Heat transfer coefficient distributions on sphere surface in pebble bed core using different turbulence models

The heat transfer and flow field characteristics around a single or multiple spheres have been investigated at relatively low Reynolds numbers (Re) in the literature. This study aimed to obtain the heat transfer coefficient distributions on multiple spheres in a three-dimensional lattice form using both experiments and computational fluid dynamics (CFD) technology at Re values of 10,000, 20,000, and 26,000. The experiments provide a full picture of the heat transfer characteristics of spheres using transient liquid crystal technique, which is a non-destructive method. The CFD calculations were conducted under the same conditions in experiments using five turbulence models: the standard k-e low-Re, AKN k-e low-Re, standard k-e two-layer, realizable k-e two-layer, and v² -f models. Comparisons of the measured and computed parameters concluded that the v² -f turbulence model gives the best agreement compared with the other models due to its superior ability to capture non-isotropic turbulence near walls.