(598b) Effect of Moisture Content On the Bulk and Flow Properties of Fine and Coarse Glass Beads

The way particles pack and flow is an essential area of study in particle technology.  Poor packing and flow can lead to segregation, clogging, and large product variability, which adversely affect the powder handling, processing, and production stages. In this work, the effect of water on the packing and flow properties of fine (cohesive) and coarse (non-cohesive) particles was experimentally investigated.  Four different particle sizes of glass beads, ranging from <10mm to 275mm, were studied as dry particles and with various weight percent of water.  The dry coarse particles flowed smoothly while the fine particles required agitation to initiate flow. The poor flow associated with fine particles is due to the formation of agglomerates.  Agglomerates form when the interparticle forces (primarily van der Waals forces) are greater than the mass of the particle.  Soft agglomerates can form with coarse particles when small amounts of moisture are added to coarse particles, creating liquid bridges between the particles. When enough moisture is added to the samples, the voids in the agglomerates fill up with water, creating a coarse dispersion or slurry.

Since sample characterization is dependent on many different conditions and properties, a multi-faceted approach was undertaken. With the use of a Freeman FT4 Powder Rheometer, measured changes in bulk density, porosity, compressibility, flow function coefficient, cohesion, and flow energy were collected as a function of water content and particle size.  The results show that both water content and particle size distribution play significant rolls on the packing and flow of the powders.  With a greater understanding of the many bulk properties associated with wetted material, changes can be implemented to improve how these materials are handled and processed, effectively lowering manufacturing costs.