CFD simulation and experimental study of oil viscosity effect on multi-stage electrical submersible pump (ESP) performance

In this study, the oil viscosity effect on ESP performance is investigated by experimental study and computational fluid dynamics (CFD) simulations. Oils with different viscosities are flowed through a DN1750ESP at varying flow rates and rotary speeds. The temperature is maintained at different levels with a heat exchanger circulated by cold water. The pressure increase over the 3rd stage as well as total 7 stages in ESP is measured with differential pressure transducers. The same geometries, fluid properties and flow characteristics are implemented into CFD simulations. The three-dimensional (3D), steady-state Reynolds-Averaged Navier-Stokes (RANS) equations with standard SST (shear stress transport) turbulence models are solved in ANSYS CFX by employing frozen-rotor technique. With high-quality structured hexahedral mesh, the simulated pressure increment is compared with corresponding experimental results. Flow structures inside ESP impeller and diffuser channels are analyzed. At pump best efficiency point (BEP), the boosting pressure decreases 30-40% when oil viscosity increases from 10 cp to 100 cp. ESP becomes ineffective when oil viscosity is higher than 200 cp. With oil viscosity increasing, pump H-Q performance curve becomes more linear. CFD simulation reveals that the recirculation flow at impeller blade trailing edge is more prominent at lower liquid flow rates.