Experimental Investigation of a Moving Packed-Bed Heat Exchanger Suitable for Concentrating Solar Power Applications

Abstract

This paper presents a thermal performance evaluation of a novel particle-to-air heat exchanger. The heat exchanger has a patented design with a shell-and-tube configuration. Solid particles move as a dense packed-bed inside the vertical tubes of the heat exchanger whereas air flows on the shell-side. This design avoids a number of limitations associated with the state-of-the-art heat exchangers in the same category, such as the stagnant/void zones and the prolonged residence time. The heat exchanger has a 50-kW thermal duty; it has been integrated into the particle-based concentrating solar power facility located at the campus of King Saud University in Riyadh, Saudi Arabia. The detailed description of the heat exchanger and the integration process is introduced. The recuperated air of the facility’s power cycle is used to heat the solid particles being circulated inside the facility. The solid particles used in this study are engineered particles called Carbobead CP with 0.3 mm mean diameter. The effect of particle flow rate on the thermal performance of the heat exchanger is investigated. The results show that as the particle flow rate increases, the overall heat transfer coefficient (U) increases; a maximum value was measured to be 150 W/m2-°C based on LMTD calculations. The measurement accuracy was verified by repeating several tests; a slight variation was observed in the measured U. The results also show that only a small air pressure drop (~5 kPa) was measured across the heat exchanger. Furthermore, it was found that a significant part of the heat exchange occurred at the bottom section of the heat exchanger.