Digital PIV Measurement of Flow Fields in a Stirred Reactor Generated by Rushton Turbine

The velocity fields in mechanically agitated vessels were investigated using digital particle image velocimetry (DPIV ) to measure the flow field w ith in a baffled tank stirred by a Ruston turbine impeller with a large impeller to tank diameter ratio. The measurement errors due to the random fluctuations of the near-instantaneous velocity field obtained from the DPIV were minimized by using time-averaged velocity measurements with an optimum sample number. The time-averaged velocity fields were used to calculate the pumping number, vorticity, and dimension one turbulent kinetic energy. The effects of rotational speed and measuring plane position on the velocity field were also investigated. The results show that the kinetic energy in the impeller region is higher than in the bulk flow. The kinetic energy is distributed asymmetrically in the axial direction, and the asymmetry variation is a function of the rotational speed due to the influence of the free surface. Key words: stirred tank; Ruston turbine; digital particle image velocimetry (DPIV ) ; flow field