Numerical investigation of the de-agglomeration mechanisms of fine powders on mechanical impaction

Keywords: Powder dispersion Impact angle Agglomerates Computational fluid dynamics Discrete element method a b s t r a c t This paper numerically investigated the mechanisms of powder de-agglomeration on mechanical impaction, aiming to explain the experimental observations in our previous study (Adi et al., 2010). A numerical model based on a coupled computational fluid dynamics (CFD) and discrete element method (DEM) approach was developed to simulate the dispersion of drug mannitol agglomerates in the customised impaction throats containing one or two angles with different flow rates. Information in terms of particle-throat and particle-fluid interactions, number of fragments, fine particle fraction (FPF) and powder deposition was monitored over the whole process and quantitatively analysed. The results indicated that the breakage of the agglomerate was mainly attributed to the mechanical impaction and less affected by the shear effect from the flow-particle interaction. While the first impaction caused the major damage to the agglomerate, the second impaction in fact generated more fine particles with size less than 5 mm, resulting much improved dispersion performance for the throats with two angles. Powder deposition, which is dependent on impaction velocity and angle and fragment size, was another important factor affecting the dispersion. The analysis of dispersion mechanisms indicated that de-agglomeration at different conditions can be characterised by the ratio of the particle-wall impaction energy and agglomerate strength. Powder dispersion in dry powder inhalers (DPIs) is a complex process controlled by interparticle cohesion, powder-flow interaction and powder-device impaction. It has been widely reported that the mechanical impaction with device is a major contribution to agglomerate breakage studied the effect of impact angle on the breakage of agglomerates and found the normal component of impact velocity is the dominant factor. However, using more plastic and softer particles, Samimi et al. (2004) found that at low impact velocity the normal component of impact velocity determines the extent of breakage, independent of the impact angle. At high impact velocity, its tangential component becomes increasingly important. Our recent attempts to understand mannitol agglomerate break-up using numerical simulations showed that increasing impact velocity improves agglomerate breakage and a 451 impact angle results in the maximum breakage for a given velocity (Tong et al., 2009; Yang et al., 2008). However, a few important issues, such as the effects of air flow, powder deposition and multiple impactions, were not considered in those studies. In fact, air flow can be very important as …