Predictive Simulation of Thermal Stratification and Transient Boil-Off from Cryogenic Liquids Using “Shortcut” Convection

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.