PARTICLE TECHNOLOGY AND FLUIDIZATION A Breakage and Adhesion Regime Map for the Normal Impact of Loose Agglomerates with a Spherical Target Duy Nguyen and Anders Rasmuson Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden Kyrre Thalberg and Ingela Niklasson Bj€ orn AstraZeneca R&D Centre, SE-431 83, M€ olndal, Sweden DOI 10.1002/aic.14922 Published online July 16, 2015 in Wiley Online Library (wileyonlinelibrary.com) Discrete element method-based analysis is conducted to investigate the effects of interface energy between particles on the breakage and adhesion of loose agglomerates upon impact with a spherical target. A mechanistic approach is tested to find a relationship between particle properties, kinetic energy, and the agglomerate structure after the impact, which resulted in a new dimensionless number, the ratio of the two interface energies. In combination with D, a dimensionless number relating incident kinetic energy to agglomerate strength (Moreno-Atanasio and Ghadiri M, Chem Eng Sci. 2006;61(8):2476–2481), a good description of the agglomerate impact is obtained. The agglomerate structure after impact is mapped using the two dimensionless numbers and is in good agreement with experimental observations. The constructed regime map can serve as a guide for selecting preliminary process parameters in adhesive particle mixing. V C 2015 American Institute of Chemical Engineers AIChE J, 61: 4059–4068, 2015 Keywords: breakage, adhesion, regime map, loose agglomerates, DEM Introduction Agglomerates of fine particles are commonly used as inter- mediate and final products in a wide array of industries to improve the flowability, the homogeneity, and the handling properties of desired components. 1 During processing, the agglomerates of fines may get exposed to different mechanisms involved in the formulation process, for example, disintegration, dispersion, and granulation. The strength of agglomerates, thus plays an important role in delivering prod- uct performance. For instance, in dry powders for inhalation, the agglomerates are disintegrated and adhered onto carrier particles to obtain a certain structure that should be strong enough to survive during handling and loose enough to be entirely dispersed during inhalation. 2,3 Therefore, controlling the agglomerate strength for the ease of processing as well as for the stability of final products is highly desirable in powder manufacturing. Due to the difficulties that arise at small length and time scales, as well as the high degree of freedom in agglomeration and deagglomeration, discrete element method (DEM) simula- tion has become the primary choice for investigating agglom- erate impact 4 and particulate flow in granular mixers. 5 Several DEM-based studies of the breakage of agglomerates can be found in the literature. 6–8 These studies show that inter- particle properties are critical factors governing agglomerate strength, in addition to primary particle properties. Mechanis- tic models have also been used to relate the interface energy between particles to breakage behavior. 9,10 Although the nature of breakage fragments after impact has significant importance in a variety of processes, for example, dry particle coating, very few in-depth studies on post-impact have been documented. A recent study 11 shows that the adhesion and the structure of breakage fragments can be controlled by adjusting impact velocity. In that work, the interface energies between fine particles and between fine and carrier particles were kept constant. In this work we will, in detail, explore the effects of inter- face energies, not only on agglomerate breakage but also on the adhesion of breakage fragments onto a target. Using DEM simulations, the effects of the interface energy between fines and the target, which has often been neglected in previous studies, is specifically taken into account and varied. A mecha- nistic approach is introduced to establish a relationship between the physical properties of primary particles and the agglomerate structure in the final state of the impact, for example, fragment size, the fraction of fines captured by the target, and the thickness of fines covering the surface. In order to generalize and utilize the results, regime maps for the corre- sponding characteristics have been constructed using two dimensionless numbers, the ratio of the two interface energies and the previously proposed D number, 9 to serve as a guide- line for selecting preliminary operating conditions and to pro- vide a prediction of impact behavior. Methodology Single collisions between fine-particle agglomerates and a spherical target (the carrier particle) were simulated using Correspondence concerning this article should be addressed to A. Rasmuson at rasmuson@chalmers.se. V C 2015 American Institute of Chemical Engineers AIChE Journal 4059 December 2015 Vol. 61, No. 12