Hydrogen is increasingly viewed as a promising energy carrier because it stores large amounts of energy per unit mass and can support low-carbon energy systems when produced through low-emission pathways. Large-scale use, however, depends on storing and transporting it efficiently. Cooling hydrogen to approximately 20 K (-253 ℃) turns it into a liquid with roughly 800 times the volumetric energy density of gaseous hydrogen under ambient conditions, making it attractive for long-distance transport and large-scale storage. The difficulty is that even modest heat ingress can trigger evaporation and increase tank pressure.
Boil-off lowers storage and may require reliquefaction, pressure management, or controlled venting, all of which add cost and complexity. Passive systems such as multi-layer insulation, polyurethane foam (PUF), and glass bubbles remain important, but each involves trade-offs in vacuum quality, aging, installation, or thermal cycling. Cooling shields have also been studied; however, many previous studies relied on passive circulation or reduced-order thermodynamic models. The cryogenic sacrificial liquid (CSF) concept proposed by the Korea Research Institute of Ships and Ocean Engineering (KRISO) instead uses externally supplied LNG or LN2 in controllable channels, allowing heat to be intercepted along selected paths before it reaches the inner vessel.
To determine how this concept should be configured, a research team led by Professor Jong-Chun Park of PNU's Department of Naval Architecture and Ocean Engineering in South Korea comprehensively evaluated a semi-active CSF-assisted insulation system for a KRISO-designed marine Type-C liquid hydrogen (LH2) storage tank. Here, "sacrificial" means that the secondary coolant takes the heat load before the hydrogen does; the fluid is intended to be reliquefied and recirculated in a closed loop rather than discarded. "The key is to intercept heat before it reaches the liquid-hydrogen vessel," explains Prof. Park. "By controlling the flow and placement of the channels, we can direct more of the incoming heat into the secondary coolant." The article was published online on April 08, 2026, in Energy Conversion and Management and appears in Volume 357, dated June 01, 2026.
Rather than relying on simplified one- or two-dimensional models, the researchers coupled three-dimensional heat conduction through the tank structure with multiphase flow and wall boiling inside the CSF channels. Their model examined a KRISO-designed Type-C tank with an inner glass-bubble insulation layer, an outer PUF layer, four structural supports, and channels carrying either LNG or LN2. By varying channel size, mass flow rate, number, and placement, the team identified which design choices most strongly controlled heat ingress and coolant vaporization.
In the baseline simulation without active CSF circulation, more than 85% of the total heat entering this particular tank traveled through the structural supports rather than the insulation layers. The supports therefore acted as thermal bridges, high-conductance shortcuts through the insulation. Guided by this result, the researchers routed cooling channels along the support centers and extended them to the head-shell junction. This targeted layout reduced heat ingress more effectively than more uniformly distributed channels, showing that placement mattered more than channel count alone.
Channel size also showed a clear point of diminishing returns. Within the investigated geometry and operating range, a channel-to-tank diameter ratio (d/D) near 0.04 marked the onset of saturation; it was not a universal optimum. In the best layouts, simulated total heat ingress decreased by 43.6% with LNG and 66.5% with LN2. LN2 provided stronger shielding because it entered at a lower temperature, but it was more sensitive to vapor generation; LNG produced a smaller yet more stable cooling response. An additional, counterintuitive result was that stronger local heat transfer inside a channel did not necessarily improve the insulation of the tank as a whole: performance depended on where the heat was redirected and how much of the coolant vaporized.
"Our findings show that effective LH2 storage is not simply a matter of adding thicker insulation or more cooling channels," notes Prof. Park. "The largest gains came from identifying the tank's thermal bridges and placing cooling exactly where the heat entered. Smarter placement, not simply more material, was the key." He adds, "This provides a practical design strategy for balancing thermal performance, coolant stability, and system complexity."
By translating a heat-interception concept into quantitative design rules, the study provides a basis for improving the thermal efficiency and operational reliability of liquid-hydrogen storage and transport systems. Its broader lesson is straightforward: first identify the dominant heat paths, then place semi-active cooling where it can intercept them most effectively.
At the same time, the reported values are specific to the modeled KRISO tank and steady-state operating conditions. The liquid hydrogen was represented as a fixed-temperature boundary, so transient self-pressurization, ullage evolution, sloshing, and actual time-dependent boil-off were not directly simulated. Experimental validation and fully coupled transient analyses are therefore the next steps toward practical deployment.
Reference
Title of original paper: Design and evaluation of cryogenic sacrificial fluid-assisted insulation for boil-off reduction in liquid hydrogen Type-C tanks
Journal: Energy Conversion and Management
DOI: https://doi.org/10.1016/j.enconman.2026.121402
About Pusan National University
Founded in 1946 in Busan, Pusan National University is one of South Korea's leading national universities. It operates campuses in Busan, Yangsan, Miryang, and Ami and is guided by the principles of truth, freedom, and service. The university serves approximately 30,000 students, 1,200 professors, and 750 faculty members; it comprises 14 colleges and schools, one independent division, and 103 departments.
Website: https://www.pusan.ac.kr/eng/Main.do
About the author
Professor Jong-Chun Park is a Professor in the Department of Naval Architecture and Ocean Engineering at Pusan National University. His research focuses on multiphysics simulation-based design for ships and offshore systems, including hydrodynamics, multiphase-thermal transport, cryogenic storage, and the coupled effects of sloshing and boil-off. Before joining PNU, he served on the faculty at the University of Tokyo and held research appointments at Japan's Port and Harbor Research Institute, now the Port and Airport Research Institute, and Texas A&M University. He earned his Ph.D. from the University of Tokyo in 1994 and serves as Director for the Hydrogen Innovation Hub & Center at PNU's Korea Ship and Offshore Research Institute (KOSORI).
Laboratory: https://sil.pusan.ac.kr/sil/40632/subview.do
ORCID Id: 0000-0002-3168-2054
