In this study, a solar-driven reduction process of nonstoichiometric cerium oxide in a fixed bed is optimized for efficient water splitting via metal-oxide-based redox cycling. Nitrogen is used as sweeping gas to scavenge oxygen from the beds during the reduction process. A transient lumped heat transfer model is developed for the simulation of the process. Parametric analysis and genetic algorithm are used to find the optimal N₂ flow rate and establish a novel N₂ feeding strategy with variable flow to maximize the thermal efficiency for water splitting. An efficiency close to 13% is estimated without solid-phase heat recovery, which is more than twice that of the best present experimental systems (∼5%). The results are regarded preliminary as a thermodynamic analysis.

Particles and condensing vapors contribute to the contamination of optical components of solar thermochemical reactors including windows and secondary concentrators and result in severe reactor performance deterioration. We propose an impinging-jet solar reactor in a distinctive topology to enhance aerodynamic-aided window protection. The vector fields on the two-dimensional inner surfaces of the impinging-jet reactor and four conventional reactors are analyzed for the first time using differential topology. The topological analysis demonstrates that the application of an impinging jet in the reactor leads to the prevention of the stagnation point in the vicinity of the window, which is inevitable in any axisymmetric flow field of the conventional reactors. The transient two-dimensional flow fields of all reactors are numerically investigated using the finite volume method to understand the effects of the reactor geometry, aspect ratio, and sweep gas mass flow rate on the window protection performance characterized by the contaminant residence time and peak volumetric concentration near the window. The impinging-jet reactors with aspect ratios of one and two are found to be the most effective designs in aerodynamic-aided window protection among all investigated configurations.