Evaluation of Planar Elongation Viscosity for Low Viscous Fluids Using Two-Dimensional Converging Channel Piston Technique

The planar elongation viscosity is one of the important properties on the processes for film formation and blow formation. In this study, a new technique to evaluate planar elongation viscosity for low viscous fluids is investigated. To generate the planar elongation flow, a rectangular cylinder piston with two-dimensional converging channel is pushed into a reservoir. The sample fluid is filled in the reservoir. The rectangular piston is inserted into the reservoir at a constant velocity by an electrical actuator. The fluid is pushed out through the two-dimensional converging channel in the piston. The elongation rate in the converging channel is a function of the velocity of the piston. The planar elongation stress is measured by the flow-birefringence method. The evaluated planar elongation viscosity of a Maxwell fluid is almost four times larger than shear viscosity and it shows this technique is appreciable accurately to evaluate the planar elongation viscosity.