Abstract
Agglomeration of fine particles in fluid flows is important for many processes in powder handling or production. In order to accurately perform numerical calculations of such processes models are needed which realistically describe particle agglomeration. For applications in the frame of an Euler/Lagrange approach such a model was developed which allows predicting the agglomerate structure and its behaviour in the point-particle approximation. The detection of collisions between primary particles or particles and agglomerates is realised by the stochastic collision model. The collision point on the particle or agglomerate surface is generated by accounting for the impact efficiency. The developed structure model is based on storing location vectors from the reference primary particle to all other particles collected in the agglomerate which is still treated as point-mass. Thereby the structure and porosity of the agglomerate is known and an equivalent agglomerate diameter (e.g. gyration diameter) is obtained. With this information the fluid dynamic forces acting on the agglomerates can be predicted correctly as well as the appropriate collision cross-section is used in the collision modelling. For testing the novel agglomerate structure model, fine particle agglomeration in homogeneous isotropic turbulence is calculated considering different properties of the primary particles or droplets. In the case of dry solid particles the van der Waals adhesion force is considered and based on an energy balance the possibility of particle sticking or rebound is calculated. Moreover, high viscous droplets are considered as primary particles, a situation also found in spray dying. For such cases the penetration of two primary particles or a primary particle and a stochastically selected primary particle within an agglomerate is modelled. The structure of the agglomerates produced under these different situations and for mono- and poly-sized primary particles are analysed and compared, using for example gyration diameter, porosity of convex hull and fractal dimension. These results demonstrate that the developed novel agglomerate structure model is applicable in the frame of an Euler/Lagrange approach and provides appropriate results.
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