Wave Reformer Channel Shape Design for Enhanced Hydrogen Pyrolysis

Abstract A wave reformer utilizes shock-wave heating resulting from pressure exchange between a driver and a driven (reactant gas) to initiate a thermal decomposition reaction. Although widely applicable to many reactions, this paper will focus on the thermal pyrolysis of methane to produce hydrogen and solid (black) carbon. It uses wave rotor technology that has been applied to other applications but developed specifically here for high-temperature pyrolysis by New Wave Hydrogen, Inc. (NWH). This research uses a quasi-two-dimensional (Q2D) model implemented in ansysfluent to study the influence of new channel design features on the unsteady flow field and performance characteristics of the wave reformer. The primary objective of the work is to investigate the impact of variable area channel design on peak temperature (a proxy for thermal pyrolysis), which has received limited attention in existing literature. The model numerically solves the three-dimensional (3D), compressible, and unsteady Navier–Stokes equations, employing the k–ω SST turbulence model for closure. Additionally, it utilizes a cell-centered approach coupled to multispecies transport equations and a one-step finite-rate chemistry model. The channel's curvature is controlled with sigmoid functions to ensure a smooth area transition along the channel. The Q2D results reveal that as the fluid traverses the converging channel, its temperature increases due to the rising internal energy, necessary for enhancing hydrogen yields. However, an over-reduction in channel cross section results in a decrease in the driven mass flow rate, subsequently lowering the mass flow ratio. This work shows that, above a given threshold, there is a significant benefit to implementing converging channel designs in wave reformers for enhanced shock heating.