An appraisal of the exit pressure method for normal stress measurements

A numerical experiment has been carried out to assess the errors involved in using Han’s exit pressure method for the determination of the first normal stress difference with a slit die. The creeping flow equations for a viscoelastic fluid model have been solved using the finite element method. The calculated exit pressures are used in the determination of normal stresses and are compared to those obtained directly from the constitutive model. The results show that the exit pressure method gives reasonably accurate estimates of the first normal stress difference.