Experimental Study on the Constant Speed Squeezing Flow of Polymer Solutions : Measurement and Analysis of Forces Generated in the Separating Motion

Abstract

Transmitting forces generated in a reverse squeezing film were measured and calculated when an upper spherical surface was caused to separate relative to a lower flat plate at a constant speed. The experimental results obtained were similar to those for normal squeezing flows, despite the opposite squeezing motion. Namely, no elastic effects were shown in the forces measured for PEO solutions. In the case of Separan solutions, however, the measured force overshoots the force estimated by consideration of viscous stress alone at the inception of reverse squeezing. In addition, the maximum rates of the overshoot were nearly equal to those obtained in normal squeezing under the same starting conditions expect for the direction of motion. A constitutive equation yielding the stress overshoot was used in the analysis of these flows under the condition where shear stress dominates. The analytical results approximately agree with the experimental ones for normal and reverse squeezing flows.