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Thermal Stratification 해석 난류모델 평가
최석기(Seok-Ki Choi),위명환(Myung-Hwan Wi),김성오(Seong-O Kim) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
Evaluation of turbulence models is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor by applying them to the experiment conducted at JNC. The turbulence models tested in the present study are the two-layer model, the k-ω model, the v2-f model and the low-Reynolds number differential stress-flux model. When the algebraic flux model or differential flux model are used for treating the turbulent heat flux, there exist little differences between turbulence models in predicting the temporal variation of temperature. However, the v2-f model and the low-Reynolds number differential stress-flux model better predict the steep gradient of temperature at the interface of thermal stratification, and only the v2-f model predicts properly the oscillation of temperature. The LES is needed for a better prediction of the amplitude and frequency of the temperature fluctuation.
소듐과 이산화탄소 반응에 의한 소듐유로막힘 및 재료손상 현상 연구
박선희 ( Sun Hee Park ),민재홍 ( Jae Hong Min ),이태호 ( Tae-ho Lee ),위명환 ( Myung-hwan Wi ) 한국화학공학회 2016 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.54 No.6
본 논문의 목적은 소듐냉각고속로(sodium cooled fast reactor, SFR)와 초임계 CO<sub>2</sub> Brayton cycle의 연계 시, 원자로 열수송 계통과 동력변환 계통의 압력 경계를 형성하는 회로인쇄형 열교환기의 경계면에 균열이 발생해 고압(약 200 bar)의 CO<sub>2</sub>가 상압 수준의 액체소듐유로 측에 유입되었을 때의 물리/화학적 현상을 파악하여 열교환기 설계에 활용 가능한 실험 자료를 생산하는 것이다. 열교환기의 소듐-CO<sub>2</sub> 경계면 균열 현상은 경계면의 균열 크기에 따라 미세 균열에 의한 소듐유로막힘(plugging) 현상과 상대적으로 큰 균열에 의한 열교환기 재료손상(wastage) 현상으로 나뉜다. Plugging 실험결과, 소듐유로 직경이 3 ㎜일 때 CO<sub>2</sub> 주입 즉시 소듐 흐름이 정지한 반면 소듐유로 직경이 5 ㎜일 때는 유량이 감소되기 시작하는 시점은 3 ㎜의 경우와 유사하게 CO<sub>2</sub> 주입 즉시 나타났지만 소듐의 흐름이 완전히 정지할 때까지는 상대적으로 오랜 시간이 소요되었다. 이러한 실험결과는 실제 열교환기의 소듐-CO<sub>2</sub> 경계면에서 미세균열이 발생했을 때, 소듐유로 직경이 3 ㎜로 좁을 경우 균열 발생과 동시에 해당 소듐유로가 반응생성물에 의해 막혀 해당 유로 외의 유로들로 지속적인 열교환기 운전이 가능하지만, 소듐유로의 직경이 5 ㎜로 넓어질 경우 소듐유로가 고체생성물에 의해 즉시 막히지 않고 생성물이 소듐유로를 따라 계통 내부를 이동하다 일정 농도 이상이 되어야 소듐유로를 막게 할 것으로 예상할 수 있는 결과이다. Wastage 실험결과, 열교환의 재질(STS316, Inconel600, G91 합금강), 운전온도(400~500℃), 노즐직경(0.2~0.8 ㎜), 시편-노즐 거리(2~6 ㎜)와 무관하게 고압(약 200~250 bar)의 CO<sub>2</sub> 분사에 의한 시편의 물리적 손상(erosion) 현상은 발생하지 않았다. 노즐에서의 분사되는 CO<sub>2</sub>의 분사속도는 마하 0.4~0.7인 것으로 확인되었다. 본 연구의 실험결과는 열교환기 파손 대처 설계에 배경 실험 자료로 활용될 것으로 기대된다. We investigated the physical/chemical phenomena that a slow loss of CO<sub>2</sub> inventory into sodium after the sodium-CO<sub>2</sub> boundary failure in printed circuit heat exchangers (PCHEs), which is considered for the supercritical CO<sub>2</sub> Brayton cycle power conversion system of a sodium-cooled fast reactor (SFR). The first phenomenon is plugging inside narrow sodium channels by micro cracks and the other one is damage propagation referred to as wastage combined with the corrosion/ erosion effect. Experimental results of plugging shows that sodium flow immediately stopped as CO<sub>2</sub> was injected through the nozzle at 300~400℃ in 3 mmID sodium channels, whereas sodium flow stopped about 60 min after CO<sub>2</sub> injection in 5 mmID sodium channels. These results imply that if pressure boundary of sodium-CO<sub>2</sub> fails a narrow sodium channel would be plugged by reaction products in a short time whereas a relatively wider sodium channel would be plugged with higher concentration of reaction products. Wastage by the erosion effect of CO<sub>2</sub> (200~250 bar) hardly occurred regardless of the kinds of materials (stainless steel 316, Inconel 600, and 9Cr-1Mo steel), temperature (400~500℃), or the diameter of the CO<sub>2</sub> nozzle (0.2~0.8 ㎜). Velocities at the CO<sub>2</sub> nozzle were specified as Mach 0.4~0.7. Our experimental results are expected to be used for determining the design parameters of PCHEs for their safeties.
위명환,김성오,어재혁,김진환 한국공업화학회 2005 응용화학 Vol.9 No.1
A Na-CO₂ heat exchanger is one of the key equipments in the concept of coupling the supercritical CO₂ Brayton cycle to the KALIMER-150 design. The exchanger is a shell and tube counter flow type with a hot sodium on the shell side and a supercritical carbon dioxide on tube side. In this study, a computational design methodology was developed and the sensitivity study was done on the major design parameters for the development of preliminary design. In the designing process, the design requirements are pressure drops and sodium maximum velocity in the shell side and aspect ratio of the heat exchanger. The evaluation revealed that the gap design of doubel wall tube has noticeable effects on the thermal-hydraulic characteristics of the heat changer. Maintaining the operating condition to be identical to those of KALIMER-150, the heat transfer area of He packed case was 4 times more than that of LBE packed case.
위명환,김성오,전원대,어재혁,김진환 한국공업화학회 2004 응용화학 Vol.8 No.2
The DWTSG concept is proposed as a advanced steam generator of liquid metal reactor to avoid sodium-water reaction incidents in the SG. The optimization of steam generator from economic viewpoint is to minimize the total cost of heat transfer area and pumping power. The baffles are primarily used in shell and tube steam generator for inducing cross flow over tube bundles, and as a results, improving heat transfer performance. In this paper a computer based design method, which covers segmentally baffled steam generator is developed for preliminary DWTSG design. And parametric sensitivity studies are done to determine required heat transfer area to meet the specified heat capacity by calculating minimum or allowable shell-side pressure loss.