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Research Papers: Other (Seals, Manufacturing)

Experimental Study of the Leakage and Rotordynamic Coefficients of a Long-Smooth Seal With Two-Phase, Mainly Oil Mixtures

[+] Author and Article Information
Min Zhang

Praxair, Inc.,
Tonawanda, NY 14150

Dara W. Childs

Leland T. Jordan Professor
Texas A&M University,
College Station, TX 77840

James E. Mclean, Jr., Dung L. Tran, Hari Shrestha

Texas A&M University,
College Station, TX 77840

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received July 10, 2018; final manuscript received December 5, 2018; published online January 22, 2019. Assoc. Editor: Daejong Kim.

J. Tribol 141(4), 042201 (Jan 22, 2019) (9 pages) Paper No: TRIB-18-1261; doi: 10.1115/1.4042272 History: Received July 10, 2018; Revised December 05, 2018

This paper experimentally studies the leakage and rotordynamic performance of a long-smooth seal with air–oil mixtures. Tests are performed with inlet gas-volume-fraction gas volume fraction (GVF) = 0%, 2%, 4%, 6%, and 10%, rotor speed ω = 5, 7.5, 10, and 15 krpm, inlet temperature Ti = 39.4 °C, exit pressure Pe = 6.9 bars, and pressure drop (PD) = 31, 37.9, and 48.3 bars. Test results show that adding air into the oil flow does not change the seal's mass flow leakage m˙ discernibly but significantly impacts the seal's rotordynamic characteristics. For all PDs and speeds, K increases as inlet GVF increases from zero to 10% except for 6% ≤ inlet GVF ≤ 10% when PD = 48.3 bars, where K decreases as inlet GVF increases. The K increment will increase a pump rotor's natural frequency and critical speed. Increasing the rotor's natural frequency would also increase the onset speed of instability (OSI) and improve the stability of the rotor. Adding air into the oil flow has little impact on cross-coupled stiffness k, direct damping C, and effective damping Ceff. Ceff = C − k/ω + mqω, where mq is the cross-coupled virtual-mass. Test results are compared to predictions from San Andrés's (San Andrés, 2011, “Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals,” ASME J. Eng. Gas Turbines Power, 134(2), p. 022503.) bulk-flow model, which assumes that the liquid–gas mixture is isothermal and homogenous. The model reasonably predicts m˙, C, and Ceff. All predicted K values are positive, while measured K values are negative for some test cases. Predicted k values are close to measurements when ω = 5 krpm and are larger than measurements when 7.5 ≤ ω ≤ 15 krpm.

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References

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Figures

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Fig. 5

Cross-section of the zero-preswirl guide insert [9]

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Fig. 4

P&ID of mainly oil mixing section

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Fig. 3

Test smooth seal (dimensions are in inches)

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Fig. 2

Section view of the test section [9]

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Fig. 1

P&ID of the 2PASS [9]

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Fig. 6

Reynolds numbers at the seal inlet

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Fig. 7

Reynolds numbers at the seal exit

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Fig. 8

Predicted and measured m˙ values at PD = 48.3 bars

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Fig. 9

Variation of m˙ with changing PD at ω = 10 krpm

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Fig. 10

Predicted and measured K values at (a) PD = 31 bars, (b) PD = 37.9 bars, and (c) PD = 48.3 bars

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Fig. 11

Predicted and measured k values at PD = 48.3 bars

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Fig. 12

Predicted and measured k values at inlet GVF = 6%

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Fig. 13

Predicted and measured of C values at ω = 10 krpm

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Fig. 14

Predicted and measured c values at (a) PD = 31 bars, (b) PD = 37.9 bars, and (c) PD = 48.3 bars

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Fig. 16

Predicted and measured mq values at PD = 48.3 bars

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Fig. 15

Predicted and measured M values at (a) PD = 31 bars, (b) PD = 37.9 bars, and (c) PD = 48.3 bars

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Fig. 17

Predicted and measured Ceff values at PD = 37.9 bars

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Fig. 18

Variation of Ceff with changing PD at ω = 10 krpm

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