High-efficiency control strategies of a hydrogen turbo-expander for a 5 t/d hydrogen liquefier

Liquid hydrogen plays a crucial role in the large-scale storage and long-distance transportation of hydrogen energy. Effectively controlling hydrogen turbo-expanders is an important strategy for reducing energy consumption during liquefaction process. This study conducts both experimental and numerical investigations on a hydrogen turbo-expander within a 5 t/d hydrogen liquefaction system. A CFD model is developed to predict the performance of hydrogen turbo-expanders, which is then validated against experimental data. The numerical predictions of isotropic efficiency closely match experimental results, with a maximum deviation of 10 %. Throughout the cooling-down process, the efficiency of the hydrogen turbo-expander varies significantly, indicating a strong dependence on the characteristic ratio. Consequently, an optimal characteristic ratio method is proposed to maintain the hydrogen turbo-expander at peak efficiency. Compared to traditional control methods based on fixed brake pressure, the proposed approach achieves a maximum efficiency enhancement of 23.8 %. At the optimal characteristic ratio, the rotational speed can be maintained at the design level by adjusting brake pressure, which remains below the design value during the cooling-down phase. This investigation presents an effective method for optimizing the control of turbo-expanders in hydrogen liquefaction systems.