INVESTIGATIONS ON CENTRIFUGAL PUMPS UNDER AIR ENTRAINMENT CONDITIONS T. Schäfer 1,* , A. Bieberle 1 and U. Hampel 1,2 1 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Fluid Dynamics, Bautzner Landstraße 400, 01328 Dresden, Germany 2 AREVA Endowed Chair of Imaging Techniques in Energy and Process Engineering, Technische Universität Dresden, 01062 Dresden, Germany thomas.schaefer@hzdr.de; a.biebrle@hzdr.de; u.hampel@hzdr.de ABSTRACT In this work, high-resolution gamma-ray computed tomography was applied to investigate the two-phase distribution in the impeller region of an industrial centrifugal pump. As an advanced tomographic method time-averaged rotation-synchronized computed tomography method has been successfully applied in addition to conventional radiography to investigate the internal gas-liquid two-phase flow. The formations of the gas holdups in different heights near to the shaft and in the impeller wheel, depending on the injected gas volume fraction, have been analyzed and the consequences on the pump operation have been discussed. Furthermore, internal accumulated gas holdup pattern and pump performance depending on the inlet gas volume fraction and inlet flow regimes have been investigated. Thus, influences of different flow regimes on the internal gas-holdup have been identified. Moreover, calculated gas holdup profiles in the six impeller chambers of the impeller wheel have been analyzed along selected streamlines. As a result, typical holdup profiles have been evaluated. KEYWORDS centrifugal pump, advanced -ray computed tomography, gas entrainment, phase fraction visualization 1. INTRODUCTION 1.1. Centrifugal pumps Centrifugal pumps are widely used in process industries and power engineering, e.g. in refineries as feeding pumps or in power plants in cooling circuits. In nuclear power plants they are operated in various places and particularly in safety-related functions, like emergency core cooling. In chemical industries these flow machines are used to transport inorganic and organic liquids as well. Furthermore, other applications of centrifugal pumps can be found in water treatment, oil industries, food production and agriculture, heating installations or shipbuilding industries. In general centrifugal pumps consist of an impeller and a diffusor. The rotating impeller is used to transfer the mechanical energy from the driving shaft into the fluid. This occurs by flow acceleration and flow redirection. Thus, the kinetic energy of the fluid increases. The diffusor is necessary to convert the imparted kinetic energy of the fluid into pressure energy. This leads to an increasing pressure, which drives the flow. Though simple in design centrifugal pumps offer advantages, like high operational efficiency and low energy consumption, smooth and steady operation and high reliability. They produce a very steady, 785 NURETH-16, Chicago, IL, August 30-September 4, 2015 785 NURETH-16, Chicago, IL, August 30-September 4, 2015