(380d) Connecting Bidisperse and Polydisperse Suspension Rheology

Authors: 
Pednekar, S., Levich Institute and Department of Chemical Engineering, City College of New York
Chun, J., Pacific Northwest National Laboratory
Morris, J. F., City College of New York
In this work, we consider spherical particles which are distributed in size, as often seen in practical applications involving suspensions. Polydisperse suspensions display lower viscosities as compared to monodisperse suspensions at the same solid volume fraction. The reduced viscosity associated with polydispersity can be explained by an increase with dispersion in particle size of the jamming fraction, or maximum flowable fraction, of solids, Φm. In fact, we show by numerical simulation that the classical Krieger viscosity relationship in which the effective viscosity diverges as (1- Φ/Φm)-2 provides a collapse of data for suspensions having contrasting particle size distributions. Prior work [1] has shown that statistically equivalent bidisperse and normal and log-normal suspensions (to third moment of the size distribution) have similar Φm. Using these arguments, this study draws parallels between flowing bidisperse and higher order polydisperse suspensions in the high shear limit demonstrating close agreement of both viscosity and normal stress response. Polydisperse suspensions and the complexities associated with understanding them can hence in theory be replaced by relatively well-understood bidisperse suspensions of equivalent rheology.

[1] Desmond, Kenneth W., and Eric R. Weeks. "Influence of particle size distribution on random close packing of spheres." Physical Review E 90.2 (2014): 022204.