(541c) Local Time-Averaged Heat Transfer Coefficient In a Pebble Bed

In real pebble bed reactor (PBR) for the 4^th generation nuclear energy, thorough understanding the phenomena of the transport of heat generated during nuclear fission from slowly moving hot pebbles to the flowing coolant gas is crucial for safe design and efficient operation. This heat transport can be quantified and characterized in terms of heat transfer coefficient. Therefore, in this work, the local heat transfer coefficient of the gas phase which is used for cooling has been investigated experimentally in a 0.3 m diameter cold-flow pebble bed. Glass bead particles of 5 cm diameter and 2.55 gm/cm³ have been used in randomly packed bed. The effect of superficial gas velocity on the heat transfer coefficient has been investigated using a wide range from 5 to 60 cm/s that cover both laminar and turbulent flow regimes. A fast-response heat transfer probe (0.02s) was developed to measure the local instantaneous heat flux and surface temperature, simultaneously, at different axial and radial positions in the bed and hence local time-averaged heat transfer coefficient. Experiments results indicate that the increase of superficial gas velocity causes an increase in the heat transfer coefficient. Also, the heat transfer coefficients in the center of the bed are higher than those near the wall of the bed for all the conditions studied.