Modelling of Liquid Hydrogen Boil-Off

Abstract

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.

Modelling of Boil-Off and Sloshing Relevant to Future Liquid Hydrogen Carriers

“…Note that the fuel depletion rates of the LH2 tanks without reliquefaction (~0.6%/day, see Table 11b) are of a similar order to the existing, stationary tank modelled in Al Ghafri et al (~0.7 to 0.8%/day) [43]. This reinforces that the tanks are appropriately insulated for calm weather, despite not being insulated enough for the boil-off rate to be equal to the fuel utilization rate, as in Section 5.2.…”

“…The control volumes are annotated with symbols representing relevant properties of the liquid and vapour phases and heat, mass, and enthalpy transfer rates to and from them. This approach is similar to those presented in Al Ghafri et al and Petitpas et al [29,43]. In this study, however, the tanks are unsealed, so the internal tank pressure is assumed to be constant.…”

“…The latter value is determined by multiplying the fuel depletion rate (measured in ton/day) by current prices per ton of each fuel [73,74]. Note that the fuel depletion rates of the LH2 tanks without reliquefaction (~0.6%/day, see Table 11b) are of a similar order to the existing, stationary tank modelled in Al Ghafri et al (~0.7 to 0.8%/day) [43]. This reinforces that the tanks are appropriately insulated for calm weather, despite not being insulated enough for the boil-off rate to be equal to the fuel utilization rate, as in Section 5.2.…”

Reducing Hydrogen Boil-Off Losses during Fuelling by Pre-Cooling Cryogenic Tank

“…When the maximum tank pressure is reached, gaseous hydrogen has to be vented to the environment to limit the pressure rise. To analyse this boil-off, especially for future large-scale storage and transport applications, many numerical models were developed [9,10]. This development lead among other things to so called zero-boil off methods where the gaseous hydrogen is e.g., re-liquefied and thus boil-off completely prevented [11,12].…”

“…Since hydrogen production and liquefaction are energy intensive and expensive, it is desirable to reduce boil-off losses as much as possible. This effect was modelled and discussed e.g., by Petitpas, however there is still no general solution or recommendation to that problem [9,13,14].…”