(303g) Scale−Bridging Models for Transfer of Liquid in Dense Particle Beds

Wet granular materials are widely used in numerous industrial processes such as mixing, granulation, coating and coking. Previous research in the area of wet granular flows mainly focused on forces involved in the formation of liquid bridges. Unfortunately, much less theory is available to describe liquid transfer upon particle-particle collisions. In this contribution we extend our previous work [1] by incorporating effects due to (i) non-uniform wetting of the particles [2,3], as well as (ii) due to surface roughness.

To study the transfer of liquid upon bridge formation and rupture, we use Direct Numerical Simulations [4] and the Discrete Element Method (DEM). This allows us to resolves the solid particle motion and the liquid interface, using either (i) the Volume of Fluid (VOF), or (ii) the Immersed Boundary (IBM) method combined with VoF. Based on these simulations, we extract data on the time evolution of the liquid bridge volume between wet particles, and parametrize a recently proposed liquid transfer model [4]. The DEM approach is supplemented with these scale-bridging liquid transfer models that enable a realistic, yet efficient simulation of liquid transfer associated with each particle-particle contact point. A probabilistic model for predicting wet collisions, as well as a sub-model for roughness effects complements these transfer models.

Using these models, we performed DEM-based simulations of granular flow to compute effective transport parameters (e.g., the liquid flux, or bridge coordination numbers) of wet granular material for a wide range of liquid properties. Specifically, we  present results for simple shear flow, spreading of liquid in a static particle bed, and dispersion of liquid in an inclined chute flow (including an experimental validation study). Our results help in identifying key system parameters that impact liquid spreading in granular flows, and guide the development of mesoscopic, continuum based models for industrial use.

References

[1]      B. Mohan, C. Kloss, J. G. Khinast, S. Radl, Regimes of Liquid Transport through Sheared Beds of Inertial Smooth Particles, submitted for publication.

[2]      F. Štepánek, P. Rajniak, Droplet morphologies on particles with macroscopic surface roughness, Langmuir. (2006) 917–923.

[3]      W.I.J. Kariuki, B. Freireich, R.M. Smith, M. Rhodes, K.P. Hapgood, Distribution nucleation: Quantifying liquid distribution on the particle surface using the dimensionless particle coating number, Chem. Eng. Sci. 92 (2013) 134–145.

[4]      S. Radl et al., On the Filling Rate of a Liquid Bridge between Wetted Particles, in: AIChE Annu. Meet. San Fr., 2013.