Retention–removal dynamics of wall adhesion in high-water-cut oil–water pipe flow during cooling

Wall adhesion in low-temperature, high-water-cut oil–water pipe flow is a dynamic multiphase interfacial process jointly governed by oil-phase retention, interfacial deformation, and hydrodynamic removal by the continuous water phase. However, the relationship between local morphological evolution and the global hydraulic response remains unclear. In this study, pressure-drop, temperature, and flow rate measurements were combined with end point weighing and wall visualization to investigate wall adhesion at water cuts of 90%, 93%, and 97% and mixture superficial velocities of 0.16, 0.32, and 0.48 m s−1. The global hydraulic response exhibited three stages: rapid growth, decelerated development, and quasi-steady fluctuation. Even after the equivalent adhesion thickness entered the quasi-steady stage, the wall-adhered oil phase continued to undergo streamwise elongation, necking, edge recession, and local rearrangement. This finding indicates that hydraulic quasi-steadiness does not correspond to a static local morphology, but instead reflects an approximate balance between continued oil-phase retention and hydrodynamic removal. Based on these observations, a retention–removal kinetic model was developed, in which wall adhesion was described as the dynamic outcome of competition between continued oil-phase retention and hydrodynamic removal. The model achieved a coefficient of determination of 0.971, a root mean square error of 0.193 mm, and a mean absolute error of 0.148 mm. Within the investigated parameter range, the model satisfactorily described the dynamic evolution of wall adhesion.