Bouncing, Sticking, and Spinning: The Agglomeration Behavior of Wetted Particles
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, May 2, 2012, 4:00 p.m. - 5:00 p.m.
Collisions between solid particles coated with a thin liquid layer are ubiquitous in nature and industry. For example, in the pharmaceutical industry, such collisions occur in both wetted granulation and agitated drying processes. In the former, controlled agglomeration is desired, whereas in the latter, the agglomeration of particles is generally undesired. Regardless of the objective, a fundamental understanding of the agglomeration and de-agglomeration processes is essential for the design of optimal-performance units. In the current effort, a combination of experiments and theory is used to understand the agglomeration and de-agglomeration behavior of wetted collisions. As a first step, collinear collisions between 3 wetted particles are explored using an apparatus inspired by a Newton’s cradle – the desktop toy composed of a line of suspended, steel spheres. The results from the "Stokes' cradle" for wetted particles are surprising compared to our experience with a dry system, but can be understood from a consideration of lubrication forces coupled with glass-transition effects. As a follow-on, the agglomeration/de-agglomeration of wetted particles undergoing oblique collisions is explored. Unlike its head-on counterpart, an outcome not associated with head-on collisions, namely agglomeration followed by separation of the rotating doublet, is observed. Here, the so-called centrifugal forces become important, and a corresponding dimensionless number that plays a key role in characterizing the regime map of outcomes is introduced.