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TECHNICAL PAPERS

Slip Factor for Centrifugal Impellers Under Single and Two-Phase Flow Conditions

[+] Author and Article Information
José A. Caridad, Frank Kenyery

Laboratorio de Conversión de Energía Mecánica,  Universidad Simón Bolívar, Caracas, Venezuela

J. Fluids Eng 127(2), 317-321 (Oct 12, 2004) (5 pages) doi:10.1115/1.1891153 History: Received February 18, 2004; Revised October 12, 2004

Throughout the history of turbomachines investigators have tried to develop reliable methods for prediction of centrifugal pump behavior. Among the parameters available to estimate the performance of this kind of machine is the slip factor. In spite of being regarded as a variable of great significance in the analysis of turbomachinery, there seem to be a misconception regarding its concept and application. Indeed, empirical correlations have been widely used to estimate the slip factor, even in the case of two-phase flow applications, where it has not been investigated. Moreover, these correlations provide a constant value of the slip factor for a given impeller only at the best efficiency point, which is an important restriction to the pump performance prediction, considering that slip factor varies with the pump flow rate. In this study, three-dimensional computational fluid dynamics simulations were carried out on an impeller of known geometry (NS=1960) from which values of slip factor were calculated for both single- and two-phase flow (water and water-air). These results include curves of the slip factor as a function of the specific capacity and the gas-void fraction. Additionally, results for the slip factor in the case of single-phase flow (water) are given for various centrifugal impellers (NS=1157, 1447, 1612, and 3513) in order to illustrate the influence of the flow rate on this parameter. Finally, based on the numerical results, a methodology for prediction of the pump head is presented. Excellent agreement with experimental results has been found. This paper attempts to contribute to a better understanding of the fluid dynamics within centrifugal pump impellers and to shed more light on the path that prediction models should follow in the future.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Impeller discharge velocity diagrams

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Figure 2

Slip factor for different GVF as a function of the specific capacity (NS=1960)

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Figure 3

Theoretical head for different GVF as a function of the specific capacity (NS=1960)

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Figure 4

Slip factor for different specific speeds as a function of the specific capacity

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Figure 5

Hydraulic losses of the impeller for different GVF as a function of the specific capacity

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Figure 6

Hydraulic losses of the diffuser for different GVF as a function of the specific capacity

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Figure 7

Comparison between numerical simulations and experimental results for different gas-void fractions (NS=1960)

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Figure 8

Comparison between numerical simulations and experimental results for different gas-void fractions (NS=1960)

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Figure 9

Comparison between numerical simulations and experimental results for different gas-void fractions (NS=1960)

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