Gas-solid flow behavior and heat transfer in a spiral-based reactor for calcium-based thermochemical energy storage

Abstract

Calcium-based thermochemical energy storage presents a viable solution to bridge the gap between energy supply and demand during periods of off-sunlight due to its high energy density, low cost, and widespread availability. However, this technology faces a challenge in enhancing heat and mass transfer in the reactor, largely due to its low thermal conductivity. This study investigated the flow behavior and heat transfer in a spiral-based reactor, both with and without the inclusion of calcium-based particles during pneumatic conveying. The results indicate that, for flow behavior, the variation in Re number with a limited amount of particle mass in the spiral-based reactor is similar to that without particle conveying, increasing with an increase in gas velocity. However, an increased amount of particle mass can lead to clogging in the spiral-based reactor, resulting in notches in the Re number variation. Furthermore, the kinetic energy variation of calcium-based particles during pneumatic conveying follows four distinct stages: rapid growth, transient stationary, secondary growth, and secondary stationary, which increases with an increase in particle mass and gas velocity. For heat transfer, the temperature remains constant in the spiral-based reactor without particle conveying. However, the variation in gas temperature is opposite to that of particle temperature due to heat transfer between them in the spiral-based reactor during pneumatic conveying. The particle temperature increases with a reduction in particle size and feeding rate, and an increase in gas velocity. Additionally, the heat transfer rate increases with a reduction in particle size and an increase in gas velocity, but the particle feeding rate has a limited effect on heat transfer rate due to the same particle size. Finally, the research on effect of flow behavior on heat transfer suggests that superior heat transfer performance is more readily achieved under the gas-solid flow condition characterized by the lower kinetic energy and larger Re number.