Specifically, they analysed heat flows and phase changes within a cryogenic fuel tank using multiphase-thermal flows.
Liquified hydrogen fuel can only be transported in cryogenic tanks (cryotanks), which maintain temperatures below -253⁰C — the boiling point of hydrogen. Despite thermal insulation, the liquefied fuel in a cryotank experiences a degree of vaporisation.
The flow rate of vaporisation is measured as “Boil-Off Gas (BOG).” Too high BOG can result in excess internal pressure inside the tank, leading to cracks and fissures. This makes understanding and controlling BOG a key factor in cryotank design.
The investigation, led by Professor Jong-Chun Park, discovered that BOG increases quadratically with the tank filling ratio (FR) and found that while the temperature within the liquid phase remained constant, the temperature of the vapor phase decreased non-linearly with FR.
The FR is the ratio of the mass of liquified fuel in the tank to the capacity of the tank at 15°C. Researchers then performed multiphase-thermal flow simulations of the tank using computational fluid dynamics, allowing them to visualise the heat transfers, thermal flows and vaporisation within the vacuum-insulated tank.
The simulation technique used here could accelerate the design of safe and efficient commercial cryogenic tanks (cryotanks) for liquified hydrogen.
The applications of this research range from automobiles and aerospace to offshore power-plants, meaning it is a step forward for the realisation of a hydrogen-centred society.
Professor Park, Pusan National University, commented, “We adopted the Rohosenow’s phase change model for the simulations, which allowed us to reproduce the vaporisation process within the tank.
“From our simulations, we were finally able to reveal the mechanism of BOG as a result of vaporisation.”
The researchers validated their simulations using the data from the experiments conducted through a collaboration with Daewoo Shipbuilding & Marine Engineering Co.
The study was made available online, published in volume 225 of the Energy Journal on 15 September 2022.
Last year, INOXCVA unveiled a 283m3 liquid hydrogen storage tank was built for a clean energy demonstration project in South Korea.
The cryogenic storage tank was built to European standards to meet Korean Gas Safety requirements and will be used in South Korea’s ‘first’ hydrogen liquefaction plant of 5 tonnes per day capacity, set to start commercial operations this year.
This new liquefier is in line with the South Korean Government’s plan to considerably densify the network of hydrogen stations in the country, with 310 stations and more than 67,000 hydrogen vehicles across the country.
Read more: INOXCVA to ship largest liquid hydrogen storage tank to South Korea