Characterization of a sediment layer of concentrated fluid-solid mixtures in tilted ducts at low Reynolds numbers

Abstract

In this paper we use a continuum mixture model to solve numerically the momentum and continuity equations associated with the sedimentation dynamics of highly concentrated fluid-solid mixtures in tilted ducts at low Reynolds numbers. The set of numerical simulations include several combinations of fluid viscosity, duct angle and solid concentration of particles. This research aims to show the phenomenology and dynamics associated with the sedimentation of monodisperse particles under different physical conditions and the characterization of the final stage of the sediment layer in two kinds of inclined geometries, with and without a horizontal section. Using scaling arguments, a mathematical expression formed by three dimensionless groups including the inertial number, particle concentration and the ratio between the sedimentation Grashof number to the Reynolds number is proposed to explain the height of the sediment layer in the slope change zone of a duct. Additionally, we have found that the initial particle concentration is a very relevant variable for knowing under what conditions the duct could get obstructed. In combination with some system angles, they might represent a risk of duct plug. Imposing a condition of obstruction, we have found dimensionless parameters that result in the blockage of the duct in the slope change zone. The results can be applied in the transport of fluid-solid mixtures and, in the engineering design of ducts with abrupt slope changes.