Examination of Constitutive Equations for Polymer Solutions

Many constitutive equations for viscoelastic fluids have been proposed, but no equation describes completely the Theological behavior of viscoelastic fluids. Consequently, it is necessary to select a constitutive equation suitable for numerical analysis.In the present paper, we studied seven constitutive equations by comparing computed values with the experimental data of the viscosity η and the first normal stress coefficient ψ1 for three polymer solutions.The results obtained are as follows;(1) All the constitutive equations can qualitatively describe the rheological behavior of η and ψ1.(2) The four constitutive equations agree quantitatively with the experimental data.(3) The Bird-Carreau model agrees best with the experimental data, because the parameters α2 and λ2 of ψ1, are independent of η.