Experimental Evaluation of Hydrogen Transfer Dynamics in a Multistage Metal Hydride Hydrogen Compressor

Metal hydride-based hydrogen compression (MHHC) is gaining interest as a non-mechanical alternative, offering silent operation and minimal moving parts, addressing key drawbacks of mechanical compressors. This study presents the development and performance analysis of a dual-stage MHHC. Two distinct thermochemical reactor configurations were designed and fabricated: a multi-spiral finned cooling tube reactor for the low-pressure stage and a tubular reactor for the high-pressure stage. The compressor absorbed hydrogen from a constant pressure source of 40-50 bar, compressing it to 130 bar in stage 1, followed by further compression to over 300 bar in stage 2. The system operated within a temperature range of 5-80 °C throughout the compression cycle. The study analyses the impact of coupling bed temperature, hydrogen inventory, cycle time, and injection pressure on compressor performance. The low-pressure bed temperature during coupling was identified as the most influential factor, impacting the hydrogen transfer rate by 1.5 times and delivery pressure by 52%. Injection pressure had a minimal effect, while hydrogen inventory significantly influenced compression performance. The rate of pressure rise dropped by 74% for 80% inventory, with delivery pressure decreasing by 45 bar when inventory dropped from 100% to 80% at identical delivery temperature. Although cycle time reduced significantly (37.8%) for 80% inventory, the highest compression rate of 14.6 L/min was achieved at 100% inventory. The developed compressor demonstrated a specific energy consumption of 55 kJ/L and achieved an isentropic efficiency of 7.4%.