• 한국재료학회지
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• 제21권11호
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.289-294
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• 1996

Feasibility study on conceptual design tool for liquid metal reactor has been conducted to optimize the thermohydraulic and neutronic design parameters. To accomplish this task the neutronic code PRISM, fuel performance code and scaling method have been included into the conceptual design support system. ALMR(PRISM 303MWe) has been adopted as the reference plant and principally according to the power level, conceptual design parameters are optimized so that energy balance and neutronics balance seem to be satisfied. This paper presents only the results of optimization on primary system including the IHX system.

• 한국세라믹학회지
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• 제48권1호
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• pp.52-56
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• 2011

Silicon carbide (SiC) is a candidate material for heat exchangers for VHTR (Very High Temperature Gas Cooled Reactor) due to its refractory nature and high thermal conductivity. This research has focused on demonstration of physical properties and mock-up fabrication for the future heat exchange applications. It was found that the SiC-based components can be applied for process heat exchanger (PHE) and intermediate heat exchanger (IHX), which are operated at $400{\sim}1000^{\circ}C$, based on our examination for the following aspects: optimum fabrication technologies (design, machining and bonding) for compact design, thermal conductivity, corrosion resistance in sulfuric acid environment at high temperature, and simulation results on heat transferring and thermal stress distribution of heat exchanger mock-up.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.1-6
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation. The VHTR can produce hydrogen from heat and water by using a thermo-chemical process or from heat, water, and natural gas by steam reformer technology. A co-axial double-tube primary hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the VHTR. In this study, a preliminary design analysis for the primary HGD of the nuclear hydrogen system was carried out. These preliminary design activities include a determination of the size, a strength evaluation and an appropriate material selection. The determination of the size was undertaken based on various engineering concepts, such as a constant flow velocity model, a constant flow rate model, a constant hydraulic head model, and finally a heat balanced model.

• 설비공학논문집
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• 제17권3호
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• pp.209-215
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• 2005

Since a transcritical $CO_2$ cycle shows lower performance than conventional air conditioners in the cooling mode operation, it is required to enhance the performance of the $CO_2$ cycle by applying advanced technologies and optimizing components. In this study, the cooling performance of a $CO_2$ system measured by varying refrigerant charge amount, compressor frequency, EEV opening and length of internal heat exchanger. As a result, the cooling COP of the basic system without internal heat exchanger was 2.1. The cooling performance of the modified cycle applying internal heat exchanger improved by $4-9\%$ over the basic cycle.

• 설비공학논문집
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• 제16권2호
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• pp.158-166
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• 2004

The performance of a heat pump using $CO_2$ is predicted and analyzed by using a cycle simulation model developed in this study. Cycle simulations are conducted by varying design parameters and operating conditions with the applications of advanced techniques to improve system performance. The applied systems in the simulations are internal heat exchanger, expander, and 2-stage compression with intercooling. As a result, the applications of advanced techniques improve the heating and cooling performances of the transcritical $CO_2$ cycle by 8∼26％ and 20∼30％, respectively, over the basic cycle.

• 설비공학논문집
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• 제24권2호
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• pp.147-154
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• 2012

Recently, many researchers have studied the performance of the transcritical $CO_2$ refrigeration cycle in order to improve the system efficiency. In this study, the length of IHX in the $CO_2$ ejector cycle was varied so as to evaluate the performance improvement. As a result, compressor work and cooling capacity was increased by 3% and 5% as the length of internal heat exchanger was changed from 3 m to 15 m. The best COP was appeared at internal heat exchanger length of 12 m, and it was 3.01. Besides, the length of internal heat exchanger has a big effect to pressure lift ratio and entrainment ratio in the ejector $CO_2$ cycle and it may be changed with operating conditions and system specifications.

• 설비공학논문집
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• 제25권1호
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• pp.20-27
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• 2013

Numerical modeling of $CO_2$ water heater was conducted prior to optimal design of medium and large sized $CO_2$ water heater, and the experimental test with small sized $CO_2$ water heater having heat capacity of 4 kW was completed to verify the present numerical model. The present model estimated the experimental data of COP(coefficient of performance), heating capacity, and the hot water outlet temperature within the range of 3% to 8% of mean deviation. As increase of EEV(electric expansion valve) opening area, decreasing of heating capacity and the hot water outlet temperature, and increasing of COP were found in both experimental and numerical investigation.

• 한국산학기술학회논문지
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• 제21권6호
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• pp.403-410
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• 2020

본 논문은 포항지역 태양광 데이터를 기반으로 태양열을 적용시켜 12kW의 소형 초임계 이산화탄소(s-CO₂) 시험 루프의 설계와 실험 시설의 이론적 연구, 안정화 및 최적화를 통한 이산화탄소의 특성 연구에 초점을 맞추고 있다. 실험 시설의 열역학 사이클은 구성 요소의 한계로 인해 액체, 가스 및 초임계 CO₂가 모두 존재하는 랭킨 사이클(임계점 순환 주기)이며, 펌프, 히터, 레귤레이터, 열교환기, 가스 부스터, 에어 컴프레서 등으로 구성된다. 현재 본 연구에서 제작된 12kW 소형 발전 시스템은 최고압력 12MPa 최고 온도 70℃의 조건에서 6.98%의 효율이 나타나도록 설계되었다. 본 실험 장치를 소형 Brayton cycle과 비교했을 때 약 2% 높은 효율을 가진다는 것을 이론적으로 확인하였고, 사이클 효율을 높이기 위해 최적의 터빈 입구 온도와 압력을 얻었으며, 이 조건에서 IHX(내부 열교환기)의 도입시 18.75%의 최대 효율을 기대할 수 있다는 결론을 도출하였다. 마지막으로, 실험 설비의 태양광 시뮬레이션 결과 5월에는 6.7%, 6월에는 6.26%의 효율로 태양열을 이용할 수 있음을 확인하였다.

• 설비공학논문집
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• 제25권4호
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• pp.173-179
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• 2013

Middle-sized $CO_2$ water heater having compressor power of 7.45 kW was designed, and its performances were experimentally tested. Besides, optimum design of the $CO_2$ water heater was conducted by cycle simulation. When ambient temperature of $7^{\circ}C$ and hot water outlet temperature of $80^{\circ}C$ the $CO_2$ water heater showed the COP of 3.2. As hot water temperature increased the COP is getting decreased due to significant increase of compressor power consumption compared to increasing rate of heating capacity. When ambient temperature increased from $-3^{\circ}C$ to $12^{\circ}C$ the COP increased by 30%. The optimum components design of a gas cooler, an internal heat exchanger, and an evaporator were conducted, and the experimental correlation between amount of EEV opening and ambient temperature, and hot water temperature was suggested.