Simulation and modeling of settling in polydisperse gas-solid flows

Sedimenting flows occur in a wide range of industrial and natural systems, such as circulating fluidized bed reactors and pyroclastic density currents (PDCs), the most hazardous volcanic process. In systems with sufficiently high mass loading, momentum coupling between the phases gives rise to mesoscale behavior, such as clustering. These structures are then capable of generating and sustaining turbulence in the carrier phase and directly impact large-scale quantities of interest, such as settling time. As an added complexity, many flows of interest consist of a polydisperse particulate phase. In this talk, we characterize the sedimentation behavior of a range of polydisperse gas-solid flows, sampled from a parameter space typically associated with PDCs. Highly resolved data is collected using an Euler-Lagrange framework and polydisperse settling behavior is contrasted with Stokes settling and analogous ensembles of monodisperse particles. Finally, a settling law is proposed which takes into account polydispersity by leveraging the first four moments of the particulate phase distribution.