Thermal radiation and the second law

The purpose of this paper is to collect and interrelate the fundamental concepts about second law analysis of thermal radiation. This heat transfer mode plays a leading role in solar energy utilization and in high-temperature devices, representing a significant contribution to irreversibility that is frequently omitted in engineering analysis. Entropy and exergy of thermal radiation are reviewed first. Radiative transfer processes are reviewed next, including exchange between surfaces, the presence of a participative medium, and the analysis of combined heat transfer modes. Emphasis is put on grey body radiation when treating with non-black body radiation, due to its relevance in engineering applications. The mathematical formulation of second law analysis of thermal radiation is complex, which limits its use in conventional heat transfer analysis. For this reason, numerical approaches reported to date deal with quite simple cases, leaving an open promising field of research.