• Nuclear Engineering and Technology
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• 제29권4호
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• pp.348-359
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• 1997

This paper reviews cooling aspects of the diverter system in Tokamak fusion devices with primary emphasis on the critical heat flux (CHF) issues for oater-cooled designs. General characteristics of four (4) coolant options for diverter cooling gases, oater, liquid metal, and organic liquid - are discussed first, focusing on the comparison of advantages and disadvantages of those options. Then results of recent studies on the high-heat-flux CHF of water at subcooled high-velocity conditions are reviewed to provide a general idea on the feasibility of the water-cooled diverter concept for future Tokamak fusion reactors. Water is assessed to be the most viable and practical coolant option for diverters of future experimental Tokamaks.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.108-112
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• 2000

This paper presents a mathematical model and simulation of the micro-actuator based on thermally induced liquid-vapor phase-change in a partially-filled closed cavity. The volume expansion by liquid-vapor Phase change can generate considerable forces and displacement $({\sim}50{\mu}m)$ required for commercial use. For optimum operation involving many cycles within the closed chamber, active(thermoelectric) heating and cooling is used. The optimization of the system is conducted according to the parameters such as input power and response time. The optimized performance of micro-actuator is reasonable compared to other actuators.

• Journal of Korean Vacuum Science & Technology
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• 제7권2호
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• pp.27-32
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• 2003

A large cryo-pumping system composed of 4 cryosorption pumps was designed and manufactured to satisfy the pressure requirements of the NBI test stand. The cryosorption pump consists of a thermal shield/baffle assembly and a cryopanel coated with activated carbon granules. The thermal shield is cooled by liquid nitrogen, and the cryopanel by a commercial helium refrigerator. The operation characteristics and vacuum performance of the cryosorption pump were investigated. The cooling down time of the cryopanel to 20 K was about 6 hours with a liquid nitrogen consumption rate of about 35 L/hr. The maximum pumping speed of the cryosorption pump for the hydrogen gas measured by the steady pressure method was about 90,000 L/s.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.820-829
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• 2004

The In-Containment Refueling Water Storage Tank (IRWST), one of the design improvements applied to the APR -1400, has a function to condense the high enthalpy fluid discharged from the Reactor Coolant System (RCS). The condensation of discharged fluid by the tank water drives the tank temperature high and causes oscillatory condensation. Also if the tank cooling water temperature approaches the saturated state, the steam bubble may escape from the water uncondensed. These oscillatory condensation and bubble escape would burden the undue load to the tank structure, pressurize the tank, and degrade its intended function. For these reasons simple analytical modeling and experimental works were performed in order to predict exact tank temperature distribution and to find the effective cooling method to keep the tank temperature below the bubble escape limit (93.3$^{\circ}C$), which was experimentally proven by other researchers. Both the analytical model and experimental results show that the temperature distributions are horizontally stratified. Particularly, the hot liquid produced by the condensation around the sparger holes goes up straight like a thermal plume. Also, the momentum of the discharged fluid is not so strong to interrupt this horizontal thermal stratification significantly. Therefore the layout and shape of sparger is not so important as long as the location of the sparger hole is sufficiently close to the bottom of the tank. Finally, for the effective tank cooling it is recommended that the locations of the discharge and intake lines of the cooling system be cautiously selected considering the temperature distribution, the water level change, and the cooling effectiveness.

• 한국초전도ㆍ저온공학회논문지
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• 제23권4호
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• pp.61-69
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• 2021

This paper presents the analysis and experiment results on the electrical and thermal characteristics of metal insulation (MI) REBCO racetrack coil, which was wound with stainless steel (SS) tape between turn-to-turn layers, under rotating magnetic field and conduction cooling system. Although the field windings of superconducting rotating machine are designed to operate on a direct current, they may be subjected to external magnetic field due to the unsynchronized armature windings during electrical or mechanical load fluctuations. The field windings show the voltage and magnetic field fluctuations and the critical current reduction when they are exposed to an external magnetic field. Moreover, the cryogenic cooling conditions are also identified as the factors that affect the electrical and thermal characteristics of the HTS coil because the characteristic resistance changes according to the cryogenic cooling conditions. Therefore, it is necessary to investigate the effect of external magnetic field on the electrical and thermal characteristics of MI-SS racetrack coil for further development reliable HTS field windings of superconducting rotating machine. First, the major components of the experiment test (i.e., HTS racetrack coil construction, armature winding of 75 kW class induction motor, and conduction cooling system) were fabricated and assembled. Then, the MI racetrack coil was performed under liquid nitrogen bath and conduction cooling conditions to estimate the key parameters (i.e., critical current, time constant, and characteristic resistance) for the test coil in the steady state operation. Further, the test coil was charged to the target value under conduction cooling of 35 K then exposed to the rotating magnetic field, which was generated by three phrase armature windings of 75 kW class induction motor, to investigate the electrical and thermal characteristics during the transient state.

• 에너지공학
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• 제10권4호
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• pp.342-348
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• 2001

A new design concept for a decay heat removal system in a liquid metal reactor is proposed. The new design utilizes a thermosyphon to enhance the heat removal capacity and its heat transfer characteristics are analyzed against the current PSDRS (Passive Safety Decay heat Removal System) in the KAL IMER (Korea Advanced LIquid MEtal Reactor) design. The preliminary analysis results show that the new design with a thermosyphon yields substantial increase of 20∼40% in the decay heat removal capacity compared to the current design that do not have the thermosyphon. The new design reduces the temperature rise in the cooling air of the system and helps the surrounding structure in maintaining its mechanical integrity for long term operation at an accident. Also the analysis revealed the characteristics of the interactions among various heat transfer modes in the new design.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.181-184
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• 2006

당사에서는 액체산소 (LOX)와 액체메탄 (LNG)를 추진제로 사용하며, 고성능의 터보펌프가 장착된 추력 10톤급 액체로켓 엔진의 개발에 성공하였다. 이러한 개발 성공은 액체메탄을 이용한 재생냉각에 대한 성능 입증, 액체산소와 액체메탄으로 구동되는 터보펌프에 대한 성능 입증, 가스발생기에 의한 터보펌프의 구동 및 추진제 가압 성능 확인, 등을 완벽히 구현함으로써 메탄 엔진 (CHASE-10)의 상업화에 보다 근접하였다고 할 수 있다.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.94-98
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• 2002

The Partial breakdown (PBD) and complete breakdown (BD) voltage characteristics in a composite insulation system of glass fiber reinforced plastics (GFRP) and liquid nitrogen are investigated to find the PBB and BD characteristics in solenoid type high temperature superconducting (HTS) coils at quench. The electrode system used is made from a coaxial spiral coil-to-cylindrical electrode with an insulation barrier and spacers, and is immersed in liquid nitrogen. A heater is mounted inside the coil electrode to generate boiling which occurs on quenched superconducting coils. The experimental results show that: (1) breakdown voltages are affected severely by the risetime of the applied voltage and the PBD inception voltage, (2) two kinds of BD mechanisms are found depending on the shape of the spacer, length of cooling channel and heater power.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.155-158
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• 2001

An intermediate cooling is indispensible to reduce the refrigeration power at superconducting system that is cooled conductively by a cryocooler without liquid cryogens. The cooling load at the intermediate stage is caused by the mechanical supports, the radiation shield and the current lead. From the cooling load calculation, a thermodynamic analysis that take into account the temperature-dependent properties of the materials and the actual performance of the cryocooler is developed. For any given physical dimensions of the various components, it is shown that there exist a unique optimum for the intermediate temperature to minimize the overall refrigeration power. The results of this study can be usefully applied to the selection of the cryocooler as well as the design of the conduction-cooled cryostat.

• 한국초전도ㆍ저온공학회논문지
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• 제18권4호
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• pp.25-29
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• 2016

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.