Experimental and numerical study on the reflectance losses of the porous volumetric solar receiver

The reflectance losses are the predominate energy losses in solar radiation transfer process for the porous volumetric solar receiver. However, few studies pay attention to the influence of geometrical parameters of porous media on the reflectance losses, and the data of reflectance losses of porous volumetric solar receiver in solar spectrum is not complete. In this paper, both experimental and numerical simulation methods are applied to comprehensively investigate the reflectance losses of the porous volumetric solar receiver. A series of silicon carbide reticulated porous ceramics (SiC RPCs) is fabricated by replica method and recoating technique. The reflectance losses are measured based on UV-VIS-NIR spectrophotometer. Meanwhile, porous models with different geometrical parameters are artificially reconstructed. Monte Carlo Ray Tracing method is used to calculate the total reflectance. The results present that the SiC RPCs exhibit small reflectance losses in the solar spectrum with a peak at about 420 nm. The geometrical parameters, such as porosity and pore diameter do not change the spectral behavior but only influence the magnitude of the reflectance. Larger porosity and larger pore diameter are beneficial for reducing the reflectance losses. The correlation of the reflectance losses as functions of pore density and porosity has been developed. Furthermore, the influence of the incident angle of radiation on reflectance losses is studied. Relatively large increase is observed as the incident angle is larger than 30°. This phenomenon becomes more obvious for the porous media with larger porosity or larger pore diameter.