Radiative Heat Loss Control from Solar Reactors with Spherical and Hemispherical Cavities

Spherical and hemispherical cavity-type solar reactors are proposed and compared with current solar reactors with cylindrical-type cavities. For solar reactors with these unique geometries, inner cavity areas directly illuminated by solar radiation are highly absorptive, while other regions are highly reflective. Ray-tracing simulations indicate that thermal emission from solar reactors with these unique geometries can be reduced by up to [Formula: see text] compared to traditional cylindrical-type solar reactors. Such a significant reduction in thermal radiation occurs because spherical and hemispherical cavities, with proper designs, are directional emitters, whereas traditional cylindrical cavities are omnidirectional emitters. Thus, thermal radiation from these two types of cavities is mainly confined to a small polar angle range, which is about the same as the divergence angle of concentrated solar radiation. The nearly one-order reduction in radiative loss from spherical and hemispherical cavity-type solar reactors allows them to operate at temperatures exceeding 1500 K under [Formula: see text] concentration, which is required for many critical thermochemical reactions, such as those for green aviation fuel production.