Contact heat transfer and heat conduction in packed beds of edged particles
A central parameter of thermal DEM is the particle-particle heat transfer coefficient during binary contacts. Contact heat transfer is always important when heat is transmitted from a wall to an adjoining bed of particles in order to conduct thermochemical processes, but in presence of steep temperature profiles it can also be significant when heat is supplied from the gas phase. Despite of its central role, simplified models, the validity of which is questionable even in case of equally sized spheres, are used to calculate contact heat transfer. Any reliable background is missing in case of edged, polyhedral particles, despite of many applications in practice (CRC/TRR application examples, but, for instance, also contact drying of active pharmaceutical ingredients).
Project B2 aims at a new and more reliable way of predicting the heat transferred when particles come for a certain period of time in contact with each other from effective packed bed thermal conductivity. Therefore, effective packed bed thermal conductivity shall be investigated by experiments and simulations for a wide range of different polyhedral particles. This will enable the prediction of effective thermal conductivity and contact heat transfer not only for spheres but also for arbitrary materials that consist of polyhedron-like particles. In this frame, packed bed porosity and the relative area of flat interparticle contacts will also be derived from X-ray µ-CT imaging results and correlated with adequately defined particle form parameters. Moreover, interstitial packed bed morphology, including pore size variability, will be characterised. Effective packed bed thermal conductivity and particle-particle heat transfer coefficient will be considered on the basis of average values in the first funding period (FP1), but shall be individualised by means of local structural data for single particleparticle contacts in FP2 and FP3. Ultimately, the research goal is to place the thermal part of the DEM on a scientifically well founded and technically easily usable basis for particles of any shape.