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| Efficiency scaling method for pumps and their systems |
| LU Wei-Gang, YAN Deng-Feng, ZHEN Feng |
| (College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou, Jiangsu 225009, China) |
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Abstract The theoretical bases of existing efficiency scaling formulas and several scaling methods recommended in some industrial standards for pumps were analyzed. It was found that those formulas are incompletely mathematical expression, experiencedominated and less universal, etc. The hydraulic loss ratios and efficiency at the best efficiency point computed with different efficiency scaling formulas were compared, and it was identified that the efficiency of the prototypes scaled from the models by using Medici's and Fromm's and Moody's formulas shows quite difference compared with the measurements. The efficiency of the prototypes estimated by the rest formulas is less difference from the tests, in which Ackeret's formula gives a minimum error. A flow regimedepended efficiency scaling method for pump and its system was put forward, in which three formulas of skin friction factor for three flow regimes were introduced according to essentials of fluid mechanics, and then the corresponding mathematically simplified formulas were proposed for they to be applied conveniently. Based on the internal flow characteristics in pumps, the basis for determining the skin friction factor was analyzed and argued, and influences of the proportional constants of pump performance parameters and skin friction factor on the efficiency scaling were studied; eventually an additional method for estimating the efficiency coefficient was resulted. For the same prototype and model of pump and its system, the efficiencies scaled with those different methods were predicted; the reasons for difference in efficiency estimated and feasibility of the methods were analyzed. The results indicate that the proportional constants have less influence on the flow regimedepended efficiency scaling method compared with Ackeret's and Hutton's formulas. Thus, as the flow regimedepended efficiency scaling method is applied, the efficiency scaled with a skin friction factor in any flow regimes doesn't seem to show significant difference.
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Received: 08 August 2012
Published: 30 November 2012
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