Pressure–composition design-space optimization of H2-He-Ne working fluids for 20–100 K shipboard LH2 cold-energy recovery

Shipboard LH 2 regasification releases substantial cold energy in the 20-100 K range, where working fluid applicability, heat matching, and pressure limits strongly constrain recovery performance. This study maps the pressure-composition design space of H 2 -He-Ne working fluids for a supercritical closed Brayton type loop coupled with a direct expansion branch. Cycle pressure and composition are optimized for net power output and total annualized cost, while working fluid mass flow rate is scanned as a cycle-scale variable. The results show that pure H 2 defines the high-output boundary, pure Ne represents a low-cost but low-utilization boundary, and the engineering compromise is located in the H 2 -rich mixture region rather than at a pure fluid endpoint. Equipment cost and exergy results indicate that high-output designs require larger compressor, expander, and heat transfer capacities. Mass flow scanning identifies a scale benefit plateau near 1.00-1.15 kg/s, beyond which further scaling provides limited benefit.