Experimental investigation of flow characteristics of high-concentration ice slurry in pipes considering melting effects

• Temporal evolutions of ice slurry flow patterns during pipe cleaning are established. • Slurry front melting dominates, while the rear aids fouling removal and collection. • The wall shear stress shows distinct sensitivities to length, fraction, and velocity. • A novel hybrid model accurately predicts slurry flowing distance before full melting. • Guidelines are provided for ice slurry pigging in actual engineering applications. High-concentration ice slurry with phase change can be used as a pipe cleaning material, producing pollution-free effluents. The required characteristics of such slurry should be determined carefully before any cleaning process to slow down its melting rate and reduce cleaning costs. Excessive pump power should be avoided to minimize energy consumption, as well as high pressure on the pipeline wall to prevent pipe breakage. In this study, the flow and melting of high-concentration ice slurry were experimentally investigated in a closed-loop pipe system to examine the impact of key parameters on ice pigging. Results show that ice slurry exhibits effective cleaning performance during steady flow. The melting at the front of the slurry appears more pronounced due to the significant temperature difference between its front and the pipe wall, as well as the large heat exchange at the interface between the slurry front and the surrounding water. The melting rate of the ice slurry increases with flow acceleration, and the flowing distance increases with the slurry injection length, concentration, and flow velocity. The wall shear stress exerted by the ice slurry also increases with these parameters, and its rate of change is closely related to the velocity gradient near the boundary layer. A novel predictive formulation was developed to estimate the ice slurry flowing distance, featuring high accuracy and low experimental data requirements, by combining a physical modelling approach with a Gradient Boosting Regressor process. This research provides important information for the practical application of ice slurry in cleaning operations.