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류승훈(Seung Hun Yoo),설광원(Kwang-Won Seul) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Gas accumulation phenomena of the piping systems for nuclear power plants have occurred since beginning of commercial operation. Gas accumulation may cause diverse safety issues such as pump cavitation, water hammering and unexpected gas intrusion to reactor vessel. In this study, Large Break Loss of Coolant Accident (LBLOCA) with the presence of non-condensable gas in the piping of Safety Injection Tank (SIT) was analyzed by RELAP5 code. The accident condition was conservatively assumed as 100% double-ended guillotine break at the reactor coolant pump discharge leg. The gas transport phenomena in the primary loop were analyzed. The portion of transported gas into the upper head, fuel assembly and pressurizer was quantified in this analysis. The analysis results showed that the choking flow was changed and the safety injection flow rate through SIT was reduced as reactor pressure was increased. The cladding temperature during the Reflood phase was increased because the gas prohibited heat transfer from fuel cladding to adjacent coolant. We concluded that the presence of non-condensable gas in the SIT piping may influence heat transfer phenomena in the reactor vessel and increase the Reflood cladding temperature in the LBLOCA analysis.
MARS-KS를 이용한 수평형 응축열교환기의 저장탱크 내의 열유동 특성 예측
신병수(Byungsoo Shin),설광원(Kwang-won SEUL),도규식(Kyusik Do) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
For the performance of a horizontal condensation heat exchanger, the flow characteristics in the storage tank are important factors to determine the heat transfer rate outside the tubes. The objective of this work is to predict the heat transfer rate and flow characteristics outside the heat exchanger tubes using MARS-KS code. To eliminate the effect of condensation heat transfer inside the tubes, the experimental results on temperature profiles were applied to the inside wall of tubes as boundary conditions. In conclusion, the numerical results of MARS-KS had good predictions with experimental results on heat transfer coefficients.
수평형 응축열교환기에서 이상유동양식에 대한 유량분배의 영향 평가
신병수(Byungsoo Shin),김남석(Namseok Kim),설광원(Kwang-won SEUL),도규식(Kyusik Do) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this study, it was performed to estimate effects of flow distributions on two-phase flow patterns in horizontal condensation heat exchanger. Detailed flow fields were calculated using commercial CFD code assuming working fluid as a single phase flow at simplified geometry. The results shows the differences of mass flow rate between heat exchanger tubes could be up to about 40% depending on averaged mass flow rate and features of geometry. At Tandon map which is one of well-known two-phase flow pattern map especially for horizontal condensation tubes, the differences could lead to the change of two-phase flow patterns. It means that performance of heat exchanger and criteria of water hammer also could be changed. Therefore, the effect of flow distribution was considered at design of horizontal condensation heat exchanger.
윤동혁(Dong-Hyeog Yoon),박주엽(Ju Yeop Park),설광원(Kwang-Won Seul) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.8
본 연구에서는 나선형 튜브내의 난류 열전달 및 하중 특성을 수치해석 방법을 이용하여 파악하였다. 열교환기와 같은 공학적 설비에서 관내 열전달을 향상시키기 위해 튜브의 형상을 나선형으로 설계한다. 이에 나선형 튜브내의 열전달 및 난류 특성에 대한 많은 실험적 연구가 이루어 졌으나, 대부분의 연구가 압력 강하 및 열전달 상관관계에 초점이 맞추어 진행되었다. 나선형 튜브내의 유동은 원심력에 의해 튜브 바깥쪽에서는 상대적으로 높은 열전달 및 전단응력이 발생하지만, 안쪽에서는 낮은 열전달 및 전단응력이 발생하게 된다. 따라서 본 연구에서는 튜브의 원주방향으로 발생하는 전단 응력 및 Nusselt 수의 변화를 Reynolds 수와 나선 코일의 지름을 변경하며 정량적으로 살펴보았다. 나선 코일 안쪽에서 국부적인 전단응력과 열전달율이 크게 낮게 특정되었으며, 이는 튜브 재질의 안정성에 영향을 미칠 것으로 판단되었다. 또한 본 연구에서는 마찰계수와 Nusselt 수에 대한 기존 상관관계식을 검증하였으며, 직관에서의 마찰계수와 Nusselt 수의 상관관계식이 나선형 튜브의 형상에도 적용될 수 있음을 관측하였다. 본 연구의 결과는 열교환기나 증기발생기의 안전성 평가를 위해 중요한 데이터로 활용될 수 있을 것이다. In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.
류승훈(Seung Hun Yoo),허병길(Byung Gil Huh),강동구(Dong-Gu Kang),설광원(Kwang-Won Seul) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The gas accumulation in the safety system has been becoming an important safety issue for operating nuclear power plant. The accumulated gas can cause cavitation or water hammering resulting in loss of safety injection. In this study, CFD(Computational Fluid Dynamics) benchmark analysis for Millstone-3 gas-water test has been conducted to evaluate the feasibility of CFD multiphase model for real phenomena. Eulerian multiphase model of ANSYS Fluent 14.5 was selected for the analysis. The CFD results showed that most of gas was transported to Residual Heat Removal pump and the marginal amount of gas was transported to Charging pump, which was the similar result of the benchmark case. We concluded that the Eulerian model could be applied to simulate the hypothetical gas-water transport phenomena in the safety system.
김형민(Hyung Min Kim),윤동혁(Dong-Hyeog Yoon),설광원(Kwang-Won Seul) 한국전산유체공학회 2013 한국전산유체공학회지 Vol.18 No.2
The goal of the research is to evaluate the open source code of OpenFOAM for the use of nuclear plant flow simulation objectively. Of the various incompressible flow solvers, simpleFoam, pimpelFoam are then tested under three validated cases (backward facing step, flow over circular cylinder and turbulent round jet flow). For the evaluation of steady state incompressible laminar flow simulation, low reynolds number of backward facing step flow was solved by simpleFoam. The resultant of the reattached lengths turned out to be similar with the other experimental and simulation results. For transient flow simulation, flow over circular cylinder and turbulent round jet flow were solved by pimpleFoam. The simulation accuracy was evaluated by comparing the resultant flow patterns with the description of the characteristics of the flow over the circular cylinder. The quantitative accuracy was evaluated for no more than 85% by comparing it to the decaying constants of the turbulent round jet velocity.