| The dual-feed rotor spinning system is a new rotor spinning innovation that can realize dual sliver feeding,dual sliver opening simultaneously,and finally integration of two slivers into one yarn.It has the advantages that two or more slivers with a significant difference in performance can be blended satisfactorily,with a good combing and uniform mixing of different slivers.However,since the dual-feed rotor spinning unit is currently under development,only little studies have been reported on the airflow characteristics,the fiber/airflow interactions and the rotor spinning mechanism in the rotor spinning unit.Hence there is a lack of theoretical basis for the optimization of the dual rotor spinning unit structure and the applications of blended yarns.Also,understanding the flow domain is somewhat challenging since the yarn forming process takes place in an enclosure which makes it a significant task to undertake.In this thesis,we employed numerical and computational modeling based on FLUENT by utilising computational fluid dynamics technique to study the airflow field and the effects of the dimensions,rotor pressure,vortex generation and turbulence on it,and finally the relationship between the airflow field and the yarn spinning process and hence yarn properties.The work of the dissertation covers four parts.The first part is to develop,calculate and analyze the airflow field in the dual feed rotor spinning channel.The second part is to compare the airflow field and its relationship with yarn properties between the dual-feed and the conventional model.The third part is to verify the simulation results.The final part is to analyze the effect of the parameters on the blended yarns experimentally.In the first step,we constructed a numerical model of the dual-feed rotor spinning unit.The model diagram was designed in SOLIDWORKS 2016 x64 Edition by considering the exact dimensions of the machine to represent the model accurately.For comparison purposes,the conventional model was also designed during this stage.The governing equations are firstly developed and the standard k-? is adopted for this study.The discrete governing equations obtained by the second-order upwind scheme are calculated using the SIMPLE algorithm.The model diagrams were then exported to ANSYS FLUENT package,thus obtaining the airflow field in the spinning channel.In the initial steps,this work extensively analyses the dual-feed model with a focus on the effect of airflow characteristics in relation to machine dimensions,negative pressure,vortical generation,Reynolds number,stream traces and turbulent viscosity.Additionally,we investigated the correlation between the yarn properties and the airflow in the dual-feed rotor spinning machine.Results demonstrate that the turbulence strength and Reynolds number increased with the rise in the velocity at the inlet.Pressure contours inside the rotor varied substantially with positive pressure observed at the exits of the channel.A slight reduction in the value of the inlet velocity keeps the air flow in the rotor interior less than 100m/s which produces desirable turbulence necessary to reduce yarn quality deterioration.The dual-feed rotor spinning innovation showed more orderly streamline patterns with fewer vortices compared to the conventional one.The second part of the thesis is conducted based on the first part.It includes an extensive comparison of the dual-feed rotor spinning unit and the conventional type,which was undertaken to reveal the distinction between the flow dynamics in the two models and discover reasons for variation in yarn properties.Finite Volume Methods(FVM)was employed.By utilizing the model designed in the first part,and setting the relevant spinning parameters and also those parameters relative to the airflow field,a set of simulations were run regarding the dual-feed and conventional rotor spinning unit.The primary interest was the flow dynamics in the rotor interior since it stands as the main component where the airflow field of the two models is affected by the transfer channel.In this section,a comprehensive analysis of the stream traces,total drag force,negative pressure,turbulence strength,vortical regions,velocity magnitude effect and a brief look at the yarn properties was investigated.Results showed that the velocity magnitude and pressure in the dual-feed unit adopt an even pattern and the total drag force reduction of up to 60-80% is realized.Comparison of the yarn quality properties such as tenacity,work of rupture,thick and thin places and hairiness of the two systems showed that the dual-feed spun yarns possess superior quality compared to the conventional yarns.The results from flow parameters showed a striking difference in the flow dynamics in the two models regarding negative pressure distribution,turbulence strength,areas of vortical structures and patterns of streamlines.This provided a firm basis for an account of improved properties in the dual-feed method which gives further opportunity to research the position of dual-channel outlets to realize an optimum design.The third part is to verify the simulation results experimentally.Cotton-viscose yarns and cotton-polyester yarns were produced on the dual-feed and the conventional type and their tenacity,hairiness,evenness and imperfections were then evaluated.The experimental results showed that blended yarns spun on the dual-feed rotor spinning unit revealed superior quality regarding improved tenacity,hairiness,evenness and imperfections compared to conventionally spun yarns.The improvements may be attributed to the better alignment which is achieved with the new dual-feed model and as demonstrated by the numerical model.On the flipside,specific yarn samples' properties such as the elongation,CVm,thin and thick places did not show statistically significant results implying that the new design does not influence these parameters.The simulation results and the experimental ones implied that the dual-feed rotor spinning unit could stand out as a competitive technique for blend yarn production.The new spinning method makes spinning of multicomponent yarns less costly and more scalable.In the final part,we conducted a deep analysis on the effect of the parameters of the dualfeed rotor spinning unit on the yarn properties.Through the experiments,the influence of the opening roller type,sliver feed method,and direction of fibre feeding into the rotor on the quality of a polyester/cotton blend yarns spun by the dual-feed method was examined.Yarn properties of 58 tex 55/45 polyester/cotton blend yarns such as tenacity,elongation at break,mass irregularity,hairiness,thick(+35%)and thin(-30%)places were tested,and the results were statistically analyzed using Minitab.ANOVA analysis showed that the tested yarn quality properties were statistically significant among groups except for thick places(+35%).Tukey's post hoc test based on the honest significant difference(HSD)was performed to determine the implication of results within groups at the value of ? = 0.05.The dual-feed blend yarn(PCLR)spun with opening roller type OK37 on the left and OK40 on the right exhibited better yarn quality characteristics compared to other samples.Results implied that better yarn properties are achievable by using specific opening rollers that are tailored to specific fibers.Overall,this work realized a numerical model based on computational fluid dynamics technique to study the airflow field in the new dual-feed spinning unit.The airflow field is investigated comprehensively using the numerical and experimental methods.The simulation data and the spinning test results revealed the significant advantages and potentials of the dualfeed rotor spinning machine on producing blended yarns.The study of the thesis provides theoretical guidance for dual-feed rotor spinning unit design and applications. |
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