Impacts of flow velocity and microbubbles on water flushing in a horizontal pipeline

• Higher water velocity improves flushing and reduces water use by 28 %. • Microbubbles (50–150 μm) enhance flushing and lower water use by 35 %. • Large bubbles (1000 μm) reduce turbulence, hindering flushing efficiency. • Optimal cleanness must balance water usage and operational cost. Water flushing to remove particle sediment is essential for safe and continuous transport of many industrial slurries through pipelines. Efficient flushing strategy may reduce water consumption and the cost associated with water usage, and help water conservation for sustainability. In this study, a computational fluid dynamics (CFD) model coupled with the kinetic theory of granular flow for the flushing process is presented. The CFD models were validated against field data collected from a coal slurry pipeline of 128 km in length, 0.575 m in diameter, achieving an average error of less than 15 % for outlet solid concentration over time. A parametric study evaluated the effects of water velocity (1.88–5.88 m /s ), bubble size (50 µm, 150 µm, and 1000 µm) and bubble volume fraction (0.05–0.2) on flushing performance including pipeline cleanness, cleanness efficiency, and water consumption. The obtained outcomes indicate that higher water velocity is preferred and an increase in water velocity from 1 . 88 m /s to 5 . 88 m /s reduces the water consumption by 28 %. Large bubbles may hinder the flushing process and increase the water consumption by 23 %. Remarkably, small bubbles facilitates the flushing process and lead to 35 % reduction in water consumption. These effects are attributed to the turbulent characteristics in the pipelines in presence of microbubbles. The study provides valuable insights into optimizing flushing operations by rationally leveraging microbubbles to improve water resource efficiency and operational reliability in industrial applications.