Experimental determination of conditions to eliminate feedpipe backmixing

Mixing at the molecular scale (micromixing) is important for fast competitive-consecutive reactions to suppress competing side reactions in mechanically-agitated reactors. Intense micromixing can be achieved by locating the feedpipe close to the impeller blade tips, which is the most turbulent region of the vessel. However, the high turbulence can also cause backmixing of the vessel contents into the feedpipe where the turbulence level is lower than that outside the feedpipe. Feedpipe backmixing can result in increased levels of by-product formation and lowering of the yield of the primary reaction.; In the present study, a conductivity technique, using NaCl in water, was developed and used to detect feedpipe backmixing and to determine the depth of the penetration of feedpipe turbulence from the vessel into the feedpipe.; Six-bladed disk turbine and HE-3 impellers of 8.9 and 12.7 cm diameters were used. The diameter of the vessel used in this experiment was 24.27 cm and the liquid level was 24.13 cm. The vessel was full of liquid during operation. The inside diameter of the glass feedpipe was 0.95 cm. Tap water was used as the vessel fluid.; The ratio of feedpipe velocity to impeller tip speed ({dollar}rm vsb{lcub}f{rcub}/vsb{lcub}t{rcub}{dollar}) was constant for laminar flow ({dollar}rm Nsb{lcub}Ret{rcub} 3,000{dollar}) in the feedpipe. The results indicate that it was more difficult for the vessel fluid to penetrate into the feedpipe counter to laminar flow than counter to turbulent flow.; The range of {dollar}rm vsb{lcub}f{rcub}/vsb{lcub}t{rcub}{dollar} to eliminate feedpipe backmixing is (for L/d = 0):(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)...