Magnetic refrigerator for hydrogen liquefaction

• This paper reviews the development status of magnetic refrigeration system for hydrogen liquefaction.
• FOM of magnetic refrigeration system for hydrogen liquefaction needs to be larger than 0.57 from a viewpoint of consuming energy.
• A high efficient system with >80% liquefaction efficiency by using the heat pipe.
• The AMR systems with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 s of the cycle were shown.
• Efficiency of magnetic hydrogen liquefaction plant for 10 kg/day is estimated to be 0.47 of FOM between 20 K and 77 K including LN2 work input.

This paper reviews the status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. When we compare the consuming energy of hydrogen liquefaction with high pressurized hydrogen gas, FOM must be larger than 0.57 for hydrogen liquefaction. Thus, we need to develop a highly efficient liquefaction method. Magnetic refrigeration using the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency >50%, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system with >80% liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 s of the cycle. By using the simulation, we estimate the efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained for operation temperature between 20 K and 77 K including LN2 work input.