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CLC number: TV131.2

On-line Access: 2017-03-07

Received: 2016-04-20

Revision Accepted: 2016-08-27

Crosschecked: 2017-02-07

Cited: 0

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Citations:  Bibtex RefMan EndNote GB/T7714


Wu-yi Wan


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Journal of Zhejiang University SCIENCE A 2017 Vol.18 No.3 P.167-178


Investigation on critical equilibrium of trapped air pocket in water supply pipeline system

Author(s):  Wu-yi Wan, Chen-yu Li, Yun-qi Yu

Affiliation(s):  Department of Hydraulic Engineering, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China; more

Corresponding email(s):   wanwuyi@zju.edu.cn

Key Words:  Hump pipe, Pipe flow, Trapped air pocket, Hydraulic experiment, Water supply pipeline

Wu-yi Wan, Chen-yu Li, Yun-qi Yu. Investigation on critical equilibrium of trapped air pocket in water supply pipeline system[J]. Journal of Zhejiang University Science A, 2017, 18(3): 167-178.

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author="Wu-yi Wan, Chen-yu Li, Yun-qi Yu",
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%T Investigation on critical equilibrium of trapped air pocket in water supply pipeline system
%A Wu-yi Wan
%A Chen-yu Li
%A Yun-qi Yu
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%I Zhejiang University Press & Springer
%DOI 10.1631/jzus.A1600325

T1 - Investigation on critical equilibrium of trapped air pocket in water supply pipeline system
A1 - Wu-yi Wan
A1 - Chen-yu Li
A1 - Yun-qi Yu
J0 - Journal of Zhejiang University Science A
VL - 18
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SP - 167
EP - 178
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PB - Zhejiang University Press & Springer
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DOI - 10.1631/jzus.A1600325

A trapped air pocket can cause a partial air lock in the top of a hump pipe zone. It increases the resistance and decreases the hydraulic cross section, as well as the capacity of the water supply pipeline. A hydraulic model experiment is conducted to observe the deflection and movement of the trapped air pocket in the hump pipe zone. For various pipe flow velocities and air volumes, the head losses and the equilibrium slope angles are measured. The extra head losses are also obtained by reference to the original flow without the trapped air pocket. Accordingly, the equivalent sphere model is proposed to simplify the drag coefficients and estimate the critical slope angles. To predict the possibility and reduce the risk of a hump air lock, an empirical criterion is established using dimensional analysis and experimental fitting. Results show that the extra head losses increase with the increase of the flow velocity and air volume. Meanwhile, the central angle changes significantly with the flow velocity but only slightly with the air volume. An air lock in a hump zone can be prevented and removed by increasing the pipe flow velocity or decreasing the maximum slope of the pipe.

Influence of an air lock in the top of a hump pipe zone on a capacity of the water supply pipeline is discussed in the manuscript. The trapped air pocket can obstruct water flow due to increase in pressure losses. Although this problem is quite well recognized in the literature, it is still important from a practical point of view. The authors analyzed the influence of water flow rate in the pipe and the volume of an air pocket on both the friction and the critical equilibrium of the trapped air. The experiments were conducted for various pipe flow velocities and air volumes, to observe the deflection and movement of the trapped air pocket and to measure head losses. To describe the drag coefficients and estimate the critical slope angles Authors proposed a simplified model of trapped air pocket, called the Equivalent Sphere Model (ESM). Thus the calculations in the article relate to the assumed shape of the air pocket.


创新点:1. 设计了具有连续坡角变化的圆弧形驼峰管道实验,该实验可以定量模拟气团体积和平衡角度;2. 建立了驼峰气阻的水头损失经验公式和恒定流情况下驼峰气阻的管道坡角和流速的对应关系式,可用于预测和消除驼峰气阻的危害。
方法:1. 通过驼峰气团的受力特性分析,获得满足量纲和谐的力学平衡方程;2. 采用试验观察和测试获得有无气泡情况下的水头损失和平衡状态下的坡角,通过等价球体方法对测试数据进行无量纲拟合,获得气阻的水头损失方程系数,并通过流速和平衡坡角建立恒定流情况下的临界平衡方程;3. 基于试验拟合获得临界平衡方程,建立预测和评估气阻的准则系数,并提出消除气阻的水流临界流速。
结论:1. 当管路流速较小时,供水管路的驼峰顶端可能滞留和聚集气体,形成驼峰气阻;气体体积越大对水流阻碍越明显,可能造成的水头损失也越大;2. 利用等价球体法可以极大地简化驼峰气阻的形状,并良好地模拟气阻的平衡特性和阻力特性;3. 管道流速是影响驼峰气阻临界平衡位置的最重要因素,通过减小管道起伏的坡角或增加水流流速可以防止和消除驼峰气阻的危害。


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