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Evaluation of dispersive mixing, extension rate and bubble size distribution using numerical simulation of a non-newtonian fluid in a twin-screw mixer
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Rathod, Maureen L.. Evaluation of dispersive mixing, extension rate and bubble size distribution using numerical simulation of a non-newtonian fluid in a twin-screw mixer. Retrieved from https://doi.org/doi:10.7282/T3125VH2

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TitleEvaluation of dispersive mixing, extension rate and bubble size distribution using numerical simulation of a non-newtonian fluid in a twin-screw mixer
NameRathod, Maureen L. (author); Kokini, Jozef L (chair); Takhistov, Paul (internal member); Yam, Kit L (internal member); Connelly, Robin Kay (outside member); Rutgers University; Graduate School - New Brunswick
Date Created2015
Other Date2015-05 (degree)
SubjectFood Science, Non-Newtonian fluids, Mixing
Extent1 online resource (xviii, 150 p. : ill.)
DescriptionInitially 3D FEM simulation of a simplified mixer was used to examine the effect of mixer configuration and operating conditions on dispersive mixing of a non-Newtonian fluid. Horizontal and vertical velocity magnitudes increased with increasing mixer speed, while maximum axial velocity and shear rate were greater with staggered paddles. In contrast, parallel paddles produced an area of efficient dispersive mixing between the center of the paddle and the barrel wall. This study was expanded to encompass the complete nine-paddle mixing section using power-law and Bird-Carreau fluid models. In the center of the mixer, simple shear flow was seen, corresponding with high γ&. Efficient dispersive mixing appeared near the barrel wall at all flow rates and near the barrel center with parallel paddles. Areas of backflow, improving fluid retention time, occurred with staggered paddles. The Bird-Carreau fluid showed greater influence of paddle motion under the same operating conditions due to the inelastic nature of the fluid. Shear-thinning behavior also resulted in greater maximum shear rate as shearing became easier with decreasing fluid viscosity. Shear rate distributions are frequently calculated, but extension rate calculations have not been made in a complex geometry since Debbaut and Crochet (1988) defined extension rate as the ratio of the third to the second invariant of the strain rate tensor. Extension rate was assumed to be negligible in most studies, but here extension rate is shown to be significant. It is possible to calculate maximum stable bubble diameter from capillary number if shear and extension rates in a flow field are known. Extension rate distributions were calculated for Newtonian and non-Newtonian fluids. High extension and shear rates were found in the intermeshing region. Extension is the major influence on critical capillary number and maximum stable bubble diameter, but when extension rate values are low shear rate has a larger impact. Examination of maximum stable bubble diameter through the mixer predicted areas of higher bubble dispersion based on flow type. This research has advanced simulation of non-Newtonian fluid and shown that direct calculation of extension rate is possible, demonstrating the effect of extension rate on bubble break-up.
NotePh.D.
NoteIncludes bibliographical references
Noteby Maureen L. Rathod
Genretheses, ETD doctoral
Persistent URLhttps://doi.org/doi:10.7282/T3125VH2
Languageeng
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.
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