Modeling and Numerical Simulation of the Acoustic Mixing of Charged Energetic Fluids – SINRAM

The market for industrial mixers is driven by many industrial sectors, like the food and pharmaceutical industries in the forefront, but also the aeronautics and armament industries. The objective of the various players is to supply equipment that makes it possible to obtain, from at least two materials, a final product that is as homogeneous as possible, in order to satisfy the quality levels required by these manufacturers at a competitive manufacturing cost. This point is all the more important as the stability of the product will depend on the quality of the mixture, which is essential when selling medical products in which the active substances are mixed with recipients and other stabilizers, or to obtain a propellant that meets the safety standards allowing its handling while maintaining an efficiency that allows its military use after storage for several years.
The most widespread industrial mixers are called intrusive because they use the rotation of blades or a grid that initiates the mixing. In these processes, mixing is only effective in a volume of fluid very close to the exciter, where velocity and shear gradients are very important. As these phenomena are much localized, obtaining a homogeneous mixture requires either a relatively long process time. In order to drastically reduce the time needed for homogenization, we are increasingly proposing to use a brand new mixer technology: "Resonant Acoustic Mixer" or RAM technology. This new, non-intrusive method generates the mixture via vertical oscillation of the container containing the components. The oscillation frequency is 60 Hz (± 2 Hz) and corresponds to the resonance frequency of the entire system. The vessel containing the components to be mixed is placed on the top plate and has a lower mass in comparison with the other three in the system. Macroscopic convective movements, but also micro-vortex movements appear inside the fluids to be mixed. The latter are generated in the whole volume to be mixed. This multitude of micro-mixing zones improves mixing and allows to obtain a homogeneous mixture very quickly (a few tens of minutes compared to several hours with traditional mixers).
This relatively recent technology is little understood, and published data is are very limited. For example, there are no data on spring stiffness or techniques for automatic frequency adjustment. Thus, mixing protocols are very empirical and are highly dependent on the fluids involved (via their viscosity), the filling rate or the pressure inside the container. In a need for repeatability, as well as technological evolution to allow the transition from a laboratory configuration (50 cl) to industrial use (> 20 L), it is essential to understand the physics inherent in this process. Currently, numerous studies on the performance of the process exist in the literature, mainly in the pharmaceutical field, but also in the propulsion sector.
The objective of SINRAM is to achieve a significant breakthrough in the implementation of a numerical simulation code for the RAM mixer. The project highlights the implementation of methods and numerical models to simulate RAM mixing at all its scales. It devotes an important part to the realization of a i) a compressible approach to the numerical modeling of instabilities and taking into account mass transfer at interfaces ii) a model to take into account the mechanical behavior of vibrated suspensions relevant for the application of mixing in acoustic resonance and iii) reliable reduced model using data and model reduction techniques (ROM). This project will combine know-how from physical modeling, numerical methods and high performance computing. Confrontation with experimental data will be present at all stages of validation.