Answer to comment on: “CFD modeling of hydrogen production using steam reforming of methane in monolith reactors: Surface or volume-base reaction model?” by Mohammad Irani et al., Int J Hydrogen Energy 2011;36:15602–15610

In this answer to comment we pointed out that due to low residence time of reactants, there is no chance to penetrate in washcoat or the penetration depth is negligible. Therefore the reaction surface is equivalent to inner surface of channel. On the other hand uncertainties in obtaining the effective diffusion coefficients in the volumetric approach may cause a variation in simulation results.