Numerical comparison of thermal energy performance between spouted, fluidized and fixed beds using supercritical CO2 as fluidizing agent

Abstract

The different thermal energy performance between spouted, fluidized, and fixed beds when using supercritical CO2 as a fluidizing agent was numerically investigated by employing a combined approach of Computational Fluid Dynamics (CFD) and Coarse-Grained Particle (CGP) methods. The model was first validated against experimental data available in the literature, confirming that the simulated particle velocity and temperature agreed well with the experimental measurements. The numerical results reveal that for the spouted bed, gas velocity, gas temperature, and convective heat transfer were higher in the spout region. Hence, most heat was transported directly from the inlet to the outlet of this system. For the fluidized bed, the particles near the gas inlet were quickly heated up at first, and a uniform temperature distribution was achieved in the whole bed during the later stages of the process. Concerning the fixed bed, its behavior is well-known with three temperature zones differentiated, which are a hot region, a cold zone, and the intermediate thermocline. Besides, numerical simulations allow further analysis in detail of the different heat transfer mechanisms in the configurations tested. Convection is the dominant mechanism in all cases. Conduction is noticeable in the fixed bed regime compared to the spouted or fluidized regimes, but even in this case, it is still an order of magnitude lower than the convection mechanism. Finally, thermal energy and exergy were also analyzed for the three beds.

Keywords

• Thermal energy storage
• Supercritical carbon dioxide
• Heat transfer
• Coarse grained particle method