Experimental investigation of flow and convective heat transfer on a high-Prandtl-number fluid through the nuclear reactor pebble bed core

For Fluoride-salt-cooled High-temperature Reactors (FHRs), a pebble bed experimental facility with internal heat generation is set up, using the Dowtherm A as the simulant fluid. Dowtherm A can match the Prandtl number of FLiBe of 520-700 degrees C at a low temperature range of 45-105 degrees C. The effects of inlet temperatures, porosity and mass flow rate are investigated on the flow and convective heat transfer characteristics. A criterion is determined for the flow regime transition from the transitional to turbulent flow. The existing correlations are unable to predict the Blake-type friction factor in the transitional flow and show mixed performance in the turbulent flow. The present empirical correlations generally underestimate the convective heat transfer coefficients of the high-Prandtl-number fluid in the pebble bed. New correlations are proposed for predicting the flow and convective heat transfer coefficients with Prandtl number at 14-19 and Reynolds number at 90-2500.