The Influence of Squeeze Films in Particle-Impeller Breakage Events

Existing theories surrounding secondary nucleation mechanisms in stirred batch crystallisations predominantly include varying forms of breakage kernels for particle-impeller collisions. The foundations of such theories lie with the assumption that high impeller tip-speeds are linked to the fragmentation of crystals as they come into contact with the blade surface. What will be outlined here is a mechanism by which crystals near the impeller may not even contact its surface due to a squeeze film boundary layer at the impeller blade's surface. Through the use of an impingement-jet particle impactor, direct imaging and tracking of particle-plane collisions was captured outlining the behaviour of crystals as they approach a target surface with initial velocities of up to 10m/s. Furthermore, A theoretical description of the squeeze film is detailed alongside its implications for future secondary nucleation kinetics dealing with breakage or attrition events near reactor surfaces.