Experimental and numerical study of oil drop motion within an ESP impeller

The Electrical Submersible Pump (ESP) is a multistage centrifugal pump used in the petroleum industry as an artificial lift method. The ESP usually works with the presence of two-phase liquid-liquid flows that constitute dispersions and emulsions, causing performance losses and operational problems. This research aims to investigate the behavior and evaluate the dynamics of individual oil drops in an oil-in-water dispersion within an ESP impeller. The study adopts experimental and numerical approaches. Initially, experiments were performed using an experimental facility with a high-speed camera and an ESP prototype working at 600 rpm and 900 rpm, for water flows around the Best Efficiency Point (BEP) and with the injection of oil drops at a low flow rate. The acquired images were processed, and a drop sample was tracked, enabling the analysis of the size, shape, path, velocity, and acceleration of the oil drops. Numerical simulations were executed in ANSYS® software to define relevant parameters related to water and oil drops, such as velocities, accelerations, forces, turbulent dissipation, and residence time. The images reveal a unique flow pattern of dispersed drops in a continuous water phase. The oil drops' diameters vary from tenths of a millimeter to around 3 mm. The drops' trajectories can be classified into three different regions within the impeller channels. The drops’ velocities stay in the order of 1 m/s, while accelerations can reach hundreds of m/s2. The velocity profiles show that the oil drops tend to decelerate during their trajectory, while the acceleration profiles suggest peaks at the channel inlet and outlet. High intense turbulence is present in the impeller entrance zone. The evaluation of the residence time and the particle Reynolds number suggest that smaller oil drops follow the water streamlines, while larger oil drops tend to be affected by external forces. The main forces that govern the oil drop motion are the drag, the pressure gradient, and the virtual mass forces. The force from the pressure gradient is tenfold greater than the force from the drag. The virtual mass effect is significant only in the impeller inlet. In general, in this research, numerical results show a satisfactory agreement with the experimental data.