Contact heat transfer and heat conduction in packed beds of edged particles
Project B2 aims at a new and more reliable way of predicting the heat transferred between particles when they come in contact with each other. The heat transfer coefficient αpp, that correlates the heat transfer rate with the particle and inter-particle properties, is derived from the effective packed bed thermal conductivity λbed which is investigated by experiments and simulations for a wide range of different polyhedral particles. This enables 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 is derived from X-ray μ-CT imaging and correlated with adequately defined particle form parameters. Moreover, interstitial packed bed morphology, including pore size variability, is characterised. 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. In more details, we expand the standard model developed for spherical particles by Zehner, Bauer and Schlünder (ZBS) to predict the effective thermal conductivity of packed beds. The model parameters of the ZBS model, such as porosity, shape factor, and relative contact area of interparticle contacts, are obtained by correlating the experimental, morphological and numerical simulation data obtained for a wide range of edged particles with different shape, size and material properties. The morphological data from µ-CT imaging are extracted for the different bed configurations also used in experiments. The reconstructed packed beds are used for heat transfer simulations, implementing conduction through both, the gas and the solid phase. The interparticle heat transfer coefficient αpp, which is the central parameter of thermal DEM, is then derived using the estimated analytical relations of λbed and αpp for different particle shapes.