Trajectory-based analysis of friction on packing and diffusion of thin pebble beds

Abstract

ABSTRACT The pebble-bed type reactor is one of the mainstreams for high-temperature gas-cooled reactor (HTGR), whose core is a packed bed composed of numerous spherical pebbles. In this work, discrete element model (DEM) is used to simulate the pebble flows in a thin pebble bed, and the packing peaks, top angles, trajectory and velocity deviations, retention time, and ratios are analyzed in detail. The effects of the pebble-pebble friction coefficient and pebble-wall friction coefficient, including their difference on the pebble flows are studied based on the trajectory analysis. The friction may bring higher packing peak, sharper top angle, larger diffusions of trajectory and velocity, as well as larger retention time, and ratio. However, if the pebble-pebble friction and pebble-wall friction are different, the effect of them on the pebble flow is quite different. The details and mechanisms are appropriately analyzed to explain the influence of pebble-pebble and pebble-wall friction on pebble flows. The results are helpful for better understanding of the pebble flow behavior under varied frictions.