A novel conductivity technique was developed to detect penetration depth of the vessel fluid into the feedpipe. For a given reactor geometry, critical agitator speeds were experimentally determined at the onset of feedpipe backmixing using Rushton 6 bladed disk turbine (6BD) and high efficiency axial flow type 3 bladed (HE-3) impellers. The ratio of the feedpipe velocity to the critical agitator speed (vf/vt) was constant for either laminar or turbulent feedpipe flow regimes. Compared to the results of fast competitive reaction, feedpipe backmixing had to penetrate at least one feedpipe diameter into the feedpipe to significantly influence the yield of the side product. However, higher vf/vt than that for L/d = 0 (position at the feedpipe end) of the conductivity technique is recommended to completely eliminate feedpipe backmixing in conservative design criteria. The conductivity technique was successful in all feedpipe flow conditions of laminar, transitional and turbulent flow regimes.

Abstract
 1. Introduction
 2. Materials and Methods
 3. Results and Discussion
  3.1. Variation of critical agitator speed, NC, withfeedpipe Reynolds number, NRet
  3.2. Trend of vf/vt vs NRet
  3.3. Effect of system geometry (G/D and D/T) onthe feedpipe backmixing
  3.4. Comparison of the results with those of thedye technique
  3.5. Comparison of the results with Bourne’s reactiondata
  3.6. Comparison of the results with those from thefast competitive reaction of this investigation
 4. Conclusions
 Nomenclature
 References

• Jeong-Gook Jang(Department of Energy Environmental Engineering, Dongseo University)
• Myung-Chan Jo(Department of Advanced Materials Engineering, Dongseo University) Corresponding Author