Advances in porous volumetric solar receivers and enhancement of volumetric absorption

Porous volumetric solar receivers are one type of solar receivers that can volumetrically absorb solar radiation and achieve efficient solar-to-thermal energy conversion. Porous volumetric solar receivers have been developed since 1980s. In this review, we focus on the development progress of the atmospheric and pressurized porous volumetric solar receivers, in which the structural designs, the material selections, the experimental research methods, the comparison of thermal performance, and the transient response characteristic of the receivers were reviewed. On the other hand, the theoretical research methods including the direct pore-scale and volume averaging simulations were introduced. The pore-scale reconstruction method and the procedure to investigate the fluid flow and heat transfer processes at the pore-scale were presented. For the volume averaging method, detailed descriptions for the selection of empirical parameters in the governing equations to be solved were summarized. Typical research results based on these methods were presented and research limitations were also pointed out. Furthermore, the methods for the enhancement of volumetric absorption and the improvement of thermal efficiency of the receivers have been comprehensively reviewed. Two methods including geometrical parameters optimization and spectrally selective absorption were presented in detail. This review will provide a better understanding of the development and research methods for porous volumetric solar receivers, and inspire future studies for the performance improvement of the receivers.