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Experimental study on friction factors for water flow in smooth pipe flow under negative pressure |
FANG Yujian1*, YUAN Shouqi1, ZHAO Liwei2, ZHANG Jinfeng1 |
1. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. Chinese Academy of Agricultural Mechanization Sciences, Beijing 100083, China |
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Abstract In order to investigate the internal mechanism why the siphon inlet has achieved a significant effect in solving the problems of some water transportation projects, some early pipe resis-tance tests had been performed by considering with and without air-traps on an undulating pipe layout in our laboratory, the friction factor measured from a DN50 pipe made of transparent acrylic tube was found far below the value estimated from Moody Chart. But this conclusion is not convincible due to there are the influence of so many bends and spherical valves in the tested undulating pipe layout, therefore a simple long straight siphon layout with a multi-hole bottom valve at its inlet was constructed in the laboratory, an experimental study on the friction factor of this circular pipe under negative pressure has been studied further. The whole pipeline was made of acrylic tube, so it can be treat as hydraulically smooth pipe. The friction factor had been derived from the measurements of the pressure difference of two taps with an interval of 18.4 m located on its straight section under various discharges, not only a lower friction factor has been obtained than that from previous researchers, but also it shows a different trend against the Reynolds number variation, therefore it is concluded that the negative pressure has an important impact on the pipe flow.
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Received: 07 March 2018
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