Slip factor is an important parameter in the hydraulic design of centrifugal pump impeller for handling viscous oils. How to extract the factor from CFD computational results and how flow rate and liquid viscosity to affect it remain unclear. In the present paper, the flip factor was estimated by means of two approaches: one is from the velocity triangles at the impeller outlet and the other is due to the impeller theoretical head of 3D turbulent viscous fluid. The velocity of water and viscous oils in the impeller and volute computed by CFD was validated with LDV measurements at the best efficiency point. The effect of exit blade angle on slip factor was clarified. It was shown that the two approaches result into two different slip factors. The factors are significantly dependent of flow rate; however, the liquid viscosity seems to take less effect on them. Volute is responsible for reduction in tangential velocity of liquid at the outlet of impeller at low flow rates. The slip factor of impeller with large exit blade angle is not sensitive to flow rate. 1. Introduction The performance of centrifugal pump handling water and viscous oils was investigated numerically by using a CFD code FLUENT based on a steady, 3D, and incompressible turbulent flow. The turbulence effect was involved with the standard turbulence model and wall roughness was taken into account with the nonequilibrium wall function in [1]. The effect of liquid viscosity on pump performance was clarified through observing the pump head and hydraulic efficiency as well as hydraulic loss coefficient in terms of flow rate. A comparison of computed and experimental overall performance of the pump was made. It was confirmed that the “sudden-rising head effect” exists and is caused from the high viscosity and certain large surface roughness. The volute results in an increasing influence on the flow around the impeller exit at a low flow rate. Slip factor is one important design parameter for deciding a correct impeller diameter of centrifugal pump. The factor can be obtained theoretically and experimentally. The typical investigations include those conducted by Kasai [2, 3], Sakai and Watanabe [4], Noorbakhsh [5], Whitfield [6], Murata et al. [7], Harada and Senoo [8], Visser et al. [9], von Backstron [10], Hassenpflug [11], Ji et al. [12], Qiu et al. [13], and so on. The slip factor depends on impeller geometry [5, 7, 9, 10, 14], flow rate [2–4, 6, 13, 15], and viscosity of the liquid pumped [16, 17]. Recently, Slip factor is increasingly estimated by using CFD approach [18–22]. Thus it is
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