KINEMATICS AND STABILITY OF DIE ENTRY FLOWS

Highly viscous material which are Newtonian in shear but also highly elastic are used to examine the kinematics and stability of die entry flows. Flow properties, which include the shear and first normal stress difference are measured at die entry flow conditions with an R16 Weissenberg Rheogoniometer. Four flow regimes are identified: vortex growth flow, asymmetric flow, rotating flow, and helical flow. The size of the secondary flow cell in vortex growth flow is successfully correlated with the fundamental fluid properties and contraction ratio. The influence of elasticity on the secondary flow in the absence of shear thinning and inertial effects is identified. The nature of the flow instability is clearly identified, its source is specified, and the conditions for its onset are quantified. A motion picture film has been made to illustrate the flow phenomena observed. © 1979.