Integration of heat recirculating microreactors with thermoelectric modules for power generation: a comparative study using CFD

Heat recirculating microreactors are being investigated for coupling with thermoelectric generators (TEGs) for power generation since they facilitate sustained combustion over a wide range of operating conditions. A major challenge in autothermal operation of the integrated microdevice is to sustain stable combustion in the presence of energy consuming devices and heat sinks, while operating below the temperature limitation of the TEG module. Although heat recirculation improves stability, proper thermal management and optimum heat recycling are necessary to meet these challenges. Hence, two heat recirculating geometries, viz. the U-bend and symmetric-heat recirculating reactor (S-HRR), are considered for integration with TEG modules and their performances as coupled devices at steady state are compared. We analyze the effect of heat recirculation in the U-bend and S-HRR geometries on the performance of the coupled devices, with power generated, fuel conversion, and extinction velocities as the performance metrics. A higher area is available for exchange of excess enthalpy between products and reactants in the S-HRR, resulting in stability at a lower equivalence ratio and higher propane conversion than in the U-bend. The impact of increased heat removal on the cold side is investigated, the performance of the reactors is compared, and the preferred operating regions for the two geometries are identified.