Multi-scale investigation on the mobility effect of spherical and non-spherical particles as part of disperse solid/fluid systems with respect to momentum and heat exchange

• Applicant: Professor Dr.-Ing. Harald Kruggel-Emden
• Subject Area: Mechanical Process Engineering
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 333932055

A core theme in the study of disperse solid/fluid flows is the detailed analysis of the flow field behavior and the phenomena induced by the presence of the dispersed phase. In dense particle-fluid flows an accurate description of the momentum and heat transfer between the two phases is desirable and can be derived from particle-resolved direct numerical simulations (PR-DNS). The complexity of these flows increases when particles are allowed to move, such as in fluidized beds in contrast to static particle ensembles such as packed beds. In these dynamic and dense particle systems, particle velocity fluctuations and inhomogeneities in the local particle distribution occur, which are referred to as mobility effects. Very recent studies have shown that mobility effects have a non-negligible influence on momentum and heat transfer of spherical particles, but a rigorous inclusion into correlations is still lacking, which is even more the case for non-spherical particles and coupled heat transfer. The objective of the proposed research work is to contribute to a broader base of PR-DNS data for gas/solid flows involving heat transfer, where particles are allowed to move freely. The PR-DNS serve to derive correlations for momentum and heat transfer that rigorously take into account mobility effects over a wide range of parameters (Reynolds number, Stokes number, solid volume fraction) for the first time. The key novelty of these new correlations will be the computation of momentum and heat transfer based on a per particle basis using relative particle position and velocity information, for which both, a physics based kernel smoothing approach and an approach based on an artificial neural network, are applied. Thereby, transversal particle/fluid forces arising from the local flow around individual particles are also inherently captured, which are insufficiently described by existing volume-averaged models. In order to quantify the benefit of the new correlations over conventional correlations, we will perform fluidized bed simulations involving heat transfer using the unresolved DEM-CFD approach and the PR-DNS approach. By comparing the simulations with respect to integral parameters, we will be able to assess the importance of considering mobility effects. In the second part of the project, we repeat this procedure for particle-fluid flows involving selected non-spherical particles (sphero-cylinder, cube, oblate). These simulations will allow insights into the relationship between particle shape and particle mobility effects for the first time and will pave the way for more accurate closures additionally taking into account the aspericity.

• DFG Programme: Research Grants
• International Connection: Luxembourg
• Cooperation Partner: Professor Dr.-Ing. Bernhard Peters