• Journal of Energy Engineering
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• v.26 no.3
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• pp.71-77
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• 2017

In the event of loss of coolant accident (LOCA) and station black out (SBO) in the primary system of a nuclear reactor, the coolant water should be injected to reactor coolant system (RCS) without any intervention of operators or active components. To satisfy the requirements, hybrid safety injection tank (Hybrid SIT) was suggested by Korea Atomic Energy Research Institute (KAERI). The pressure equalizing time of Hybrid SIT is an important parameter to determine the timing of coolant injection. To predict the pressure equalizing time of the Hybrid SIT, a separate effect test facility was constructed and sensitivity tests were conducted in various conditions. The main parameter determining the pressure equalizing time was obtained from separate effect test (SET) results. The wall of condensation on the inner wall of SIT and direct contact condensation on the water surface affected to the pressure equalizing time very much. In this study, the effect of each condensation phenomena on pressure equalizing time was quantitatively analyzed from results of SET and a prediction method of pressure equalizing time was proposed.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.29 no.4
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• pp.48-54
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• 2000

자성재료에 자기장을 걸어주변 가열되고 자기장을 제거하면 냉각되는 성질이 있는데, 이를 자기열량효과(magnetocaloric effect)라고 하며, 이것을 이용해서 저온을 생성시키는 방법을 자기냉동(magnetic refrigeration)이라고 한다. 큐리 온도(Curie temperature) 부근의 강자성체에 자 기장이 가해지면 전자례도내에서 쌍을 이루지 않은 전자들의 자기모벤트들이 자기장에 평행 하게 배열되는데, 이로 인해 열역학적 무질서의 척도인 엔트로피는 낮아지고 이러한 손실을 보상하기 위해 재료의 온도가 올라가게 된다.반대로 자기장이 제거되면 자기모벤트가 본래의 무질서한 상태로 돌아오며, 엔트로피가 증가하 고 재료의 온도는 떨어지게 되는 것이다. 역사적으로 보면 1881년에 Warburg가 큐리온도 부근의 철에서 자기열량효과를 처음 발견하였으며. 1926년과 1927년에 Debye와 Giauque가 각각 단열소자볍 (adiabatic demagnetization)을 제안함으로써 실용화되기 시작하여 주로 극저온을 얻는 방법으로 이용되어 왔다. 1950년도 이전의 연구는 절대온도 영도(OK)에 도달하고 자 하는 순수과학적인 노력으로서 개방사이클(open cycle)을 이용한 단열냉각 방식을 추구하 였으나, 1950년 이후부터는 공학적인 응용을 목적으로 밀폐사이클(closed cycle)을 형성하는 자기냉동기에 관한 연구가 진행되었다. 1976년에 Brown은 희토류(rare earth) 금속인 가돌리늄(Gd)을 사용하여 유체(물 80%와 에틸 알코올 20%)를 재생시킴으로써 상온에서 작동 하는 자기냉동기를 보고한 바 있다. 그는 7 T의 큰 자장을 이용하였으며, 고온부와 저온부의 온도는 각각 $46^{\circ}C와\;-1^{\circ}C로서\;47^{\circ}C$의 온도간격을 얻었다. 자기냉동에 있어서의 또 하나의 중요한 진전은 1978년과 1982년에 Steyert와 Barclay에 의해서 능동자기재생기(active magnetic r regenerator)의 개념이 소개되고 개발된 것으로, 이는 자성재료가 냉매로서 뿐만 아니라 열전달 유체의 재생기로도 사용되는 방식이다. 이상과 같은 자기냉동기술의 발달에 이어서 1997년에 미국의 Astronautics사(Wisconsin주 Madison시 소재)와 Ames 연구소(Iowa주 Ames 시 소재)의 공동연구팀이 발표한 두 가지의 새로운 진전으로 인해 공기조화 및 냉동분야에 적용할 수 있는 자기냉동기의 실용화 가능성이 한층 높아졌다. 이들의 연구결과는 (1) 자기냉동이 실온에서도 실현 가능한 기술이며 증기압 축식 냉동에 필적할 만하다는 것을 보인 것과 (2) 이미 알려져 있던 자기냉동재료보다 자기 열량효과가 훨씬 큰 새로운 재료를 발견한 것이다. 이로써 자기냉동에 대한 관심과 기대가 한결 커지고 있다. 본 원고에서는 자기냉동의 원리가 되는 자기열량효과와 이를 이용한 자기냉동의 방법 그리고 최근에 이루어진 새로운 진전에 대해 소개하고 공기조화 및 냉동분야에의 적용 가능성을 전망해 보고자 한다.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.211-221
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• 2016

The increase of world's population and economic development are the keys drivers behind growing demand for energy. Especially the demand for electricity would eventually result in an increase of coal usage. Therefore ultra supercritical circulating fluidized bed boiler has been developed as solutions of economic eco-friendly technologies for coal and of increasing supplies of low grade fuels. Ultra supercritical circulating fluidized bed boiler has an once through type of steam cycle different from drum type in subcritical circulating fluidized bed boiler. Also, the duplication of a proven commercial module with 100-300 MWe subcritical circulating fluidized bed might be the key for design of 500~800 MWe ultra supercritical circulating fluidized bed boiler. After 2017, ultra supercritical circulating fluidized bed boiler might become standard model over subcritical circulating fluidized bed boiler. Therefore, this paper will help you to understand ultra super critical circulating fluidized bed (USC-CFB) through describing the background, status and prospect of the CFB technology.

• Nuclear Engineering and Technology
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• v.24 no.3
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• pp.274-284
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• 1992

A 1/15-scale CREARE experiment, which simulates the thermal-hydraulic behavior in the reactor pressure vessel of a PWR during a hypothetical Loss Of Coolant Accident, has been analyzed using CATHARE code for the associated model assessment to represent the phenomenon. The key parameters examined in the CREARE experiment were known as ECC water injection rate. ECC water subcooling, system pressure, and steam flow rate coming out from the core bottom. The present CATHARE simulation, however, has been mainly focused on qualitative analysis of a countercurrent flow in the downcomer. The discrepancy of the simulation results with the experimental data is considered arising primarily from an inadequate numerical representation as well as an interfacial friction model. Accordingly it is suggested from the sensitivity studies that either multidimensional approach or further examination of momentum equations at a junction near a volume element in CATHARE be necessary in order to represent the phenomenon more realistically.

• Composites Research
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• v.13 no.4
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• pp.33-41
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• 2000

In this research, the mathematical modeling of the formation of SiC layer on the activated carbon was studied to improve the durability and the oxidation resistance of catalyst supports. SiC layer on the activated carbon was formed by permeating SiC from dichlorodimethylsilane(DDS) into pores and depositing while the porous structure was kept. The best conditions of manufacturing the support were found by studying the characteristics of SiC/C which was modelled under various deposition conditions. Changes of the amount of deposition, the pore diameter, the surface area with time were obtained by simulating convection, diffusion and reaction in an isothermal reactor at a steady state. The uniform deposition in the pores of samples was obtained at a lower concentration of the reactant and a lower pressure. Additionally, it was observed that the pore diameter and the surface area have points of inflection at certain times of deposition, because deposition occurred on the inside surface of the pore at first and then on the outside surface of the particle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1079-1085
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• 2010

A steady-state analytical model was presented for a loop heat pipe (LHP) with an evaporator that has a flat geometry. On the basis of a series of reviews of the relevant literature, a sequence of calculations was proposed to predict the temperatures and pressures at each important part of the LHP: the evaporator, liquid reservoir (compensation chamber), liquid line, vapor line, and condenser. The analysis of the evaporator, which is the only part in the LHP that has a capillary structure, was emphasized. Thin-film theory is applied to account for the pressure and temperature in the region adjacent to the liquid-vapor interface in the evaporator. The present study introduced a unique method to estimate the liquid temperature at the interface. Relative freedom was assumed in the configuration of a condenser with a simplified liquid-vapor interface. Our steady-state model was validated by experimental results available in the literature. The relative error was within 3% on the absolute temperature scale, and reasonable agreement was obtained.

• Proceedings of the Korea Society for Simulation Conference
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• 2000.11a
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• pp.61-66
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• 2000

The KEPRI has been upgrading the KNPEC(Korea Nuclear Power Education Center) #2 simulator, a replica of Yonggwang Unit 1 & 2, due to the outdated systems. The scenarios, such as the continuous load change, are selected to verify and validate the simulator, and the data required to V&V are generated with the best-estimated codes, RETRAN and MARS. The reactor coolant system and steam generator system are cut up into volumes and junctions for the accurate model of the scenarios, and other components and control systems are modeled. For the model the operation and design data of the plants is used and in some cases the data of Kori Unit 3 & 4 is used to fill up the lack of required data. The results of some selected analyses with the models are compared with the operating data of the plants to verify the models, and the analyses of the scenarios are carried out to generated the data for the V&V of the simulator

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.965-973
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• 1992

Boilers, which are considered to be one of the basic equipment in industry, consume large potion of nation's petroleum and their demand is growing everyday. In recent, the technology improvement in production of high efficiency boilers and their effective utilization is needed for design of boiler which steam condition is the large capacity of high temperature and high pressure. It is necessary that boiler control system be studied for high efficiency, high reliability and smooth operation. The control of drum pressure and water level particularly becomes an important task for greater accuracy with the avail ability of boiler operation. To achieve this aim, dynamic analysis of a boiler is accomplished by choosing a boiler as a model. Transfer function thus obtained is made a comparison of measurement with reckoning to technical design data. The results of comparison makes it possible to verify thermodynamical analysis on the dynamic behavior of the overall system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.1016-1022
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• 2010

An Experimental study of cleaning solution has been performed on a high capacity steam boiler burning heavy fuel oil to on-line cleaning of deposit. The deposit is mixture of soot, slag, ash, metal oxide and clinker. The traditional technology of deposit cleaning was carried hand-crafted. The conventional technology of boiler cleaning method is mechanical removal by the worker while the boiler shut down operation. In this experiment, the deposit of mixture of soot, slag, ash, metal oxide and clinker has been removed by the cleaning agents without shut down of boiler burning. This study found out the optimum cleaning solution composition. The best results have been obtained when the mixture of ammonium nitrate and $MgNO_3$ were used in cleaning solution. The various transition metal effect was investigated for optimum mixing condition. In this research, the metal compound additive of the clean solution compoition was obtained. The combustion efficiency was improved by on-line cleaning with derived clean solution compoition. On-line cleaning method prevents the fouling and corrosion in the boiler and heat exchanger.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.67-67
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• 2010

탄소나노튜브(CNT)는 우수한 기계적, 화학적, 전기적 특성으로 인해 다양한 분야에서 차세대 응용재료로서 각광을 받고 있다. 다양한 CNT의 합성방법 중 CNT 구조제어가 가장 용이한 방법으로는 열화학증기증착법(TCVD)와 플라즈마지원(PE) CVD법이 있으며, 대량합성을 위해서는 TCVD가 보다 일반적으로 이용되어지고 있다. 일반적으로 CNT를 합성하기 위해서는 전이금속의 촉매가 필요하며 촉매의 활성화 및 탄소를 포함하는 원료가스의 분해를 위하여 고온공정이 요구된다. 그러나 향후 산업적 응용을 고려한다면 저온합성법의 개발은 시급하게 해결해야 할 과제로 인식되고 있다. 또한 기판 위에 CNT를 합성하는 경우 촉매와 기판재료 사이의 합금화를 방지하기 위하여 산화막층을 삽입하게 되는데, 이는 CNT의 높은 전도성을 이용하고자 할 경우 저해요소로 작용하게 된다. 따라서 CNT를 완충층의 도움 없이 금속기판 위에 직접 성장시키는 기술 역시 향후 CNT응용에 있어서 중요한 과제라 할 수 있다. 상기와 같은 배경으로 본 연구에서는 금속기판 위 CNT의 저온성장을 목적으로 연구를 진행하였다. CNT 합성기판으로는 SUS316L 및 Inconel과 같은 촉매금속을 자체 함유한 금속기판을 선정하였고, 플라즈마 전처리를 통한 기판표면 제어를 통하여 CNT의 저온성장을 도모하였다. 직류전원의 아르곤 플라즈마를 이용하여 금속기판을 처리하였을 때 기판온도 및 플라즈마 파워가 증가함에 따라 기판의 표면조도가 증가하는 것을 AFM분석을 통해 확인할 수 있었다. 아세틸렌 가스를 원료가스로 이용한 TCVD합성에 있어서는 플라즈마 처리한 기판이 무처리 기판보다 동일 합성온도에서 더 두꺼운 CNT박막을 형성하였고, 합성온도는 $400^{\circ}C$ 부근까지 내릴 수 있었다. 이는 플라즈마 처리로 증가된 기판의 표면조도가 저온에서 CNT의 핵생성에 유리하게 작용했음을 추측하게 한다.