Duct flows of solid-liquid slurries are frequently encountered in many engineering applications. The literature about the behaviour of such mixtures in correspondence to hydraulic singularities — such as sudden variation of duct section, perforated plates and bar screens — is rather poor, despite they are integral part of the plants. The technical difficulties faced whilst performing experimental tests made CFD almost the only possible way to study the flow field in detail. In the present work the flow of sand-water mixtures through a sudden expansion in a rectangular horizontal duct is investigated by means of a two-fluid model. Due to the lack of experimental data available, a sensitivity analysis is performed to quantify the influence of the terms of the two-fluid model which proved negligible in the horizontal pipe case, topic of previous investigations. Computations were performed for either dilute or dense mixtures, in order to study the effect of the mean solids concentration on the flow field. Moreover, the effect of channel width is investigated to assess the validity of the hypothesis of two-dimensionality of the flow.

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