2. Methods
The highly exothermic reactor is illustrated schematically in Figure 1 with a catalytic heat-recirculating reaction chamber. The catalytic heat-recirculating micro-combustors are modeled as parallel plates of infinite width. This study focuses on the heat-recirculating combustor, for which there are two catalytically active inner walls, two outer walls, and one side wall. Unless otherwise stated, all walls are 0.2 millimeters thick. The combustion chamber length is 8.0 millimeters, with a gap size of 0.8 millimeters. This gap size is typical to the geometrical confinements of practical honeycomb combustors. Due to the high aspect ratio of the combustion channel, the combustor is modeled as a two-dimensional system. For the heat-recirculating combustor, premixed methane-air mixtures are sent into the central combustion chamber at ambient temperature, and then the hot products formed are split into two streams that flow into two recirculation chambers, each with a gap size of 0.4 millimeters. The 180° turns occur at 8.0 millimeters. The length of each recirculation chamber is 8.4 millimeters, as a result of the additional space from the turns. Based on these, the length of each outer wall is 8.6 millimeters, and the length of side wall is 2.4 millimeters. Unless otherwise stated, the inlet velocity is 0.8 meters per second, and a uniform inlet velocity profile is assumed. These values represent the nominal operating conditions. The parallel plate geometry implies that the third dimension is much larger than these gap sizes in order to ensure two-dimensional validity. To minimize the computational intensity, only half of the system is modeled by taking properly into account the geometrical symmetry.