Title  : Basic processes and multidimensional population assessment

Animators  : Alain Liné – Frédéric Chardard

 Under the effect of environmental, physicochemical or hydrodynamic constraints implemented during the transformation processes (crystallization, grinding, fermentation, degradation, flocculation, decantation, transport, filtration, …), the dispersed media can undergo transformations of different kinds. Starting from a supersaturated solution or a dispersion of individual objects, it is thus possible to observe nucleation, growth, aggregation, agglomeration or flocculation processes leading to structured solids, fractal or otherwise, of compactness or porosity more or less important. These evolutions can also be accompanied by a deformation of the original objects or products after aggregation, and give rise to processes of de-structuring or re-structuring. Moreover, some treatment processes (such as grinding or biological treatment) can generate within the solid material, cracking phenomena or the creation of break points that may lead to embrittlement, or even rupture of the material giving rise to new entities with their own morphological characteristics.

The different research themes related to this axis are the   :

– development of devices   “tests or models  “, to work under controlled conditions (environmental, physico-chemical or hydrodynamic) to identify what is the factor behind the transformation process. For example, if we are interested in a precipitation process, we can use a fast pre-mixer to work at a constant degree of supersaturation to analyze the impact of this parameter on the agglomeration of crystals. Similarly, the analysis of the effect of hydrodynamic conditions on a flocculation process could be carried out by carrying out experiments under controlled hydrodynamic conditions (pure shear Taylor-Couette reactor, elongational flow Taylor, Taylor four-roller reactor, … ).

Analysis of the relationship between the measured quantity and the local hydrodynamics, according to the size of the observation window or in the case of the use of intrusive sensors, because of the  disturbance of hydrodynamics by the presence of the sensor. It is here the representativity of the measurement in relation to the physical reality in the reactor that is analyzed.

– development of mathematical and numerical tools for the modeling of the flows of systems dispersed in complex geometries (reactors, pipes, confined spaces, blood vessels, .. ). Multi-scale (asymptotic) analysis related to small parameters, microscopic and macroscopic scale ratios. Modeling of growth or degradation laws comprising several morphological descriptors. Considered in the population balance, reduced in this case to a hyperbolic PDE. Study of his mathematical properties.

– modeling aggregation nuclei, deformation, rupture, … on the basis of morphological analyzes according to the key factors identified. Writing the corresponding kinetic laws, at the population level, in the form of integro- differential equations . Study of their mathematical properties (similarity, asymptotic behavior, possible freezing …).

– validation of models by comparison with morphological data using model devices.