Effective thermal conductivity of packed beds made of cubical particles

Abstract

This work addresses the parameterization of the Zehner-Bauer-Schlünder model (ZBS), a standard model for the determination of the effective thermal conductivity of packed beds, based on thermal simulations in ANSYS. Data are presented for the effective thermal conductivity of packed beds of cubical particles, obtained from simulations of heat conduction in particle systems generated by rigid body dynamics using the open-source software Blender. The particle-to-gas thermal conductivity ratio is varied over many orders of magnitude in these simulations. Punctual validation is provided by heat conduction measurements with cubes made of plastic and aluminum in air. Structural results are validated by micro-computed X-ray tomography. Emphasis is set on bed porosity and on the relative interparticle contact area. Comparisons elucidate ZBS behavior at the limit of non-conducting particles. In the region of medium particle-to-fluid conductance, ZBS shape factor is for the first time evaluated for cubes. At high solid conductance, the effective thermal conductivity of the bed is dominated by areal contacts between particles. Such contacts are large with cubes, but they are also shown not to be thermally perfect. Contact imperfection limits the increase in bed conductivity with increasing particle conductivity and requires the introduction of an additional empirical parameter in the ZBS model. In total, a full parametric setting of ZBS is provided for cubical particles. Several sets of this kind would help to generalize the model for applicability to particles of arbitrary shape.