Development of a microreactor as a thermal source for microelectromechanical systems power generation

An alumina ceramic 12.5 X 12.5 X 5.0 mm microreactor was constructed using a modified stereolithography process. The design was based on a "Swiss roll" concept of double spiral-shaped channels to facilitate a high level of heat transfer between the reactants and combustion products and wall surface contact of the flow through the microreactor body. Self-sustained combustion of hydrogen and air mixtures was demonstrated over a wide range of fuel/air mixtures and flow rates for equivalence ratios from 0.2 to 1.0 and chemical energy inputs from 2 to 16 W Depositing platinum on gamma alumina on the internal walls enabled catalytic ignition at or near room temperature and self-sustained operation at temperatures to 300 degreesC. Catalyst degradation was observed at higher operating temperatures and reignition capabilities were lost. However, sustained operation could be obtained at wall temperatures in excess of 300 degreesC, apparently stabilized by a combination of surface and gas-phase reaction phenomena. A global energy balance model was developed to analyze overall reactor performance characteristics. The reactor design and operating temperature range have potential applications as a heat source for thermoelectric and pyroelectric power generation at small scales compatible with microelectromechanical systems applications.