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

초록

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.

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