Leakage Flow Modeling for Multiphase Twin Screw Pumps
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Twin screw pumps (TSPs) are commonly used for multiphase boosting systems to enhance oil and gas production. TSPs are a positive displacement pump that can efficiently handle fluids with a wide range of gas volume fractions (GVFs). The present study has developed a model to predict the performance of TSPs for varying GVFs, pump speeds, suction pressures, and differential pressures. A two-phase compressible flow model is used to determine the rate of leakage backflow through clearances within the pump. The model incorporates the possibility of choking due to sonic flow. Hydraulic imbalances cause rotor deflection, and the model accounts for increased leakage flowrates due to the induced eccentric rotation. The model was validated with experimental data from a Colfax MR-200 TSP, and there is good agreement in most test cases. However, cases with low speeds and high differential pressures were not as reliable. This may be due to uncertainty of the rates of gas infiltration into the clearances at low pump speeds. The study reveals that pump performance is generally better when operating at high pump speeds, high GVF, low suction pressures, or low differential pressures. Linear pressure distributions throughout the pump’s chambers generally indicate lower volumetric efficiency compared to steep, concave pressure distributions. The effects of rotor deflection are generally small, but in a few cases they should not be ignored. Choking occurred at the circumferential, flank, and root clearances in 18%, 13%, and 99% of the test cases, respectively. The presence of choked leakage flow marginally improved the pump performance.
Shive, Jeffrey Shiao-Jeh (2017). Leakage Flow Modeling for Multiphase Twin Screw Pumps. Master's thesis, Texas A & M University. Available electronically from