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A volumetric solar receiver with composite porous structure is proposed, where a porous foam with different pore parameters from that in the other region of receiver is placed in the inlet near-wall region. Thermal performance of the solar receiver is numerically investigated. The local thermal non-equilibrium model is utilized to represent the energy transport within the porous foam. Radiative transfer in the porous foam due to high temperature combined with the transport of concentrated solar radiation inside the receiver is solved using the P1 approximation. Thermal behavior comparison is made between the receiver with composite porous structure and that with single porous layer. The effects of different pore parameter designs are discussed. The results indicate that there exists a large temperature gradient in the solid phase for a solar receiver with single porous layer. Using low porosity and small mean cell size in the inlet near-wall region for the receiver with composite porous structure can reduce the solid temperature gradient and increase the mean fluid outlet temperature. [ABSTRACT FROM AUTHOR]

The absorption of concentrated solar radiation within volumetric receiver is the key step that governs the global efficiency of solar thermal systems. An integrated radiative transfer model combined the dish concentrator, solar window and porous absorber is developed. The distribution of absorbed radiation energy in the porous absorber and the optical performance of the entire system are investigated by a Monte Carlo ray tracing simulation. The detailed radiation transport within the solar window and porous absorber is fully considered. The effects of porous structure parameters, slope error of concentrator and the alignment error of receiver are analyzed. The results show that the optical losses due to the back scattering from porous absorber and the absorption and reflection of solar window have a significant influence on the optical performance of system. The porous structure parameters greatly affect the distribution of solar radiative source within the porous absorber. In addition, the optical efficiency decreases noticeably when the slope error and alignment error exist. [ABSTRACT FROM AUTHOR]