Combustion in catalytic microreactors finds several applications due to the high energy density of hydrocarbon fuels. These include portable power generation, micro-propulsion, decentralised processing of fuels in thermally integrated micro-reactors, etc. Due to high surface area to volume ratio, high rates of catalytic reactions can be obtained compared to conventional devices. However, the large surface area also makes the system susceptible to extinction due to heat losses.
Heat recirculating geometries have shown to increase the range of stable operation of micro-reactors. The working principle for heat recirculating reactors is that the incoming cold reactant stream is preheated by transferring the excess enthalpy of the hot product stream. This involves carrying out reaction in a heat exchanger like assembly, to facilitate heat exchange between hot outlet and cold reactant streams. This can be achieved in simple geometries such as counter-current reactor, or in more complex Swiss-Roll geometries. Swiss-Roll geometry is especially popular in homogeneous and catalytically stabilised combustion in micro-burners.
In this work, we present numerical simulations for a new heat recirculating geometry. Specifically, we modify the Swiss Roll geometry to develop a heat recirculating micro-reactor with a spiral geometry. The inner walls are coated with catalyst. Thorough numerical simulations are presented for understanding the role of heat recirculation on thermal management and stability of the microreactor. The proposed geometry is simpler than the Swiss-Roll, while retaining the main advantage of larger area for heat transfer between the combustion channel and the incoming cold inlet stream. Coupling the micro-reactor with energy generation is also investigated using simple heuristics. We analyse the effect of geometry on stability of propane combustion in the micro-reactor, and compare the reactor with more traditional geometries.