Numerical investigation of the heat transport in a very loose packed granular bed air receiver with a non-uniform energy flux distribution

This study analyzes the heat transfer of the solar energy absorbed by the porous media receiver to air where the porous media can reach temperatures up to 1000 °C. The heat transfer was studied numerically for a packed granular bed air receiver with a non-uniform energy flux distribution. The conduction is modeled as an effective thermal conductivity with the Ergun equation used to describe the pressure drop. The radiative heat transfer is modeled by a modified P-1 radiative heat transfer model. The local thermal non-equilibrium model is used to relate the air temperatures to the porous media temperatures. Comparisons with experimental data show that this model can accurately predict the heat transfer in the packed granular bed air receiver. The model is used to analyze the effects of flow direction, gas mass flow rate per unit area, particle emissivity, estimated fractional contact area, and particle size. The results illustrate that downward flows, larger gas mass flow rates, higher particle emissivities, larger estimated fractional contact areas, and smaller particle sizes all enhance the heat transport and that the packed bed receiver outlet air temperature does not vary much for relatively short term fluctuations of the solar flux.