• 대한방사선기술학회지:방사선기술과학
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• 제38권2호
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• pp.155-161
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• 2015

본 연구는 고주파 열치료 시 내부냉각방식 cool-tip의 냉각수 온도에 따른 소작 특성을 확인하기 위하여 소간을 이용하여 냉각수 온도변화에 따른 소간의 소작 특성의 변화를 통해 냉각수 온도변화와 소작 특성의 상관관계를 확인하고자 하였다. 실험에 사용된 소간은 2 cm cool-tip 사용 시 $4{\times}4{\times}4cm^3$, 3 cm인 cool-tip 사용 시에는 $6{\times}6{\times}6cm^3$로 소간을 절제하였으며, 소작된 소간은 MRI를 이용하여 영상검사를 실시하였으며, Freehand 기법으로 소작된 부위의 면적과 둘레를 측정하였다. 2 cm, 3 cm cool-tip을 사용하여 6분, 12분 소작 시 cool-tip 온도가 상승함에 따라 면적과 둘레는 감소함을 나타냈으며, cool-tip 온도와 면적 및 둘레의 상관관계는 통계학적으로 유의한 결과를 나타내었다(p=.000). 소작 범위에 대한 실제 측정과 MRI을 이용한 측정을 비교한 결과 MRI를 이용한 면적과 둘레 측정이 더 정확한 것을 확인하였으며, 대응표본 T-검정을 이용한 통계적 결과 또한 유의하였다(p=.038). 고주파 열치료 장비의 cool-tip 냉각수 온도가 증가함에 따라 소간의 소작 범위가 감소한 원인은 고주파 열치료 장비의 에너지가 정확히 전달되지 못하고 탄화가 발생하기 때문이다. 따라서 고주파 열치료에서 탄화의 발생을 줄이고, 고주파 에너지가 정확히 전달되어 치료 효과를 높이기 위해서는 냉각수의 온도를 낮은 온도로 일정하게 유지하여 사용하여야 고주파 열치료의 효과가 증대될 것이라 사료된다.

• Journal of Astronomy and Space Sciences
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• 제2권2호
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• pp.153-174
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• 1985

The one of critical factor in gas turbine engine performance is high turbine inlet gas temperature. Therefore, the turbine rotor has so many problems which must be considered such as the turbine blade cooling, thermal stress of turbine disk due to severe temperature gradient, turbine rotor tip clearance, under the high operating temperature. The purpose of this study is to provider the temperature distribution and heat flux in turbine disk which is required to considered premensioned problem by the Finite Difference Method and the Finite Element Methods on the steady state condition. In this study, the optimum aspect ratio of turbine disk was analysed for various heat conductivity of turbine disk material by Finite Difference Method, and the effect of laminating method with high conductivity materials to disk thickness direction by Finite Element Methods in order to cool the disk. The laminating method with high conductivity material on the side of the disk is effective.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1953-1958
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• 2007

This paper presents the results of a series of performance tests for the integral Stirling cryocooler. Infrared sensor systems incorporating cryocoolers are required to be qualified to the appropriate environmental specification. Integral Stirling cryocooler for thermal imaging system have matured to the stage of undergoing formal qualification test program. The thermal environmental test of the Stirling cryocooler is presented in this paper. We performed that low and high temperature keeping test from $-40^{\circ}C$ to $+71^{\circ}C$ and operating test at high and low temperature cyclic range with acceptance tests performed at scheduled intervals. Cooldown time to 80K and steady state input power at 80K were determined as a function of cooler components temperatures at the compressor, hot end and cold tip. Tests performed on this cooler have been successful with a measured cooldown time to 80K of less than 5 minutes 24seconds for $71^{\circ}C$ ambient temperature with input power of 11W

• 한국초전도ㆍ저온공학회논문지
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• 제6권2호
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• pp.46-51
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• 2004

This paper presents the results of a series of performance and reliability tests for the Stirling cryocooler. Infrared sensor systems incorporating cryocoolers are required to be qualified to the appropriate specification for the performance and reliability. FPFD Stirling cryocooler is currently under development for cooling infrared detector. Manufactured Stirling cryocooler delivers approximately 0.9W cooling at 80K for 30W∼40W of input power. It takes approximately 2 minutes to cool down to 80K at the ambient temperature of 23$^{\circ}C$. Performance characteristics for the vibration, acoustic noise, EMI and leak rate of the Stirling cryocooler are evaluated. We performed low and high temperature keeping test from -32$^{\circ}C$ to +52$^{\circ}C$ and operating test at high and low temperature cyclic range with acceptance tests performed at scheduled intervals. Cooling capacity is determined as a function of the temperatures at the compressor, hot end and cold tip at the expander. Finally, we describe the experimental facility for the MTTF evaluation and some typical results of the Stirling cryocooler.

• 한국해양공학회지
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• 제23권2호
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• pp.69-73
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• 2009

The objective of this study was to obtain a better understanding of the delayed hydride cracking (DHC) of Zr-2.5Nb alloy. The DHC model has some defects: first, it cannot explain why the DHC velocity (DHCV) becomes constant regardless of an applied stress intensity factor, even though the stress gradient is affected by the applied stress intensity factor at the notch tip. Second, it cannot explain why the DHCV has a strong dependence on the method of approaching the test temperature by a cool-down or a heating-up, even under the same stress gradient, and third, it cannot predict any hydride size effect on the DHC velocity. The DHC tests were conducted on Zr-2.5Nb compact tension specimens with the test temperatures reached by a heating-up method and a cool-down method. Crack velocities were measured in hydrided specimens, which were cooled from solution-treatment temperatures at different rates by being furnace-cooled, water-quenched, and liquid nitrogen-quenched. The resulting hydride size, morphology, and distributions were examined by optical metallography. It was found that fast cooling rates, which produce very finely dispersed hydrides, result in higher crack growth rates. This different DHC behavior of the Zr-2.5Nb tube with the cooling rate after a homogenization treatment is due to the precipitation of the $\gamma$-hydrides only in the water-quenched Zr-2.5Nb tube. This experiment will provide supporting evidence that the terminal solid solubility of a dissolution (TSSD) of $\gamma$-hydrides is higher than that of $\delta$-hydrides.