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Journal of Zhejiang University SCIENCE A

ISSN 1673-565X(Print), 1862-1775(Online), Monthly

Cavitation evolution and damage by liquid nitrogen in a globe valve

Abstract: Valves are key components of the safety of fluid transportation systems because of induced disturbance and cavitation damage in them. In this study, a 2D model of a cryogenic globe valve with liquid nitrogen (LN2) as working fluid was established by Fluent, and thermal effects were specially considered in the simulation. The validity of the LN2 cavitation model was verified by the experimental data of hydrofoil LN2 cavitation from earlier studies by NASA. Cavitation characteristics of LN2 in the cryogenic globe valve under three typical working conditions were investigated. The average pressure and pressure pulse at different positions of the wall were further studied to reveal cavitation risks from fatigue and vibration. Results show that with similar valve structure and openings, the pressure pulsation frequencies of LN2 are lower than those of water, and the shape and location of the cavitation clouds also show significant differences. For LN2 cavitation, an extended period of valve opening at 66% should be avoided since its pressure pulse peak is the largest compared to openings of 33% and 100%, and reaches 5×107 Pa. The opening of 33% should also be monitored because of the large torque caused by the pressure difference between the two sides of the valve baffles. To prevent resonance, a critical state for the valve opening and the connecting pipe length is proposed. These predictions of cryogenic cavitation in the globe valve are helpful for the safe and reliable operation of cryogenic fluid transport systems.

Key words: Cavitation; Thermal effect; Cryogenic liquids; Cryogenic globe valve

Chinese Summary  <29> 低温截止阀内液氮空化演变和危害研究

目的:阀内流体空化将对阀门壁面产生冲击,造成气蚀剥蚀和噪音,并影响流体输运系统的安全运行。低温流体和常温流体物性区别大,并且低温流体空化有更为复杂的机理。本文旨在讨论低温截止阀内液氮空化的发展规律,并进一步研究空化对壁面产生的压力冲击,以及如何避免阀门系统发生共振,从而为阀门系统的安全运行提供参考。
创新点:1.在数值模拟中加入能量方程,并考虑低温流体在空化过程中压力和温度的相互影响;2.分析在不同阀门开度下液氮空化的发展过程和壁面不同位置受到的压力冲击。
方法:1.利用Fluent空化模型和Mixture模型,建立低温截止阀空化模型(图3);2.模拟不同开度下阀内液氮的空化过程(图6~9);3.分析壁面各监测点的压力变化情况,提取压力幅值和流体脉动频率,并与阀门固有频率比较(图12,13,15和20)。
结论:低温截止阀内液氮空化呈现周期性特征,并且空化周期随阀门的开度增大而减小;2.最大压力脉冲峰值出现在中等开度(66%);3.最大振动位移出现在阀体处,且存在临界管长,使得阀门系统的固有频率和流体脉动频率相等。

关键词组:空化;热效应;低温液体;低温截止阀


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DOI:

10.1631/jzus.A2100168

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On-line Access:

2022-02-28

Received:

2021-04-11

Revision Accepted:

2021-09-17

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