Experimental velocity distribution measurements of high density polyethylene flowing into and within a slit

Abstract

Using the Laser doppler technique we report experimental velocity profile measurements of molten polyethylene flowing into a slit die. Our experimental measurements are restricted to the centreline of the flow and three transverse sections within the slit. The results indicate that with the exception of a high flowrate centreline velocity overshoot, the normalised velocity profiles are relatively insensitive to both temperature, polymer grade and flowrate. We have also carried out an analysis and simulation to establish the effect on velocity measurements of both velocity gradients and solid boundaries within the probe volume of the intersecting laser beams used to measure the velocity profiles. Our results indicate that for our own experimental conditions we might expect to measure a finite velocity at the wall and that the presence of velocity gradients will not significantly effect the time dependence of the auto correlogram.