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 is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Bagley, E.B. and Birks, M., ‘Flow of polyethylene into a capillary’, Journal of Applied Physics 31(3), 1959, 556–561.
Boger, D.V. and Walters, K., Rheological Phenomena in Focus, Elsevier Science Publishers, Amsterdam, 1993.
Durst, F., Melling, A. and Whitelaw, J.H., Principles and Practice of Laser-Doppler-Anemometrie, 2nd edition, Academic Press, New York, 1981.
Feigl, K. and Öttinger, H.C., ‘The flow of a LDPE melt through an axisymmetric contraction: A numerical study and comparison to experimental results’, Journal of Rheology 38(4), 1994, 847–874.
Feigl, K. and Öttinger, H.C., ‘The flow of a LDPE melt in a planar contraction: A numerical study and comparison to experimental results’, Journal of Rheology 40(1), 1996, 21–35.
Galt, J. and Maxwell, B., ‘Velocity profiles of polyethylene melts in tubes’, Journal of Polymer Science 62, 1962, 50–53.
Galt, J. and Maxwell, B., ‘Velocity profiles of polyethylene melts’, Modern Plastics 42, 1964, 115–132.
Giesekus, H., ‘Secondary flows in viscoelastic fluids – A retrospect’, Applied Rheology 6(4), 1996, 155–165.
Giesekus, H. and Langer, G., ‘Die Bestimmung der wahren Fließkurven nicht-newtonscher Flüssigkeiten und plastischer Stoffe mit der Methode der repräsentativen Viskosität’, Rheologica Acta 16, 1977, 1–22.
Kramer, H., ‘Geschwindigkeitsfelder und Deformation bei der Strömung einer Polyethylen-Schmelze durch eine Schlitzdüse’, Ph.D. Thesis, ETH Zürich, 1993.
Kramer, H. and Meissner, J., ‘Application of the laser doppler velocimetry to polymer melt flow studies’, in Proceedings of the 8th International Congress of Rheology, Vol. 2, Fluids, G. Astarita, G. Marucci and L. Nicolais (eds.), Plenum, New York, 1980, 463–468.
Knobel, B., ‘Untersuchung der Einlaufströmung einer Polyethylenschmelze in eine Düse von kreisförmigen Querschnitt mit der Laser-Doppler-Anemometrie’, Ph.D. Thesis, ETH Zürich, 1991.
Lawler, J.V., Muller, S.J., Brown, R.A. and Armstrong, R.C., ‘Laser-Doppler-velocimetry measurements of velocity fields and transitions in viscoelastic fluids’, Journal of Non-Newtonian Fluid Mechanics 20, 1986, 51–92.
Mackley, M.R. and Moore, I.P.T., ‘Experimental velocity distribution measurements of high density polyethylene flowing into and within a slit’, Journal of Non-Newtonian Fluid Mechanics 21, 1986, 337–358.
Münstedt, H., Kurzbeck, S. and Egersdörfer, L., ‘Influence of molecular structure on rheological properties of polyethylenes; Part II: Elongational behaviour’, Rheological Acta 37(20), 1998, 21–29.
Münstedt, H., Schmidt, M. and Wassner, E., ‘Stick and slip phenomena during extrusion of polyethylene melts as investigated by laser-Doppler velocimetry’, Journal of Rheology, 2000, accepted for publication.
Ramamurthy, A.V., ‘Velocity measurements in the entry region of a capillary rheometer’, Journal of Rheology 24(2), 1980, 167–188.
Ruck, B., Laser-Doppler-Anemometrie, AT-Fachverlag, Stuttgart, 1987.
Schmidt, M., Wassner, E. and Münstedt, H., ‘Investigations of the converging flows of low-density polyethylenes by LDV’, in Proceedings of the Fifth European Rheology Conference, I. Emri and R. Cvelbar (eds.), Steinkopff, Darmstadt, 1998, 495–496.
Tordella, J.P., ‘Capillary flow of molten polyethylene – A photographic study of melt fracture’, Transactions of the Society of Rheology 1, 1957, 203–215.
Wassner, E. and Münstedt, H., ‘Investigations of flow instabilities on high-density polyethylene by LDV’, in Proceedings of the Fifth European Rheology Conference, I. Emri and R. Cvelbar (eds.), Steinkopff, Darmstadt, 1998, 173–174.
Wassner, E., Schmidt, M. and Münstedt, H., ‘Entry flow of a PE-LD melt into a slit die: An experimental study by Laser-Doppler-Velocimetry’, Journal of Rheology 43(6), 1999, 1339–1353.
Yeh, Y. and Cummins, H.Z., ‘Localized fluid flow measurements with an He-Ne-laser-spectrometer’, Applied Physical Letters 4(10), 1964, 176–178.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Schmidt, M., Wassner, E. & Münstedt, H. Setup and Test of a Laser Doppler Velocimeter for Investigations of Flow Behaviour of Polymer Melts. Mechanics of Time-Dependent Materials 3, 371–393 (1999). https://doi.org/10.1023/A:1009820500869
Issue Date:
DOI: https://doi.org/10.1023/A:1009820500869