Experimental investigation of the variation of the local gas velocities in a cold flow pebble bed reactor (PBR) using a hot wire anemometry technique

Obtaining accurate results and new benchmark data for the local velocity of the gas flowing within the pebble bed reactor (PBR) is a key step for understanding and benchmarking simulations of the thermal hydraulics in the PBR core as it significantly affects the design and safety operation of these reactors. Therefore, this work focused on studying the local gas velocities inside a pebble bed using a sophisticated hot wire anemometry (HWA) technique, which was supported with a novel probe-protector case that protected the probe, allowing the measurements to be conducted at various locations in a pebble bed with pebble diameter of 5cm and an aspect ratio of 6. The measurements were conducted at various superficial inlet gas velocities (0.3 < Ug< 2.4m/s), covering both transitional and turbulent flow conditions (993.78 < Re < 7950.24) at three axial levels and four radial locations (r/R = 0, 0.33, 0.67, 0.9). The results highlighted the effect of the wall on the variation of the local gas velocities inside the pebble bed, as higher gas velocities were recorded at the near-wall region, where the void fractions are higher, providing a path of the least resistance to the flow of the gas, compared to the center of the bed. Furthermore, a second order polynomial correlation with an R2 = 93.96% and an AARE equal to 1.47% was developed for the prediction of the local gas velocity inside the bed, within the experimental range of the study. The accurate gas velocity measurements obtained in this study can serve as benchmark data for the validation of CFD simulations coupled with heat transfer calculations.