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Modelling of counter rotating twin screw extrusion

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  1. Tez No: 403097
  2. Yazar: ALİ GÖĞER
  3. Danışmanlar: DR. JHON VLACHOPOULOS, DR. MICHAEL R. THOMPSON
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya Mühendisliği, Chemical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2013
  8. Dil: İngilizce
  9. Üniversite: McMaster University
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 145

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Özet (Çeviri)

Intermeshing counter-rotating twin screw extruders (ICRTSE) are used extensively in the polymer processing industry for pelletizing, devolatilization and extrusion of various plastic products. ICRTSE have better positive displacement ability and are more suitable for shear sensitive materials compared to other types of twin screw extruders. The present study started with an extensive literature search of both co-rotating and counter-rotating twin screw extruders. Surprisingly, it was noticed that several authors have reported negative pressure (as large as -13bar) in the simulation of twin screw extruders. Of course, negative pressure is meaningless. It is presented that negative pressure was due to the poor choice of boundary conditions. Several suggestions were provided to explain how to overcome this problem. The objectives of this thesis are to understand the flow mechanism and the effects of screw geometries and processing conditions in the conveying element of ICRTSE. This is done by two different methods. First, a simple flow model based on a volume of the conveying element of ICRTSE was used to calculate flow rate. Since ICRTSE do not give complete positive displacement, the various leakage flows were identified and taken into account in the simple flow model. Although the simple flow model provided reasonable results in terms of flow rate, computer simulations were found necessary due to the limitations of simple flow model. Second, a 3D computer simulation of ICRTSE was developed for various screw pitch lengths, ratios of flight width-to-channel width and the screw speeds. Both Newtonian and non-Newtonian fluids were examined. A quasi-steady state finite element method was used to avoid time dependent moving boundaries. A number of sequential geometries were used to present a complete screw rotation in the ICRTSE. The flow behaviour in the conveying element of ICRTSE was characterized by its axial velocity distribution and flow rate. In addition, dispersive mixing in the conveying element of ICRTSE was characterized by using shear stress distribution and a mixing parameter , which quantified the elongational flow components. Comparison of flow behaviour and dispersive mixing were also discussed for different screw pitch lengths, ratios of flight width-to-channel width and screw speeds. It was shown the simple model based on geometrical parameters for pumping behaviour give reasonable prediction of flow rate. It was found that determination of negative pressure should be taken into account in numerical simulations. The pumping efficiency is influenced positively by the ratio of flight width-to-channel width but it is affected negatively by the screw pitch length. It is negligibly changed with screw speed. Finally, the dominant flow is shear flow in ICRTSE and therefore, dispersive mixing capacity is very limited due to a lack of elongational effects.

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