(13d) DEM Investigation on the Dynamics of Singlet-Doublet Collisions of Cohesive Particles

Particulate and multiphase flows can be impacted significantly by interparticle cohesion such as the van der Waals force, liquid-bridging and electrostatics. Research toward the establishment of a general theory for cohesive particles is an active area of research. For relatively rapid flows, such a theory is comprised of a kinetic-theory-balances coupled to the population balance . Population balances track the evolution of agglomerate size distributions via source and sink terms, which are one of the most challenging aspects of closing such theories. Specifically, developing robust closures for these terms requires a criterion to differentiate between different outcomes (daughter distribution) of collisions among cohesive particles and/or agglomerates. While the criterion is well understood for binary collisions, it remains less explored for collisions involving agglomerates. In this work, we study the dynamics of a cohesive particle (singlet) impacting an agglomerate of two particles (doublet) via DEM simulations. Compared with binary collisions where two singlets either agglomerate or bounce depending on their impact velocity, four collision outcomes are observed in single-doublet collisions, including agglomeration, bounce, transfer and breakage. The occurrence of each outcome is affected by the pre-collisional configurations with four degrees of freedom. Sweeping the parameter space of the pre-collisional configurations reveals oscillatory transitions between different collision outcomes with increasing impact velocity. Detailed kinematic analysis suggests the oscillatory transitions are caused by the multiple, consecutive collisions between the singlet and the two particles in the doublet. By summarizing the DEM results in non-dimensional form, we propose a general method to estimate the transition criteria of collision outcomes, which can be applied to derive the closures for the population balances in the continuum theory to predict the behavior of granular and multiphase flows of cohesive particles.