Design and optimization of a uniform full-circumference solar thermal chemical reactor operating at high temperature based on elliptical bifocal optical properties

A solar reactor design methodology utilizing elliptical bifocal optical properties is proposed to address severe temperature non-uniformity caused by uneven flux distribution in high-temperature solar thermochemical processes. The system features an optical configuration where point-focused radiation is concentrated at the primary focal point, diverged by a specially designed refractor, and subsequently reflected by the ellipsoidal cavity to uniformly reconverge onto the reactor surface at the secondary focal point. Based on an error-validated model, simulations were performed to synergistically optimize key parameters—including elliptical eccentricity, reactor position, and prolate-pear refractor geometry—through parametric investigation and particle swarm optimization. This reduced the relative standard deviation of energy flux density to 17.82, representing an 80.1 % improvement over conventional direct irradiation systems. Multiphysics validation using methane steam reforming demonstrated exceptional performance: maximum temperature difference was reduced to 28.53 K (71.98 % decrease) while achieving 99.12 % methane conversion (8.67 percentage-point increase). This design strategy demonstrates broad applicability in high-temperature solar thermochemical processes, including methane dry and steam reforming. By fundamentally shortening the radiative heat transfer path, it effectively eliminates thermal resistance-induced temperature imbalances in porous media, thereby preventing the formation of local hotspots and avoiding potential damage such as sintering and carbon deposition in solar reactors.