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| Computational and experimental study on hydraulic loss in water pipeline with entrapped air and siphon head |
| ZHANG Jinfeng*, CAI Haikun, FANG Yujian,CHEN Shengbo, XU Jie, LI Yalin |
| National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China |
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Abstract To explore the influence of entrapped air in a water pipeline on its hydraulic loss, a small slope siphon test rig, which is an undulating pipe with a long downward sloping pipeline, was built. Experiments were carried out under different inlet conditions, namely natural inlet, low siphon inlet and high siphon inlet(with a multi-hole siphon head). At first, an entrapped air resistance factor β was innovatively introduced to account for the increase of hydraulic loss due to the entrapped air in a pipe, and the formulas for determining the flow resistance in the pipe were deduced. Then, the flow resistance characteristics of the pipe were analyzed based on the experimental data obtained under diffe-rent inlet conditions with and without entrapped air. The mechanism for entrapped air to increase flow resistance was verified. The results show that the entrapped air can reduce the effective flow cross-sectional area and increase the hydraulic loss in the water pipeline considerably, and the more the numbers of undulations and pipe fittings in the pipeline, the larger the entrapped air resistance factor β. Compared with natural inlet, a siphon inlet can reduce the hydraulic friction factor of the pipeline, and the hydraulic friction factor is the smallest for the high siphon inlet. If a multi-hole siphon head is designed properly, the multi-hole structure can automatically adjust its own resistance and opening according to the flow rate in the pipeline, then can effectively control the air flow rate at the pipeline inlet, eventually, reduces the hydraulic loss in the pipeline.
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Received: 04 March 2019
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