Achieving global net-zero targets requires a transition from fossil fuels to renewable energy sources, with solar power playing a pivotal role in the decarbonisation of the energy sector. However, the efficiency of solar thermal systems is limited by the maximum working temperature of conventional heat transfer media, such as molten salts, which degrade above 565 °C. To overcome this barrier, particle-based fluidised beds have emerged as a promising alternative due to their ability to operate at temperatures exceeding 1000 °C, their chemical stability, and their potential to significantly improve thermal efficiency in concentrated solar power (CSP) applications.
In this study, a tubular fluidised bed reactor was designed and constructed to assess its performance as an indirect high-temperature solar thermal receiver. The effects of key parameters, including particle material, size and air flow rates, on the system's thermal performance were investigated. Three particle types (silicon carbide (SiC), silica sand (SiO₂), and ordinary sand) with different densities and two average particle sizes (310 and 440 μm) were tested. Experiments were conducted at three superficial air flow rates, while maintaining wall temperature at 60 °C, 80 °C, and 100 °C to simulate external solar heating. A high-speed camera was employed to capture the fluidization behavior and flow patterns within the bed, enabling visual assessment of regime transitions and particle dynamics under different operating conditions.
The results revealed that higher air flow rates decreased outlet air temperature but enhanced overall thermal efficiency, due to improved heat transfer. Smaller particles (e.g., SiO₂ at 310 µm) achieved higher bed and outlet air temperatures, while larger particles led to reduced thermal performance. These findings underscore the significance of particle size, density, and fluidisation dynamics in optimising solar receiver performance.
To complement the experimental work and gain deeper insight into the fluidisation dynamics, a coupled Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) simulation model was developed. This numerical approach enabled detailed analysis of particle-scale interactions and gas–solid flow behavior within the fluidised bed under varying operational conditions. Model predictions showed strong agreement with experimental results, in particle velocity distribution, bed expansion behavior and flow patterns. This integrated approach provides a robust framework for scaling up fluidised bed solar receivers and advancing the design of next-generation CSP systems.
