Hydraulic Impacts on the Impeller of Vertical Axial Pumps Installed in Selected Intake Structures

Abstract

Laboratory water-intake models were used to evaluate and to optimize pump-approach flow patterns to the cooling-water pumps in thermal power stations. The intake performance was described and evaluated by means of the generally accepted criteria, such as pump-throat velocity distributions, prerotation, and vortex formation. The model intake structures were tested at a smaller scale prior to testing with an axial pump built at a larger scale. By means of the axial pump, characteristic curves (Q-H curves) were determined through an inductive flow meter and a differential pressure gage. The pump speed was varied in order to determine the influence of Reynolds and Froude numbers which were identified as the most significant parameters in water-intake modeling. In order to obtain detailed information of the mechanical impact generated by the surrounding intake structure on the pump, a vertical, high specific speed axial pump was built at Kaiserslautern University. The pump was equipped with a newly developed force measurement shaft. Strain gages were installed in the pump shaft to obtain the torque, axial thrust, the eccentricity of the axial thrust, and the radial force that comes to existence due to an unbalanced loading of the pump impeller. In addition, pump vibrations were recorded using a vibration sensor that was located on the vertical pump column. All the data were transmitted by a contactless telemetry module placed inside the shaft that rotated at a high angular speed. By means of a radio receiver connected to a computer aided data aquisition system the data were collected at high sample rates. Furthermore, various typically-used intake structures in prototype cooling-water systems were tested with and without sub-surface vortex suppressors, such as splitters and corner fillets. Mechanical impacts on the pump were quantified under these test conditions.