This study numerically investigates a large liquid hydrogen (LH2) liquefier equipped with one AL630 and two AL330 cryocoolers to evaluate the scalability of cryocooler-based liquefaction systems. A CFD model validated against experimental data from a small-scale liquefier was developed, in which phase change was represented using the Lee model to capture condensation and re-liquefaction behavior. Three configurations with different AL330 cold head lengths (80, 199, and 318 mm) were examined to determine their influence on thermal fields and LH2 production. The results show that the AL630 unit provides the primary cooling capacity, while the AL330 units enhance re-liquefaction in the vapor region. Increasing the cold head length expands the low temperature zone and promotes vapor mixing, leading to higher overall production rates. The LH2 production increased from about 14.87 L/h in the baseline case to nearly 18.2 L/h for the longest cold head configuration, with only minor reductions in tank volume. These findings demonstrate that cold head geometry is a key design parameter for improving multi-cryocooler liquefier performance and provide guidance for developing compact LH2 production systems suitable for fueling and transport applications.

This study presents an experimental investigation of boil-off gas (BOG) generation in liquid hydrogen storage based on direct flow measurement under controlled thermal loading conditions. A dedicated experimental framework incorporating a BOG generator and a vent-line Coriolis mass flow meter was developed to enable direct and reproducible quantification of BOG without reliance on indirect pressure-based or model-dependent estimation methods. A baseline BOG generation rate corresponding to intrinsic heat ingress was identified under a zero-supply condition, and induced vaporization was systematically achieved by controlled thermal input. The measured BOG flow rates exhibited a clear and monotonic response to the imposed thermal loading, demonstrating the capability of the proposed methodology to distinguish intrinsic heat ingress from externally imposed vaporization effects. The results provide an experimentally grounded and transparent framework for evaluating BOG generation and thermal performance in liquid hydrogen storage systems, offering practical insight for the assessment of zero boil-off concepts and heat ingress mitigation strategies.

The increasing deployment of proton exchange membrane water electrolysis (PEMWE) systems for renewable hydrogen production requires reliable real-time fault diagnosis under dynamically varying operating conditions. This study proposes a dynamic model-based hardware-in-the-loop simulation (HILS) framework for real-time fault diagnosis of a PEM water electrolysis system. A physics-based dynamic model of a 300 W class PEMWE system was developed and validated against experimental data under steady-state and transient conditions, demonstrating good agreement in voltage and temperature responses. Based on the validated model, representative system-level fault scenarios were systematically generated and used to develop a real-time fault diagnosis model capable of identifying single and multiple fault conditions. The proposed framework was implemented in a HILS environment using a PXI-based real-time platform and evaluated with live experimental data. The results confirm reliable detection and isolation of pump and sensor faults while accounting for dynamic thermal behavior and realistic timing constraints. The proposed HILS-based framework provides a practical solution for enhancing the reliability and safety of PEM water electrolysis systems in renewable hydrogen production applications.

In this study, a liquid hydrogen (LH2) safety valve evaluation device was developed to enable safe and stable performance testing of pressure safety valves (PSVs) under realistic cryogenic and high-pressure conditions. The device was designed for flexible use by mounting all components on a mobile frame equipped with wheels, and the pressurization rate inside the vessel was controlled through a boil-off gas (BOG) generator. Two experiments were conducted to investigate the effect of LH2 production rate on PSV operation. When the production of LH2 increased by about 2.4 times, the number of PSV operations rose from 15 to 20, and the operating pressure range shifted slightly upward from 10.68 similar to 12.53 bar to 10.68 similar to 13.2 bar, while remaining within the instrument's error margin. These results indicate that repeated valve cycling and increased hydrogen production contribute to gradual changes in PSV operating characteristics. Additionally, the minimum temperature experienced by the PSV decreased with repeated operations, reaching approximately 77.9 K. The developed evaluation system provides an effective platform for analyzing PSV performance under realistic LH2 production and storage conditions.

This study developed a high-temperature superconducting (HTS) cryostat designed to drive an HTS coil using the cryogenic cooling capacity of liquid hydrogen. The HTS cryostat was specifically engineered to cool the HTS coil by utilizing liquid hydrogen as a cooling medium. The design of the main components aimed to minimize external heat intrusion during the circulation of helium gas cooled by liquid hydrogen. Taking into account the head loss of the entire piping system, the specifications of the cryogenic blower were selected to ensure that the helium gas could withstand the differential pressure within the piping and circulate smoothly while exchanging heat with the liquid hydrogen. As a result, it was observed that the entire HTS coil, including the HTS heat exchanger (HX), was successfully cooled to below 30K by controlling the rotational speed of the cryogenic blower and venting hydrogen gas. It was confirmed that the HTS coil could be cooled to below 30K through indirect heat exchange with helium gas using the cryogenic cooling capacity of liquid hydrogen, enabling the application of a current exceeding 200A.

In this study, we investigated the influence of hole pattern on the quench propagation behavior of hightemperature superconducting (HTS) wires utilizing a metal stitching technique. A nano-second laser processing system was used to fabricate precise micro-hole patterns through the metal and insulation layers of the HTS conductor. To evaluate the quench performance, HTS wires were prepared with various hole spacing patterns (5 cm, 2.5 cm, and 1 cm) and compared with an unmodified original wire. The results showed that as the hole spacing decreased, the decay of the central magnetic field after quench became significantly faster. In particular, the sample with 2.5 cm spacing exhibited a sharp drop in central field from 44 G to 3 G after quench. Additionally, a metal-insulated coil incorporating a 2 cm-spacing metal stitching pattern demonstrated a magnetic flux density decay rate exceeding 40 G/sec, indicating improved responsiveness in quench detection and protection systems. These findings confirm the potential of metal stitching as a structural strategy to enhance the quench safety in HTS applications.

This study focuses on developing fuel cell power technology for charging superconducting coils using variable resistor. For this purpose, a variable resistor is fabricated, and experimental equipment is built to control the amount of current applied to the superconducting coil by fixing the amount of gas supplied to the fuel cell and adjusting its driving voltage. The current and magnetic flux densities increase and decrease depending on the variable resistor. A variable resistor is modified by considering the characteristic curve of the fuel cell, and the flow rate supplied to the unit cell is controlled to overcome inefficient energy use. The amount of current charged to the superconducting coil increases depending on the supplied flow rate. Therefore, the measured magnetic flux density increases according to the charged current. Consequently, the fuel cell characteristic evaluation results and data measured while driving the superconducting coil are almost identical.

This study developed a numerical methodology for predicting the performance of various cryocoolers used in the pre-cooling stage of a hydrogen liquefaction system. In the experimental investigation, the temperature distribution of the cold head of the cryocooler and the heat pipe attached to its bottom part was measured based on the flow rate of hydrogen gas. A cryocooler model was developed using FLUENT with user-defined functions (UDFs) to investigate the temperature variations at the outlet of the heat pipe and the cold head of the cryocooler. The computational results obtained using the present simulation agreed well with the experimental results, showing highly good accuracy and validity of the present numerical methodology. In the present study, the temperature results at the outlet and cold head were obtained through numerical simulation for various cryocoolers of 80 K. As a result, the outlet temperature of the copper pipe and the cold head temperature were heavily affected by the flow rate of hydrogen gas and the type of cryocooler.

In this study, an analysis system was developed for baking insulation materials at high temperatures. The residual gas analysis system and furnace were included in the whole system in addition to the vacuum exhaust system at a high level of 1×10−6 torr or less, in order to accurately measure the component of outgassing for vacuum-insulation materials. Experimental investigations are sequentially conducted to measure and evaluate the outgassing components of the insulation materials based on the baking temperature using a residual-gas analysis system. Various materials used for insulation, such as steel use stainless (SUS) tubes, multilayer insulation (MLI), fiber-reinforced plastics (FRPs), and aluminum (Al) tape, are baked at high temperatures. The types of outgasses generated depending on temperature are analyzed experimentally. Hydrogen, water, nitrogen, and carbon dioxide are discovered to be the main components of residual gas for the insulation materials, except for Al tape. The vacuum pressures for the MLI and FRP changed rapidly with respect to the baking temperature compared with those for the aluminum tape. The vacuum level is governed by the baking temperature, and the effect of bakeout on the performance of vacuum insulation is determined by the insulation material used in the residual-gas analysis system.