Single-Channel Parametric Study

In the ensuing calculations, power outputs were computed and eombustion efficieneies were estimated. The wall thermal conductivity was set to — 2.0 or 14 W/mK, thus simulating a eeramie and a metalhc reactor (those values roughly correspond to cordierite and FeCr alloy materials, respectively). Mixture compression was fixed at p = 2.5 bar, the equivalence ratios were q — 0.40, 0.35 and 0.33, while the channel wall thickness was (5 = 0.1 mm. The fortheoming diagrams were constructed by one-parameter continuation of the mixture inlet velocity Uw, which was increased until a critical value was reached with a marked drop in reactor performance. The main objective was to construct power eurves for a given set of reactor geometry, properties, and inlet conditions. An example of the results obtained can be seen in Fig. 5.3, where temperature and fuel distributions 

Thermal power curves and combustion efficiencies for a reactor of length L — 15 mm with a channel cross-section of 1 x 1 mm are summarized in Fig. 5.4. The velocity ranges from C/jn = 0.5 m/s, set as initial velocity for all cases studied in this work, to 5.0 m/s the latter is arbitrarily chosen as a representative value where the combustion efficiency (defined as the temperature rise of the gas at the channel outlet over the potential adiabatic temperature gain) drops significantly. 

For moderate inlet velocities, which can reach up to 2.5 m/s for the conditions of Fig. 5.4, a linear increase in power output is observed with rising inlet velocity. The combustion efficiency remains high since almost complete fuel conversion is achieved ( 99.99%), while the power output is directly proportional to the equivalence ratio. As long as fuel conversion is nearly complete, no difference is observed between reactors of different solid thermal conductivities. The linearity in reactor response ceases as the inlet velocity approaches a critical value. With increasing inlet velocity, every power curve reaches a maximum. These maxima lie at combustion efficiencies (i.e. fuel conversions) of 71-83% for all cases considered. 

The effect of wall thermal conductivity is pronounced at high inlet velocities, where increased efficiency is observed in the case of high solid thermal conductivity, as seen in Fig. 5.5 pertaining to U-m = 3.7 m/s. In this graph, axial profiles of the energy heat balance terms in the solid are provided in terms of all modeled heat transfer modes heat generated via reactions on the surface, heat convected to the 

A small amount of heat is conducted inside the solid wall for = 14 W/mK (the 

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The foregoing parametric study of a single catalytic channel dictated the construction of a mesoscale combustor with metallic walls, operating at high inlet velocities and low equivalence ratios, with the dimensioning mentioned in the experimental section. The combustor was subsequently tested for the experimental conditions of Table 5.2. 

A propane-fueled, catalytic, mesoscale combustor was investigated numerically and expetimentaUy to assess its apphcabihty for a portable, gas-turbine-based power generahon system. After detailed parametric numerical studies of a single catalyhc channel, a subscale model of the metallic catalytic combustor was constructed. Experimental testing verified the suitability of the proposed mesoscale combustor after meeting flie required power output at the nominal mass throughput. A continuum model was used to simulate the two-dimensional temperature field of the monolith and allowed for a detailed description of the heat loss mechanisms in the monolith. 

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