Liquid redistribution in sheared wet granular media

Abstract

Shearing wet granular systems causes a redistribution of the interstitial liquid, which can affect the material's bulk behavior. Using the discrete-element method, we study the early rapid transients, the intermediate states, and the slow long-term evolution of liquid redistribution for various material parameters and different initial wetting conditions in an inhomogeneous split-bottom ring-shear cell featuring a wide shear band away from the system walls. In our model, liquid exists in two states, either in liquid bridges between particles or in liquid films on the particle surfaces. Under deformations like shear, the liquid is redistributed due to the rupture of existing and formation of new liquid bridges. Since we assume the immediate redistribution limit as a new model parameter, a liquid bridge limit volume is imposed to avoid extensive clustering of liquid. Studying the effect of the local shear rate on the liquid redistribution, two distinct effects are observed: For small amounts of shear, i.e., small strain amplitude, the interstitial liquid is randomly redistributed locally, and for larger amounts of shear, liquid is transported away from the shear zone. The local redistribution quickly results in a characteristic probability distribution of liquid bridge volumes, independent of the initial wetting conditions, but the mean and the shape of the distribution are dependent on the limit volume. Although the shear-driven diffusion-like liquid transport is active from the beginning, it dominates the transport in the long term, when the liquid moves out of the shear band, making the shear band dry. Ongoing theoretical analysis suggests a competition of drift and diffusive mechanisms in a different set of coordinates that can explain all our observations by defining a local Péclet number that quantifies the relative strength of the two transport mechanisms.

Drift-diffusive liquid migration in partly saturated sheared granular media

“…While an initial transient behaviour shows random local re-distribution of the liquid, a larger shear leads to transport of liquid from the shear zone (Roy et al. 2018). The resultant liquid concentration profile in the shear cell geometry is worth describing in detail.…”

“…While the liquid redistribution phenomenon is limited to small shear scale, i.e. happens at the beginning of shearing (Roy, Luding & Weinhart 2018), overall liquid transport is rather a slow process driven by the local shear rate and is the subject matter of this paper.…”

Liquid migration in flowing granular materials

“…The liquid is initially added as liquid films on the particles, following an updated version of Mani's liquid migration model [8], recently proposed by Roy et al [6]. When two particles come into contact, a capillary bridge forms between them.…”

“…In industry, liquid migration can be found in pharmaceutical applications such as spray coating of tablets and granulation processes, where an in-homogeneous liquid distribution can deteriorate the quality of the final product [5]. Yet, the few available liquid migration models are built on various approximations, and their parameterization is based on empirical testing or assumptions, mainly because their experimental observation is extremely challenging [6,7]. Furthermore, it is still unclear how to deal with liquid redistribution upon bridge rupture, and how this interplays with the flow behaviour of granular media.…”

“…In this work, using DEM simulations, we examined the effect of capillary forces and liquid transfer on liquid distribution and flow behaviour of particles in a rotating drum apparatus. For this, adequate parameter values of the recently modified version of Mani's liquid bridge model [6,8] were identified. Liquid migration in the moving par-…”