A coupled CFD-DEM approach to model the in-trough mixing in a multi-stage solar particle receiver

Concentrated solar power (CSP) is expected to reach economic competitiveness with conventional power plants in the foreseeable future. The use of fine-grained ceramic particles as a heat transfer fluid (HTF) for CSP is a promising alternative to other HTFs such as molten salts and nanofluids. However, research on ceramic particle based CSP is stymied due to the inherent difficulty in obtaining indepth particle mixing processes. Acquiring this highly sought information would allow engineers and scientists to improve the design and optimization of next-generation CSP receivers thereby potentially leading to improved thermal efficiencies. To this end, a high-fidelity numerical model, namely a coupled computational fluid dynamics and discrete element method (CFD-DEM) is developed and implemented on a novel multi-stage solar particle receiver to provide an in-depth analysis of the dynamical and temporal evolution of the in-trough particle mixing processes. The results obtained from this numerical model will assist engineers and scientists to better optimize particle based CSP systems. The validated numerical model accounts for particle-particle, particle-wall, particle-fluid interactions of multiphase solid-gas flows in a novel multi-stage solar particle receiver. This study is the first attempt to conceptualize a novel multi-stage solar and to develop and implement a high-fidelity numerical model to provide an in-depth analysis of the in-trough particle mixing processes. For the first time, important flow characteristics, namely particle mixing, of the particle curtain are investigated. The results showed that the 'catch-and-release' troughs have a profound implication on the in-trough mixing process depending on the location of the particle in the particle curtain. The numerical model revealed that specific regions of the multi-stage receiver exhibit high particle residence times and low particle velocities. The rear particle of a curtain takes about 15% longer to reach the 2nd bin compared to the front and centre particle, and the rear particle remains immersed in the 2nd bin for about 14% longer compared to the front and centre particle. As such, the large particle residence time due to the in-trough mixing could potentially lead to better heat transfer performance of a solar receiver. The high-fidelity numerical model could potentially serve as an advanced tool for engineers and scientists to carefully design, optimize, and guide-the scale up and commercialization of novel solar particle receivers, particle heat exchangers, and various other industrial applications such as solar gasification (syngas) and green hydrogen technologies. (C) 2021 The Authors. Published by Elsevier Ltd.