Multilayer active magnetic regenerator refrigeration for high-efficiency hydrogen liquefaction

Magnetocaloric refrigeration offers a potential approach for cryogenic hydrogen liquefaction by providing refrigeration near the hydrogen boiling point of 20.3 K. The system mainly comprises an active magnetic regenerator (AMR) packed with magnetocaloric material and a magnetic source composed of a NbTi superconducting magnet. Due to the appreciable magnetocaloric effect and wide operational range of HoAl 2 , it is commonly used for hydrogen liquefaction applications. To further improve the performance of magnetocaloric refrigeration systems, multilayer AMRs are used to widen the operating temperature span. The performance of dual-layer AMR beds composed of ErAl 2 + HoAl 2 and HoB 2 + HoAl 2 is numerically investigated and compared with a single-layer HoAl 2 AMR. A finite-element model developed using COMSOL Multiphysics is employed to analyze the transient thermal behavior and evaluate the refrigeration capacity ( Q R ) and second-law efficiency ( η II ) at a cold-end temperature of 20 K and hot-end temperatures of 25–35 K. Different packing ratios of the constituent magnetocaloric materials are examined to identify suitable multilayer configurations. The ErAl 2 + HoAl 2 configuration achieves a maximum Q R of 87.9 W, compared with 84.9 W for HoB 2 + HoAl 2 and 55.3 W for single-layer HoAl 2 . The corresponding maximum η II values are 0.809, 0.512, and 0.517, respectively. These results demonstrate that appropriately designed dual-layer magnetocaloric materials can enhance AMR refrigeration capacity and, under suitable operating conditions, second-law efficiency over the investigated temperature range, highlighting their potential for cryogenic hydrogen liquefaction.