Bidisperse suspension

Figure 12 shows Chong et al. (28) data for monodisperse and bidisperse (bimodal) suspension systems. In a bidisperse suspension, the volume fraction of small spheres (diameter d) in the mixture is kept constant at 25% of the total solids. The figure shows that the viscosity of a bidisperse suspension is a strong function of the particle size ratio, d/D, where D is the diameter of the large particles. The viscosity decreases substantially by decreasing d/D at a given total solids concentration. The data for the unimodal system fall well above the bimodal suspensions. Also, the effect of particle size distribution decreases at lower values of total solids concentration. 

Kim and Luckham (140) suggested that the relative dynamic viscosity of a bidispersed suspension may be estimated by using the product of the two component relative viscosities each computed from the Krieger-Dougherty equation as if they were alone in the suspension. This treatment has been commonly used since Farris (139). However, it is valid only when concentration of either component is large, that is, eL - 1 or L - 0, and the particle sizes are very different from each other, that is, ds dL- When the two concentrations are similar, that is, eL 0.5, the estimation of the apparent viscosity using this approach gives a much lower value than the experimental values. This behavior is same for dynamic viscosity as the steady shear viscosity. 

Rodriguez et al. (130) showed that the behavior of steady shear viscosity versus the shear stress for a binary system is no different from that of a monodisperse suspension. A universal equation may be obtained for both the monodisperse and bidisperse suspensions. Hence, we may further infer from the literature results available that the steady shear viscosity for a polydispersed (multimodal) suspension can be treated the... 

In this section we turn our attention to bidisperse suspensions, following which we will briefly discuss polydisperse suspensions. It is known that for a bidisperse suspension the relative viscosity decreases significantly in comparison to that of a monodisperse suspension of the same material and with the same solids volume fraction. 

SHAPIRO, A.P. 8c PROBSTEIN, R.F. 1992. Random packings of spheres and fluidity limits of monodisperse and bidisperse suspensions. Phys. Rev. Lett. 68, 1422—1425. 

Law H-S, Masliyah JH, MacTaggart RS, Nandakumar K. Gravity separation of bidisperse suspensions light and heavy particle species. Chem Eng Sci 42 1527-1538,1987. 

Nasr-El-Din H, Masliyah JH, Nandakumar K, Law D H-S. Continuous gravity separation of a bidisperse suspension in a vertical column. Chem Eng Sci 43 3225-3234, 1988. 

G.P. Krishnan, S. Beimfohr, and D.T. Leighton. Shear-induced radial segregation in bidisperse suspensions. Journal of Fluid Mechanics, 321 371-393, 8 1996. 

Krishnan, G.R, Beimfohr, S., and Leighton, D.T. (1996). Shear-induced radial segregation in bidisperse suspensions. /. Fluid Mech. 321, 371-393. 

Turning again to the problem of bidisperse suspensions, we will show below that the presence of even minute amounts of tiny particles can greatly affect the dynamic mobility of large latex particles. Comparison between experimental data and theoretical approaches to the calculation of m in the... 

---