Computational modeling of flow-induced alignment of nano-cellulose fibrils
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Journal Title
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Volume Title
Insinööritieteiden korkeakoulu |
Master's thesis
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Authors
Date
2017-06-12
Department
Major/Subject
Structural Engineering
Mcode
ENG3039
Degree programme
Rakenne- ja rakennustuotantotekniikan koulutusohjelma
Language
en
Pages
58+10
Series
Abstract
Long continuous cellulose fibers are synthesized from cellulose nanofibrils (CNF) by using wet and dry spinning techniques. The quality of cellulose fibers will depend on several properties such as plant source, aspect ratio and alignment of cellulose nanofibrils. Nanofibrils are aligned during the flow in a capillary tube while spinning. Variation of flow parameters and geometry of the capillary tube can change the alignment of fibrils. In the present work, flow fields inside the capillary tube were generated by simulating the suspension by using a commercial finite element software and the parameters were changed systematically to observe their effect on the flow profiles and to co-relate the results with experimental studies conducted in Aalto University. Parameters selected for the present work were flow rate, concentration of CNF suspension, diameter and length of the capillary tube. Carreau model was used to predict the non-Newtonian behavior of CNF suspensions and its parameters were obtained by plot-fitting the rheological data. The work met with certain complexity due to highly non-linear behavior of the Carreau model with parameters fitted for rheological data of CNF suspensions. However, some important conclusions have been obtained from the results. It has been shown that the main parameter which affects the alignment of fibrils inside the flow is shear rate. Decreasing diameter and increasing flow rate both have resulted in increase in shear rate throughout the diameter of the capillary tube. Simulation of CNF suspensions with different concentrations resulted in an unexpected trend for velocity profiles and change in length of capillary did not affect velocity profiles or shear rate inside the capillary tube. The effect of these parameters was also studied for shear stress and it was shown that the change in diameter, flow rate and concentration of suspensions significantly change the trend of shear stress profiles.Description
Supervisor
Niiranen, JarkkoThesis advisor
Niiranen, JarkkoKeywords
cellulose nanofibrils, non-Newtonian fluid, CNF suspension, simulation