• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.181-184
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• 2002

The purpose of this study is to analysis the charging gas effect on the resonance and performance characteristics of the linear compressor for small scale FPFD Stirling refrigerator. To ensure high performance of FPFD type Stirling refrigerator, the operating frequency of the refrigerator should be around the natural frequency of compressor. The gas spring effect which is induced from pressure change in cylinder due to motion of pistons has significant effect on the natural frequency of the compressor. The numerical results show the linear compressor has high natural frequency when the charging pressure of working fluid is high.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.9-17
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• 2002

최근에 초전도 산업과 저온 작동 정밀 센서 기술의 발전으로 극저온 냉동기 또는 극저온 한제에 의해 냉각된 저온 용기의 저온 유지 기술이 필요하게 되었다. 또한 의료용 MRI, 야간 투시경용 적외선 센서, 이동통신무선기지국용 초전도 필터 등과 같이 일반인들도 극저온을 이용하게 되어 보다 사용하기 쉽고 안정적인 저온용기가 요구되고 있다. 저온용기의 저온 유지 기술은 진공 및 복사 단열 기술 뿐만 아니라 극저온 발생기술과 진공 발생 기술이 같이 고려되어야 하는 복합기술로서 앞으로 전자, 정보 통신, 나노, 바이오 산업 등에도 널리 활용될 수 있는 기반 기술로 자리 매김 할 것으로 보여 관련 연구자들의 많은 노력과 관심이 요구된다.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.18-23
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• 2002

고품질의 극저온 환경의 생성 및 유지는 고품질 대용량 정보통신, 의료진단, 초전도 및 고집적반도체 제조공정 등의 차세대 유망 산업 분야에서 필수적인 요소로 자리 잡고 있으며, cryopump, 민수용 및 군수용의 적외선 검지기 및 초전도 RF 필터의 효과적 냉각을 위해 보다 높은 신뢰성과 수명, 고효율의 극저온 냉동기에 대한 수요는 점차 증대될 것으로 기대된다. 스터링 냉동기 및 맥동관 냉동기는 짧은 역사에도 불구하고, 다양한 분야에서 기존의 한제 및 극저온 냉동기를 대치하여 활용될 수 있을 것으로 전망된다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.588-593
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• 2007

The 600kJ class high temperature superconducting magnetic energy storage (HTS SMES) system is being developed by Korean Electrotechnology Research Institute (KERI). The system is operated in cryogenic temperature and high vacuum condition. The SMS magnet was cooled by conduction cooling method using a Gifford-McMahon cycle cryocooler. Thus, electric insulation design at cryogenic temperature and high vacuum is a key and an important element that should be established to accomplish compact design is a big advantage of HTS SMES. This paper describes the electric insulation design, fabrication and experimental results for a mini model of conduction cooled HTS SMES.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.194-197
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• 1999

Thermodynamic cycle analysis has been performed to maximize the liquid amount for two hydrogen liquefaction systems using two-stage GM(Gifford-McMahon) refrigerator. the optimal operating conditions have been analytically sought with real properties of normal hydrogen for the two-stage GM direct contact system and the two-stage GM precooled L-H (Linde-Hampson) system. In the precooled system, there existed optimal values for compressed mass flow and compressed pressure to maximize the liquefied mass. It was recommended to use a cryocooler, which had a large precooling capacity between 70 and 100K.

• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.49-52
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• 2013

An experiment to investigate the natural circulation of a cryogen has been performed. The study is motivated mainly by our recent development of cryogenic cooling system for prototype superconducting cyclotron without any circulating pump. In the natural circulation loop system, a cooling channel is attached on the outer surface of the aluminium block and the liquid nitrogen passes through inside of the channel to cool the block indirectly. A cryocooler as a heat sink is located at the top to re-condense cryogenic vapor coming from the aluminium block in which electrical heater is installed as a heat source. The main dimensions are determined using the relevant analysis and the natural circulation loop is successfully fabricated. The temperature distributions in the loop are measured during initial cool-down process and in steady state, from which the modified Grashof numbers are calculated and compared with the existing correlation estimated with one-dimensional analysis for steady state flow.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.358-359
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• 2008

The heat generated in the high-Tc superconducting (HTS) devices is related with the cost efficiency and safe factor of HTS devices. This paper deals with the quench at the conduction-cooled joint between the HTS wire and copper terminals. The 3-D numerical simulation of this phenomenon was implemented and compared with the experimental results. The experiment was implemented with the HTS wire mounted on the copper blocks cooled with a Gifford McMahon (GM) cryocooler.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.35-38
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• 2000

A preliminary design of gas-gp thermal switch is presented to reduce the cooldown time of superconducting system conduction-cooled by a two-stage refrigerator without liquid cryogens. The switch connects thermally the first and the second stages (ON) to take advantage of the larger refrigeration capacity at the first stage during the beginning period. After the cryogenic temperature is reached, the switch should isolate thermally the two stages (OFF) in order to reduce the heat leak to the cold end. In this paper, a new concept for the performance index is introduced to evaluate the reduction of the cooldown time and the increase of the cooling load at the same time. In addition, the design of a gas-gap switch is discussed as a closed container of several staggered concentric tubes filled with gas, which is frozen at low temperatures for the shut-off of heat without any mechanical actuation. Some of the detailed features in the design is quantitative investigated by the gas convection model in the continuum or the rarefied gas region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.149-150
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• 2005

According to the trend for electric power equipment of high capacity and reduction of its size, the needs for the new high performance electric equipments become more and more important. On of the possible solution is high temperature superconducting (HTS) power application. Following the successful development of practical HTS wires, there have been renewed activities in developing superconducting power equipment. HTS equipments have to be operated in a coolant such as liquid nitrogen ($LN_2$) or cooled by conduction-cooling method such as using Gifford-McMahon (G-M) cryocooler to maintain the temperature below critical level. In this paper, the dielectric strength of unfilled epoxy and filled epoxy in $LN_2$ was analyzed. The filled epoxy composite not only compensates for this fragile property but enhances its dielectric strength.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.33-35
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• 2003

There are three types that geometrical arrangement of the pulse tube and regenerator - in line type, U type, and coaxial type. The most compact and convenient one practical applications is the coaxial type. It can replace Stirling cryocooler without any change to the Dewar or the connection to the cooled devices. To investigate effects of the inertance tube, we perform experiments with varying inertance tube inner diameter and length. The experimental results show that optimum inertance tube inner diameter and length are 1.3mm, 1900mm respectively.