Kinetic theory of shear thickening for a moderately dense gas-solid suspension: from discontinuous thickening to continuous thickening

TL;DR

This paper uses kinetic theory and simulations to analyze how shear thickening behavior in gas-solid suspensions transitions from discontinuous to continuous as particle density increases, highlighting the effects of inelastic collisions and density on rheology.

Contribution

It introduces a kinetic theory model for dense gas-solid suspensions under shear, revealing the transition from discontinuous to continuous shear thickening with increasing density.

Findings

Flow curve depends on particle volume fraction.

Transition from discontinuous to continuous shear thickening with density.

Theoretical predictions agree with simulations for moderate densities.

Abstract

The Enskog kinetic theory for moderately dense gas-solid suspensions under simple shear flow is considered as a model to analyze the rheological properties of the system. The influence of the environmental fluid on solid particles is modeled via a viscous drag force plus a stochastic Langevin-like term. The Enskog equation is solved by means of two independent but complementary routes: (i) Grad's moment method and (ii) event-driven Langevin simulation of hard spheres. Both approaches clearly show that the flow curve (stress-strain rate relation) depends significantly on the volume fraction of the solid particles. In particular, as the density increases, there is a transition from the discontinuous shear thickening (observed in dilute gases) to the continuous shear thickening for denser systems. The comparison between theory and simulations indicate that while the theoretical predictions for the kinetic temperature agree well with simulations for densities $\varphi \lesssim 0.5$, the agreement for the other rheological quantities (the viscosity, the stress ratio and the normal stress differences) is limited to more moderate densities ($\varphi \lesssim 0.3$) if the inelasticity during collisions between particles is not large. [This paper has been published in Phys. Rev. E {\bf 96}, 42903 (2017) but we have realized that there are some typos and mistakes after its publication. So we add the Erratum which will be published in PRE in the top of this paper.]