In this study, the heat transfer characteristics of a liquid hydrogen (LH2) tank with multilayer insulation (MLI) were numerically investigated. The temperature distribution inside the LH2 tank and within the MLI, as well as the temperature variation according to positional changes, heat transfer rate, and boil-off rate (BOR), were compared and analyzed. The results showed a distinct stepwise temperature drop in Case 4 with 20 MLI layers and Case 8 with 40 MLI layers, where the insulation thickness was greatest. Under the same number of layers, the temperature gradient became more gradual as the MLI thickness increased. In addition, the temperature variation in the tank head region indicated that increasing the number of MLI radiation layers reduced the radiative heat flux, resulting in a gentler temperature variation and a longer temperature drop range. Furthermore, the analysis of heat transfer and BOR showed that both rates decreased under the condition with the greatest MLI thickness and number of layers, demonstrating the best insulation performance. In particular, under the same 40-layer condition, the BOR value of Case 8 was more than three times lower than that of Case 5, indicating a significant improvement in thermal insulation efficiency.

This study simulated the thermal characteristics of a liquefied hydrogen (LH) tank with varying multi-layer insulation (MLI) thickness and surrounding conditions. A transient heat conduction simulation was conducted using ANSYS Fluent software to predict the temperature distribution of the LH tank. The LH tank is composed of carbon fiber reinforced plastic (CFRP), MLI, and an Air layer for thermal insulation. A large MLI thickness delayed temperature changes inside the MLI due to its low thermal diffusivity. And then, the temperature rapidly increased near the outer wall, resulting in thermal non-uniformity. Therefore, when designing a LH tank with MLI materials, it would be necessary to optimize the design (i.e., MLI thickness) by considering structural stability issues caused by thermal non-uniformity. In addition, as the surrounding temperature increased and the convective heat transfer coefficient became higher, the enhanced heat transfer led to a higher temperature gradient within the LH tank, bringing the outer wall temperature of the LH tank closer to the environmental conditions. The results of this study will significantly contribute to establishing a comprehensive thermal database for predicting the thermal-structural behaviors, considering the thermal stress induced by the thermal distribution of LH tanks, which depends on the installation conditions and environment.

Liquified hydrogen is considered a new energy resource to replace conventional fossil fuels due to environmental regulations by the IMO. When building tank for the storage and transportation of liquified hydrogen, materials need to withstand temperatures of -253°C, which is even lower than that of LNG (-163°C). Austenitic stainless steel mainly used to build liquified hydrogen tank. When building the tanks, both the base material and welding zone need to have excellent strength in cryogenic condition, however, manual arc welding has several issues due to prolonged exposure of the base material to high temperatures. Laser welding, which has some benefits like short period of exposure time and decrease of thermal affected zone, is used many industries. In this study, laser bead on plate welding was conducted to determine the laser butt welding conditions for STS 304 and STS 316L steels. After the BOP test, cross-section observations were conducted to measure and compare four bead parameters. These tendency result of laser BOP test can be used as conditions laser butt welding of STS 304 and STS 316L steel.

금속의 취성화는 수소와 접촉하는 구조물을 안정적으로 설계하는데 있어서 큰 문제가 되어왔다. 본 논문에서는 분자동역학 해석을 통해 균열선단 주변에 모인 수소원자들이 전위 이동 현상을 억제하고, 이로 인해 벽개 파괴 현상이 발생하는 것을 확인하였다. 다양한 수소 농도, 하중 속도, 수소 확산 속도 등을 바꾸어가며 분자동역학 해석을 수행하였고, 이에 따른 수소 취성화를 최소화시킬 수 있는 조건들을 조사하였다. 분자동역학 해석 결과는 기존의 실험결과와 잘 일치하였으며 이를 바탕으로 수소 취성화 현상을 정량화하여 평가하였다.