Review charts potential paths forward for non-Brownian suspension rheology

In everything from bread dough to blood to industrial injection molding, each of the numerous ways we interact with suspension fluids provides a new opportunity for mathematical descriptions of their fluid flow. How particles in a fluid interact to cause large increases in viscosity, however, is still poorly understood. A new review of the recent progress in this field hopes to further bridge the gap between experimental results and computational approaches to understanding suspensions.

Roger Tanner published the review comparing recent experimental and computational findings of non-Brownian suspension rheology. Focusing on compact, rigid particles in Newtonian fluids, Tanner identifies areas that are still ripe for further exploration, including extensional, unsteady and oscillatory flows. He also presents suggestions based on a modified Reiner-Rivlin model, which describes incompressible fluids, demonstrating the need for more elongational and other nonviscometric experiments and simulations.

“Among the results, the surprising dominance of interparticle friction emerges strongly,” Tanner said. “The relative lack of results for elongational and unsteady flows becomes obvious and further work on these subjects is needed in order to assist in the generation of a useful constitutive model of suspensions.”

Among his findings, Tanner reports that the modified Reiner-Rivlin model is simple and useful for numerical work on concentrated suspensions, especially when large strains are present. For flows of very long duration it might be necessary to also consider particle diffusion.

Tanner also presents new medium strain oscillatory data, demonstrating that these conditions are not modeled well. Because of the limited scope of his review, he notes that it will be necessary to explore non-Newtonian matrices in the future, as they make up many polymer processes.

Source: “Review Article: Aspects of non-colloidal suspension rheology,” by Roger I. Tanner, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5047535 .