Rheological Models For Homogeneous Slurries

In Newtonian fluids, a linear relationship exists between the shear stress and the shear rate in laminar flow. 

The viscosity of a slurry can be measured if the particles settle slowly. For dilute suspensions of fine particles, slurries may exhibit Newtonian behaviour. In this case, the viscosity of a very dilute suspension (solids volume fraction less than 2%) of uniform, spherical particles can be described by the theoretical equation derived by Einstein (Einstein, 1906). Einstein s equation is  

At high particle concentrations, slurries are often non-Newtonian. For non-Newtonian fluids, the relationship between the shear stress and shear rate, which describes the rheology of the slurry, is not linear and/or a certain minimum stress is required before flow begins. The power-law, Bingham plastic and Herschel-Bulkley models are various models used to describe the flow behaviour of slurries in which these other types of relationships between the shear stress and shear rate exist. Although less common, some slurries also display time-dependent flow behaviour. In these cases, the shear stress can decrease with time when the shear rate is maintained constant (thixotropic fluid) or can increase with time when the shear rate is maintained constant (rheopectic fluid). Milk is an example of a non-settling slurry which behaves as a thixotropic liquid. 

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