Modeling interparticle interactions in gas-particle flows

Abstract

Flows of gas-particle mixtures are ubiquitous in nature and in various processes. Interparticle interactions, including van der Waals’ (vdW) interactions and electrostatic interactions, can significantly impact gas-particle flows through agglomeration, defluidization, and particle segregation. This dissertation focuses on modeling the effect of vdW interactions and electrostatic interactions on the dynamics of gas-particle flows. Particles pick up and exchange electrostatic charges through tribocharging, a process which is essential for modeling electrostatic interactions. We first develop and test a tribocharging model that can be coupled with particle flow simulations and used to probe the effect of charging on gas-particle flows. We study the effect of particle size on tribocharging through a combination of vibrated bed experiments and Discrete Element Method (DEM) simulations of systems with different particle sizes, domain sizes, and wall materials and develop a phenomenological model that can capture this effect. In a similar approach, we investigate the effect of ambient gas on tribocharging using vibrated bed experiments and complementary DEM simulations and show that charge difference in different gases can be captured by imposing the gaseous dielectric strength as an additional constraint in the tribocharging model. We then discuss the modeling of dry powder inhalers (DPIs), a complex gas-particle system consisting of a very large number of particles. Since highly-resolved Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) is computationally expensive, we assess the efficacy of Discrete Parcel Method and the representative particle approach proposed in this dissertation. We discuss the viability and limitations of both approaches in a model inhaler by only considering vdW interactions and demonstrate the advantage of the representative particle approach. We finally present a computational study of agglomerate-wall collision tests considering both vdW and electrostatic interactions and show that deagglomeration is primarily affected by vdW interactions.