Dynamics of cryogenic hydrogen storage in insulated pressure vessels for automotive applications

A dynamic model is used to characterize cryogenic H₂ storage in an insulated pressure vessel that can flexibly hold liquid H₂ and compressed H₂ at 350 bar. A double-flow refueling device is needed to ensure that the tank can be consistently refueled to its theoretical capacity regardless of the initial conditions. Liquid H₂ charged into the tank is stored as supercritical fluid if the initial tank temperature is >120 K and as a subcooled liquid if it is <100 K. An in-tank heater is needed to maintain the tank pressure above the minimum delivery pressure. Even if H₂ is stored as a supercritical fluid, liquid H₂ will form as H₂ is withdrawn and will further transform to a two-phase mixture and ultimately to a superheated gas. The recoverable fraction of the total stored inventory depends on the minimum H₂ delivery pressure and the power rating of the heater. The dormancy of cryogenic H₂ is a function of the maximum allowable pressure and the pressure of stored H₂; the evaporative losses cannot deplete H₂ from the tank beyond 64% of the theoretical storage capacity.