Instability of Jets of Non-Newtonian Fluids

The instability of jets of some non-Newtonian fluids under the influence of externally controlled disturbances was studied. Dispersion curves were generated over a range of frequencies. Jets of a 0.1% solution of Carbopol in water, a viscoinelastic fluid, showed a breakup pattern similar to that of jets of water. The dispersion curve matched a viscosity intermediate to the zero shear viscosity of the solution and the viscosity that corresponds to the average shear rate in the tube. Subject to external disturbances, jets of Separan solutions showed a remarkably ordered and regular pattern. On jets of 0.1% Separan, sinusoidal wave formation was absent and a ligament-droplet configuration formed from the outset. On the less elastic 0.05% Separan jets, there is an initial region in which sinusoidal waves grow exponentially; the growth is later arrested and a ligament-droplet configuration results. In the initial region the growth rates are about equal to the growth rates that a jet of a Newtonian fluid of the same zero shear viscosity would develop. The ligaments that form on jets of Separan are shown to undergo a stretching motion accounting in part for their unusual stability.