Thermal management in catalytic microreactors

In reactors with one or two physical dimensions in the microscale and the remaining dimensions in the mesoscale or macroscale, thermal uniformity is often assumed. However, this assumption is not necessarily correct, especially for well-insulated reactors with fast reaction chemistries. In this paper, a catalytic microreactor with "tunable" wall thermal resistance (conductivity and thickness) is fabricated. Changing the thermal properties of the wall of this reactor is found to have a substantial effect on reactor thermal uniformity but only a slight effect on conversion and extinction limits. Further experiments show that the flow rate and feed composition for this reactor have a large effect on the operating temperature but only a moderate effect on thermal uniformity. An analysis of the overall energy balance of this system indicates that more than 50% of the generated heat is lost to the surroundings before the fluid exits the reactor, although this energy exchange becomes less efficient as the flow rate increases. Computational fluid dynamics simulations suggest that the reaction is limited by heat transfer near the entrance and by mass transfer further downstream, despite the small length scales of this system.