• 한국수소및신에너지학회논문집
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• 제19권5호
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• pp.403-409
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• 2008

Polymer electrolyte membrane fuel cell (PEMFC) is very interesting power source due to high power density, simple construction and operation at low temperature. But it has problems such as high cost, improvement of performance, effect of temperature and initial start at low temperature. These problems can be approached to be solved by using experiment and mathematical method which are general principles for analysis and optimization of control system for heat and hydrogen detecting management. In this paper, insulation vessel and control system for stable operation of fuel cell at low temperature were developed for experiment. The constant temperature capability and the heating time at sub-zero temperatures with insulation control system were studied by using a heating bar of 60W class. PEMFC stack which was made by 4 cells with $50\;mc^2$ active area in each cell is a thermal source. Times which take to reach constant temperature by the state of insulation vacuum were measured at variable environment temperatures. The test was performed at two conditions: heating mode and cooling mode. Constant temperature capability was better at lower environment temperature and vacuum pressure. The results of this experiment could be used as basis data about stable operation of fuel cell stack in low temperature zone.

• Composites Research
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• 제20권5호
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• pp.20-25
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• 2007

열주기법은 다공성 소재의 열확산도를 측정하는데 유용한 방법이다. 본 논문의 주 목적은 진공환경에서 다공성 소재의 열확산도 측정 시스템을 개발하고 검증하는데 있다. 이 방법을 검증하기 위하여 알루미나 시편과 폴리스티렌 폼의 열확산도를 측정하였다. 이 시편들의 열확산도는 참고값과 일치하였다. 탄소/에폭시 소재와 다공성 단열소재의 열확산도를 대기상온과 대기진공 환경에서 측정하였다. 탄소/에폭시 소재와 다공성 단열소재의 진공환경에서 열확산도는 대기환경에 비하여 각각 66.4%와 64.9% 감소하였다. 이 차이는 소재내의 기공에 있는 공기의 영향으로 추정된다.

• 한국태양에너지학회 논문집
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• 제37권4호
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• pp.35-47
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• 2017

Energy efficiency solutions are being pursued as a sustainable approach to reducing energy consumption and related gas emissions across various sectors of the economy. Vacuum Insulation Panel (VIP) is an energy efficient advanced insulation system that facilitates slim but high-performance insulation, based on a porous core material evacuated and encapsulated in a barrier envelope. Although VIP has been applied in buildings for over a decade, it wasn't until recently that efforts have been initiated to propose and adopt a global standard on characterization and testing of VIP. One of the issues regarding VIP is its durability and aging due to pressure and moisture dependent increase of the initial low thermal conductivity with time; more so in building applications. In this paper, the aging of commercially available VIP was investigated experimentally; thermal conductivity was tested in accordance with ISO 8302 standard (guarded hot box method) and long-term durability was estimated based on a non-linear pressure-humidity dependent equation based on study of IEA/ECBCS Annex 39, with the aim of assessing durability of VIP for use in buildings. The center-of-panel thermal conductivity after 25 years based on initial 90% fractile with a confidence level of 90 % for the thermal conductivity (${\lambda}90/90$) ranged from 0.00726-0.00814 (W/m K) for silica core VIP. Significant differences between manufacturer-provided data and measurements of thermal conductivity and internal pressure were observed.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.65-70
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• 2022

A vacuum system is designed for thermal insulation of a 10 ton/day class air liquefaction cold box for liquid air energy storage. The vacuum system is composed of a turbomolecular pump, a backing pump and vacuum piping for the vacuum pumps. The turbomolecular pump is in combination with the backing pump for pumping capacity. The vacuum piping is designed with system installation conditions, such as distance from the cold box, connections to vacuum pumps and installation space. The capacity of the vacuum pump combination, namely pumping speed, is determined by analysis of the vacuum system, and pump-down time to 1×10^-5 mbar is estimated. Vacuum piping conductance, system pumping speed and outgassing rate are calculated for the pump-down time with the ultimate pumping speed range of the vacuum pump combination of 1400 - 2300 l/s. Although the pump-down time gets shorter by larger capacity vacuum pumps, it mainly depends on target vacuum degree and outgassing rate in the cold box. The pump-down time is estimated as 3 - 6 hours appropriate for cold box operation for the pumping speed range. Considering the outgassing rate has uncertainty, the vacuum pump combination with pumping speed of 1900 l/s is chosen for the vacuum system, which is middle value of the pumping speed range.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.45-45
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• 2010

This paper discusses the simulation and LI(light impulse) test of the shieldless vacuum interrupter concept. The shields of vacuum interrupter play an important role in absorbing the metal vapor. But shield distort the electric field distribution of inner vacuum interrupter. Therefore, the insulation efficiency will improve. if shield of vacuum interrupter inside does not exist. As a result, FEM simulation show that improve distribution of electrical field and equi-potential line. But LI test result dissimilar to FEM simulation result. Shieldless vacuum interrupter model lower BIL(breakdown impulse light) than vacuum interrupter have installed shield. Because conditioning process occurred metal vapor. This paper compared that FEM analysis and LI test of installed shield model and shieldless model.

• 한국기계가공학회지
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• 제20권7호
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• pp.1-7
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• 2021

Restrictions on the emissions of nitrogen oxides, sulfur oxides, carbon dioxide, and particulate matter from marine engines are being tightened. Each of these emissions requires different reduction technologies, which are costly and require many pieces of equipment to meet the requirements. Liquefied natural gas (LNG) fuel has a great advantage in reducing harmful emissions emitted from ships. Therefore, the marine engine application of LNG fuel is significantly increasing in new ship buildings. Accordingly, this study analyzed the internal support structure, insulation type, and fuel supply piping system of a 35 m3 International Maritime Organization C type pressurized storage tank of an LNG-fueled ship. Analysis of the heat transfer characteristics revealed that A304L stainless steel has a lower heat flux than A553 nickel steel, but the effect is not significant. The heat flux of pearlite insulation is much lower than that of vacuum insulation. Moreover, the analysis results of the constraint method of the support ring showed no significant difference. A553 steel containing 9% nickel has a higher strength and lower coefficient of thermal expansion than A304L, making it a suitable material for cryogenic containers.

• 한국수소및신에너지학회논문집
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• 제8권2호
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• pp.57-65
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• 1997

Thermal analysis has been performed to design a high-performance $LH_2$ vessel with about 1% per day evaporation loss. Analysis includes the combined insulations of MLI(Multi-Layer Insulation) and VCS (Vapor-Cooled Shield) under high vacuum. Combined insulation of MLI and VCS shows the existence of optimal location of VCS to minimize evaporation loss. Comparison of parallel-type DVCS (Double Vapor-Cooled Shield) and serial-type DVCS is also made to show the effectiveness of the system. The results indicate that the serial-type DVCS vessel is better than the parallel-type DVCS vessel with respect to overall evaporation loss. The combined insulation of SVCS (Single Vapor-Cooled Shield) with a partial MLI can give a similar performance characteristics compared to that with MLI and DVCS.

• 한국초전도ㆍ저온공학회논문지
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• 제17권4호
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• pp.43-46
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• 2015

The heavy ion accelerator that will be built in Daejeon utilizes four types of superconducting cavities. Cryomodules holding the superconducting cavities in them supply thermal insulation for cavities operating in 4.3 K or 2.1 K. A Prototype of cryomodule which holds two HWR (Half Wave Resonator) cavities was fabricated and tested. Since the operating temperature of the HWR is 2.1 K, the superfluid helium was generated with warm vacuum pumping system. The cyromodule was successfully cooled down below lambda point temperature of helium and any detectable leak was not observed during the test. The static thermal load at 4.2 K was measured. The result and the experience for the cool-down below lambda point of helium are reported in this paper.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.104-104
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• 2015

Due to the demand of the cold neutron flux in the neutron science and beam utilization technology, the cold neutron source (CNS) has been constructed and operating in the nuclear research reactor all over the world. The majority of the heat load removal scheme in the CNS is two-phase thermosiphon using the liquid hydrogen as a moderator. The CNS moderates thermal neutrons through a cryogenic moderator, liquid hydrogen, into cold neutrons with the generation of the nuclear heat load. The liquid hydrogen in a moderator cell is evaporated for the removal of the generated heat load from the neutron moderation and flows upward into a heat exchanger, where the hydrogen gas is liquefied by the cryogenic helium gas supplied from a helium refrigeration system. The liquefied hydrogen flows down to the moderator cell. To keep the required liquid hydrogen stable in the moderator cell, the CNS consists of an in-pool assembly (IPA) connected with the hydrogen system to handle the required hydrogen gas, the vacuum system to create the thermal insulation, and the helium refrigeration system to provide the cooling capacity. If one of systems is running out of order, the operating research reactor shall be tripped because the integrity of the CNS-IPA is not secured under the full power operation of the reactor. To prevent unscheduled reactor shutdown during a long time because the research reactor has been operating with the multi-purposes, the introduction of the standby cooling system (STS) can be a solution. In this presentation, the design considerations are considered how to design the STS satisfied with the following objectives: (a) to keep the moderator cell less than 350 K during the full power operation of the reactor under loss of the vacuum, loss of the cooling power, loss of common electrical power, or loss of instrument air cases; (b) to circulate smoothly helium gas in the STS circulation loop; (c) to re-start-up the reactor within 1 hour after its trip to avoid the Xenon build-up because more than certain concentration of Xenon makes that the reactor cannot start-up again; (d) to minimize the possibility of the hydrogen-oxygen reaction in the hydrogen boundary.

• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.58-65
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• 2003

The high temperature superconductivity(HTS) cable must be cooled below the nitrogen liquefaction temperature to applicate the cable in power generation and transmi-ssion system under the superconducting state. To obtain superconducting state. a reliable cryocooler system is required. Structural and thermal design have been performed to design cryocooler system operated with reverse Brayton cycle using gas neon as refrigerant. This cryocooler system consists of compressor. recuperator. coldbox. control valves and has 1 kW cooling capacity. Heat loss calculation was conducted for the given cryocooler system by considering the conduction and radiation through the multi-layer insulation(MLI) and high vacuum. The results can be summarized as: conduction heat loss is 7 W in valves and access port and radiation heat loss is 18 W through the surface of cryocooler. The full design specifications were discussed and the results were applied to construct in house HTS cable cooling system.