Interfacial stability of multilayer viscoelastic fluids in slit and converging channel die geometries

Interfacial stability of stratified Oldroyd-B liquids with constant and shear rate dependent viscosity in slit and converging channel die geometries has been examined by utilizing both asymptotic and numerical techniques. To elucidate the mechanisms by which shear thinning viscosity and elasticity influence interfacial stability, neutral stability contours in the parametric space of viscosity, depth, and elasticity ratio as well as interfacial tension and Reynolds number have been constructed. Our results indicate that elasticity and viscosity stratification as well as inertial forces affect the stability of the interface at all disturbance wavelengths. Moreover, it is found that neutral stability contours are substantially altered in converging channel flows. Overall, our analysis indicates that under certain physical (i.e., viscosity and elasticity ratio) and geometric conditions (i.e., depth ratio and channel convergence) stable regions at all disturbance wavelengths can be attained. Hence, based on this analysis guidelines for stable coextrusion of viscoelastic fluids can be provided.