Temperature-dependent matching of heat transfer and catalysis in cryogenic heat exchangers with ortho-para hydrogen continuous conversion

The energy-intensive nature of hydrogen liquefaction underscores the critical need for efficiency improvements. This study presents an approach to enhance the design and performance of hydrogen heat exchangers by optimizing the cold-to-hot fluid mass flowrate ratios across various temperature ranges, leading to substantial improvements in the Continuous Conversion Proximity Index (CCPI). A dynamic simulation model is developed to explore the complex interactions between temperature distribution, mass flowrate ratio, inlet conversion rate, and the heat transfer and catalytic efficiency in cryogenic hydrogen heat exchangers. Optimal cold-to-hot fluid mass flowrate ratios, ranging from 3.31 to 8.44 across the 80-33 K temperature range, are identified. In particular, a 23.0% improvement in CCPI is observed in the 40-33 K range, significantly optimizing the continuous catalytic conversion process. The results show that inlet conversion rates between 96% and 94% ensure effective heat transfer and high ortho-para hydrogen conversion efficiency, whereas rates below 94% lead to rapid conversion but insufficient cooling. These findings provide a theoretical foundation for the design of highly efficient hydrogen heat exchangers and demonstrate that optimizing the mass flowrate ratio can enhance the process within the exchanger, bringing it closer to an ideal continuous conversion form.