Role of Flow Inertia in Aggregate Restructuring and Breakage at Finite Reynolds Numbers

Forcesacting on aggregates depend on their properties, such assize and structure. Breakage rate, stable size, and structure of fractalaggregates in multiphase flows are strongly related to the imposedhydrodynamic forces. While these forces are prevalently viscous forfinite Reynolds number conditions, flow inertia cannot be ignored,thereby requiring one to fully resolve the Navier-Stokes equations.To highlight the effect of flow inertia on aggregate evolution, numericalinvestigation of aggregate evolution in simple shear flow at the finiteReynolds number is conducted. The evolution of aggregates exposedto shear flow is tracked over time. Particle coupling with the flowis resolved with an immersed boundary method, and flow dynamics aresolved using a lattice Boltzmann method. Particle dynamics are trackedby a discrete element method, accounting for interactions betweenprimary particles composing the aggregates. Over the range of aggregate-scaleReynolds numbers tested, the breakage rate appears to be governedby the combined effect of momentum diffusion and the ratio of particleinteraction forces to the hydrodynamic forces. For higher shear stresses,even when no stable size exists, breakage is not instantaneous becauseof momentum diffusion kinetics. Simulations with particle interactionforces scaled with the viscous drag, to isolate the effect of finiteReynolds hydrodynamics on aggregate evolution, show that flow inertiaat such moderate aggregate Reynolds numbers has no impact on the morphologyof nonbreaking aggregates but significantly favors breakage probability.This is a first-of-its-kind study that establishes the role of flowinertia in aggregate evolution. The findings present a novel perspectiveinto breakage kinetics for systems in low but finite Reynolds numberconditions.

Automated summary

The forces acting on aggregates depend on their properties, such as size and structure. The study investigates the evolution of aggregates in shear flow at finite Reynolds number to highlight the effect of flow inertia. The findings establish the role of flow inertia in aggregate evolution and present a novel perspective into breakage kinetics in low but finite Reynolds number conditions.