Leakage and Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Wet Annular Seal: Measurements and Predictions

[+] Author and Article Information
Xueliang Lu

Research Assistant, Mechanical Engineering Dept. Texas A&M University College Station, TX 77843, USA

Luis San Andres

Mast-Childs Chair Professor, Fellow ASME, Mechanical Engineering Dept. Texas A&M University College Station, TX 77843, USA

1Corresponding author.

ASME doi:10.1115/1.4041270 History: Received July 30, 2018; Revised August 01, 2018


In subsea environments, multiphase pumps add pressure to the process fluid thus enabling long distance tie back systems that eliminate topside oil and gas separation stations. One challenge to construct a reliable multiphase pump is that they must handle a mixture whose gas volume fraction (GVF) changes suddenly. The mixture GVF affects the static and dynamic forced performance of seals, and which could lead to an increase in rotor lateral or axial vibrations. This paper extends prior work with uniform clearance seals and presents the static and dynamic performance of a three-wave surface annular seal designed to deliver a significant centering stiffness. The test element has length L=43.4 mm, diameter D=127 mm, and mean radial clearance cm=0.191 mm. At a shaft speed of 3.5 krpm (23 m/s surface speed), an air in ISO VG 10 oil mixture with an inlet GVF, 0 to 0.9, feeds the seal at 2.5 bara pressure and 37 °C temperature. The mixture mass flow rate decreases continuously with an increase in inlet GVF. The liquid seal (GVF=0) shows frequency independent force coefficients. However, operation with a mixture produces stiffnesses that vary greatly with excitation frequency. The direct damping coefficients are not functions of frequency albeit dropping rapidly in magnitude as the GVF increases. The extensive test campaign reveals a wavy-surface seal offers a centering stiffness ability, a much desired feature in vertical submersible pumps that suffer from persistent static and dynamic stability issues.

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