Geometrical modifications of rotary mixers within a vertical pipe for improving oil-air flow mixing in ESP applications: A computational approach

Maintaining a homogeneous mixture within multiphase pumps is essential to ensure performance, avoid phase separation, and prevent gas lock, particularly at high gas volume fractions (GVF). This study investigates geometrical modifications of a rotary mixer within a vertical pipe to improve oil-air mixing efficiency in Electric Submersible Pump (ESP) applications. Various mixer configurations were evaluated using unsteady Computational Fluid Dynamics (CFD) simulations, focusing on GVF distribution, uniformity index (UI), and pressure drop. The results indicated that increasing the number of blades slightly improves UI but significantly increases pressure drop. Introducing perforations in the blades (four holes per blade) enhanced mixing efficiency while minimizing pressure drop compared to solid blade designs. The UI values for perforated mixers with 2, 3, 4, and 6 blades were 70.7 %, 72.7 %, 74 %, and 75 %, respectively. Further analysis on 2-blade and 6-blade mixers revealed that varying the number of holes had minimal effect on GVF distribution in the 2-blade configuration but notably influenced inlet pressure in the 6-blade design. The 2-blade mixer with three holes provided the best trade-off, achieving a uniform gas dispersion and reducing inlet oil pressure by up to 28.4 % compared to the 6-blade configuration. Additionally, the effect of shaft speed (1000–3000 rpm) was evaluated, with 1500 rpm found to offer optimal mixing with minimal energy consumption. This work offers a practical, low-energy solution for enhancing ESP performance under multiphase flow conditions, particularly by mitigating gas lock and improving mixture homogeneity.