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정한식,정효민,김경근,노승탁,Chung, Han Shik,Jeong, Hyo Min,Kim, Kyung Kun,Ro, Sung Tack 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.2
The turbulent natural convection in the membrane type LNG carrier cofferdam with heating points has been studied by numerical method. As the numerical methods, we introduced the three turbulence model, a standard $k-{\varepsilon}$ model and two case of a low Reynolds number models. The parameters considered for this study ore number and capacity of heating points i.e., $1{\leq}Ns{\leq}12$ and $1.0{\times}10^5{\leq}Qs(W/m^3){\leq}1.0{\times}10^8$. The results of the isotherms and velocity vectors have been represented for various parameters. The temperature and velocity at upper position in the space ore shown to be higher than those at lower position. For obtaining the optimal temperatures, $20{\sim}30^{\circ}C$ in the cofferdam space, the heating capacities show $2.0{\times}10^7W/m^3$ at g-heating points and $1.0{\times}10^7W/m^3$ at 12-points. The mean temperature in the cofferdam space can be expressed as a function of number and capacity of heating points.
브라인 재가열을 이용한 증발식 해수담수화설비의 성능개선
정한식,이영호,박용호,김정태,최순호,정광운 한국마린엔지니어링학회 2019 한국마린엔지니어링학회지 Vol.43 No.6
As thermal seawater desalination requires a fairly large amount of energy to produce freshwater compared with other processes, it is very important to reduce energy consumption through the improvement of a process. This paper proposes a method to reduce energy consumption for multistage flashing desalination (MSF) plants, which currently operate mainly in the Middle East region. In the MSF process, the brine that has not been evaporated in the preceding stage is supplied to the next stage; this supplied brine is evaporated in the next stage at lower pressure and temperature conditions. This process is continued from the first stage to the last stage. In this study, the energy consumption could be reduced by reheating the brine to the top brine temperature (TBT) and by transferring a part of brine to the stage following the next stage, or by reheating the brine supplied to the next stage up to the TBT. According to the calculation results, the specific energy required to produce 1 kg of freshwater can be reduced by up to approximately 5 % if the proposed brine reheating method is applied to MSF plants that are currently in operation. 증발식 해수담수화설비는 타방식에 비해 담수생산을 위한 에너지소비가 매우 크기 때문에 공정개선을 통해 에너지를 절감하는 것은 매우 중요하다. 본 연구에서는 중동지역에 이미 설치되어 운전 중인 대용량의 다단플래싱방식의 증발식 해수담수화공정을 대상으로 에너지절감방안을 제안하고 있다. 다단플래싱방식에서는 전단에서 증발하고 남은 브라인이 전단보다 낮은 온도와 압력으로 운전되는 후단으로 이송되어 단계적으로 증발하는 방식을 취하는데, 본 연구에서는 전단에서 후단으로 넘어가는 브라인의 일부를 최전단의 증발기로 공급되는 브라인 온도까지 재가열 후에 후단 혹은차후단으로 공급하는 공정개선을 통해 에너지절감을 달성하였다. 본 연구의 계산결과에 따르면 현재 운전 중인 다단플래싱방식의 해수담수화플랜트에 브라인 재가열방식을 적용하는 경우 담수 1 kg을 생산하는데 필요한 비에너지를 최대약 5 %까지 절감할 수 있음을 확인하였다.
Study on low pressure evaporation of fresh water generation system model
정한식,Supriyanto Wibowo,Berkah Fajar,Yonghan Shin,정효민 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.2
A low pressure evaporation fresh water generation system is designed for converting brackish water or seawater into fresh water by distillation in low pressure and temperature. Distillation through evaporation of feed water and subsequent vapor condensation as evaporation produced fresh water were studied; tap water was employed as feed water. The system uses the ejector as a vacuum creator of the evaporator, which is one of the most important parts in the distillation process. Hence liquid can be evaporated at a lower temperature than at normal or atmospheric conditions. Various operating conditions, i.e. temperature of feed water and different orifice diameters,were applied in the experiment to investigate the characteristics of the system. It was found that these parameters have a significant effect on the performance of fresh water generation systems with low pressure evaporation.
APR1400 증기발생기 주급수관 파단사고 시 파단 위치에 따른 주급수 박스에 대한 수력 하중 및 응력에 대한 영향 검토
정한식,김종인 대한기계학회 2023 大韓機械學會論文集A Vol.47 No.12
APR1400 증기발생기는 설계기준사고 중 하나인 주급수관 파단사고 시에도 내부구조물의 건전성이 확보되도록 설계를 요구하고 있고, 이를 확인하기 위한 평가를 수행하고 있다. 주급수관 파단사고가 발생하면 순간적으로 증기발생기 내부의 유체가 빠져나오면서 압력이 급격히 하락하게 되어 내부구조물에 수력하중이 발생하게 된다. 수력하중을 산출하기 위해 사고해석 코드가 사용되며, 파단사고는 주급수 노즐 출구를 파단 위치로 요구하고 있으나, 보수적인 평가를 위해 주급수 노즐 입구에서 파단을 가정하여 수력하중을 산출하고 있다. 본 연구에서 주급수관 파단사고 발생 위치에 따른 수력하중 및 증기발생기 내부구조물 중 하나인 주급수 박스에 대한 응력 영향을 확인하고자 한다. The APR1400 steam generator requires a design to secure the integrity of the internal structure during a feedwater line break accident, which is a design-based accident, and an evaluation is conducted to confirm this. When the feedwater line break occurs, the fluid inside the steam generator is momentarily released and the pressure drops rapidly, resulting in a hydraulic load on the internal structure. The accident analysis code is used to calculate the hydraulic load, and the break accident requires the end of the feedwater line nozzle as the location of the accident. This study analyzes the effect of the hydraulic load and stress on the feedwater box depending on the location of the feedwater line break accident.
2개(個)의 수직(垂直) 평판(平板)핀을 가진 전도관(傳導管)으로 부터의 자연대류(自然對流) 열전달(熱傳達)
정한식,이철재,권순석,Chung, H.S.,Lee, C.J.,Kwon, S.S. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.4
Conjugate heat transfer by steady laminar natural convection from a conducting tube with two vertical axial fins has been studied by a finite difference numerical procedure under basic conditions; $Ra=10_6$, Pr = 5 and $L_F=0.15$. The maximum local tube Nusselt number appears at ${\theta}=140^{\circ}$ for $L_F=0.06$, at ${\theta}=130^{\circ}$ for $L_F=0.30$ and at ${\theta}=120^{\circ}$ for $L_F=0.30$, $L_F=0.06$, respectively. The maximum mean Nusselt number shows at $L_F=0.18$ for the downward fin and at $L_F=0.12$ for the upward fin. Therefore the optimized fin length is $L_F{\approx}0.15$ under these conditions. At $L_F=0.15$, the mean Nusselt number by increasing Rayleigh number is remarkably increased for downward fin and then is slowly increased except for downward fin, it by increasing Prandtl number is apparently increased at $Pr{\leq}2$, and slightly increased at Pr>2.