Predicting pressure-drop for pseudo-homogeneous slurry flows using the mixture model at high solids concentrations

Abstract

The main contribution of this paper is applying computational fluid dynamics (CFD) using the two-phase mixture model with algebraic slip, and turbulent dispersion to the slurry flow experiment of Kaushal et al. (2012). The results obtained were compared to the experimental results and numerical results reported by the same authors who used the mixture model as well as a more advanced Eulerian granular flow model. The authors reported that the mixture model predicted the pressure drops with very high errors, especially for the highest solids loading simulated with errors as high as 400% compared to their experimental data. They conclude that the mixture model cannot be used to predict the pressure drop of the slurry flow investigated at higher concentrations (30-50% solid fraction). In contrast to this, the pressure-drop predictions of the two-phase mixture model with algebraic slip and turbulent dispersion used in this study were in good agreement with the measured values. This calls the conclusion of Kaushal et al. (2012). to question, because they did not present any justification for 3-4 times higher pressure drop observed in their study using the mixture model in combination with the fact that no anomalies in particle concentration profiles were observed by them for the mixture model. A comparison between the two mixture models reveals that although they differ in some details, the basic structure of the models is the same. We conclude that the mixture model with algebraic slip, turbulent dispersion, and a suspension viscosity model can be used for pressure drop predictions for the slurry flow investigated even for high solids fraction. We also demonstrate that the laterally averaged solids concentration profiles are not predicted very accurately by the mixture model as well as the more complex granular model. The concentration profiles predicted by the mixture model is easily understood in contrast to the profiles predicted by the granular flow model. From an engineering viewpoint, preference should be given to a simpler model, as was used in this study which can predict pressure drop with similar accuracy compared to a more complex approach with a larger number of uncertainty parameters. Further research is necessary to correctly predict the solids concentration profile for slurry flow in pipelines.