Shear Rates in Mixing of Viscoelastic Fluids by Helical Ribbon Impeller

One of the basic problems in the mixing of non-Newtonian fluids and especially diluted polymer solutions is the determination of the prevailing shear rates during the mixing process. The significant method of Metzner and Otto for calculation of the effective shear rate is limited to the laminar region and it is not valid in the transition region. In this article, the local shear rate and the Metzner-Otto method for helical ribbon impeller have been studied using laser Doppler anemometry (LOA) for viscoelastic liquids. It is also shown that the variation of the local shear rate against the impeller speed is better correlated by a power equation, i.e., y= k s.Nb· in the transition region, i.e., 70 Re 6700. In addition, a correlation between the improved coefficient, k s and the elasticity number of the viscoelastic liquid is given that can be helpful in designing the mixing of viscoelastic as well as inelastic non-Newtonian fluids by means of relating the rheological properties to the kinematical and dynamical parameters of the mixing process.