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곽효서 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.4
Hydrogen is considered as one of the most promising future energy carriers due to its noteworthy advantages of renewable and high calorific value. The long-term storage of liquid hydrogen with low heat leakage is essential for future deep space exploration. Because of low critical temperature and volatility, liquid hydrogen tank poses severe requirements to multi-layer insulation (MLI). In order to reduce heat leak into tank, vapor cooled shield (VCS) was set up to cool MLI by retrieving the heat of discharged cryogenic gas hydrogen. This paper presents an parametric study on insulation system in liquid hydrogen storage vessel with MLI and VCS. Thermal model was developed, and heat transfer analysis by varying VCS position was conducted. Temperature and heat flux distributions along time passing were derived, and effect of VCS position on insulation performance was investigated.
액체수소 저장 탱크의 돔부 형상에 따른 열-구조 연성해석
곽효서 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.6
Decarbonization plays an important role in future energy systems for establishing a zero-carbon society. Hydrogen is believed to be a promising energy source that can be converted, stored, and utilized efficiently, leading to a broad range of possibilities for future applications. Hydrogen can be stored in various forms, including compressed gas, liquid hydrogen, hydrides, adsorbed hydrogen. Among these, liquid hydrogen has high gravimetric and volumetric hydrogen densities. There are a lot of previous studies on thermal behavior of MLI and VCS and optimization insulation system, but research on the insulation performance by varying the head shape of the tank has not been conducted. In this study, thermal-structural coupled analysis was conducted on the insulation system with VCS positioned between two layers of MLI for a liquid hydrogen storage tank. The analysis considered dome shapes (torispherical, circle, ellipses), and heat flux and temperature were derived from thermal analysis to predict insulation performance. Maximum equivalent stress and deformation were calculated from the structural analysis, and the optimal dome shape was proposed.
곽효서 대한기계학회 2023 大韓機械學會論文集A Vol.47 No.12
정부는 2050년 탄소중립을 선언하면서 핵심 에너지원으로 수소를 꼽았다. 액체수소는 높은 에너지 저장 밀도로 인해 차세대 에너지로 주목받고 있으나, -253°C의 극저온에서 액화하기 때문에 기화 손실이 중요한 이슈이다. 따라서 액체수소의 이송 및 저장을 위해서는 고도화된 단열 기술이 필요한데, 국내는 해외 기술 의존도가 높으므로 국산화 기술 개발이 절실하다. 이에 본 연구에서는 다층단열재(MLI) 및 증기냉각복사쉴드(VCS)로 구성된 액체수소 저장 탱크의 단열 시스템을 개발하였다. MLI와 VCS의 유한요소 모델을 생성하여 단열 성능에 미치는 영향을 파악하였다. 4개의 단열층 모델(one layer MLI, MLI-VCS, MLI 1-VCS-MLI 2, MLI 1-VCS 1-MLI 2-VCS 2-MLI 3)의 과도 열전달 해석을 수행하였으며, 온도 및 열유속 분석을 통해 단열 효율 향상을 위한 MLI 및 VCS 단열층 모델을 제안하였다. Liquid hydrogen (LH2) attracts widespread attention because of its highest energy storage density. However, evaporation loss is a serious problem in LH2 storage owing to the low boiling point (– 253°C). Efficient insulation technology is an important issue in the study of LH2 storage. This paper presents a novel cryogenic insulation system consisting of multilayer insulation (MLI) and a self-evaporating vapor-cooled radiation shield (VCS) for storage of LH2. A thermodynamic model was established to analyze the coupled heat transfer characteristics of MLI and VCS in the insulation system and the effect of VCS on insulation performance. Transient heat transfer analyses of four insulation structures (One layer insulation, MLI-VCS, MLI 1-VCS-MLI 2, and MLI 1-VCS 1-MLI 2-VCS 2-MLI 3) were performed. Temperature and heat flux were quantitatively analyzed. Design strategies for MLI and VCS are explained to obtain better insulation performance.
클램프 하중 향상을 위한 Valve out tool의 Collet 설계
곽효서 한국기계기술학회 2022 한국기계기술학회지 Vol.24 No.6
The flange spreader has been used to withdraw butterfly valves during maintenance. The typical flange spreaders required an excessive working space, and the pipe and flange are damaged by the load. In the previous study, the author developed a valve easy out tool with collet, and designed collet shape to ensure structural safety. However, clamping force of the collet had not been checked. In this study, design of collet shape was performed to improve clamping force. Techniques of structural analysis were established and design parameters were selected. Through parametric study, the collet shape with clamping force of 159,748N was suggested. This will contribute to stability and efficiently of valve maintenance.
곽효서 대한기계학회 2022 大韓機械學會論文集A Vol.46 No.12
Valve lockouts have been used to prevent safety accidents due to human error; however, conventional lockouts have problems of failure of the locking function and lack of durability. This study developed a new type of lock device with clamps to improve the clamping force. A structural analysis of the basic model was conducted to identify its problems, and the clamp groove shape was optimized using the response surface method to maximize the clamping force. A performance test of a prototype was conducted to examine the clamping force and verify the optimal model. The harm to human life due to human error is expected to be reduced using the developed lock device at plants, achieving economic saving and improvement in working efficiency. 전력, 가스, 석유 등을 생산하는 플랜트에서는 작동유를 제어하는 밸브를 사용하는데, 허가받지 않은 작업자의 밸브 오동작으로 인한 사고를 막기 위해 밸브 잠금 장치를 이용하고 있다. 기존의 체인-자물쇠 및 래칫 방식 마스터락 장치는 작동 환경에 최적화되어 있지 않아 내구성, 작업 효율성 및 안전성에 문제가 있다. 이에 본 연구에서는 기존 제품의 문제점을 해결하기 위해 클램프 타입 스테인리스 바디 소재의 밸브 잠금 장치를 개발하였다. 클램프을 적용하여 와이어의 접지력을 증가시켰으며, 플라스틱 바디의 내구성 향상을 위해 SUS304 소재를 적용하였다. 클램핑 하중 극대화를 위하여 구조해석을 통한 클램프의 그루부 형상을 최적화하였으며, 목표 값 만족 여부를 판단하기 위해 최적 모델의 시제품 제작 및 클램핑 하중 테스트를 수행하였다.
구조해석을 통한 Valve out tool의 Collet 설계
곽효서 한국기계기술학회 2022 한국기계기술학회지 Vol.24 No.5
The flange spreader has been used to withdraw gaskets and valves during butterfly valve maintenance. When using the conventional flange spreader, an excessive working space (pipe separation distance) appears, and the pipe and flange are damaged by the load. Also, the equipment can’t be operated safely when the pipe has eccentric fitting. To solve the problems, a valve easy out tool with collet was developed for safely fixing and spreading flange. By using Ansys Workbench 2021 R2, the structural analysis of the original collet was performed, and shape design of the collet was carried out to improve structural safety.