The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning

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dc.contributor.advisorRawatlal, Randhiren_ZA
dc.contributor.authorKotze, Tyroneen_ZA
dc.date.accessioned2014-07-31T11:09:01Z
dc.date.available2014-07-31T11:09:01Z
dc.date.issued2008en_ZA
dc.descriptionIncludes abstract.
dc.descriptionIncludes bibliographical references (leaves 121-126).
dc.description.abstractThe production of synthetic yarns requires a cost efficient process whilst simultaneously incorporating process methods which ultimately lead to a high quality fibre. A critical part of the production process is the spinning of the molten polymer into individual filaments which are brought together to form the filament bundle. During this process a quench air stream is blown across the filament bundle to aid in cooling the molten polymer. Here, heat transfer limitations may cause inter-filament property variations, which will adversely affect the quality of the yarn. This thesis focuses on the development of a model which allows for an a priori prediction of the influence of major process variables on the degree of fibre property uniformity. Fibre quality is characterised by the high degree of uniformity in the properties which affect the structural features of the yarn. Yarn morphology is dictated by the degree of crystallinity and molecular alignment of the polymer macro-molecules parallel to the fibre axis. These properties are strongly influenced by online tensile stress and local temperature which are, in turn, affected by heat transfer effects between the quench air and filament surface. A model that predicts the influence of heat transfer limitations on the uniformity of the as-spun fibre is therefore needed. Previous research in this field is limited with most work focussed on single filament model development. In this investigation, a monofilament model developed by previous workers (Jarecki et al., 2000) is integrated into a multifilament framework. This model assumes Newtonian behaviour of the polymer with viscosity strongly dependent on local temperature and crystallinity. The development of the multifilament model involves dividing the spinning zone into a number of cells, in which the filament properties are modelled using the monofilament model. The change in quench air temperature is estimated by means of an energy balance incorporating air flow terms and heat transfer through forced convection from the filament surface. A novel iteration approach is proposed in which the temperature of the quench air exiting each cell is iterated for until convergence is met. In simplifying the model, it was found that uniform quench air flow profile could be assumed, since the quench flow channel length was found to fall far short of the length required for turbulent flow to develop. However, it is known that increased contact time for heat transfer would occur if air were dragged down with the filament. Although modelling this effect is beyond the scope of the project, the heat transfer gradients are worsened by air-dragging and hence the model presented in this thesis reveals whether polymer uniformity is possible even under the best possible flow patterns. A negative result therefore indicates that non-uniformity will definitely occur.en_ZA
dc.identifier.apacitationKotze, T. (2008). <i>The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering. Retrieved from http://hdl.handle.net/11427/5304en_ZA
dc.identifier.chicagocitationKotze, Tyrone. <i>"The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering, 2008. http://hdl.handle.net/11427/5304en_ZA
dc.identifier.citationKotze, T. 2008. The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Kotze, Tyrone AB - The production of synthetic yarns requires a cost efficient process whilst simultaneously incorporating process methods which ultimately lead to a high quality fibre. A critical part of the production process is the spinning of the molten polymer into individual filaments which are brought together to form the filament bundle. During this process a quench air stream is blown across the filament bundle to aid in cooling the molten polymer. Here, heat transfer limitations may cause inter-filament property variations, which will adversely affect the quality of the yarn. This thesis focuses on the development of a model which allows for an a priori prediction of the influence of major process variables on the degree of fibre property uniformity. Fibre quality is characterised by the high degree of uniformity in the properties which affect the structural features of the yarn. Yarn morphology is dictated by the degree of crystallinity and molecular alignment of the polymer macro-molecules parallel to the fibre axis. These properties are strongly influenced by online tensile stress and local temperature which are, in turn, affected by heat transfer effects between the quench air and filament surface. A model that predicts the influence of heat transfer limitations on the uniformity of the as-spun fibre is therefore needed. Previous research in this field is limited with most work focussed on single filament model development. In this investigation, a monofilament model developed by previous workers (Jarecki et al., 2000) is integrated into a multifilament framework. This model assumes Newtonian behaviour of the polymer with viscosity strongly dependent on local temperature and crystallinity. The development of the multifilament model involves dividing the spinning zone into a number of cells, in which the filament properties are modelled using the monofilament model. The change in quench air temperature is estimated by means of an energy balance incorporating air flow terms and heat transfer through forced convection from the filament surface. A novel iteration approach is proposed in which the temperature of the quench air exiting each cell is iterated for until convergence is met. In simplifying the model, it was found that uniform quench air flow profile could be assumed, since the quench flow channel length was found to fall far short of the length required for turbulent flow to develop. However, it is known that increased contact time for heat transfer would occur if air were dragged down with the filament. Although modelling this effect is beyond the scope of the project, the heat transfer gradients are worsened by air-dragging and hence the model presented in this thesis reveals whether polymer uniformity is possible even under the best possible flow patterns. A negative result therefore indicates that non-uniformity will definitely occur. DA - 2008 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2008 T1 - The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning TI - The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning UR - http://hdl.handle.net/11427/5304 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/5304
dc.identifier.vancouvercitationKotze T. The influence of heat transfer limitations on the properties of PET yarn produced by melt spinning. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering, 2008 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/5304en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Chemical Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherChemical Engineeringen_ZA
dc.titleThe influence of heat transfer limitations on the properties of PET yarn produced by melt spinningen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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