• Transactions of the Korean hydrogen and new energy society
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• v.9 no.4
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• pp.169-176
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• 1998

An experimental study on effect of vapor-cooled heat stations in a 5.5 liter cryogenic vessel has been performed. The cryogenic vessel is made of stainless steel of thickness of 1mm and insulated by the combined insulation of vacuum, MLI(multi-layer insulation) and vapor-cooled radiation shield. Vapor-cooled heat stations are also constructed based on the 1-dimensional thermal analysis to reduce the heat inleak through a filling tube. Thermal analysis indicates that the vapor-cooled heat stations can substantially enhance the performance of vessel for cryogenic fluids with high $C_p/h_{fg}$ where $C_p$ the specific heat and $h_{fg}$ the heat of vaporization, such as $LH_2$ and LHe. The experimental results for $LN_2$ shows that the total heat inleak into inner vessel consists of 14% radiation and 86% conduction through the filling tube. Therefore, it is expected that the conduction heat in leak of the vessel for high $C_p/h_{fg}$ cryogenic fluids can be significantly reduced. powders. The amount of copper coating was 20wt%. In order to examine corrosion behavior of the electrodes, the corrosion current and the current density, in 6M KOH aqueous solution after removal of oxygen in the solution, were measured by potentiodynamic and cyclic voltamo methods. The results showed that Co in the alloy increased corrosion resistance of the electrode whereas Ni decreased the stability of the electrode during the charge-discharge cycles. The electrode used Si sealant as a binder showed a lower corrosion current density than the electrode used PTFE and the electrode used Cu-coated alloy powders showed the best corrosion resistance.

• Journal of Radiation Protection and Research
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• v.26 no.2
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• pp.67-71
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• 2001

In order to shield the neutrons affecting the background of Low Level Gamma Ray Spectrometer, a neutron shielder was designed. The method used in this study for neutron shielding was the deceleration of fast neutrons by high density polyethylene(HDPE) and the absorption of those slowing-down neutrons by $B_4C$. The calculation results of neutron Interaction in HDPE using Monte Carlo simulation code MCNP4B showed that the thermal-neutron flux was maximum at 10 cm thickness of HDPE. The results also showed that 95% of the thermal neutrons were absorbed by 2 mm thickness of $B_4C$ absorber Consisted of 30 w% $B_4C$ and 70 w% polymer. The results of the Monte Carlo calculation were in good agreement with the experimental value obtained by a neutron shielding apparatus designed for this purpose.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.4
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• pp.271-277
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• 2016

For a stable electric power supply in the space, nuclear batteries have been used as the main power source in a spacecraft owing to their long lifetime and high reliability. In accordance with the plan for lunar mission in Korea, nuclear batteries will supply electricity to the rover that needs to be developed. According to the information about the estimated payload, Korea Atomic Energy Research Institute started with the conceptual design based on the previous studies in USA and Russia. Because a nuclear battery converts the decay heat of the radioisotope into electricity, thermal design, radiation shield, and shock protection need to be considered. In this study, two types of nuclear batteries, radial type and axial type, were designed according to the alignment of the thermoelectric module. Heat transfer analyses were performed to compare their thermoelectric efficiency, and test mockups were fabricated to evaluate their performances.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.4
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• pp.205-212
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• 2010

In a typical data center, large numbers of IT sever racks are arranged multiple rows. IT environments, in which extensive electronic hardware is air-cooled, cooling system inefficiencies result when heated exhaust air from equipment prematurely mixes with chilled coolant air before it is used for cooling. Mixing of chilled air before its use with heated exhaust air results in significant cooling inefficiencies in many systems. Over temperatures may not only harm expensive electronic equipment but also interrupt critical and revenue generating services. Cool shield is a cost effective aisle partition system to contain the air in cold aisles and hot aisles of an IT server room. This paper focuses on the use of performance metrics for analyzing aisle partition system in data centers.

• Journal of the Korean Vacuum Society
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• v.22 no.2
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• pp.45-54
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• 2013

The cryopump of the pulse tube type has been developed successfully, and manufacturing of a prototype pump is finished under leading of Woosung Vacuum. The target pumping speed of the prototype pump is above 3,600 L/s for nitrogen with the intake port of 14 inches I.D (16 inches O.D). For designing optimally the pump structure including the charcoal array, thermal shield, and baffle, the pumping speed was simulated for various configurations through Monte Carlo method. Pumping performances of the protype cryopump manufactured on the basis of optimal design were conformed experimentally with a standard test system and procedures. The measured $N_2$ pumping speed of the prototype cryopump was 4,600 L/s which agreed well with simulated one and exceeded the target value.

• Nuclear Engineering and Technology
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• v.40 no.6
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• pp.439-450
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• 2008

The KSTAR device succeeded in first plasma generation on $13^{th}$ June of 2008 through comprehensive system test and commissioning. Among various kinds of the key factors that decisively affected the project, success in the construction and assembly of the major tokamak structure was most important one. Every engineering aspects of each structure were finally confirmed in the integrated commissioning period, and there were no severe troubles and failures prevented the KSTAR device from operating during the commissioning and the first plasma experiments. As a result, all of the experiences and technologies achieved through the KSTAR construction process are expected to be important fundamentals for future construction projects of superconducting fusion devices. This paper summarizes key engineering features of the major structures and of the machine assembly.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.36-36
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• 2000

KSTAR 토카막은 보조가열 장치로 2005년까지 1대(최종적으로는 2대)의 중성입자빔 입사장치(NBI)를 설치하여 장치의 기본 설계값에 도달할 예정이다. KSTAR NBI는 3개의 이온원을 가지고 있으며 총 수소 유입량은 70 Torr.L/s인 반면 고속 중성 입자빔량은 모두 11 Torr.L/s로 기체 배기량은 59 Torr.L/s에 달하고 압력은 장소에 따라 10-5~10-6 Torr로 유지되며 총배기속도가 1~2$\times$106 L인 펌프가 필요하다. 이때 크라이오 펌프(cryopump) 방식이 거의 유일한 해결책이라고 할 수 있다. 크라이오 펌프는 고속 입자빔 수송로의 양편에 각각 설치되는데 총면적 30m2 내외의 극저온 냉각판(cryo-pnael)들과 이를 상온 열복사로부터 보호하기 위한 열차폐(thermal shield) 및 흡기구 배플(baffle), 그리고 적절한 냉각장치로 구성된다. 시운전 단계에서는 15K GM 냉동기와 활성탄이 부착된 냉각판을 사용하는 방식과 4K GM 냉동기로 냉각하는 방식이, 최종 운전단계에서는 3.7K 액체 헬륨을 사용하는 방식이 고려되고 있다. 크라이오 펌프의 구조설계에 앞서 우선 배기속도, 흡？량, 작동압력, 냉각판 온도, 열손실량 등 설계사양을 확정하고 정리하는 일이 진행되고 있다. 또 냉각방식과 상관없이 동일한 개념으로 만들어지는 배플과 열차폐의 최적설계를 위한 몬테카를로 계산과 열전도 계산을 병행하고 있다. 이 곳에서는 KSTAR NBI 장치의 주배기계로서 사용될 크라이오 펌프의 설계방향과 전반적인 구조 및 예상성능 등에 대해 발표하려고 한다.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2999-3005
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• 2022

The new experimental setup has been built at the 11b channel of the IBR-2 research reactor at FLNP, JINR, to study the elemental composition of samples by registration of prompt gamma emission during thermal neutron capture. The setup consists of a curved mirror neutron guide and a radiation-resistant HPGe high-purity germanium detector. The detector is surrounded by lead shielding to suppress the natural background gamma level. The sample is placed in a vacuum channel and surrounded by a LiF shield to suppress the gamma background generated by scattered neutrons. This work presents characteristics of the experimental setup. An example of hydrogen concentration determining in a diamond powder made by detonation synthesis is given and on its basis, the sensitivity of the setup is calculated being ~4 ㎍.

• Prospectives of Industrial Chemistry
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• v.20 no.4
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• pp.1-20
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• 2017

질화붕소나노튜브(BNNT: Boron Nitride Nanotubes)는 근래에 들어 전 세계적으로 많은 주목을 받고 있는 나노신소재이다. CNT와 유사한 기계적 특성과 열전도, 열팽창 특성을 가지고 있지만 동시에 세라믹의 특성도 가지고 있어 열적/화학적 안정에 있어서는 CNT와 비교하여 매우 우수하다. 특히 BNNT를 구성하고 있는 붕소는 열중성자를 흡수할 수 있는 능력이 CNT를 구성하고 있는 탄소와 비교하여 20만 배나 높기 때문에, 우수한 기계적 특성을 이용한 경량화와 방사선 차폐능을 동시에 보유할 수 있는 미래 우주공학 물질로 매우 유용하다. 그러나 제조하는데 상대적으로 많은 에너지가 필요하고, 전 세계적으로 아직 대량생산이 이루어지지 않고 있으며, 제조 시 생성되는 불순물의 양이 많은 것이 단점이다. 또한 BNNT를 정제하는 것은 매우 어려워 산업적 응용은 아직 제한적이라 할 수 있지만, BNNT가 CNT와 세라믹의 특성을 동시에 보유하고 있다는 물질의 우수성과 활발한 연구개발 활동을 감안하면, 이에 대한 해결점을 찾을 수 있을 것으로 예상된다. 본 고찰에서는 다양한 BNNT의 제조방법과 각 방법의 장단점을 소개하고, 현재 연구되고 있는 BNNT의 산업적 응용에 대해 소개할 것이다. 이를 통해 국내에서 매우 미진한 BNNT 관련 연구가 활성화되는 계기가 될 것을 기대한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.