Impact of Channel Wall Material Properties

The more favorable start-up times for cordierite are mainly attributed to its lower thermal conductivity. Before ignition, axial heat conduction in the solid is less pronounced for the ceramic material, due to its lower k. Heat generated on the surface cannot diffuse away from the reaction front located near the channel exit at a fast enough rate this leads to the formation of a spatially confined reaction zone (see in Fig. 8.9a the more pronounced hot spot at the reactor rear-end), which in turn promotes faster fuel consumption and leads to faster light-off. This faster light-off is also attributed to the fact that less heat is accumulated in the cordierite compared to the FeCr alloy. In Fig. 8.10, thermal power generated by surface 

While at steady state in both cases the same thermal power output is achieved ( 99.99% fuel conversion), in Case 5 (cordieritc) a smaller amount of energy is stored in the reactor wall as sensible heat. By integrating the Pacc curves in Fig. 8.10 until it is deduced that for cordierite 11.8 J are required to raise the 

It should be emphasized that the aforementioned observations regarding material behavior are in stark contrast to steady-state catalytic microreactor results [17]. At steady state, FeCr alloy microreactors provided more robust combustion (extended stability limits) against imposed external heat losses when compared to ceramic ones. On the other hand, the present transient studies clearly show the advantage of ceramic materials in terms of start-up. However, in either steady or transient operation, cordierite microreactors lead to higher wall temperatures (see Fig. 8.9). Both facts must be considered when selecting appropriate reactor materials for specific applications. 

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