Calibration of parameters for DEM simulations of solar particle receivers by bulk experiments and surrogate functions

Kurzfassung

Bauxite particles known as proppants from the fracking industry are an emerging heat transfer medium for solar thermal power plants. The discrete element method (DEM) has just recently been applied to these systems and the information on parameters for contact force models is scarce; calibrated parameters cannot be found. In this work a novel, three-stage calibration approach based on multiple bulk experiments and surrogate functions is presented. The experiments comprise the angle of repose, the residence time on a horizontal conveyor and the impact on an inclined plate. Particle-particle and particle-wall parameters for the Hertz contact force model and the modified linear spring dash-pot rolling friction model are determined for five different proppants and two wall materials. The assumptions of the calibration procedure and the calibration results themselves are checked and discussed on the basis of a sensitivity analysis. It is shown that almost all parameters can be constricted to unique values by the approach and that most parameters only gradually differ between particle types. Additionally, the influence of coarse graining on the parameters is examined. The behavior of the restitution coefficients is explained in detail by kinetic gas theory. It is found that only the particle-wall restitution coefficient is invariant to coarse graining, but not the particle-particle restitution coefficient, which must decrease with coarse-graining factor.