Design of experiments-based optimization of supersonic nozzles for enhanced methane capture

Abstract

Computational fluid dynamics (CFD) simulations are employed in this study to optimize key geometric parameters of supersonic nozzles, aiming to enhance methane capture efficiency through non-equilibrium condensation mechanisms. A Design of Experiments (DoE) approach was used to systematically vary key geometric parameters of a converging-diverging Laval nozzle, including inlet radius, throat radius, divergence angle, and section lengths. The non-equilibrium condensation of CH4 under metastable conditions was modeled using a custom implementation of Classical Nucleation Theory. The computational model demonstrated high accuracy when validated against experimental data for both steam and CO₂, supporting its reliability for multi-species condensation simulations. Performance metrics including exergy loss, thermal efficiency, and condensation efficiency were evaluated across 32 nozzle configurations. Four designs demonstrated superior performance, with one configuration (Run ID 22) emerging as optimal, exhibiting the highest condensation efficiency and extensive supercooling zones. The optimized design maintained stable performance across a range of inlet temperatures (240–260 K) and pressures (65–75 bar). The optimized design maintained thermal efficiencies above 91% and exergy losses below 10% and maximum condensation efficiency of 17% across a range of inlet conditions. This work establishes a foundation for designing efficient supersonic separators for methane capture, with potential applications in natural gas processing and greenhouse gas mitigation.