Granular materials are of great importance industrially, yet not completely understood in regard of their thermal behavior in mixers, dryers, reactors and other types of contact processing equipment. In such equipment heat is supplied to a mechanically agitated bed of particles from heating surfaces. Continuum models are used traditionally for the description of the process. An example is the penetration model (PM) which describes the heating process of the particles as a sequence of penetration periods and mixing steps. As an alternative to the PM the thermal discrete element method (DEM) was applied in newer work. To validate the DEM simulation an experimental set-up and a new contactless measurement method were developed, and applied to the thermal relaxation in packed beds composed by a fraction of warm and a fraction of cold particles. In these thermal investigations aluminum spheres which are coated with thermochromic pigments are used. Thermochromic pigments are pigments that change color with heat supply as a result of a structural phase transition. Such a measuring technology allows for the experimental determination of temperature distributions in the disperse phase and thus, for a quantitative comparison with the results of the thermal DEM simulation. In this work the experimental results of 2D, 3D, stagnant and agitated beds are presented and compared with corresponding numerical computations using the discrete element method. Still existing deviations are partially caused by undesired heat losses and will be discussed in the contribution.

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