Analysis on inertia effect of carbon dioxide dry gas seal at high speed and pressure under laminar condition

doi:10.11949/j.issn.0438-1157.20180418

Abstract

Abstract:

The real gas property of carbon dioxide was expressed by third term virial equation, both the choked flow effect and the variation of gas viscosity were taken into account, the influence of inertia effect on the steady characteristics of pumping-inward and pumping-outward spiral groove dry gas seal (S-DGS) under laminar condition have been numerically investigated by referencing the theory of gas thrust bearing which considering inertia effect. Compared with the assumptions of ideal gas and inertialess, the results show that inertia effect induce a stronger influence on carbon dioxide real gas S-DGS. Inertia effect reduced leakage rate and opening force of pumping-inward S-DGS but the opposite was obtained for pumping-outward S-DGS. Taken pumping-inward S-DGS as example, the influence of inertia effect on the steady characteristics of carbon dioxide S-DGS (i.e. leakage rate and opening force) gradually enhanced with the increase of sealed gas pressure and rotational speed, while it being weaken with increased gas film thickness. The relative deviations of leakage rate and opening force caused by the inertia effect are 62.21% and 35.03% when sealed gas pressure is 10 MPa, gas film thickness is 3μm and rotational speed is 20000 r·min^-1, and the critical entrance pressure which causes a choked flow at exit is improved. In addition, the closer the temperature of carbon dioxide is to its critical temperature, the more obvious the inertial effect is.

Key words: spiral groove dry gas seal, inertia effect, real gas, carbon dioxide, numerical analysis, laminar

摘要：

借鉴考虑惯性效应的气体止推轴承理论，以维里三项截断式描述二氧化碳的实际气体行为，同时考虑阻塞流效应和密封端面间气膜的黏度变化，采用有限差分法分别分析了层流状态下惯性效应对泵入式、泵出式螺旋槽干气密封稳态性能的影响规律，并与理想气体无惯性假设模型的计算结果进行了对比。结果表明：与理想气体相比，惯性效应对二氧化碳实际气体干气密封性能的影响程度更高。惯性效应使泵入式螺旋槽干气密封泄漏率和开启力均减小，而对泵出式螺旋槽干气密封的影响程度恰好相反。以泵入式螺旋槽干气密封为例，惯性效应对二氧化碳干气密封性能（泄漏率、开启力）的影响分别随密封压力和转速的增大而增强，随气膜厚度的增大而减小，密封压力为10 MPa，气膜厚度为3 μm，转速为20000 r·min^-1时，惯性效应使泄漏率降低62.21%，开启力降低35.03%，使二氧化碳泵入式螺旋槽干气密封发生阻塞流动的临界进口压力提高。此外，二氧化碳的温度越接近其临界温度，惯性效应表现得越明显。

关键词: 螺旋槽干气密封, 惯性效应, 实际气体, 二氧化碳, 数值分析, 层流

CLC Number:

S277.9
TH136

XU Hengjie, SONG Pengyun, MAO Wenyuan, DENG Qiangguo, SUN Xuejian. Analysis on inertia effect of carbon dioxide dry gas seal at high speed and pressure under laminar condition[J]. CIESC Journal, 2018, 69(10): 4311-4323.

许恒杰, 宋鹏云, 毛文元, 邓强国, 孙雪剑. 层流状态下高压高转速二氧化碳干气密封的惯性效应分析[J]. 化工学报, 2018, 69(10): 4311-4323.

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