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

Abstract

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.

Numerical Investigation on Bubble Distribution of a Multistage Centrifugal Pump Based on a Population Balance Model

“…The homogeneous flow model does not consider the slip velocity [26] between the gas and liquid phases. As the gas volume fraction increases, the slip velocity between the gas and liquid phases also increases.…”

“…The numerical simulation results of the inhomogeneous flow coupled with the bubble size of 0.1 mm are larger than the experimental values, whereas the numerical simulation results of the inhomogeneous flow coupled with the bubble size of 0.2mm are lower than the experimental values at C2 and C3, but higher than the experimental values at C4, C5, and C6. The homogeneous flow model does not consider the slip velocity [26] between the gas and liquid phases. As the gas volume fraction increases, the slip velocity between the gas and liquid phases also increases.…”

Improvement of the design of hydraulic transport devices for the transport of hydroabrasive media in the enrichment industry

“…The first includes such means of protection as dynamic balancing, antiphase synchronization, changing the nature of disturbing influences, changing the structural elements of the source of excitation, changing the frequency of vibrations, etc. They are used, as a rule, at the stage of designing and manufacturing of equipment [22].…”

“…Installation of machines on spring shock absorbers is more effective than on rubber shock absorbers, as it provides lower natural frequencies of vibrating mechanism vibration [22].…”

Theoretical research of hydraulic turbine performance based on slip factor within centripetal impeller

“…[7][8][9][10] In addition to the calculation formulas of slip factor which are fit for singlephase fluid, it also has the calculation formula of slip factor which is fit for two-phase flow. 11 It also has slip phenomenon in some prime motors, for example, hydraulic turbine and steam turbine. Their slip values are different for the working machine.…”