Characterization and Prevention of Vortices at Centrifugal Pump Intakes

BMBF-Project SAVE: “Safety-relevant Analysis of the Performance of Centrifugal Pumps, Valves and Inlet Geometries, including stress-related Events“

(FKZ: 02NUK023A)

Motivation

  •  The occurrence of vortices in cooling water reservoirs poses a high safety risk for the safe operation of cooling systems.
  • Vortices lead to entrainment of angular momentum and gas in the cooling pumps which reduces or interrupts the flow of cooling water and damages pump inlets.
  • To prevent critical vortex formation the empirical ANSI correlation is often used for the determination of the submergence h:

                       



Objectives

  • investigation of the influences of different parameters on vortex formation
  • optimization of existing analytical models and design recommendations for the prevention of air entrainment.

Experimental Set-up

For the investigation of vortices in cooling water reservoirs a pilot plant (VR = 50 m³) was built in the testing facility at the Institute of Multiphase flows.

  • The pump inlet is of the same scale as the pump inlet of a light-water reactor (dPipe = 0.2 m)
  • Maximum capacity of centrifugal pump: 110 kW
  • Max. volume flow rate 1300 m³·h-1.

Additionally a laboratory scale model of the plant was built from acrylic glass with a downsize factor of 13.3. In this model all experimental setups were tested before the implementation in the model plant.

Procedure

  • Experimental investigation of vortices and the occurring air cores are realized to analyze the influences of volume flow rate, induced angular momentum and position of the pump inlet.
  • High-speed PIV measurements are conducted to determine the tangential velocity field inside the vortices from a horizontal plane at different heights.
  • All experiments are also carried out in a laboratory scale model of the plant to observe scaling effects.
  • Additionally CFD simulations are made to validate the semi-analytical vortex model of Burgers-Rott.
    • Model assumptions:


       
    • Resulting azimuthal velocity
           

Experimental Results

First experiments show that the submergence h and the angular momentum are the dominant factors for the forming of an air core vortex. Further experiments will be conducted to quantify the influences.

                                                              

Numerical Results

The simulations show qualitatively good agreement with the Burgers-Rott model. Quantitatively the air cores are under-estimated by the simulation.