• Nuclear Engineering and Technology
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• 제42권4호
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• 한국압력기기공학회 논문집
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• 제14권2호
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• pp.77-87
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• 2018

In the case of high-energy line breaks in nuclear power plants, supersonic steam jet is formed due to the rapid depressurization. The steam jet can cause impingement load on the adjacent structures, piping systems and components. In order to secure the design integrity of the nuclear power plant, it is necessary to evaluate the load characteristics of the steam jet generated by high-energy pipe rupture. In the design process of nuclear power plant, jet impingement load evaluation was usually performed based on ANSI/ANS 58.2. However, U.S. NRC recently pointed out that ANSI/ANS 58.2 oversimplifies the jet behavior and that some assumptions are non-conservative. In addition, it is recommended that dynamic analysis techniques should be applied to consider transient load characteristics. Therefore, it is necessary to establish an evaluation methodology that can analyze the dynamic load characteristics of steam jet ejected when high energy pipe breaks. This research group has developed and validated the CFD analysis methodology to evaluate the transient behavior of supersonic impinging jet in the previous study. In this study, numerical study on the transient load characteristics of supersonic steam jet impingement was carried out and amplitude and frequency analysis of transient jet load was performed.

• 에너지공학
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• 제12권2호
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• pp.74-83
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• 2003

APR1400과 같은 차세대 원자력발전소에서는 원자로 안전성을 증진시키기 위하여 SDVS와 같은 계통을 도입하고 있다. 완전급수상실사고와 같은 경우는 POSRV가 개방되어 수조내 Sparger를 통하여 증기가 방출·응축되게 된다 증기가 응축함에 있어서 설계에서 고려해야 될 사항은 하중과 수조 혼합이며 증기제트 응축의 물리적 현상 이해를 통하여 적절한 대처를 마련할 수 있다. 수조내 Sparger를 통하여 분사되는 증기 응축에 대하여 하중과 수조 혼합 검토에 도움이 될 수 있도록 증기제트 응축의 물리적 현상 이해에 대한 검토와 평가를 수행하였다.

• 한국압력기기공학회 논문집
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• 제12권2호
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• pp.58-65
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• 2016

Since, in case of high energy piping, steam jets ejected from the rupture zone may cause damage to nearby structure, it is necessary to design it into consideration of nuclear power plant design. For the existing nuclear power plants, the ANSI / ANS 58.2 technical standard for high-energy pipe rupture was used. However, the US Nuclear Regulatory Commission (USNRC) and academia recently have pointed out the non-conservativeness of existing high energy pipe fracture evaluation methods. Therefore, it is necessary to develop a highly reliable evaluation methodology to evaluate the behavior of steam jet ejected during high energy pipe rupture and the effect of steam jet on peripheral devices and structures. In this study, we develop a method for analyzing the impact load of a jet by high energy pipe rupture, and plan to carry out an experiment to verify the evaluation methodology. In this paper, the basic data required for the design of the jet impact load experiment equipment under construction, 1) the load change according to the jet distance, 2) the load change according to the jet collision angle, 3) the load variation according to structure diameter, and 4) the load variation depending on the jet impact position, are numerically obtained using the developed steam jet analysis technique.

• 한국염색가공학회지
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• 제18권6호
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• pp.69-79
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• 2006

The washing characteristics of steam jet heating process have been compared with other washing processes, such as low temperature process(standard process, below $40^{\circ}C$) and high temperature process(boiling process, up to $95^{\circ}C$) with the standard soil fabric, EPMA 105. Steam jet heating process showed almost the same washing efficiency as high maximum temperature process for pig's blood and wine. This result can be explained with the higher surface temperature of washing materials in steam jet process compared with direct boiling process. In terms of the energy and water consumption, the steam jet washing process showed significant savings compared with direct boiling type washing process.

• 한국압력기기공학회 논문집
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• 제14권2호
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• pp.1-10
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• 2018

Structures, systems and components of nuclear power plants should be able to maintain safety even in the event of design-basis accidents such as high-energy line breaks. The high-pressure steam jet ejected from the broken pipe may cause damage to the adjacent structures. The ANSI/ANS 58.2 code has been adopted as a technical standard for evaluating the jet impingement load. Recently, the U.S. NRC pointed out the non-conservativeness of the ANSI/ANS 58.2, because it does not take into account the blast wave effect, dynamic behavior of the jet, and oversimplifies the shape and load characteristics of the supersonic steam jet. Therefore, it is necessary to improve the evaluation method for the high-energy line break accident. In order to evaluate the behavior of supersonic steam jet, an appropriate numerical analysis technique considering compressible flow effect is needed. In this study, numerical analysis methodology for evaluating supersonic jet impingement load was developed and verified. In addition, the conservativeness of the ANSI/ANS 58.2 model was investigated using the numerical analysis methodology. It is estimated that the ANSI jet model does not sufficiently reflect the physical behavior of under-expanded supersonic steam jet and evaluates the jet impingement load lower than CFD analysis result at certain positions.

• 에너지공학
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• 제8권2호
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• pp.298-308
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• 1999

과냉각수조로 분사되는 증기의 직접접촉 응축특성을 알아보기 위하여 다섯 개의 수평 노즐에 대해 증기 질량유량과 수조 온도를 여러 가지로 변화시키면서 실험적 연구를 수행하였다. 증기응축현상을 육안관찰과 고속 비디오 카메라를 사용한 방법으로 분석한 결과, 안정된 증기제트인 경우 증기 질량속과 수조온도가 변화함에 따라 타원형 및 원추형 증기제트 형상이 나타나는 것을 관찰하였다. 증기제트 팽창비, 증기제트 길이 및 응축연전달계수를 구하였고, 증기 질량속, 수조온도 및 노즐 내경이 미치는 영향을 분석하였다. 증기제트 길이와 응축열전달계수를 증기 질량속 및 응축추진 포텐셜의 함수로 나타낸 상관식을 구하였다. 증기제트 내부와 주위 수조온도 분포를 구했으며 증기 질량속, 수조온도 및 노즐 내경이 미치는 영향을 분석하였다. 처깅, 천이처깅, 응축진동, 안정응축, 방울응축진동 및 간헐진동응축 등 여섯 가지 영역으로 구분된 응축 영역도를 작성하였다. 그 외, 수조 벽면에서의 동압을 측정하였고, 증기 질량속과 수조온도에 따라 변화하는 증기 응축모드와 동압과는 밀접한 연관성이 있음을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.240-245
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• 2001

Phenomena of direct contact condensation (DCC) heat transfer between steam and water are characterized by the transport of heat and mass through a moving steam/water interface. Application of the phenomena of DCC heat transfer to the engineering industries provides some advantageous features in the viewpoint of enhanced heat transfer. This study proposes a simple condensation model on the steam jets discharging into subcooled water from a single horizontal pipe for the prediction of the steam jet shapes. The analysis model was derived from the mass, momentum and energy equations as well as a thermal balance equation with condensing characteristics at the steam/water interface for the axi-symmetric coordinates. The extremely large heat transfer rate at the steam/water interface was reflected in the effective thermal conductivity estimated from the previous experimental results. The analysis results were compared with the experimental ones. The analysis model predicted that the steam jet shape (i. e. radius and length) was increasing as the steam mass flux and the pool temperature were increasing, which was similar in trend to that observed in the experiment.

• 한국의류산업학회지
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• 제8권1호
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• pp.134-138
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• 2006

The washing efficiency of two types of washing machine- drum(drum washing) and drum using steam jet system(steam drum washing) was studied. The purpose of this paper is to clarify the performance of new steam drum washing. The relationship between washing temperature and washing efficiency(reflectance(%)) by soil removal, and that between washing temperature and electric energy consumption, Fabric damage evaluated by Danish wear method, Fabric shrinkage(%) during laundering were investigated, and compared with those in drum washing machine. Washing efficiency of steam drum washing according to washing temperature is better than that of drum washing. Electric energy consumption and fabric damage in steam drum washing are lower than those of drum washing. Fabric damage increased as washing temperature increased. Shrinkage of fabrics in steam drum washing and drum washing are about same. Therefore, we assumed that in the case of steam drum washing using steam jet system, washing efficiency remarkably increased, and fabric damage decreased, even with a lot of saving in given electric energy and water used.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.513-514
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• 2006

A CFD analysis for a thermal mixing experiment during steam jet discharge was performed to develop the analysis methodology for the thermal mixing between steam and subcooled water and to find the optimized numerical method. In the CFD analysis, the steam condensation phenomena by a direct contact was modelled by the so-called condensation region model. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small temperature difference was locally found at some locations. However, the commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behaviour reasonably well when a sufficient number of mesh distribution and a proper numerical method are adopted