Study of High Deborah Number Flow of Polyisobutylene in Square Die

摘要

A large capacity RAM extruder was designed which provides the opportunity to study high Deborah number (D) flows, with D < 1, 000. A modified version of particle image velocimetry was developed to enable the measurement of the velocity field in dies of arbitrary cross section. During the measurement process, tracer particles were simultaneously illuminated by both a focused laser beam locally and a lamp globally. Only those particles that passed through the laser beam were taken into account. The beam was scanned to achieve full field measurements. This method of measurement allowed us to find the location of a particle in the direction of the optical axis of the lens, i. e. that which makes the particle image on the CCD detector of the video camera. A device employing this method was designed and used to measure velocity profiles. The results of these measurements in two cross sections of the square die, at three values of pressure, are presented. The velocity was defined as the ratio of displacement to the elapsed time during which this displacement occurred. Errors in measurements of the coordinates and the observation time of particles were estimated as +- 20 #mu#m and less than 0.1%, respectively. A large plateau in the axial velocity profile was found at relatively small Deborah numbers, e.g. D approx = 28. In flows with higher Deborah numbers, e. g. D approx = 766, an almost flat velocity profile was detected. Two components of velocity, one longitudinal and one transversal, were measured simultaneously. However, the transversal component appeared to be less than the error of measurements and less than 1% of the axial velocity.