Multi-stage fluidized-bed heat exchanger modeling for high-temperature energy storage: Particle transport and heat transfer

Abstract

Concentrated Solar Power (CSP) systems, combined with Thermal Energy Storage (TES), enhance stability and reliability of renewable energy. The particle-based approach in CSP offers advantages due to its high-temperature stability and design flexibility. The fluidized-bed particle heat exchanger, provides a high heat transfer coefficient on the particle side, thereby enhancing the overall heat transfer performance. However, because of the randomness of particle motion within the fluidized bed, understanding the thermodynamic parameters at various locations is both challenging and critical for modeling heat transfer process and, in thermochemical particle heat exchangers, chemical reactions. This study developed a fluidized-bed particle transport model based on Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) and a Markov chain-based statistical model. The unloaded bed startup process can be categorized into three distinct stages, with particles exhibiting favorable transport behavior in the later stages, thereby creating beneficial conditions for enhancing the heat transfer performance. A dynamic heat transfer model in two dimensions was formulated, showing variations in bed temperature that align with experimental observations. The more pronounced variation along the flow direction of working fluid is linked to the distribution differences of particles, while the less pronounced variation along the bed height direction is attributed to the significant particle transport behavior. Finally, a comparison between the dynamic heat transfer model and experiments showed an average Pearson correlation coefficient (r) > 0.93. This work provides a modeling framework and establishes a baseline for creating coupled heat transfer and chemical reaction models.