Nature-inspired geometrical design of a chemical reactor

We explore the possibility to actively use the system geometry to search for states of minimum entropy production in a chemical reactor. This idea is inspired by the energy-efficient mass and energy transfer that takes place in the reindeer nose thanks to its complex geometry. A cylindrical plug-flow reactor for oxidation of sulfur dioxide is used as example, while optimal control theory is used to formulate the problem. We hypothesize that the nasal anatomy of the reindeer has evolved to its present shape to help reducing energy dissipation during respiration in extreme ambient temperatures. A comparable optimal diameter-profile in the plug-flow reactor resulted in 11% reduction of the total entropy production, compared to a cylindrical reference reactor. With, in addition, an optimal reactor length, the reduction is 16%. These reductions are largely due to reductions in viscous dissipation. In practice, this translates into smaller pressure drops across the system, which reduce the loads of upstream/downstream compressors. Moreover, the peak in the temperature profile was reduced with respect to that obtained by controlling the temperature of the cooling medium. With today's technological solutions, the optimal diameter profile might be easier to realize than other optimal control strategies. The possible gains from this first example are encouraging, and may serve as inspiration for further applications. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.