The impact of porous walls on the rheology of suspensions

• Published in: Chemical engineering science 2021-02, Vol.230, p.116178, Article 116178
• Main Authors: Rosti, Marco E., Mirbod, Parisa, Brandt, Luca
• Format: Article
• Language: English
• Subjects: Effective viscosity; Elasticity; Numerical evidence; Numerical simulations; Parametric study; Particle rotations; Particle suspension; Permeability; Porosity; Porous materials; Rheology; Shear flow; Suspension rheology; Suspension viscosity; Velocity fluctuations; Viscosity; Wall permeability
• ISSN: 0009-2509; 1873-4405; 1873-4405
• DOI: 10.1016/j.ces.2020.116178

•We study rigid particle suspensions in a Couette flow with porous walls.•The porous walls induce a decrease in the suspension effective viscosity.•The presence of porous walls weakens the wall blocking effect.•We provide a closed set of equations for the suspension viscosity. We study the effect of isotropic porous walls on a plane Couette flow laden with spherical and rigid particles. We perform a parametric study varying the volume fraction between 0 and 30%, the porosity between 0.3 and 0.9 and the non-dimensional permeability between 0 and 7.9×10-3 We find that the porous walls induce a progressive decrease in the suspension effective viscosity as the wall permeability increases. This behavior is explained by the weakening of the wall-blocking effect and by the appearance of a slip velocity at the interface of the porous medium, which reduces the shear rate in the channel. Therefore, particle rotation and the consequent velocity fluctuations in the two phases are dampened, leading to reduced particle interactions and particle stresses. Based on our numerical evidence, we provide a closed set of equations for the suspension viscosity, which can be used to estimate the suspension rheology in the presence of porous walls.