STATIC AND ROTORDYNAMIC CHARACTERISTICS OF LIQUID ANNULAR SEALS WITH A CIRCUMFERENTIALLY-GROOVED STATOR AND SMOOTH ROTOR USING THREE LEVELS OF CIRCUMFERENTIAL INLET-FLUID ROTATION

摘要

Test results are presented for a smooth-rotor/circumferentially-grooved, annular pump seal. The seal's geometry and operating conditions are representative of electrical submersible pumps (ESPs) as used for oil recovery; however, most ESPs use grooved rotors instead of grooved stators. Test results include static and rotordynamic data at speeds ω of 2, 4, 6 krpm, axial pressure drops ΔP of 2.1, 4.1, 6.2, 8.3 bars. The grooved seal has a length-to-diameter ratio L/D of 0.5 and a minimum radial clearance C_r of 203 μm. It employs 15 circumferential grooves with a length G_l, and depth G_d of 1.52 mm, which are equally-spaced by a land length of 1.52 mm. Tests are conducted for eccentricity ratios ε_0 of 0.00, 0.27, 0.53, 0.80. Three different inlet-fluid prerotation inserts are used upstream of the test seals to create a range of inlet preswirl ratios. Pitot tubes are used to measure the circumferential velocity at one location immediately upstream of the test seal and one downstream location near the seal exit. The test fluid is ISOVG2 oil @ 46 °C. Test results for the grooved seal are compared to test results for a smooth annular seal with the same L, D, and minimum C_r. The grooved-seal's leakage rate Q, ranges from a low 15.64 LPM at ω = 6 krpm, and ΔP = 2 bar, to a high 56.36 LPM at ω = 2 krpm, and ΔP = 8 bar. When compared to the smooth seal, the grooved seal provides a 20% Q reduction at ω = 2 krpm, and a 6% reduction at ω = 6 krpm. The grooved seal's rotordynamic coefficients are generally not sensitive to changes in ε_0. The smooth seal's stiffness and damping coefficients are not very sensitive to changes in ε_0 in moving from ε_0 = 0 to 0.5, but typically increase dramatically in magnitude in moving from ε_0 = 0.5 to 0.8. From a rotordynamic viewpoint, the major difference between the two seals concerns the direct stiffness coefficients, with the grooved seal having near zero to negative values and the smooth seal having larger positive values, particularly at increased ε_0 values. The grooved seal generally produces lower-magnitude cross-coupled stiffness and direct damping coefficient values than the smooth seal.