Prediction of boil-off gas in cryogenic tanks using a multi-zone thermodynamic model: filling height effects

Abstract

This study presents a comprehensive modelling and validation framework for accurate prediction of boil-off gas (BOG) in open-vent (quasi-isobaric) cryogenic liquid tanks containing LNG, LH₂, or LN₂. A multi-zone thermodynamic model (M–TDM) partitions the tank into vapour, interfacial, and liquid zones and couples them through a thermal-resistance network that resolves zone-specific, time-varying heat ingress as the instantaneous filling height evolves.

Whereas conventional TDM models estimate BOG with emphasis on total heat input and latent heat, the proposed M–TDM provides a more detailed treatment by explicitly modelling convective heat-transfer coefficients and effective contact areas, and by decomposing heat ingress into wall–to–liquid, wall–to–vapour, and interfacial components.

To verify the model’s predictive capability, experimental validation was conducted under open-vent operation using a horizontal Type-C LN₂ tank at three initial filling ratios (50%, 65%, and 80%), allowing quantitative comparison of time-dependent BOG rates. The M–TDM accurately reproduces the measured BOG trends with average errors below 5.4%, while achieving substantial computational efficiency—reducing the runtime from approximately 2.5 h (as required by SINDA/FLUINT) to about 10 s.

In particular, the results highlight that BOG generation is more strongly governed by the evolving wetted surface area and interfacial heat-transfer dynamics than by the initial fill level alone, offering new physical insights into cryogenic tank behavior. These findings demonstrate that the M–TDM, when combined with experimental validation and physical interpretation of filling-height effects, serves not merely as a numerical tool but as a physically grounded, experimentally supported methodology for insulation design, BOG management, and cryogenic system optimization.