Feedpipe backmixing in an agitated vessel was investigated using a newly developed conductivity technique. By this technique, the onset of feedpipe backmixing could be detected and the penetration depth of the vessel fluid into a feedpipe was determined. For a give feedpipe flowrate, critical agitator speeds to eliminate feedpipe backmixing were determined using Rushton six-bladed disk turbine impeller (6BD) and high efficiency, axial-flow type 3- bladed impeller (HE-3) of 8.89 and 12.70 cm diameters in 11.2 liter reactor. The ratio of the feedpipe velocity to the critical agitator speed (v_f/v_t) was determined as a function of feedpipe
Reynolds number (N_Ret). The conductivity technique was successful either in the laminar regime, the transitional regime, or in the turbulent regime in the feedpipe.