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Solid bed erosion by liquids flowing in horizontal concentric annulus

Bandelis G.E. , Kelesidis Vasilis

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Summary

In this paper, solid bed erosion processes and the mechanisms involved when a two-phase liq- uid-solid mixture flows over a bed of solids in a horizontal annulus are analyzed. There are few such studies available with some authors argu- ing that the flow rate for erosion is always less than the flow rate for the suspension of solid particles thus necessitating further study and analysis of such phenomena. Tests were run to determine the mechanism of erosion and the erosion velocities of the solid bed formed in a concentric annulus for three flu- ids, water, a low concentration water solution of Carboxyl-methyl-cellulose (CMC), which be- haved as a Newtonian fluid and a higher con- centration CMC water solution which behaved as a power law fluid. Glass spheres of 2 mm nominal diameter were used as solids. The flow rate at which erosion occurred to- gether with the mechanism of bed erosion were determined visually, while the whole process was video recorded. Our tests indicated different erosion mechanisms and different erosion ve- locities for the three tested liquids, with the liq- uid viscosity playing a major role. The first mechanism, observed for water flow, gives ero- sion from the front of the bed while the second mechanism, observed for the flow of the two viscous fluids, gives erosion from the top of the bed. The role of each of the parameters to erosion is investigated, whether it is turbulent flow with the turbulent fluctuations being more capable to remove the solids from the formed bed or whether it is liquid viscosity, which results in the hydrodynamic shearing force. The results demonstrate that liquid viscosity plays a role in the erosion mechanism and yields different erosion velocities of the solid bed hence, it should be taken into account when modeling flow pattern transitions for solid- liquid flows. Prior studies have not identified this and it could be the reason of the disagree- ment between theoretical models and experi- mental and field data.

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