Novel active inline mixer for yield stress fluids: from fundamental science to industrial processing optimization – NaiMYS

An experimental and numerical study of a novel active online mixing and heat transfer device for yield stress fluids encountered in food industry is proposed. Simple dimensional arguments indicate that, by reducing the effective length of the active mixer, one gains quadratically in the energy needed to yield the materials making this device an ideal candidate for industrial scale mixing applications where the energetic efficiency is crucial. This collaborative project will be carried on two tracks (experimental and numerical ones). On the experimental side, we propose a novel experimental technique able to quantitatively assess both the space-time dynamics of the flow fields and the efficiency of transport of mass and heat.

The second track concerns numerical simulations. It will be conducted following three steps. A parametric study using 2D numerical simulations will be first undertaken in order to identify an adequate flow and geometry configuration suitable to be built for the experimental setup of the active inline mixer. Then high-resolution 3D computations will be used in conditions corresponding exactly to the experimental benchmark, to compare the flow fields and the measures of mixing efficiency with those obtained experimentally and also to make a comparison between 2D and 3D numerical results. Finally, an original approach, using genetic algorithm (GA) applied to the results of a large number of CFD numerical simulations will be performed with a multi-objective design optimization. The aim is to achieve both minimized total pressure loss and maximized mixing and heat transfer abilities of the inline active mixer.

The global aim of the project is two-fold. From a practical perspective, we aim to implement an energy efficient active online mixing technique. To do so, by a combined experimental and numerical approaches, we will build a transport efficiency chart in terms of the yield stress of the material and the forcing parameters (energy input). This transport efficiency chart will be ultimately summarized into a user friendly piece of software able to provide a quick solution to an industrial mixing/heat transfer problem. From a fundamental standpoint, the project will address for the first time several fundamental issues. First, we will systematically characterize the distribution of the residence times and Finite Time Lyapnuov exponents within the active mixing element and assess for the first time their correlation with the yield stress. Second, the decay regime of mixing will be systematically characterized by combined experiments and numerical simulations. The practical question that will be addressed here is how the optimal mixing times depend on the yield stress.

Project NaiMYS is based on the collaboration of two research units in the University of Pau and Nantes in France (respectively the « Laboratoire des Sciences de l’Ingénieur Appliquées à la Mécanique et au génie Electrique » – SIAME – EA 4581 of the CNRS Fédération IPRA 2952 and the « Laboratoire de Thermocinétique » UMR CNRS 6607).
To fulfill the objectives, the project requires funding mainly for the building of the experimental facility with its optical equipment and some complementary computing facilities which are necessary to implement the new numerical predictive tools envisaged for the NaiMYS project. A PhD funding (co-supervised between LTN and SIAME) is required for conducted the experimental work in Nantes (two years) and part of the numerical work in Pau (one year). Additionally, a 18 months post-doctoral fellowship is needed for helping of the development of extensive numerical tools.