A DEM-embedded finite element method for simulation of the transient heat conduction process in the pebble bed

A DEM-embedded-finite-element-method (DEFEM) with a 2D-asymmetric circular particle heat conduction model is proposed. DEFEM combines the discrete-element (DE) and finite-element model (FEM) with heat conduction. With embedded discrete elements (EDE), DEFEM solves heat conduction between particles and temperature field inside particles. EDE solves heat conduction in asymmetric circular element, and FEM simulates transient heat conduction after the heat flux at boundaries is known. Verified by experiments, results show that DEFEM can accurately simulate transient heat conduction of pebble beds. Discrete-model (DM) and continuum-model (CM) are comparatively analyzed under the same thermal responses and temperature distributions. In CM, the standard function of thermal conductivity is fitted with an attenuation part, an increment part and a constant part. The constant part is defined as effective thermal conductivity (ETC) of CM, which is directly proportional to that of DM, and independent of heat capacity. Herein, ETC of the CM is a key parameter, which could be used to measure the overall heat transfer capability of the bed