THE SCIENTIFIC ACTIONS
The composition of a particle and its evolution over time have an impact on its transport, its storage and its implementation. An optimization of those processes which involve complex particles, requires the quantification of the physical-chemical, structural and mechanical properties of powders, together with their evolution throughout the production chain. In order to reach this optimization, the consortium can count on a rich combination of expertise, of experiences, and ability to develop instruments and suitable experimental techniques, thanks to its academic partners. The project’s consortium developed some skills in order to produce particles with controlled mechanical properties (functionalised particles) which will be used during the project’s life. The consortium takes advantage of its experimental techniques in order to measure some particle properties; these measurements are fundamental for understanding how particles evolve and how they influence their flowability properties during their transport and implementation process.
The consortium characterizes in particular:
– the size and form of particles;
– the mechanical properties of particles,
– their hydration properties;
– their electrical properties;
– the effect of adding additives;
– the rheology.
These measurements are carried out in collaboration with the laboratories of partners’ universities, according to their specific skills. The consortium is then carrying out a comprehensive study on the physical-chemical and mechanical properties of powder particles with an industrial relevance. These measurements are necessary to develop physical models for numerical simulations (action 7) in order to adopt efficient numerical tools which may foresee the flowability behaviour of powders in complex situations, as those which may be found in industrial plants.
The Institute for Mechanical and Process Engineering of the University of Kaiserslautern deals with several scientific topics which fall under the domain of particles technology. The researches of the department approach fundamental themes of mechanical and process engineering, from the generation and formulation of particles to define the properties of some dispersed substances to the separation of the particles dispersed in a gas or liquid phase.
In order to characterize these dispersed particles, the department develops its own solutions of sensor technology, which are not just used on a laboratory scale. In the field of solids process technology, numerical and experimental simulations are essential to observe the macroscopic effects of bulk materials when they are stocked and to consider the micromechanics of particles when they interact among them or when they separate. At the core of any research activity lies the creation of individual simulation situations, among which the modelisation of multiphasic disposal plays a central role.
In the framework of PowderReg project, the problems related to powders storage are examined in order to avoid fluctuations in mass flows and problems concerning disposal.
Besides experimental research, numerical methods (such as Discrete Element Method & Computational Fluid Dynamics) are used in order to simulate silo discharge and shear processes, for which micromechanical interactions are modelled and calibrated.
In the framework of the European project “PowderReg”, the team of the university of Saarland is dealing with granular matter flow research. In the first year of the project we focused on developing and testing measurement techniques for the rheology of granular matter, and on setting up related experiments. For our scientific purposes, we use a standard rheometer in a cup and plate configuration to research granular matter samples with large amplitude oscillatory shear (LAOS). Our first results were presented at the Rheology 360 conference in Luxembourg (19.03.2018). During the first year, we also began to implement the first tube rheometer set-up.
Fruitful collaboration within academic and industrial world helped us develop a work plan for 2018 and the following years. We discussed with Prof. Caceres (Balseiro Institute Argentina), summing-up the previous work carried out on powder flow to develop a theory on granular gases related to the van der Walls approach, and considering the necessity to find a suitable set up which could reconcile research and experiments. We carried out a discussion with Dr. Pedro Pury (FAMAF, Argentina) about granular matter rheology for studying the thermodynamics of the tube Rheometer. We also discussed about additional experiments with the tube rheometer in order to measure the dissipated energy and estimate the configurational entropy.
We took contact with the company CERATIZIT, Luxembourg (www.ceratizit.com), and had three meeting in November and December (one in their industrial plant and two in our laboratories) focusing on the different stages of the metallurgical process they carry on to produce cutting tools. We structured our collaboration inviting the company to join the Committee for Innovation and Impact in order to further develop a cooperation about tasks related to innovation in powder processing technologies.
The powder flow properties and compaction dynamics of granular materials are closely related, as demonstrated in a series of experiments performed during the last decade. One understands that the mobility of each grain in a granular assembly is directly linked to the flowability of this system, or the way it can densify when gently vibrated. Shaking a granular medium increases its packing fraction. While extensively studied, this phenomenon, called compaction, remains puzzling. Indeed, the compaction dynamics is determined by many parameters like the grain shapes, the grain sizes and the type of vibration. In the present
study, we focus on the distribution of grain sizes. In particular, we present an experimental investigation of the packing fraction for various mixtures of spherical grains with different sizes. The compaction dynamics is also analyzed for different vibration strengths and orientations.
Numerical simulation is a beneficial tool in the design and optimization of dense granular flow systems. Continuum models are favorable in terms of light computation cost but is challenged by the outstanding closure problem. A unified closure model for both dilute and dense granular systems does not exist. The efforts of extending the kinetics theory from dilute granular systems to dense systems or formulating new rheological laws are not well supported by the limited
measurements in the experimental studies. Carrying out particle-scale dynamics simulation with XDEM has the potential of providing detailed insights for exploring granular bulk behaviors. In the framework of this project, we will numerically probe the granular flow dynamics in two prototype systems: a Couette cell and an inclined plane. Ensemble averaging method is employed to derive macro-scale information such as stresses, strains and granular temperature from particle-scale interaction simulations. We aim to find out generalized relationships among flow dynamic parameters and formulate stress-strain rheological relationships for continuum model closure.