Evaporation prediction method for long-term storage of large liquid hydrogen tanks incorporating para- and ortho-hydrogen conversion heat effects

Accurately predicting liquid hydrogen phase change and the associated unsteady heat and mass transfer, along with identifying the dominant mechanisms governing pressurization, remains a significant challenge for liquid hydrogen storage and transportation systems. To address this, an evaporation-pressurization prediction model is proposed for liquid hydrogen tanks. This model accounts for para-hydrogen and ortho-hydrogen conversion driven by vapor-liquid temperature and property differences. The model's accuracy is validated against experimental data. A quantitative analysis method is introduced to evaluate how hydrogen vapor thermophysical parameters influence the pressurization rate under varying operational conditions. Using this method, the effects of tank volume, vapor superheat, and liquid filling level on internal pressure, temperature, and phase change are investigated. The results indicate that the pressurization rate decreases with increasing tank volume. Concurrently, a more rapid vapor temperature rise enhances the heat absorption associated with para to ortho hydrogen conversion, which further suppresses evaporation. Vapor superheat influences the internal temperature and evaporation rate via its effect on vapor phase enthalpy and by driving para to ortho hydrogen conversion. Under high vapor superheat conditions, variations in the corrected density become the dominant factor affecting the pressurization rate. Furthermore, the filling level primarily governs the vapor temperature rise, thereby regulating both the evaporation rate of liquid hydrogen and key pressurization factors. Higher filling levels correspond to a lower pressurization rate.