• 대한기계학회논문집B
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• 제25권3호
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• pp.366-372
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• 2001

The ice plugging process consists of placing liquid nitrogen around a pipe and removing heat until the water in the pipe freezes and provides a solid plug or seal against fluid movement. This technique enables us to repair or inspect a pipe system without shutdown of entire system. A set of test apparatus for investigation of the liquid freezing phenomena during ice plugging is prepared. This study shows the characteristics of the liquid freezing and the heat transfer with various pipe and freezing jacket conditions. And in case there is flow of the fluid inside the pipe, the flow rate which can be able to form the ice plug is identified with the effect of the pipe diameter and freezing jacket length on the plug formation. The permissible maximum flow rate for the complete plug formation is approximately proportional to the freezing jacket length at the same pipe diameter condition.

• Nuclear Engineering and Technology
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• 제34권2호
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• pp.105-116
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• 2002

In special industrial fields such 3s nuclear power plants and chemical plants, it is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. A temporary ice plugging method for blocking internal flow is considered as a useful method in that case. According to the pipe freezing guideline of the nuclear power plant, the length of a freezing jacket must be longer than twice of the pipe diameter. However, for applying the ice plugging to short pipes which do not have enough freezing length because of geometrical configuration, it is inevitable to use shorter jacket less than twice of the pipe diameter. In this study, the integrity evaluation for short pipes in the nuclear power plant Is conducted by an experiment and the finite element analysis. From the results, the ice plugging process in short pipes can be safely carried out without any plastic deformation and fracture.

• 대한기계학회논문집A
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• 제22권1호
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• pp.227-237
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• 1998

In case the systems have radioactivity, toxic liquid or expensive fluid, and have to be performed repair work at one point of the system pipe, the formation of an internal ice plug by the removal of heat from the pipe is often consideredas a useful method. In this procedure, an annular jacket is placed around the pipe, and the jacket is then filled with liquid Nitrogen(-196.deg. C). Thermal analysis by the finite element method based on the laboratory experiments has been constructed. The result of the finite element analysis on the experimental model shows to be reasonable, and thus the finite element analysis for different pipe size, material and thickness has been performed to see if the ice plugging procedure in various applications can be safely performed without possibility of damage to the pipe. It has been confirmed that in carbon steel pipes the maximum stress is found around the boundary of the freezing jacket, and the stress increases as pipe thickness increases, but the maximum stress shows no consistency along the increment of the pipe diameter. The maximum stresses appear lower than yield stress in carbon steel. It has been also shown that in stainless steel pipes the maximum stresses are also found around the boundary of the freezing jacket, but almost the same value in spite of different pipe size an thickness, and the maximum stresses show slightly higher than the yield stress of the stainless steel.

• 에너지공학
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• 제26권3호
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• pp.105-112
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• 2017

우리는 원자력발전시스템에서부터 상수도까지 많은 배관시스템을 사용하고 있다. 그리고 이들 배관시스템의 적절한 운용을 위하여 배관시스템의 유지 및 보수 등을 수행하고 있다. 특히 한국지역난방공사와 같은 대형플랜트 배관시스템의 고장은 기업의 생산성과 이익에 직결된 문제일 뿐만 아니라 국민의 안전과 편익과 같은 매우 중요한 문제를 유발할 수 있기 때문에 빠른 대응과 안전한 수리가 가장 중요한 문제로 대두되고 있다. 본 연구에서는 한국지역난방공사 사용 중인 이중보온 열수송관(300A)의 유지보수를 위하여 액화질소를 이용한 배관 동결차수공법을 개발하였다. 본 연구에서는 전산해석기법을 채용하여 대상 열수송관과 전용 재킷에 대한 내부 유동 및 열전달 해석을 수행하여 최적의 시스템을 선정하고, 상세 모델을 설계, 제작하였다. 실험실 규모 시험장치를 개발하여 차수공법에 대한 자체시험을 수행하고, 한국지역난방공사 세종지사 Test bed에서 현장적용 성능평가 시험을 수행하였다.

• 설비공학논문집
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• 제24권4호
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• pp.336-342
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• 2012

Large-scale active solar heat systems are generally using heat exchanger between collector and storage tank loops to prevent damage by freezing. It is difficult to maintain stratification in a storage tank in the system owing to greater flow rate enhancing heat transfer. In the previous study, we introduced a spiral-jacketed storage tank and obtained good results to keep system performance of general level without better stratification. We added a scroll-shaped heat exchanger coil on the upper part in the spiral-jacketed storage tank. As a result of the experiment, it was verified that degree of stratification of the new type storage tank is higher than that of the previous one with a possibility of better collector efficiency and solar fraction.