Comparison of flows and heat transfers in reactor cores with spherical-particle fuels and cylindrical-rod fuels

The HTGR reactor core is always composed of packed fuel pebbles and helium gas. The fluid flows around spherical particles and cylindrical rods are always encountered in the reactor core of nuclear powers. The flows past the spherical particles and cylindrical rods were simulated here. Two aspects were considered: comparison of heat transfers between the spherical particles and the cylindrical rods, and effects of different stacking modes on flows and heat transfers in the pebble bed. For the first aspect, a parallel model and a ZBS model were used to calculate the effective thermal conductivity. Comparing the average heat transfer coefficient and temperature distribution, the heat transfer capacity of spherical particles is stronger at the price of larger overall temperature difference. For the second aspect, different stacking modes mainly refer to different angles between the spherical particles in adjacent layers. A relationship between different stacking modes and the correlation coefficients (drag coefficient, average heat transfer coefficient) was given.