Assessment of elongational stresses of dilute polymer solutions and a related examination of some constitutive equations.

Abstract

Elongational stresses of dilute polymer solutions have been assessed by utilizing the flow through small orifices under the condition of no vortex upstream of the orifice plane. The flow was approximated with a linearly converging flow toward an apex of a cone, its propriety being confirmed by the measured velocities, and the elongational stresses were determined from the measured thrusts of dilute polymer solutions. On the other hand, elongational stresses were theoretically obtained with the modified Maxwell model and the second order fluid. A comparison was made between the experimental and the theoretical results and the following points were clarified ; below the elongational rate 2×104(s-1) the modified Maxwell model gives elongational stresses close to the experimentally determined ones, but above the elongational rate it deviates from the experimental results. the second order fluid is not sufficient to describe the stresses in this kind of elongational flow and an acceleration term such as δ2eij/δt2 may be necessary in this case.