Testing and model validation of a prototype moving packed-bed particle-to-sCO2 heat exchanger

The performance evaluation and model comparison of a prototype 100 kWt moving packed-bed heat exchanger for particle-to-sCO2 heat transfer is reported. The heat exchanger design entails a shell-and-plate configuration where particles move in a dense granular flow under the force of gravity. Details of the heat exchanger test including particle heat addition, sCO2 working fluid delivery, and thermal performance measurement technique are reported. Overall heat transfer coefficients at intermediate temperature (<500 °C) were measured to be 50-80 W/m2-K based on LMTD calculations for off-design conditions using three of four heat-exchanger banks. Estimated heat transfer coefficients from finite element modeling studies of the actual flow geometry predicted heat transfer coefficients of ∼120 W/m2-K at off-design conditions. The heat exchanger performance appears to be below the model predicted values due to low thermal conductivity of the packed bed or high near-wall thermal resistance when the particles are in a flowing state and as-built dimensions that differ from the designed geometry. Future plans for testing the complete four-bank heat exchanger configuration at the design temperature (775 °C) utilizing the falling particle receiver as the heat source are detailed.