Effect of Geometric Scale on Heat Recirculation and Syngas Production in a Noncatalytic Counter-Flow Reformer

Hydrogen-based systems, such as fuel cells, are a promising means to satisfy portable and remote power demands. Hydrogen transportation and storage challenges can be met with point-of-use reforming of hydrocarbon fuels to hydrogen-rich syngas. Applications may require geometric scaling of system components, including the fuel reformer. This study computationally investigates, via a two-dimensional computational fluid dynamics (CFD) model, the effect of scaling on a noncatalytic counter-flow reformer that utilizes heat recirculation to convert hydrocarbon fuels to syngas. The dimensions of the counter-flow reactor studied previously are used as reference values, and the reactor volume is scaled relative to the reference volume by varying either channel height or length. Operating range maps are developed that indicate where reactor operation is obtained as a function of equivalence ratio and inlet velocity. Heat recirculation, hydrogen, carbon monoxide, and methane conversion efficiencies are quantified over a range of inlet velocities and equivalence ratios. Computationally determined peak gas and wall temperatures are compared to adiabatic equilibrium temperatures. This analysis relates the degree of superadiabicity, the extent to which the temperature exceeds that predicted by equilibrium in the reactor to the more readily measured wall temperatures, which have previously been shown to be important indicators of reactor performance.