Design of a novel hat-shaped spiral solar thermochemical reactor with improved thermal matching for enhanced hydrogen production

The transition toward low-carbon energy systems has increased the demand for clean hydrogen production. However, conventional steam methane reforming (SMR) relies on fossil fuel combustion and leads to significant CO 2 emissions. Solar-driven thermochemical reforming provides a promising alternative, but non-uniform solar flux distribution in concentrating systems results in severe temperature gradients and limits reactor performance. To address this issue, a novel hat-shaped double-spiral solar thermochemical reactor is proposed to achieve three-dimensional thermal matching between non-uniform solar irradiation and reaction pathways. A comprehensive numerical model incorporating heat transfer, fluid flow, and reaction kinetics is developed to investigate reactor performance. The results show that reactants are progressively converted along the spiral channel, with intensified reactions in the central high-temperature region due to enhanced heat utilization, where methane conversion exceeds 50% and hydrogen production dominates. A trade-off between conversion efficiency and temperature uniformity is observed under different inlet configurations. Under edge inlet conditions, a solar thermochemical conversion efficiency of 39.76% is achieved, accompanied by a large temperature difference of 458.85K. By introducing reactants directly into the central high-temperature region, the maximum efficiency further increases to 39.97%, while the temperature difference decreases to 116.05K, representing a 3.95-fold improvement in temperature uniformity. Exergy analysis further confirms that the proposed thermal-matching strategy improves the utilization of concentrated solar energy while reducing thermodynamic irreversibility. Overall, the proposed reactor provides an effective strategy for simultaneously enhancing solar energy utilization, thermochemical conversion efficiency, exergy performance, and temperature uniformity in solar thermochemical hydrogen production.