• Journal of Energy Engineering
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• v.6 no.2
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• pp.119-128
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• 1997

A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external heating on the thermal stratification flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt number distributions are analyzed under heating conditions. The numerical results of this study show that the maximum dimensionless temperature difference between hot and cold sections of the inner wall of pipe is 0.424 at dimensionless time of 1,500 and the thermal stratification phenomenon disappears at about dimensionless time of 9,000.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.857-863
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• 1998

배관내에서 서로 다른 온도의 유체가 밀도차에 의해서 층이 분리된 채 존재하는 현상을 열성층 (thermal stratification) 현상이라 부르며, 이 현상에 의한 과도한 열응력은 배관의 건전성을 저해할 수 있다. 국내 원전의 경우 영광 3,4호기 이전의 밀림배관에서는 열성층 영향을 고려치 못하여 이에 대한 건전성 평가가 요구되고 있다. 본 연구에서는 고리 4호기 가압기 밀림배관을 대상으로 밀림배관내 유동해석 및 발전소 전 운전조건에 대하여 밀림배관 단면 온도분포 실측실험을 통하여 열성층화 현상의 발생 정도를 확인 하였으며 실측 온도 데이터를 이용하여 열응력해석 등을 수행함으로써 밀림배관의 열성층 영향을 평가한 결과 건전함이 확인되었다.

• Solar Energy
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• v.14 no.2
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• pp.3-16
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• 1994

The major objectives of the study are to suggest the optimal basic design conditions for the horizontal storage tank system. For this purspose computer simulation has been carried out to find the characteristics of flow patterns in horizontal storage tank, and experiments have been carried out for the duration of one turnover, Experimental parameters are volume flow rate(1 LPM to 4 LPM), amount of heat generated from heat sources(0 W to 100 W), and inlet and outlet port types of the storage tank(DD type, DO type, ID type, IO type).

• Proceedings of the Korean Nuclear Society Conference
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• 1998.10a
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• pp.133-133
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• 1998

• Nuclear Engineering and Technology
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• v.28 no.1
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• pp.27-35
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• 1996

In this paper, an unsteady analytical model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to investigate the temperature profile, flow characteristics, and thermal stress in the pipe. In this model, the interface level, between hot and cold fluid, is assumed to be a function of time while the other models had developed for time independent or steady state. The dimensionless governing equations are solved by using a SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The analysis result for an example shows that the maximum dimensionless temperature difference is about 0.78 between hot and cold sections of pipe wall and the maximum thermal stress by thermal stratification is calculated about 276 MPa at the dimensionless time 27.0 under given conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.670-678
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• 1997

A method to mitigate the thermal stratification phenomenon of pressurizer surge line is proposed by heating bottom outside of horizontal pipe. Unsteady two dimensional model has been used to numerically investigate an effect of heating the bottom of pipe. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature and streamline profiles of fluids and pipe walls with time are compared with the previous study result. The numerical result of this study shows that the outside heating can relaxate the thermal stratification flow of the pressurizer surge line. Maximum dimensionless temperature difference between hot and cold sections of the pipe inner wall which causes thermal stratification was reduced from 0.514 to 0.424 at dimensionless time 1, 632 and 1, 500 respectively.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1597-1602
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• 2003

Numerical analysis is carried out to assess the temperature distribution on the mixing tee line of Residual Heat Removal System (RHRS). In RHRS, hot and cold fluids of main and bypass piping are mixed and unmixed by the flow rate or piping layout. Thermal stratification phenomenon is a cause of major degradation on RHRS piping. According to the analysis for each operation modes, maximum temperature difference between top and bottom of piping were evaluated about 60K when the flow rate of main and bypass lines is same. Temperature difference will be decreased at the elbow on RHRS piping if the length of vertical piping is increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1449-1457
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• 1996

In this paper, the unsteady two dimensional model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to numerically investigate the heat transfer and flow characteristics. The dimensionless governing equations are solved by using the Control Volume Formulation and SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The temperature profile of fluids and pipe wall with time are shown when the thermal stratification occurs in the horizontal pipe. The numerical result shows that the maximum dimensionless temperature difference is about O.514 between hot and cold section of pipe wall at dimensionless time 1,632.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.680-688
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• 1996

In this paper, the unsteady state calculational model is proposed for the thermal stratification analysis in the feedwater line of the PWR plant. By defining dimensionless parameters in the two-dimensional polar coordinate system and applying SIMPLE algorithm, the temperature and flow profiles due to the thermal stratification are obtained. Base on the fact that the most significant condition occurs when the fluid temperature difference between the piping ends reaches as high as 166.deg. C, the present result shows that max. Dimensionless temperature difference of 0.6 (about l00.deg. C) obtained between hot and cold sections of pipe wall at dimensionless time 47.0.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.110-114
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• 2001

A numerical analysis has been perfonned to estimate the effect of turbulent penetration and thermal stratified flow in the branch lines piping. This phenomenon of thermal stratification are usually observed in the piping lines of the safety related systems and may be identified as the source of fatigue in the piping system due to the thermal stress loading which are associated with plant operating modes. The turbulent penetration length reaches to $1^{st}$ valve in safety injection piping from reactor coolant system (RCS) at normal operation for nuclear power plant when a coolant does not leak out through valve. At the time, therefore, the thermal stratification does not appear in the piping between RCS piping and $1^{st}$ valve of safety injection piping. When a coolant leak out through the $1^{st}$ valve by any damage, however, the thermal stratification can occur in the safety injection piping. At that time, the maximum temperature difference of fluid between top and bottom in the piping is estimated about $50^{\circ}C$.