Can extensional viscosity be measured with opposed-nozzle devices?

Low-flow limit in slot coating of dilute solutions of high molecular weight polymer

“…The breaks between sets of points associated with each solution are where the nozzle diameter was changed. This sensitivity of the measurements to the nozzle diameters has been reported before (see [8]). The apparent extensional viscosity could not be measured at lower apparent extension rate because the torques generated were below the range of the sensor.…”

“…Eq. (8). The discrete version of the mapping equations is generally referred to as mesh generation equations.…”

Modelling the new stress for improved drag reduction predictions of viscoelastic pipe flow

“…The present turbulence model, and that of Cruz and Pinho [12], were calibrated on the basis of the measurements of the extensional viscosity made by Escudier et al [13] using opposed jet rheometry. This technique is known to have deficiencies [21], but is still the best technique available to measure the extensional viscosity of dilute polymer solutions of low consistency over a wide range of strain rates. Simultaneously, the DNS studies are based on a constitutive model whose rheology has not been fully compared with that of real fluids, especially on what concerns extensional rheology, so statements of good performance of DNS based on comparison with experiments must also be critically assessed.…”

Effect of polymer–surfactant interactions on elongational viscosity and atomization of peo solutions

“…Hermansky and Boger [27] attributed these deviations from constant elongational viscosity with a Trouton ratio of 3 to the effect of fluid inertia, and they developed an empirical correction method. Subsequent experiments and theoretical analysis by Dontula et al [29] show that other fluid mechanical force terms, such as shear stresses acting on the nozzle surfaces and viscous dissipation losses outside the extensional flow field, are comparable in magnitude to the inertia term. Dontula et al also identify numerical errors in the original formula of Hermansky and Boger, and they derive a revised formula for correcting opposing jet elongational viscosities, although they caution that their formula may not always be reliable.…”