Hydrogen has been touted as the fuel of the future, but challenges remain in improving the storage efficiency of liquefied hydrogen fuel for large scale commercial transport and storage. Researchers from South Korea have conducted experiments and simulations to investigate the heat flows and phase changes within a cryogenic fuel tank using multiphase thermal flow simulations, with the goal of designing safe and efficient cryotanks. 

The transportation industry sees hydrogen fuel as the most promising alternative energy source to fossil fuels, and researchers are increasingly looking at the use of liquefied hydrogen fuel. However, liquefied hydrogen fuel can only be transported in cryogenic tanks that maintain temperatures below -253 ºC, which results in vaporization. Excess internal pressure inside the tank can lead to cracks and fissures, making understanding and controlling the boiloff gas (BOG) a key factor in cryotank design. 

Led by Professor Jong-Chun Park of Pusan National University in South Korea, a research team investigated how BOG varies with tank filling ratio (FR) – the ratio of the mass of liquefied fuel in the tank to the capacity of the tank at 15 ºC. The researchers found that BOG increases quadratically with FR, and while the temperature within the liquid phase remained constant, the temperature of the vapor phase decreased nonlinearly with FR. 

“In our study, we performed experiments, as well as simulations, to analyze the thermodynamic characteristics of the tank,” says Professor Park. 

The researchers used multiphase thermal flow simulations of the tank using computational fluid dynamics to visualize the heat transfers, thermal flows and vaporization within the vacuum-insulated tank. They adopted the Rohsenow phase change model for the simulations, which allowed them to reproduce the vaporization process within the tank. 

“From our simulations, we were finally able to reveal the mechanism of BOG as a result of vaporization,” explains Professor Park. The researchers validated their simulations using data from experiments conducted through a collaboration with Daewoo Shipbuilding & Marine Engineering Co., Ltd. 

The study’s multiphase thermal simulation technique could accelerate the design of safe and efficient commercial cryotanks for liquefied hydrogen. The applications of this research are wide-ranging, from automobiles and aerospace to offshore power plants, making it a critical step forward for the realization of a hydrogen-centered society.

Image: Researchers from South Korea have explored, experimentally and numerically, the thermodynamic characteristics and thermal flows inside cryogenic liquefied tanks used in transportation by studying the changes in boiloff gas (BOG) with variations in tank filling ratio. Credit: Pusan National University