Clustering in Gas-Solid and Liquid-Fibre Suspension: Friend or Foe?
Time: Thu 2019-09-19 10.30
Lecturer: Stefan Radl (TU Graz)
Location: Teknikringen 8
Abstract. Clustering phenomena in freely sedimenting suspensions are triggered by various mechanisms including (i) particle inelasticity, (ii) cohesive particle-particle interactions and entanglement, or (iii) the nonlinear nature of drag forces. Over the past twenty years, computer simulations acted as a powerful tool to better understand the consequences of clustering. This has revealed that clusters increase particle and fluid agitation, but greatly reduce momentum, heat and mass transfer between the phases.
In the first part of my talk I will discuss models, closures and computer algorithms that are used to describe relevant suspension flows. Our journey will touch on (i) particle-resolved simulations, (ii) pragmatic approaches such as the so-called CFD-DEM approach, and (iii) filtered, i.e., “LES-like” models of suspension flows. A focus will be on the anisotropic nature of fluid and particle velocity fluctuations, and the resulting challenges when formulating closures for drag and stress in gravity-driven suspension flows.
In certain scenarios, e.g., fluidized gas-solid suspensions, predictions of clustering phenomena have already improved our ability to engineer, troubleshoot, and optimize industrial equipment. In the second part I will focus on applications that may benefit from advances in flow modeling in the near future. Examples will include (i) drying and coating of wet particles, (ii) gas-solid reactors, and (iii) liquid-fibre suspensions. With respect to the latter, a focus will be on “reverse filtration”, i.e., the extraction of fine particles from flocculated fibres in pipe flow.