NUMERICAL EVALUATION OF A METHOD FOR DETERMINING EXTENSIONAL VISCOSITY OF FLUIDS USING CONTRACTION FLOW-ANALYSIS

We report an evaluation of the use of Binding's method (Ref 11) for de termining extensional viscosity values from capillary die rheometry en trance pressure drop data. A constitutive relation defining the fluid' s rheological behaviour is first postulated, from which the pressure d rop in a contraction region is calculated by numerical simulation for a range of flow rates. Extensional viscosity estimates axe then made f rom the simulated pressure drop data using Binding's method, and these estimates are compared with the exact extensional viscosity determine d from the constitutive relation. A highly accurate augmented spectral method is used to perform the numerical simulation. The Binding estim ates obtained are good for certain types of fluid, but poor for others . A simple empirical correction of the Binding method, however, is fou nd to give good agreement in all the cases studied.