Particulate materials, powders or bulk solids are used widely in almost all areas of the process industries, such as in the pharmaceutical, chemical and food industries. Hence a good understanding of the physics of particulate materials is desirable in order to design efficient processing and handling systems. A successful mixing process is essential in the powder processing industries, as a pre-requisite for quality products. However, segregation is a formidable problem in mixing processes as it destroys mixtures and causes other kinds of inhomogeneities, all of which will have significant effects on the economics of production.
Basically, segregation is about how particles move and flow under various conditions. The objective of this study is to determine the influence of particle-wall friction and particle size distribution on particle flowability and segregation. Research on the impact of particle-wall friction and particle size distribution on particle flowability in a transparent cell was conducted and reported. Generally, data obtained from the particle flowability test revealed that the volumetric flow rate of the particles escaping from the test bin increases with decreasing particle-wall friction and particle sizes. Differences in particle-wall friction cause variations in speed during flow and in turn encourage segregation. The larger the difference in friction coefficient is, the more severe the segregation problem is going to be.
Results obtained also indicated that the larger the particle size distribution is, the worse the segregation condition is going to be. This is because larger particle size distribution means that the gaps between larger particles are bigger, thereby allowing smaller particles to percolate through them easily. Another reason is because the bigger the particles are, the more space they create when they shift up during vibrations, resulting in more spaces available for those smaller particles to settle into, preventing the larger particles from moving back down.