less