Flow of Wet Granular Materials

Abstract

The transition from frictional to lubricated flows of a dense suspension of non-Brownian particles is studied. The pertinent parameter characterizing this transition is the Leighton number Le=eta(s)gamma / sigma, the ratio of lubrication to frictional forces. Le defines a critical shear rate below which no steady flow without localization exists. In the frictional regime the shear flow is localized. The lubricated regime is not simply viscous: the ratio of shear to normal stresses remains constant and the velocity profile has a universal form in both frictional and lubricated regimes. Finally, a discrepancy between local and global measurements of viscosity is identified, which suggests inhomogeneity of the material under flow.

An attempt to categorize yield stress fluid behaviour

“…(i) Thixotropic yield stress fluids: particle and polymer gels (Moller et al 2008), attractive glasses (this paper), 'soft' colloidal glasses , adhesive emulsions (Ragouilliaux et al 2007), dry granular systems (Da Cruz et al 2002), pastes (Huang et al 2005), hard-sphere colloidal glasses (this paper). (ii) Simple yield stress fluids: emulsions and foams (Bertola et al 2003;Moller et al 2009), hair gel (Moller et al 2009), carbopol (Moller et al 2009).…”

Cooling and Aggregation in Wet Granulates

“…This change in bulk properties can be attributed to the differences in the underlying particle interactions [4,5]. Whereas in collisions of dry particles, a certain fraction of the initial kinetic energy is dissipated into the atomic degrees of freedom of the particles, in the wet case, the interaction is mainly due to the interfacial forces exerted by liquid capillary bridges which form between adjacent particles and dissipate energy upon rupture.More recently, the dynamics of wet granular media has been addressed in several studies [5,6,7,8,9, 10], focusing on nonequilibrium phase transitions [10], agglomeration [6,7], shear flow [8] and cooling in one dimension [9]. A particularly important aspect of free cooling in cohesive gases is the structure of the emerging clusters.…”

“…More recently, the dynamics of wet granular media has been addressed in several studies [5,6,7,8,9, 10], focusing on nonequilibrium phase transitions [10], agglomeration [6,7], shear flow [8] and cooling in one dimension [9]. A particularly important aspect of free cooling in cohesive gases is the structure of the emerging clusters.…”

Colloidal crystals and water: Perspectives on liquid–solid nanoscale phenomena in wet particulate media

“…(Figure 15a) readily demonstrate that the CC is more resilient to yielding (steeper loading curves) upon growing load rates and, correspondingly, H and E increases with the rate (Figure 15b). Such rate-dependent performance evidences a marked viscoplastic response [161] and is comparable to the behavior usually observed in dense suspensions [159,160] or capillary suspensions [31], in which the shear stress increases with the shear rate. Typically in nanoindentation experiments, the viscous character of a medium is revealed by the occurrence of creep displacement h (Figure 15a) [169].…”

“…As expressed above, although dense particulate media are in general viscoplastic, dry materials show a rather frictional-dominated behavior while dense suspensions exhibit viscous-dominated response because of the viscosity of the interstitial liquid and the lubricated contacts between grains [158,159]. Interestingly, rheology of both systems can be described with a common framework by properly substituting the inertial time scale by a viscous time scale including the viscosity of the fluid phase [160].…”