Experimental investigation of hydrogen liquefaction performance and ortho-para hydrogen conversion kinetics in a small-scale hydrogen liquefier

Small-scale hydrogen liquefiers are promising for distributed hydrogen storage, but the coupled behavior of liquefaction performance and ortho-para hydrogen conversion requires further experimental investigation. In this study, an experimental small-scale hydrogen liquefaction platform was developed to investigate the effects of intake mode, pressure, and liquid nitrogen precooling. The results show that precooling significantly enhances liquefaction performance. At 160 kPa, the liquefaction rate increases from 0.053 kg/h without precooling to 0.159 kg/h with precooling, representing a threefold enhancement, and reaches 0.185 kg/h at 200 kPa. Continuous and intermittent intake modes achieve comparable liquefaction rates (0.159 and 0.161 kg/h, respectively), while intermittent intake provides flexible pressure control with reduced flow regulation requirements. During zero-boil-off storage, the para-hydrogen concentration was well described by a first-order model, yielding an effective mass-normalized conversion parameter of 0.27 min −1 .A variable-mass analysis further reveals the coupling between hydrogen dilution and catalytic conversion during liquefaction.