Lagrangian modelling of direct mixing gas phase hetero-agglomeration in turbulent pipe flows

Hetero-agglomeration, the functional mixing of particles of different materials, has the potential to yield novel and remarkable properties in dispersed products. As a broader process understanding for hetero-agglomeration especially in the gas phase is missing an exemplary process involving mixing, agglomeration and deposition of small particles ($0.3<d_p<2.5\mu m$) as part of a turbulent pipe flow was considered as part of this study and was numerically investigated. The utilized modelling employed an improved discrete random walk model for Lagrangian particle tracking and a stochastic agglomerate structure model. The obtained simulation results demonstrate a pronounced dependence on the configurations of three considered initial particle distributions (uniform, laterally offset, and radially offset) across six pipe diameters (8-13 mm). Notably, the interplay between deposition and agglomeration led to local maxima in agglomerate number and hetero-contacts. The ratio of hetero- to homo-contacts is pipe diameter-dependent, due to the combined effects of mixing and the outcome of collisions, which is influenced by the turbulent intensity and the material properties. The selection of pipe diameter and mixing configuration has a significant impact on the size and composition of hetero-agglomerates, which has to be considered when designing gas phase hetero-agglomeration processes.