Mixing Performance Of Coaxial Mixers In A Stirred Tank With High Viscosity Fluids

The power characteristic and mixing performance with coaxial mixerswere studied in the standard elliptical bottom tank with diameter of0.48m.Experiments with corn syrup and CMC solutions (Sodium Carboxy MethylCellulose) as the Newtonian and non-Newtonian fluids were carried out withthe liquid level equaling to tank diameter. Four coaxial mixers were combinedwith either CBY or Pfaudler as the inner impeller, and Anchor or HelicalRibbon as the outer one.Results show that the Metzner constant, Ks of HR increases from56to113, corresponding to n of0.492in3%CMC solution and0.727in2%CMCsolution, respectively, in good agreement with the previous results.Researches on the interaction between inner and outer impellers ofcoaxial mixers reveal that in high viscosity fluid, the interaction between innerand outer impellers depends on both the overlapping range of the flow areascaused by the inner and outer impellers and their power consumptions. Whenthe range of overlapping is big enough, the inner impeller with higher powerdraw plays the leading role in determining the fluid pattern in the entire tank,which makes sure that using the Ks of the inner impeller as that for the coaxial mixer becomes acceptable.The experimental power consumption data were calculated based on theequations proposed by Bao et al in2011, and the generalized power numberswere compared for different coaxial mixers.The mixing performance of four coaxial mixers were compared based onthe mixing time, dimensionless mixing time and mixing rate for differentspecific power inputs or Reynolds numbers. Results show that Pfaulder-HR isthe optimized combination among those four coaxial mixers in this work,which can provide the shortest mixing time at the given power input.The numerical simulations of the fluid flow and power consumptionswith coaxial mixers were also carried out by using the CFD Code CFX.