• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1959-1963
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• 2007

SMES systems need cryogenic cooling systems. Conduction cooling system has more effective, compact structure than cryogen. In general, 2 stage GM cryocoolers are used for conduction cooling of HTS SMES system. 1st stages of cryocoolers are used for the cooling of current leads and radiation shields, and 2nd stages of cryocoolers for HTS coil. For the effective conduction cooling of the HTS SMES system, the temperature difference between the cryocooler and HTS coil should be minimized. In this paper, a cryogenic conduction cooling system for HTS SMES is analyzed to evaluate the performance of the cooling system. The analysis is carried out for the steady state with the heat generation of the HTS coil and effects of the thermal contact resistance. The results show the effects of the heat generation and thermal contact resistance on the temperature distribution.

• 한국기계가공학회지
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• 제7권3호
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• pp.50-54
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• 2008

This study is analyzed by the simulation of heat exchanger. As heat conduction happens as contact begins, the temperature increases until $70^{\circ}C$ at the contact part. The displacement increases until 33mm at its maximum and maximum equivalent stress at final stage increases 20 times as much as that of first contact. The expenses about maintenance, repair and management of parts can be reduced largely by applying the simulation about various parts of heat exchanger.

• 전력전자학회논문지
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• 제27권6호
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• pp.489-497
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• 2022

This work investigates the commutation characteristics of the current flowing through an electrical-contact-type switch to the semiconductor switch branch during the breaking operation of hybrid DC switchgear. A simple, reliable, low-cost natural commutation method is proposed, and the current commutation characteristics are analyzed in accordance with the conduction voltage drop of the semiconductor switch branch through experiments. A prototype 400 V/10 A class natural commutation type hybrid DC switchgear is set up. Its performance is verified, and its characteristics are analyzed.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.30-34
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• 2002

In this Paper, Insulation of current lead in the conduction-cooled DC reactor for the 1.2kV class 3 high-Tc superconducting fault current limiter(SFCL) is studied. Thermal link which conducts heat energy but insulates electrical energy is selected as a insulating device for the current lead in the conduction-cooled Superconducting DC reactor. It consists of oxide free copper(OFC) sheets, Polyimide films, glass fiberglass reinforced Plastics (GFRP) plates and interfacing material such an indium or thermal compound. Through the test of dielectric strength in L$N_2$, polyimide film thickness of 125 ${\mu}{\textrm}{m}$ is selected as a insulating material. Electrical insulation and heat conduction are contrary to each other. Because of low heat conductivity of insulator and contact area between electrical insulator and heat conductor, thermal resistance of conduction-cooled system is increased. For the reducing of thermal resistance and the reliable contact between Polyimide and OFC, thermal compound or indium can be used As thermal compound layer is weak layer in electrical field, indium is finally selected for the reducing of thermal resistance. Thermal link is successfully passed the test. The testing voltage was AC 2.5kVrms and the testing time was 1 hour.

• KSTLE International Journal
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• 제1권1호
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• pp.63-68
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• 2000

Angular contact ball bearings are mainly used in the spindle, which requires high speed and stiffness. The heat generation is studied by experiments and simulations using a pair of angular contact ball bearings. The temperature variation of inner and outer races and the temperature increment distribution are measured by using thermocouples for the rotational speed, preload, viscosity of lubricant. The measured values from experiments are used to estimate the heat conduction rate. The method of oil-air lubrication is used for the experiment. The amount of conduction heat transfer to the test spindle and the convection heat transfer coefficients long the spindle are computed by using inverse method with temperature increment distribution. Total heat generation rate is estimated with the heat partition rate which is calculated from temperatures of inner and outer races. In addition, the empirical factor of oil-air lubrication method for Palmgren's heat generation model is suggested. The empirical friction coefficients, which are obtained from the experiments, depend on the preload condition, and can give us more accurate estimation of the heat generation in ball bearings.

• 한국항공우주학회지
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• 제32권7호
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• pp.117-125
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• 2004

기 수립한 열해석 모델을 바탕으로 접촉열전도가 있는 부위의 민감도 해석을 수행함으로서 향후 기계적 접속 부위 설계 변경시의 열설계에 대한 연구를 수행했다. 해석의 편의를 위해 비교적 간단한 열해석 모텔을 선택했다. 위성 버스 전압과 접촉열저항의 크기를 다양하게 변화시켜 해석을 수행했으며, 그 결과 향후 통일한 모듈에서 기계적 접속 조건 변경시 접촉열저항을 원래의 설계원용치를 기준 값으로 해 히터의 용량을 충분히 크게 설계할 경우 성공적인 열설계가 가능하리라 여겨진다.

• 한국전기전자재료학회논문지
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• 제22권9호
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• pp.717-723
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• 2009

Ni/Al ('/' denotes deposition sequence) contacts were deposited on Al-implanted 4H-SiC for ohmic contact formation, and the conduction properties were characterized and compared with those of Ni-only contacts. The thicknesses of the Ni and Al thin film were 30 nm and 300 nm, respectively, and the films were sequentially deposited bye-beam evaporation without vacuum breaking. Rapid thermal anneal (RTA) temperature was varied as follows : $840^{\circ}C$, $890^{\circ}C$, and $940^{\circ}C$. The specific contact resistivity of the Ni contact was about $^{\sim}2\;{\pm}\;10^{-2}\;{\Omega}{\cdot}cm^2$, However, with the addition of Al overlayer, the specific contact resistivity decreased to about $^{\sim}2\;{\pm}\;10^{-4}\;{\Omega}{\cdot}cm^2$, almost irrespective of RTA temperature. X-ray diffraction (XRD) analysis of the Ni contact confirmed the existence of various Ni silicide phases, while the results of Ni/Al contact samples revealed that Al-contaning phases such as $Al_3Ni$, $Al_3Ni_2$, $Al_4Ni_3$, and $Ab_{3.21}Si_{0.47}$ were additionally formed as well as the Ni silicide phases. Energy dispersive spectroscopy (EDS) spectrum showed interfacial reaction zone mainly consisting of Al and Si at the contact interface, and it was also shown that considerable amounts of Si and C have diffused toward the surface. This indicates that contact resistance lowering of the Ni/Al contacts is related with the formation of the formation of interfacial reaction zone containing Al and Si. From these results, possible mechanisms of contact resistance lowering by the addition of Al were discussed.

• 한국초전도ㆍ저온공학회논문지
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• 제17권4호
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• pp.1-7
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• 2015

This paper addresses technical problems of thermal contact conductance or resistance which inevitably occurs in most cryogenic engineering systems. The main focus of this paper is to examine what kind of physical factors primarily influences the thermal contact resistance and to suggest how it can be minimized. It is a good practical rule that the contact surface must have sub-micron roughness level with no oxide layer and be thinly covered by indium, gold, or Apiezon-N grease for securing sufficient direct contact area. The higher contact pressure, the lower the thermal contact resistance. The general description of this technique has been widely perceived and reasonable engineering results have been achieved in most applications. However, the detailed view of employing these techniques and their relative efficacies to reduce thermal contact resistances need to be thoroughly reviewed. We should consider specific thermal contact conditions, examine the engineering requirements, and execute each method with precautions to fulfil their maximum potentials.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.404-409
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• 2004

The electrical contact resistance is here estimated using the multiscale microcontact distribution of elastic contact between rough surfaces, simulated from the Archard's model, and the electrical contact conduction theory suggested by Greenwood. These analysis confirms that the electrical contact resistance is converged to a values, larger than would be obtained if the contact spots were widely separated and hence independent. In multiscale process, the base potential is close to the value of the potential difference between the contact surface and the extremity of body, suggesting a possibility to obtain the multiscale electrical contact resistance relations.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2214-2219
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• 2008

The thermal contact resistance(TCR) of nanosized contact spots has been investigated through a multiscale analysis which considers the resolution of surface topography. A numerical simulation is performed on the finite element model of rough surfaces. Especially, as the contact size decreases below the phonon mean free path, the size dependent thermal conductivity is considered to calculate the TCR. In our earlier model which follows an elastic material, the TCR increases without limits as the number of nanosized contact spots increases in the process of scale variation. However, the elastoplastic contact induces a finite limit of TCR as the scale varies. The results are explained through the plastic behavior of the two contacting models. Furthermore, the effect of air conduction in nanoscale is also investigated.