Micro scale study of solid and fluid phenomena in interparticle collisions under dry and wet conditions

• Applicant: Professor Dr.-Ing. Stefan Heinrich
• Subject Area: Mechanical Process Engineering
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 438775980

Due to the very good heat, mass and momentum transfer, fluidized beds are widely applied in several industrial fields, e.g. chemical engineering, combustion, pharmaceutical and food industry, whereby a liquid is often injected for granulation or coating purposes. These macro-processes or unit operations in turn consist of a large number of interconnected, parallel micro-processes. Such micro-processes, such as the collisions between wetted particles, determine the behavior of the entire unit operation as well as the quality and properties of the final product. An understanding and description of such micro-mechanisms is therefore of crucial importance for the design of processes and for ensuring product quality and properties. Despite the high relevance, the literature currently shows a lack of fundamental understanding or experimental confirmation of existing theories for a large number of phenomena at the micro level. The project aims to close the existing knowledge gaps regarding the phenomena occurring during collisions between particles, both under dry and wetted conditions. The results will significantly improve the prediction and control of solids processes, such as fluidized beds or spray dryers. To investigate the processes at the micro level, collision experiments between two particles are carried out in an experimental setup that was specially developed for this purpose as part of the HE 4526/28-1 project. In this setup, the particle collisions are recorded with two highspeed cameras, which enables a three-dimensional movement measurement of the particles and liquids. By extending the setup, dependencies of the collision behavior of the particles are identified by extensive variation of the collision and material properties. In particular, liquid effects and their influence on the collision dynamics are the focus of the investigation. Regarding the influence of liquids on interparticle collisions, agglomeration conditions, liquid bridge geometry, liquid bridge volume evolvement, bridge rupture length, liquid distribution between the particles after the collision, as well as the formation conditions of satellite droplets are considered. Where available, the experimental results are compared with existing modeling approaches. Existing weaknesses in the models are identified and eliminated by model adaptation. The development of new models for phenomena that have not yet been considered in detail ensures a significant increase in the accuracy of process simulations.

• DFG Programme: Research Grants