Setup and Test of a Laser Doppler Velocimeter for Investigations of Flow Behaviour of Polymer Melts |
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Authors: | Schmidt M Wassner E Münstedt H |
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Affiliation: | (1) Institute of Polymer Materials, Department of Materials Science, University Erlangen-Nürnberg, Martensstr. 7, D-91058 Erlangen, Germany; E-mail |
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Abstract: | The flow behaviour of a low-density polyethylene melt is investigated in a specifically developed flow channel by means of
Laser Doppler Velocimetry (LDV). The used flow channel is a slit die with a planar contraction of 14:1. The investigation
of the velocity fields was performed in the steady state of flow. The optics of the LDV system as well as the used frequency
analyser proved to be reliable for measurements of velocities down to 250μm/s.
By adding TiO2 tracer particles to the pellets the signal quality as well as the signal frequency were improved. It is demonstrated that
the Laser Doppler Velocimeter is suited to detect velocities of polymer melts with an error of a few per cent by comparing
the measured volume flow rate to the directly determined mass flow rate.
Using simple fluid mechanics the viscosity function is obtained by measuring only one velocity profile within the fully developed
flow in the slit die. Over a wide range of shear rates the viscosity function obtained via LDV measurement corresponds with
the viscosity function which was determined by the classical mass-flow-rate method. Both resulting viscosity functions were
additionally checked by performing measurements with a capillary rheometer.
The LDV setup described in this paper is a powerful experimental tool to investigate the flow behaviour of polymer melts.
Its accuracy and the high spatial and temporal resolution opens a way to get more quantitative insight into the flow of polymer
melts and to check the validity of model calculations.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | accuracy tests Laser Doppler Velocimetry polyethylene melts slit die velocity profiles viscosity function |
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