• Nuclear Engineering and Technology
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• 제56권1호
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• pp.19-33
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• 2024

In nuclear thermal-hydraulic system codes, most correlations used for vertical pipes, under downward two-phase flow, have been developed considering small pipes or pool systems. This suggests that there could be uncertainties in applying the correlations to accident scenarios involving large vertical pipes owing to the difference in the characteristics of two-phase flows, or flow conditions, between large and small pipes. In this study, we modified the Multi-dimensional Analysis of Reactor Safety KINS Standard (MARS-KS) code using correlations, such as the drift-flux model and two-phase multiplier, developed in a plant-scale air-inflow experiment conducted for a pipe of diameter 600 mm under downward two-phase flow. The results were then analyzed and compared with those based on previous correlations developed for small pipes and pool conditions. The modified code indicated a good estimation performance in two plant-scale experiments with large pipes. For the siphon-breaking experiment, the maximum errors in water flow for modified and original codes were 2.2% and 30.3%, respectively. For the air-inflow accident experiment, the original code could not predict the trend of frictional pressure gradient in two-phase flow as / increased, while the modified MARS-KS code showed a good estimation performance of the gradient with maximum error of 3.5%.

• 한국유체기계학회 논문집
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• 제8권6호
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• pp.40-46
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• 2005

Because of design and manufacturing costs, it is important to predict an expected life of bellows with component stresses of bellows as its design factors and material characteristics. In this study, numerical analyses are carried out to elucidate the thermal and flow characteristics of the bellows-seal gate and globe valves for high temperature (max. $600^{\circ}C$) and for high pressure (max. $104 kgf/cm^2$) conditions. Using commercial codes, FLUENT, which uses FVM and SIMPLE algorithm, and ANSYS, which uses FEM, the pressure and temperature fields are graphically depicted. In addition, when bellows have an axial displacement, thermal stress affecting bellows life is studied. The pressure and temperature values obtained from the flow analyses are adopted as the boundary conditions for thermal stress analyses. As the result of this study, we got the reasonable coefficients for valve and thermal stress for bellows, compared with existing coefficients and calculated values.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2789-2802
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• 2020

Small Modular Reactors (SMRs) are attracting wide attention due to their outstanding performance, extensive studies have been carried out for lead-based fast reactors (LFRs) that cooled with Lead or Lead-bismuth (LBE), and small modular natural circulation LFR is one of the promising candidates for SMRs and LFRs development. One of the challenges for the design small modular natural circulation LFR is to master the natural circulation thermal-hydraulic performance in the reactor primary circuit, while the natural circulation characteristics is a coupled thermal-hydraulic problem of the core thermal power, the primary loop layout and the operating state of secondary cooling system etc. Thus, accurate predicting the natural circulation LFRs thermal-hydraulic features are highly required for conducting reactor operating condition evaluate and Thermal hydraulic design optimization. In this study, a thermal-hydraulic analysis code is developed for small modular natural circulation LFRs, which is based on several mathematical models for natural circulation originally. A small modular natural circulation LBE cooled fast reactor named URANUS developed by Korea is chosen to assess the code's capability. Comparisons are performed to demonstrate the accuracy of the code by the calculation results of MARS, and the key thermal-hydraulic parameters agree fairly well with the MARS ones. As a typical application case, steady-state analyses were conducted to have an assessment of thermal-hydraulic behavior under nominal condition, and several parameters affecting natural circulation were evaluated. What's more, two characteristics parameters that used to analyze natural circulation LFRs natural circulation capacity were established. The analyses show that the core thermal power, thermal center difference and flow resistance is the main factors affecting the reactor natural circulation. Improving the core thermal power, increasing the thermal center difference and decreasing the flow resistance can significantly increase the reactor mass flow rate. Characteristics parameters can be used to quickly evaluate the natural circulation capacity of natural circulation LFR under normal operating conditions.

• 동력기계공학회지
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• 제16권4호
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• pp.24-29
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• 2012

The numerical analysis by using CFX 11.0 commercial code was done for prediction of fluid flow and thermal field in the vertical heat exchanger. The present experimental studies were also conducted to investigate the effects of circulating solid particles on the fluid flow and temperatures in the fluidized bed vertical shell and tube type heat exchanger with counterflow, at which the solid particles of glasses (3 $mm{\Phi}$) were used in the fluidized bed with a smooth tube. The effect of circulation on the distance(L) of tube inlet and baffle plate was also examined. The present experimental and numerical results showed that the particles in the distance (Ds) of 15 mm showed a more efficient circulation without stacked the space and the LMTD(Log Mean Temperature Difference) in the fluidized bed type was much lower than that in the typical type shell and tube heat exchanger.

• 한국추진공학회지
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• 제6권1호
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• pp.1-11
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• 2002

Thermal stripping을 수반한 난류유동장에 대한 해석방법론 정립에 필요한 신뢰성 있는 난류모델을 선정하기 위하여 온도변화가 있는 비정상 난류유동장에 $\kappa$-$\varepsilon$ 모델, 수정 $\kappa$-$\varepsilon$ 모델, 그리고 full Reynolds stress(FRS) 모델을 적용하였다. 검증대상으로는 thermal stripping 현상이 자주 관찰되는 원자로 혹은 추진기구부 등에서 보이는 수직평판과 수평평판에 대한 제트유동이 있는 유동장을 선정하였으며 이 때의 유체로는 물 혹은 액체나트륨을 사용하였다. 분석결과 비정상 난류유동장은 FRS를 사용하여 3-D로 해석할 때 가장 나은 결과를 얻을 수 있었다. 그러나 경계면 부근을 비롯한 유동장내에서의 열전달 특성 분석의 정확성을 제고하기 위해서는 이를 위한 수정모델의 도입이 요구된다. 아울러 제트유동의 운동량이 thermal stripping 현상에 미치는 영향을 평가하기 위하여 제트유동의 유속을 변화시켜 이에 따른 영향을 점검한 결과 운동량의 증가는 유동장의 혼합능력을 증가시키고 온도변화 진폭을 상승시키는 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2642-2647
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• 2007

This study represents numerical study on the thermal and fluid flow characteristics of exhaust gas in a motorcycle muffler. The reference engine was used 124.cc small displacement. Numerical analysis with computational fluid dynamics(CFD) was carried out to investigate the exhaust gas that flow into a motorcycle muffler. The STAR-CD S/W used to three dimensional steady state CFD analysis in a muffler. And than We got the information of static pressure it is used to structural analysis ant the first baffle plate using the commercial CAE code ANSYS workbench. Exhaust gas flow third chamber from frist chamber and running second chamber. A simulation result shows that each chamber of muffler temperature is about 460 K, 445 and 463K and pressure is about 22,000 Pa, 16,000 Pa and 10,000 Pa.

• 한국수소및신에너지학회논문집
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• 제9권2호
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• pp.53-64
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• 1998

Thermal analysis on a Linde-Hampson hydrogen liquefaction system using cryogenic refrigerators as precooling has been carried out. Three commercially available models of cryogenic refrigerators, such as CTI l020CP, CVI CGR009 and CVI CGR011, are considered in the performance analysis. The effect of ortho-para conversion process during hydrogen liquefaction is also studied in detail. The results obtained indicate that the optimal hydrogen mass flow rate and the optimal compressed pressure exist for the maximum hydrogen liquefaction rate. The optimal compressed pressure is increased in the range of 80 - 120 bar with an increase in the hydrogen mass flow rate. It is also found that better performance could be obtained with a cryogenic refrigerator, which produces high cooling capacity at precooling temperature in the range of 80 - 100 K.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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• pp.92-97
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• 2011

Nowdays the most critical problem is global warming and the most important reason is the high emition of carbondioxide. 23% of the use of carbondioxide is used in building and decreasing the use of it is very important. One of the biggest factor that can decrease the use of energy is developing the heat conducting ratio of the materials we use in building. Heat conducting ratio is the important factor in the use of reducing energy comsumation. In this research, there are methods about how to measure the heat conducting ratio, and the existing the representing measuring method which is Heat Flow Meter HFM 436, Laser Flash Analysis and find out about the TCi of the new method C-Therm and compare the results.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.245-251
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• 1999

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seem that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stresses.

• Bulletin of the Korean Chemical Society
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• 제21권1호
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• pp.69-74
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• 2000

Applicability of Thermal field flow fractionation (ThFFF) was investigated for the analysis of masticated natural rubber (NR) adhesives produced bya hot melt mastication process. An optimum ThFFF condition for NR analysis was found by using tetrahydrofuran (THF) as a solvent/carrier and a field-programming. Low flowrate (0.3 mL/min) was used to avoid stopping the flow for the sample relaxation. Measured molecular weight distribution was used to monitor degradation of rubber during the mastication process. Rubber samples collected at three different stages of the mastication process and were analyzed by ThFFF. It was found that in an anaerobic process rubber degradation occurs at the resin-mixing (compounding) zone as well as in the initial break-down zone, while in an aerobic process most of degradation occurs at the initial breakdown zone. It was also found that E-beam radiation on NR causes a slight increase in the NR molecular weight due to the formation of a branched structure.