Abstract
Modelling the macroscopic rheology of non-Brownian suspensions is complicated by the non-linear behaviour that originates from the interaction between solid particles and the liquid phase. In this contribution, a model is presented that describes suspension rheology as a function of solid volume fraction and shear rate dependency of both the liquid phase, as well as the suspension as a whole. It is experimentally validated using rotational rheometry (varphi ≤ 0.40) and capillary rheometry (0.55 ≤ varphi ≤ 0.60) at shear rates > 50 s−1. A modified Krieger-Dougherty relation was used to describe the influence of solid volume fraction on the consistency coefficient, K, and was fitted to suspensions with a shear thinning liquid phase, i.e. having a flow index, n, of 0.50. With the calculated fit parameters, it was possible to predict the consistency coefficients of suspensions with a large variation in the shear rate dependency of the liquid phase (n = 0.20–1.00). With increasing solid volume fraction, the flow indices of the suspensions were found to decrease for Newtonian and mildly shear thinning liquid phases (n ≥0.50), whereas they were found to increase for strongly shear thinning liquid phases (n ≤0.27). It is hypothesized that this is related to interparticle friction and the relative contribution of friction forces to the viscosity of the suspension. The proposed model is a step towards the prediction of the flow curves of concentrated suspensions with non-Newtonian liquid phases at high shear rates.
Highlights
Concentrated suspensions of solid particles in Newtonian and non-Newtonian liquid phases are common in nature and industry
In the case of polyethylene glycol (PEG) and gum arabic, the viscosity is independent of shear rate, indicating Newtonian behaviour with a flow index nl of 1.0
The results suggest that Eq (4) can be used to calculate the consistency coefficient of the suspension when the liquid phase changes, provided the rheology of the liquid phase is known and the solid phase properties remain the same
Summary
Concentrated suspensions of solid particles in Newtonian and non-Newtonian liquid phases are common in nature and industry. These multiphase systems are often subjected to transport or shaping processes where shear rates typically vary between 100 and 103 s−1 (Barnes et al 1989). The prediction and control of these processes are complicated by the variation in composition of the suspensions. For instance, the solid volume fraction can lead to a substantial increase in pressure requirements, leading to complications in both humans (JóźwikPlebanek et al 2020) and machines (El Cheikh et al 2017). The modelling and optimization of these processes requires a description of the flow behaviour of the suspensions at process relevant conditions, and as a function of their composition
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