Topology optimization of microreactors for hydrogen production by ammonia catalytic decomposition

Microreactor is a promising technique for producing hydrogen by ammonia catalytic decomposition. In this study, a topology optimization (TO) model is developed to optimize the distribution of porous catalysts in microreactors to improve the conversion from ammonia (NH₃) to hydrogen (H₂), which considers the fully coupled processes of flow, heat transfer, mass transport and reaction with variable physical properties. Dual objectives of reducing the flow resistance and decreasing the average temperature of the microreactor are employed for the TO model to generate innovative structures. The effects of different weight coefficients, input heat, volume fractions of the catalyst, and microreactor sizes on TO structures are explored. As validated by three-dimensional (3D) simulations, the TO microreactor can obtain lower pressure drop, lower average temperature, and higher NH₃ conversion compared to traditional microreactors. At a weight coefficient of 0.95 and a catalyst volume fraction of 0.6, the optimized microreactor shows a 5.78% increase in NH₃ conversion, an 18.05% decrease in pressure drop, and a 4.26% decrease in average temperature compared to the traditional straight-channel microreactor. Finally, it is interesting to find that all TO structures generated are characterized by the gradually decreased size of the catalyst block along the flow direction which allows more NH₃ to be decomposed at higher temperature regions with higher reaction rates, leading to higher conversion. The present study provides valuable insights for the design of next generation microreactors with enhanced performance.