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Research Papers: Fundamental Issues and Canonical Flows

Prediction of the Effect of Impeller Trimming on the Hydraulic Performance of Low Specific-Speed Centrifugal Pumps

[+] Author and Article Information
D. G. J. Detert Oude Weme

Flowserve Etten-Leur,
Parallelweg 6,
Etten-Leur 4878 AH, The Netherlands;
Department of Mechanical Engineering,
University of Twente,
P.O. Box 217,
Enschede 7500 AE, The Netherlands

M. S. van der Schoot

Flowserve Etten-Leur,
Parallelweg 6,
Etten-Leur 4878 AH, The Netherlands
e-mail: mschoot@flowserve.com

N. P. Kruyt

Department of Mechanical Engineering,
University of Twente,
P.O. Box 217,
Enschede 7500 AE, The Netherlands

E. J. J. van der Zijden

Flowserve Etten-Leur,
Parallelweg 6,
Etten-Leur 4878 AH, The Netherlands

1Flowserve Hengelo.

2Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received July 12, 2017; final manuscript received January 25, 2018; published online March 29, 2018. Assoc. Editor: Bart van Esch.

J. Fluids Eng 140(8), 081202 (Mar 29, 2018) (7 pages) Paper No: FE-17-1426; doi: 10.1115/1.4039251 History: Received July 12, 2017; Revised January 25, 2018

The effect of trimming of radial impellers on the hydraulic performance of low specific-speed centrifugal pumps is studied. Prediction methods from literature, together with a new prediction method that is based on the simplified description of the flow field in the impeller, are used to quantify the effect of trimming on the hydraulic performance. The predictions by these methods are compared to measured effects of trimming on the hydraulic performance for an extensive set of pumps for flow rates in the range of 80% to 110% of the best efficiency point. Of the considered methods, the new prediction method is more accurate (even for a large impeller trim of 12%) than the considered methods from literature. The new method generally overestimates the reduction in the pump head after trimming, and hence results less often in impeller trims that are too large when the method is used to determine the amount of trimming that is necessary in order to attain a specified head.

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References

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Figures

Grahic Jump Location
Fig. 1

Effect of trimming on the hydraulic performance. The head, flow rate, and efficiency of the untrimmed impeller are denoted by (H, Q, η), while the corresponding performance of the trimmed impeller is (H′,Q′,η′). The best efficiency points are denoted by BEP and BEP′.

Grahic Jump Location
Fig. 3

Graphical representation of the difference method. Left: Theoretical head curve Hth(Q) according to Eq. (7) and measured head curve Htest(Q); both with the original, untrimmed impeller. Right: Theoretical head curve H′th(Q) with the trimmed impeller and prediction for the head curve H′pred(Q) of the trimmed impeller; ΔH(Q) is defined in Eq. (8).

Grahic Jump Location
Fig. 2

(a) Meridional geometry with the definition of the inlet and outlet diameters, D1 and D2, respectively, and the axial width b2 and (b) planar geometry of the impeller with the definition of the blade angle β2 and the blade thickness t2; here, the number of blades Z = 5

Grahic Jump Location
Fig. 4

Left: Comparison between the experimental head curve after trimming H′test(Q) and the predicted head curve after trimming H′pred(Q) according to the geometrical scaling method, Eq. (1). Also shown is the experimental head curve Htest(Q) with the original, untrimmed impeller. Right: Error Herr(Q) in the prediction method, as defined in Eq. (10). The hatched rectangle indicates the range of flow rates between 80% to 110% of the BEP. Results given here are for the pump with the large trim of 12.23% (see Table 1).

Grahic Jump Location
Fig. 5

Left: Comparison between the experimental head curve after trimming H′test(Q) and the predicted head curve after trimming H′pred(Q) according to the difference method, Eq. (8). Also shown is the experimental head curve Htest(Q) with the original, untrimmed impeller. Right: Error Herr(Q) in the prediction method, as defined in Eq. (10). The hatched rectangle indicates the range of flow rates between 80% to 110% of the BEP. Results given here are for the pump with the large trim of 12.23% (see Table 1).

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