Thermodynamic analysis of the effect of initial ortho-hydrogen concentration on thermal behaviors for liquid hydrogen tanks

Abstract

Due to the extra evaporation loss caused by the ortho-para hydrogen conversion (OPHC) during the storage and transportation of liquid hydrogen (LH2), the initial concentration of ortho-hydrogen (o-H2) plays an important role in the large-scale safe operation and utilization of LH2. However, there are very limited studies focusing on clarifying the impact of the OPHC on thermal behaviors of LH2 tanks. In light of this, this paper establishes and develops an extended thermal multi-zone model that couples the OPHC process with the mass and energy conservation equations of the ullage and liquid for an LH2 tank. With the help of the model, a thermodynamic analysis of the pressurization rate is performed to obtain the dominant parameter that evaluates the effect of the initial o-H2 concentration on the pressure build-up process. The results indicate that the interfacial mass transfer rate caused by the OPHC is the dominant parameter accounting for more than 90% of the effect of all parameters on the pressurization rate during a 10-day process with an initial liquid fill ratio of 90% and a heat leakage of 40 W. Additionally, the effect of the initial o-H2 concentration on the optimal liquid fill ratio is discussed in this paper. The results indicate that when the initial o-H2 concentration changes from 0.2% to 10%, the optimal liquid fill ratio decreases from 82.5% to 74%. The present work provides theoretical support and guidance for controlling the o-H2 concentration to realize the long-term and high-efficiency storage of LH2.