Chinese Journal of Chemical Engineering, Vol.9, No.1, 77-83, 2001
Investigation of the viscoelastic effect on the Metzner and Otto coefficient through LDA velocity measurements
The Metzner and Otto correlation is the single practical method for incorporating non-Newtonian effects in the mixing process. In this article, the Metzner and Otto's idea, the role of viscoelasticity on the Metzner and Otto coefficient, k(s), effects of how regime on k(s) and the determination of k(s) for Rushton turbine impeller have been studied using the direct method of the laser Doppler anemometry (LDA) velocity measurement for the case of viscoelastic liquids. The normalised mean tangential velocity profiles are independent of Rushton turbine impeller speeds. Contrary to literature findings, it is shown that the variation of local shear rate against the impeller speed is better correlated by the power equation, i.e. (gamma )over dot = k(s)'.N-b', in the transition region, i.e. similar to 30 < Re
Keywords:viscoelastic;mixing;Rushton turbine impeller;laser Doppler anemometry (LDA);Metzner and Otto coefficient