Ammonia Decomposition for Hydrogen Production in Catalytic Microchannels with Slip/Jump Effects

The rarefaction effects on the catalytic decomposition of NH۳ in ruthenium–coated planar microchannels is numerically simulated in the Knudsen number range ۰.۰۱۵-۰.۰۳. A colocated finite–volume method is used to solve the governing equations. A concentration jump model derived from the kinetic theory of gases is employed to account for the concentration discontinuity at the reactive walls. A detailed surface reaction mechanism for ammonia decomposition on ruthenium along with a multi-component species diffusion model are used to study the effects of concentration jump coupled with velocity slip and temperature jump on the walls. The velocity-slip, temperature-jump and concentration-jump boundary conditions have miscellaneous effects on flow, temperature and species concentration fields. The results suggest that the velocity-slip boundary condition only slightly influences the species distribution at the edge of the Knudsen layer as well as inside the channel, while the temperature-jump boundary condition affects the heat and mass transfer characteristics the most. The concentration-jump effect, on the other hand, can counter balance the temperature-jump effects in some cases.

Keywords:

Ammonia decomposition , Heterogeneous reactions , Concentration jump , Velocity slip , Temperature jump , Microchannel