Flow of polyethylene melts within and into rectangular ducts investigated by laser-Doppler velocimetry [Elektronische Ressource] = Strömungsverhalten verschiedener Polyethylenschmelzen im Einlauf und im Inneren von Schlitzdüsen / vorgelegt von Daniela Hertel

Hertel

Informations

• Publié par: friedrich-alexander-universitat_erlangen-nurnberg
• Publié le: 01 janvier 2008
• Nombre de lectures: 27
• Langue: Deutsch
• Poids de l'ouvrage: 4 Mo

Extrait

Flow of polyethylene melts within and into rectangular
ducts investigated by laser - Doppler velocimetry

Strömungsverhalten verschiedener Polyethylenschmelzen im
Einlauf und im Inneren von Schlitzdüsen
-
Untersuchungen mit der Laser-Doppler Anemometrie

Der Technischen Fakultät der
Universität Erlangen-Nürnberg

zur Erlangung des Grades
DOKTOR – INGENIEUR

vorgelegt von

Daniela Hertel

Erlangen – 2008









Als Dissertation genehmigt von
der Technischen Fakultät der
Universität Erlangen-Nürnberg





Tag der Einreichung: 26.11.2007
Tag der Promotion: 10.03.2008
Dekan: Prof. Dr. J. Huber (Universität Erlangen-Nürnberg)
Berichterstatter: Prof. Dr. H. Münstedt
Prof. Dr. J.-F. Agassant (Ecole des Mines de Paris, France)
Table of contents I

Table of contents

1 Introduction........................................................................................................................ 1
2 German introduction………..............................................................................................3
3 Fundamentals……………….............................................................................................6
3.1 Rheological behaviour of polymer melts ....................................................................... 6
3.1.1 Viscous behaviour..............................................................................................6
3.1.2 Elastic ................................................................................................9
3.2 Fluid mechanics............................................................................................................ 10
3.2.1 Conservation equations....................................................................................10
3.2.2 Constitutive equations......................................................................................11
3.2.3 Flow profiles in a duct 12
3.2.4 Flow through a contraction .............................................................................. 15
3.3 Flow phenomena of polymer melts 16
3.3.1 Secondary flow.................................................................................................17
3.3.2 Main flow along the channel symmetry axis ................................................... 21
3.3.3 Three-dimensionality of the entrance flow ...................................................... 23
3.3.4 Open questions and aims with regard to the flow of polymer melts within
rectangular ducts .............................................................................................................. 25
4 Characterisation of the materials used ............................................................................. 27
4.1 Materials....................................................................................................................... 27
4.1.1 Linear low density polyethylene (LLDPE) ...................................................... 27
4.1.2 Low density polyethylene (LDPE)................................................................... 28
4.2 Molecular structure......................................................................................................28
4.3 Shear properties............................................................................................................ 29
4.3.1 Thermal stability..............................................................................................29
4.3.2 Rotational rheometry........................................................................................30
4.4 Elongational properties................................................................................................32
4.4.1 Transient elongational viscosity....................................................................... 32
4.4.2 Stationary elongational viscosity ..................................................................... 33
4.5 Elastic properties.......................................................................................................... 34
5 Experimental setup and measuring method 37
II Table of contents

5.1 Experimental setup.......................................................................................................37
5.1.1 Extrusion system..............................................................................................37
5.1.2 Flow cell and coordinate system ...................................................................... 38
5.1.3 Laser-Doppler velocimetry (LDV)................................................................... 40
5.2 Experimental procedure...............................................................................................41
5.2.1 Preliminary tests41
5.2.2 Accuracy and reproducibility of the LDV-measurements ............................... 42
5.2.3 Velocity fields in the entrance region .............................................................. 44
5.2.4 Velocity distribution along the channel axis .................................................... 49
6 Three-dimensional flow fields of the two polyethylenes ................................................. 54
6.1 Velocity profiles........................................................................................................... 54
6.1.1 Velocity profiles in the x-y-plane..................................................................... 54
6.1.2 Velocity profiles in the x-z-plane 59
6.1.3 Velocity profiles in the y-z-plane 61
6.2 Discussion.................................................................................................................... 63
6.3 Conclusions.................................................................................................................. 73
7 Entrance flow of the LDPE in the symmetry plane z = 0 in a 180°-die entry.................. 76
7.1 Secondary flow region – the vortex size ...................................................................... 76
7.1.1 Influence of outer parameters on the vortex size ............................................. 79
7.1.2 Discussion........................................................................................................84
7.2 Main flow along the channel symmetry axis ............................................................... 91
7.3 Secondary flow region – the rotational velocity ........................................................ 105
7.3.1 Influence of outer parameters on the rotational velocity................................ 106
7.3.2 Discussion......................................................................................................108
7.4 Conclusions................................................................................................................ 123
8 Velocity Overshoot of the LDPE….. …….. .................................................................. 126
8.1 Influence of outer parameters on the velocity overshoot ........................................... 126
8.2 Conclusions 131
9 Influence of the die entrance angle on the entrance flow behaviour of the LDPE ........ 132
9.1 Secondary flow region – the vortex size .................................................................... 132
9.2 Main flow along the channel symmetry axis ............................................................. 136
9.3 Secondary flow region – the rotational velocity ........................................................ 139
9.4 Conclusions................................................................................................................ 140
10 Summary and outlook .................................................................................................... 142
Table of contents III
11 German abstract.............................................................................................................. 146
Appendix ................................................................................................................................ 150
A Abbreviations and acronyms...................................................................................... 150
B Adjustment of the measuring volume within the flow channel ................................. 154
C Calculation of the ratio between the mean and the maximum velocity ..................... 157
D Influence of the die entrance angle on the entrance flow behaviour of the LLDPE .. 158
E Relationship between the vortex size and the detachment length.............................. 159
F Measured data............................................................................................................161
References .............................................................................................................................. 185
Acknowledgements ................................................................................................................ 193

Inhaltsverzeichnis V


Inhaltsverzeichnis


1 Einleitung (englisch).......................................................................................................... 1
2 Einleitung (deutsch)....................................