Liquid hydrogen is often described as a clean-energy solution with a deceptively difficult storage problem. Turning hydrogen into a liquid requires cooling it to approximately 20 kelvin, or −253 °C. At that temperature, hydrogen occupies far less space than it does as a gas, giving it roughly 800 times the volumetric energy density of gaseous hydrogen under ambient conditions. That advantage could make liquid hydrogen valuable for shipping, aviation, heavy transport, and large-scale energy storage. Yet a small amount of heat entering a storage tank can cause the liquid to evaporate, increasing pressure and reducing the amount of fuel available.
Researchers at Pusan National University in South Korea have now proposed a targeted way to limit that heat flow. In a study led by Professor Jong-Chun Park, the team evaluated a semi-active insulation system that uses a secondary cryogenic fluid to intercept heat before it reaches the liquid-hydrogen vessel. The approach, known as cryogenic sacrificial fluid-assisted insulation, or CSF, could reduce heat ingress substantially when its cooling channels are positioned at the tank’s most vulnerable locations.
The word “sacrificial” refers to the role of the secondary coolant, not to a disposable material. LNG, or liquefied natural gas, and LN₂, or liquid nitrogen, are circulated through dedicated channels outside the inner hydrogen vessel. These fluids absorb heat that would otherwise travel toward the stored hydrogen. In a practical system, the coolant would be managed in a closed loop, with vaporized fluid potentially reliquefied and returned to the circuit. The concept therefore acts as a controllable thermal shield rather than simply adding another passive insulation layer.
The team studied a marine Type-C liquid-hydrogen tank designed by the Korea Research Institute of Ships and Ocean Engineering. The modeled tank included an inner layer of glass-bubble insulation, an outer layer of polyurethane foam, four structural supports, and channels through which LNG or LN₂ could flow. Instead of treating the system as a simple one-dimensional insulation problem, the researchers built a three-dimensional model that combined heat conduction through the tank structure with multiphase flow and wall boiling inside the cooling channels.
That detailed approach revealed an important weakness in the baseline design. More than 85 percent of the modeled heat entering the tank traveled through the structural supports, rather than directly through the insulation layers. The supports functioned as thermal bridges: relatively conductive pathways that created shortcuts through materials intended to block heat. This finding changed the design strategy. Rather than distributing cooling channels evenly around the tank, the researchers aligned them with the centers of the supports and extended them toward the junction between the tank head and shell, where heat could also concentrate.
The results suggest that channel placement may matter more than simply increasing the number of channels. In the most effective configurations, simulated heat ingress fell by 43.6 percent when LNG was used as the coolant and by 66.5 percent when LN₂ was used. LN₂ produced the stronger reduction because it entered the system at a lower temperature, providing a larger temperature difference for absorbing heat. However, that advantage came with a cost: the colder fluid was more sensitive to vapor generation, which could make flow control and stable operation more challenging.
The researchers also identified a limit to the benefits of enlarging the cooling passages. Within the geometry and operating conditions examined, performance began to show diminishing returns when the channel-to-tank diameter ratio, represented as d/D, approached approximately 0.04. This value should not be interpreted as a universal design rule for every liquid-hydrogen tank. Instead, it marks the point at which making the channels larger offered progressively smaller improvements in the specific modeled configuration.
One of the study’s most striking conclusions is that stronger heat transfer inside a cooling channel does not automatically translate into better protection for the hydrogen. What matters is where the heat is redirected, how effectively the channel intercepts the dominant thermal bridge, and how much of the coolant vaporizes along the way. A channel that removes heat very efficiently in one location may still provide limited overall benefit if it fails to protect the tank’s primary heat-flow paths. The researchers therefore present the CSF system as a problem of thermal targeting, flow management, and structural design rather than a simple race to maximize cooling intensity.
The findings could influence future storage systems for ships and other applications in which liquid hydrogen must remain cold for long periods. Lower heat ingress could reduce boil-off, pressure-management demands, reliquefaction requirements, and the need for controlled venting. The study also highlights why advanced tank design must account for structural components, not just insulation thickness. However, the reported reductions come from simulations of one KRISO-designed Type-C tank under steady-state conditions. The liquid hydrogen was represented as a fixed-temperature boundary, so the model did not directly capture transient self-pressurization, changing ullage volume, sloshing, or time-dependent boil-off. Experiments and fully coupled transient studies will be needed before the concept can be assessed for commercial deployment.
Subject of Research: Computational simulation/modeling
Article Title: Design and evaluation of cryogenic sacrificial fluid-assisted insulation for boil-off reduction in liquid hydrogen Type-C tanks
Web References: https://doi.org/10.1016/j.enconman.2026.121402
References: Energy Conversion and Management; DOI: 10.1016/j.enconman.2026.121402
Image Credits: Professor Jong-Chun Park, Pusan National University (PNU)
Keywords
Liquid hydrogen, cryogenic storage, LNG, liquid nitrogen, boil-off reduction, thermal bridges, hydrogen transport, cryogenic insulation, computational modeling, energy storage
