Revisiting and improving models for the breakup of compact dry powder agglomerates in turbulent flows within Eulerian–Lagrangian simulations

• Published in: Powder technology Vol. 348; pp. 105 - 125
• Main Authors: Breuer, M., Khalifa, A.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.04.2019; Elsevier BV
• Subjects: Agglomerates; Agglomeration; Breakup; Breakup of agglomerates; Computational fluid dynamics; Computer simulation; Coordination numbers; Deagglomeration; Drag; First principles; Fluid flow; Fragments; Large eddy simulation; Literature reviews; Modelling; Post-breakup behavior; Powder; State-of-the-art reviews; Strength of dry powder agglomerates; Stresses; Turbulence; Turbulent particle-laden flows; Turbulent, drag and rotary stresses; Breakup of agglomerates; Turbulent particle-laden flows; Strength of dry powder agglomerates; Turbulent, drag and rotary stresses; Post-breakup behavior; Large-eddy simulation
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2019.03.009

The present study is concerned with breakup models for agglomerates in turbulent flows. First, a brief literature review is provided describing the state of the art concerning the description and modeling of breakup of agglomerates with special emphasis on the role of fluid forces. That comprises turbulent and drag (inertia) stresses. Furthermore, the breakup by rotary stresses is taken into account. Based on the idea to describe these processes using first principles within an Eulerian–Lagrangian approach relying on the large-eddy simulation methodology, modeling ideas from the literature are revisited and extended in order to be applied in a four-way coupled simulation. Building on a deterministic collision and agglomeration model, the breakup process is tackled in a similar manner leading to a highly efficient procedure, which allows to track a huge number of agglomerates and particles but with the restriction to compact dry powder agglomerates. For this kind of agglomerates an enhanced evaluation of the strength is derived relying on an improved determination of the average porosities and coordination number. Furthermore, special emphasis is put on the post-breakup treatment, i.e., models for the sizes and velocities of the generated fragments. Finally, the proposed models are applied to a test case inspired by the experimental study of Weiler [1] for the deagglomeration in a dry powder disperser. The effect of the different physical mechanisms (turbulence, drag, rotation) is analyzed concerning breakup rates and resulting size distributions. Furthermore, the dominant breakup regions are identified separately. Since agglomeration processes are simultaneously taken into account, re-agglomeration of the fragments is found to play a non negligible role. Finally, the effect of the properties of the powder on the breakup and re-agglomeration processes is investigated. [Display omitted] •Revisited and improved models for the breakup of compact dry powder agglomerates.•Breakup models for turbulent, drag and rotary stresses in turbulent flows.•Methodology within an Eulerian-Lagrangian approach relying on large-eddy simulations.•Enhanced evaluation of the strength of compact dry powder agglomerates.•Comparison with experimental investigation of deagglomeration in a disperser.