Numerical modelling of the breakage of loose agglomerates of fine particles

a r t i c l e i n f o Keywords: Loose agglomerates Breakage Discrete element method Fine particles This paper presents a numerical study of the breakage of loose agglomerates based on the discrete element method. Agglomerates of fine mannitol particles were impacted with a target wall at different velocities and angles. It was observed that the agglomerates on impact experienced large plastic deformation before disintegrating into small fragments. The velocity field of the agglomerates showed a clear shear zone during the impacts. The final breakage pattern was characterised by the damage ratio of agglomerates and the size distribution of fragments. While increasing impact velocity improves agglomerate breakage, a 45-degree impact angle provides the maximum breakage for a given velocity. The analysis of impact energy exerted from the wall indicated that impact energy in both normal and tangential directions should be considered to characterise the effects of impact velocity and angle. Agglomerates are often presented as intermediates or manufactured products in many industries such as chemical, pharmaceutical and food industries [1]. The knowledge of the mechanical strength and breakage pattern of agglomerates under various conditions are important to process control and optimisation. Many studies have been carried out to investigate the fundamentals governing agglomerate breakage [2–4]. Experimentally it is difficult to obtain detailed and quantitative information about breakage mechanisms due to small size of agglomerates and short duration of impacts, so experimental investigations are largely restricted to post-impact analysis of the fragments [5–7]. Numerical models based on the discrete element method (DEM) are increasingly applied to investigate agglomerate breakage since they are able to provide information that is difficult to access from experiments (e.g. forces on individual particles). By modelling the impact of an agglomerate with a target wall at different velocities, Thornton et al. [8,9] observed a minimum velocity below which no significant damage occurs and the agglomerate behaves like a large single particle. The results from Subero et al. [10] showed that the extent of breakage increases with impact velocity, but eventually reaches a limit beyond which the breakage approaches an asymptotic value. Moreno et al. [11,12] studied the effect of impact angle on the breakage of agglomerates and found that the normal component of impact velocity is the dominant factor. They also presented a mechanistic model based on the modified Weber number to describe the effect of surface energy of powder. In many processes particles …