Improving hydrogen liquefaction efficiency based on the temperature-distributed refrigeration method in regenerative refrigerators

Liquid hydrogen has more advantages than gaseous hydrogen in terms of economy and convenience of storage and transportation owing to its higher energy density. Therefore, the hydrogen liquefaction technology is conducive to promotion and application for hydrogen energy in many sectors. The small-scale regenerative refrigerators usually use helium as the working fluid, which is of the high-low temperature cycle, and bring about a significant entropy generation during the cooling process. In this work, the study on the liquefaction rate and FOM (figure of merit) is implemented with a working fluid of hydrogen. It shows that the entropy generation much decreases when applying the distributed refrigeration method comparing to the high-low temperature cycle, and the COP (coefficient of performance) reaches 80 % when cooling the sensible heat load and conversion heat. The calculation results indicate that the liquefaction rate of the temperature-distributed cycle reaches 34.32 L/d at a refrigeration power of 15 W (a representative case). While the maximum of FOM is 0.483, which is improved by 21.7 % compared with the high-low temperature cycle.