Granular flow around the horizontal tubes of a particle heat exchanger: DEM-simulation and experimental validation

Moving bed heat exchangers are a central element in solar thermal power plants using granular heat transfer fluids. Their performance is determined by a complex granular flow field in the device. This calls for accurate simulation models forming the basis for novel design tools. In this study we propose a discrete element model (DEM) to calculate the dense granular flow field around the horizontal tubes of a moving bed heat exchanger. The simulation results are compared to measurement data using particle image velocimetry (PINT). In the upper part of the tube the model agrees well with the experiment, capturing the relevant flow phenomena like the stagnant zone on top of the tube. Below the tube, a void area is observed both in the experiment and the simulation. However, the PIV analysis of the experimental data doesn't resolve the void area and the associated flow phenomena due to the highly dynamic flow state, the inherent nature of Ply technique and additional disturbing effects in the setup. Therefore, the model can't be validated in the corresponding regions. Still, the deviations between simulation and experiment are confined to a very narrow region directly at the tube surface in the lower part of the tube. In the rest of the flow field, the model proves to be a reliable tool for further investigations and will be used in future studies.