A model has been developed and implemented in the software package BoilFAST that allows for reliable calculations of the self-pressurization and boil-off losses for liquid hydrogen in different tank geometries and thermal insulation systems. The model accounts for the heat transfer from the vapor to the liquid phase, incorporates realistic heat transfer mechanisms, and uses reference equations of state to calculate thermodynamic properties. The model is validated by testing against a variety of scenarios using multiple sets of industrially relevant data for liquid hydrogen (LH2), including self-pressurization and densification data obtained from an LH₂ storage tank at NASA’s Kennedy Space Centre. The model exhibits excellent agreement with experimental and industrial data across a range of simulated conditions, including zero boil-off in microgravity environments, self-pressurization of a stored mass of LH₂, and boil-off from a previously pressurized tank as it is being relieved of vapor.

Boil-off from cryogenic liquids is a significant economic, operational, and safety challenge across the global energy industry, yet existing models lack the scope and predictive capability needed to simulate boil-off across a range of fluids and storage conditions. This work introduces a new, one-dimensional lumped parameter model for predicting boil-off from a variety of fluids under a range of storage conditions. The new model divides the liquid into discrete, homogeneous layers coupled by a set of heat and mass transfer equations and can capture liquid-phase thermal stratification effects and compositional changes as the tank both self-pressurises and operates isobarically. During pressurisation, the model simulates convection within the liquid by dividing it into conduction and convection domains and calculating boundary layer and recirculation flowrates within the latter. During isobaric operation, the model applies a shortcut convection term that allows ambient heat ingress into a layer to be transferred to the liquid surface where it generates boil-off instead of heating the liquid. Unlike previously published works, this model does not require manipulation of adjustable parameters to describe pressurisation and boil-off rates relative to experimental data. It thus offers improved predictive capability compared to existing homogeneous-phase models, with applications to the design of boil-off handling systems, maritime shipping, and long-term storage of cryogenic liquids.