In this paper we study the transient elongational viscosity of a PIB/PB Boger fluid (fluid B) by performing both experiments and model calculations. The experimental results have been obtained by using a filament stretching device was described by van Nieuwkoop and Muller von Czernicki (J. Non-Newtonian Fluid Mech. 67 (1996) 105–123). We have been able to obtain large strains, up to a Hencky strain of 8. A plateau for the Trouton ratio of close to 104 is found while approaching a strain of 8. The plateau value appears to be independent of the strain rate history. The predictions using various multi-mode constitutive models (Giesekus, FENE-P, Hinch, FENE) show that the FENE model is the only model which predicts values for the Trouton ratio that are very close to the experiments for the whole range from strain 1 up to 8. The predictions of the models are computed with the actual strain rate as determined during the experiments in the middle of the filament. During relaxation, both the FENE-P and the FENE model perform well. In order to be able to make predictions without carrying out the relatively expensive FENE calculations, we have developed a new closed form constitutive equation. The model is based on the dumbbell theory in which the connector force used leads to a viscous stress term. The predictions of the model in transient extensional flows are very good and comparable to the FENE model.
Verhoef, M. R. J., Brule, van den, B. H. A. A., & Hulsen, M. A. (1999). On the modelling of a PIB/PB Boger fluid in extensional flow. Journal of Non-Newtonian Fluid Mechanics, 80(2-3), 155-182. https://doi.org/10.1016/S0377-0257(98)00080-9