Modelisation of a new mixing device : flows simulations, experimental validations and process optimization
Modelisation of a new mixing device : flows simulations, experimental validations and process optimization.
Thèses de doctorat,
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The blending of two polymers has been the subject of fairly extensive studies. This topic directly concerns the polymer processing industry which is constantly looking for new methods to obtain materials with improved properties. These material are generally obtained by liquid-liquid mixing and induced properties are dependent on the microstructure whose length scale is much smaller than the one associated with the macroscopic ﬂow. The usual mixing equipments, such as internal mixers or extruders, mainly generate shear flows and their efficiency is limited whereas tools based on elongational flows are assumed to be more efficient for dispersive mixing. In this context, we developed a new type of mixer (later called RMX) based on a convergent/divergent flow unit which favours the elongational component of the flow. In this study, physical effects create by this new mixing device will be obtained in some experiments and numerical simulations for creeping flow of Newtonian - of low and high viscosity - shear-thinning and viscoelastic fluids. To characterize the mix, we used a method which allows to determine the characteristic size, shape and orientation of the microstructure by predicting the change in the local morphological measure due to this velocity or deformation gradient. This approach, called the micromixing analysis, which treats by the use of area tensor, some local characteristic morphological measure as a ﬁeld variable and can incorporate additional physics like kinetics of break-up and coalescence of droplets. These methods have highlighted some fundamental mixing elements like fluid striation in viscoelastic cases.
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