Further investigation of the effect of elongational viscosity on entrance flow

Anew model for strain-rate dependence of elongational viscosity of a polymer is introduced. The proposed model can capture the initial strain thickening, which is followed by a descent in elongational viscosity as the elongation rate is further increased. Effect of the four rheological parameters in the new model on a 4:1 entrance flow is analyzed. It is confirmed that the entrance pressure loss and recirculating vortices in an entrance flow grow significantly as the Trouton ratio is increased. The center-line velocity near the abrupt contraction in a 4:1 entrance flow is found to overshoot its value for a fully developed flow in the downstream channel, if the Trouton ratio has a local minima beyond the Newtonian limit of the polymer.