• 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.

• Nuclear Engineering and Technology
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• v.28 no.4
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• pp.379-389
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• 1996

To experimentally investigate the several wave patterns for the horizontal countercurrent stratified air-water flow, a series of systematic experimental studies have been performed. The experiments are carried out in a horizontal pipe with 4m in length and 102mm in inner diameter. The oater and air superficial velocities vary from 0.0004 to 0.0204 and from 0 to 6m/s, respectively. The instantaneous water thickness is measured by parallel-wire conductance probes, and the wave field is recorded by high speed video camera. Also, to evaluate the wave effect on interfacial friction factor, the pressure drop is measured. Statistical data anal)sis is accomplished in order to obtain the fundamental wave parameters such as un amplitude, length and velocity, and spatial growth factor. By using these statistical parameters, the wave regime boundaries can be verified.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.886-893
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• 2000

The Characteristics of dividing the dispersed bubble, plug, and slug steam-water flow in the horizontal junctions with horizontal branches have been experimentally investigated. The experimental investigation of the separation phenomena in a $45^{\circ}$ horizontal wye with equal pipe inner diameter of 25 mm is presented to provide a data base for the development and verification of the analytical models. The phase separation and pressure distribution in the three legs of each test section are obtained through the set of measurements made in the present work. And the dependence of phase separation on different parameters, such as inlet quality and mass flux, is discussed.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.742-747
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• 2001

A study on the ultrasonic effect for turbulence enhancement is carried out in the horizontal flow field of a coaxial circular pipe. A large transparent acryl tank is made to perform several experiments for the above research. The front flow field from jet exit is divided as 4 measuring regions to observe characteristics of the above flow field according to those with and without ultrasonic. An ultrasonic transducer with 2MHz high frequency is used to give them the ultrasonic forcing. Characteristics such as the velocity distribution, the kinetic energy and the turbulence intensity are visualized, observed, examined and considered at Re No. 2000. In results, it is clarified that the ultrasonic increases the turbulence enhancement. And the optimum and harmonious intensity suited to the power of flow is needed to maximize the turbulence enhancement.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.727-732
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• 2001

The purpose of this study is to compare the time mean velocity distribution, the time mean kinetic energy, and the time mean turbulence intensity between vertical and horizontal flow fields in a coaxial circular pipe by PIV measurement. Experiments are performed at a Reynolds number 2,000, measuring regions divided as the section regions A, B, C, D in flow fields. The angle of the high-frequency ultrasonic is selected in the direction of $45^{\circ}$ to the flow axes and it is reflected several times. In results, it is clarified that the effect of gravity is given in the vertical flow field compared with the horizontal flow field and the ultrasonic affects the turbulence enhancement. And kinetic energy and turbulence intensity with ultrasonic are shown slightly bigger than those in flow field without it.

• 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.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.103.1-103.1
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• 2005

• Journal of the Korean Society of Safety
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• v.32 no.1
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• pp.75-81
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• 2017

A series of laboratory experiments has been performed in order to investigate the behavior of water-air two-phase flow in a horizontal pipe. A conductivity meter has been applied to detect the irregular alternation of air at the specific points in flows. The experimental condition has been established according to the water and air flowrates. Passing time, which is the time length for a measuring probe to pass through the entire length of a specific bubble, has been defined to evaluate the size of bubbles in the flow. Passing length, which can be considered as the equivalent value to bubble size and determined from the product of passing time and cross-sectional averaged velocity, and its corresponding occurrence frequency have been analyzed to classify the air flow patterns according to the condition of air and water fluxes. From the result, the dependancy of flow patterns on the variation of air-water flux ratio has been investigated and the existence of thresholds also checked for classifying the behavior of air in the flow.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.95-101
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• 1996

In this paper, the steady 2-dimensional model for a long horizontal line with different end temperatures undergoing natural convection at very high Rayleigh number is proposed to numerically investigate the heat transfer and flow characteristics. The dimensionless governing equations are solved by using SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm which is developed using control volumes and staggered grids. The numerical results are verified by comparison with the operating PWR test data. The analysis focuses on the effects of variation of the heat transfer rates at the pipe surface, the thermal conductivities of the pipe material and the thickness of the pipe wall on the thermal stratification. The results show that the heat transfer rate at the pipe surface is the controlling parameter. A significant reduction and disappearance of thermal stratification phenomenon is observed at the Biot number of 5.0$\times$10$^{-2}$. The results also show that the increment of the thermal conductivity and thickness of the wall weakens the thermal stratification and somewhat reduces azimuthal temperature gradient in the pipe wall. Those effects are however minor, when compared with those due to the variation of the heat transfer rates at the surface of the pipe wall.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.879-882
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• 2004

Two-phase flow exists in many industrial components. Characteristics of two-phase flow have been studied by many researchers; however, a further study of the two-phase is required for flow-induced vibration. Characteristics of two-phase flow were measured by force sensor at the end of a vertical pipe. The predominant frequency of fluctuation was obtained for various speeds of flow pattern. A correlation to slug frequency for horizontal flow was obtained by Heywood & Richardson (1979), while Legius et al (1997) for vertical flow. A coefficient based on the correlation is estimated and then compared to the existing ones. The existing empirical formulations for average void fraction were proposed by Wallis (1969), Zuber et al (1967) and Ishii (1970). In the present result, flow parameters, such as flow quality and real velocity, are evaluated with void fraction.