Abstract

Seals in multiphase pumps must be able to operate without degrading the system dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal. The 14-grooves seal has diameter D=127 mm, length L=0.34 D, and clearance c=0.211 mm; each groove has depth dg ~2.6 c and length Lg ~ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The leakage decreases with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when inlet GVF= 0.1. As the gas content increases, 0.2 = GVF = 0.5, the seal K becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. The direct damping is invariant with frequency. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

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