Bombas Axiales

Energy Conversion and Management 44 (2003) 1817–1829
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Experimental study on regaining the tangential velocity energy of axial flow pump
Durmus Kaya
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TUBITAK-MRC, Energy Systems and Environmental Research Institute, P.O. Box 21, 41470 Gebze-Kocaeli, Turkey Received 22 April 2002; accepted 3 August 2002

Abstract Axial flow pumps are widely used in a widerange of applications. Although a different range of axial pump designs can be observed, axial flow pumps are usually designed for high flow rate and low pressure applications. In this study, two different axial flow pump impellers with and without guide vanes are experimentally investigated. The impellers used in the experiments consist of three and four blades. The guide vanes have seven vanes. Theexperimental set up mainly includes an axial pump, electrical drive motor, storage and calibration tanks and control system. Different impellers are attached to the pump, and the pump characteristics are obtained. As a result of the investigation, it is found that using guide vanes and regaining the tangential velocity energy of the pump improves the total pump efficiency about 3%. Also, the maximumefficiency improvement is obtained at 1000 rpm using guide vanes with a four blade impeller as 65.3%. Ó 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Axial flow pumps; Impeller; Efficiency; Guide vanes; Pump characteristics

1. Introduction In a hydraulic machine, energy is transformed from one form into another, e.g. mechanical energy into an output of fluid energy (in pumps and compressors)or an input of fluid energy into mechanical energy (turbines). As a general rule, axial flow pumps are usually selected for pumping large volumes of water against relatively low heads (1–15 m). The rotating element of an axial flow pump has the shape of a propeller. It is often mounted in a pipe or duct, and the fluid passes in an axial direction through the pump. It is not deflected away from theaxis as with centrifugal pumps.
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Tel.: +90-262-641-23-00x3924; fax: +90-262-641-23-09. E-mail address: durmus.kaya@posta.mam.gov.tr (D. Kaya).

0196-8904/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 9 6 - 8 9 0 4 ( 0 2 ) 0 0 1 8 7 - 5

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D. Kaya / Energy Conversion and Management 44 (2003) 1817–1829

Fig. 1. Velocity vector diagrams for anaxial flow pump.

The basic elements of the pumps are the impeller and guide vanes, which are usually fitted after the impeller. The cross section of the blades is in an aerofoil form, and the relative flow pattern is in many ways similar to flow around the wing of an aircraft [1]. Fig. 1 shows the flow through an axial flow pump on the basis of velocity vector diagrams at the inlet and outlet sections.Energy transfer in axial flow pumps differs from that of centrifugal pumps in the following points: • the fluid is not accelerated by centrifugal forces since it passes axially through the impeller, and therefore, the tangential velocity of the impeller does not change for a given stream filament between the inlet and outlet (u1 ¼ u2 ); • no real channel flow between blades is formed as withcentrifugal pumps, hence, the transformation of kinetic energy into pressure due to expansion of channel cross sectional area does not take place with axial flow pumps; • similarly, the blades are not much curved, and the deflection of flow is small. For these reasons, the total head increase for axial flow pumps is small compared to that of centrifugal pumps. Energy transfer takes place mainly through thetangential acceleration of the fluid due to the impact of the impeller, which can be seen by the fact that the fluid leaves the impeller in a vortex (C2 is not in the axial direction). Pumps are sometimes offered with open or closed impellers. Closed impellers have shrouds on both sides of the vanes, while open impellers have only one shroud opposite the impeller entrance (see Fig. 1). Advantages of...