Boil-Off Gas Generation in Vacuum-Jacketed Valve Used in Liquid Hydrogen Storage Tank

The boiling point of liquid hydrogen is very low, at −253 °C under atmospheric pressure, which causes boil-off gas (BOG) to occur during storage and transport due to heat penetration. Because the BOG must be removed through processes such as re-liquefaction, venting to the atmosphere, or incineration, related studies are required to estimate the heat transfer of storage and transport devices and to improve insulation to reduce BOG generation. In this study, a vaporization analysis was performed on a vacuum-jacketed valve used in liquid hydrogen storage and transport devices to calculate the amount of BOG generation considering the flow characteristics at the vena contracta and the saturation temperature. At a pressure of 1 bar in the liquid hydrogen storage tank, the maximum fluid flow velocity and minimum static pressure occurred at the vena contracta, with values of 62.9 m/s and −0.4 bar, respectively, and the BOG generation rate was estimated as 0.132 m3/h, where the saturation temperature was minimized at 19.3 K. Furthermore, through case studies, when the pressure in the liquid hydrogen storage tank increased to 1.5 and 2 bar, the static pressure and saturation temperature decreased, and the BOG generation rate increased to 0.221 and 0.283 m3/h, respectively.