Flow characteristic analysis under variable conditions in a hydrogen turbo-expander for a 5 t/d hydrogen liquefier

Liquid hydrogen plays a critical role in large-scale hydrogen storage and long-distance transport. The primary cost associated with liquid hydrogen supply is attributed to the liquefaction consumption. The hydrogen turbo-expander, a pivotal component in industrial hydrogen liquefaction plants, is instrumental in determining liquefaction costs. Improving the efficiency of the expander offers a significant opportunity for cost reduction. This paper commences by validating the loss model employed to assess the hydrogen turbo-expander using numerical simulation results. Subsequently, a regional division model is introduced for the expander impeller passage to identify the locations of various losses. Under diverse operational conditions, the boundaries of regions are determined through a comparison between the loss model and numerical simulation. Finally, an examination of losses in the hydrogen turbo-expander is conducted using Computational Fluid Dynamics (CFD) results under varying operating conditions, yielding the following insights. With an increase in the expansion ratio of the hydrogen turbo-expander, the isentropic efficiency initially rises and then declines. Among the various losses observed under variable working conditions, incidence loss emerges as the most critical factor. When the expansion ratio is small, a negative attack angle forms at the impeller inlet, causing chaotic flow within the channel and an increase in passage loss.