Balancing size and density segregation in bidisperse dense granular flows

Abstract

Several experimental studies have illustrated a balance between the segregation forces arising due to size-and density-differences. However, no detailed studies have been carried out to quantify this balance. In 2014, by utilising discrete particle simulations, we presented a simple relationship between the particle sizeand density-ratio,ŝ a =ρ , where 'a' determines whether the partial pressure scales with the diameter, surface area or volume of the particle. For a 50:50 mix (in volume) of bidisperse granular mixtures, we found the partial pressure to scale with the volume of the particle, i.e. a = 3. Moreover, there also exists a range of size-and density-ratios that satisfy the relationŝ 3 =ρ , where the bidisperse mixture remains homogeneously mixed. However, in this proceeding, we deviate from the conventional 50:50 mixes and consider a slightly extreme case of mixes, such as the 10:90 (in volume) mixes, which are often found in nature and industries. By doing so we observe that the partial pressure does not scale with the particle volume and, more importantly, the zerosegregation relation is not as simple asŝ a =ρ . However, there does exist a range of size-and density-ratios for which the mixture weakly segregates.

Remarkable simplicity in the prediction of nonspherical particle segregation

“…However, at much larger volume ratios than those studied here (greater than about 64), a larger intruder sinks due to its increased weight relative to the upward contact forces from the smaller bed particles [5]. Further demonstrating the complexity of the physics associated with segregation, in bidisperse mixtures of spherical particles that vary in both volume and density, the segregation depends not only on the volume ratio and density ratio [32] but also on the species concentration [33][34][35]. Therefore, the physics of segregation is, at least in part, dependent on both the relative size, here characterized by the volume ratio, and the mass (or density) ratio between particle species.…”

Asymmetric concentration dependence of segregation fluxes in granular flows

“…Flowing mixtures of granular material with differing properties, including size [2][3][4][5][6][7][8], density [9][10][11][12][13][14][15][16], surface roughness [17,18], and shape [19,20], tend to segregate, and they are common in geophysical flows [21][22][23][24] and industrial settings such as during hopper filling and discharging [25][26][27], in rotating tumblers [9,[28][29][30][31][32], and in chute flow [1,33,34]. The simplest explanation for segregation relies on the idea, for size-disperse mixtures, that small particles fall through voids generated between large particles and accumulate in the lower regions of the flowing layer, while large particles are forced upward by concentrated regions of small particles.…”