Catalytic wall microreactors external

In Chap. 7, the investigation on combustion stabihty is extended to propane-fueled catalytic microreactors, using the catalytic and gas-phase chemical reaction schemes of propane combustion on platinum proposed and validated in Chap. 4. The steady hetero-Zhomogeneous combustion of lean propaneZair and methaneZair mixtures in a platinum-coated, catalytic plane channel-flow microreactor were investigated at pressures of 1 and 5 bar, channel heights of 1.0 and 0.3 mm, and wall thermal conductivities of 2 and 16 WZmK. Stability limits were assessed as a function of fuel type, inlet velocity, and imposed external heat losses. Parametric studies were performed with a full-eUiptic, two-dimensional numerical model employing detailed gas-phase (homogeneous) reaction schemes for both fuels. 

In this chapter, a numerical investigation is undertaken to study the eoupled catalytic and gas-phase combustion processes in a methane-fueled microreaetor with catalytically aetive Pt walls. Simulations were carried out with the 2-D fiill elliptic model for both the gas and solid phases. Elementary hetero-Zhomogeneous chemical reaction schemes were included along with heat eonduction in the walls, surface radiation heat transfer, and external heat losses. The main objeetives were to investigate the interplay of hetero-Zhomogeneous combustion, transport, and heat transfer mechanisms in the microreactor and to delineate combustion stability maps in terms of the underlying parameters. 

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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