• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.23-28
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• 2010

A draft tube which has impeller to elevate bottom water and spread it over surface of lake water, induces convective circulation of lake water, a Long-Distance Circulation (LDC). Circulation of lake water make stratified water mixed and enhance DO (Dissolved Oxygen) of bottom water. Circulation rate of water is determined by draft rate of the tube, which is dependent on design parameters of the draft tube system, i. e. dimension of impeller and diffuser, inclined angle of impeller, impeller shape, and rotational speed. In this study, change in draft rate and power consumption of circulation equipment was investigated numerically with changing impeller dimension, angle and rotational speed. It was found that flowrate of draft water was increased as the dimensions of draft tube and impeller, and rotational speed and inclined angle of impeller increased. The power consumption was also elevated with increasing parameter values, and final selection of parameter values was made to satisfy target flowrates and power consumption.

• Nuclear Engineering and Technology
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• v.28 no.4
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• pp.405-414
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• 1996

In this paper, the unsteady 2-dimensional turbulent flow model for thermal stratification in a pressurizer surge line of PWR plant is proposed to numerically investigate the heat transfer and flow characteristics. The turbulence model is adapted to the low Reynolds number K-$\varepsilon$ model (Davidson model). The dimensionless governing equations are solved by using the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The results are compared with simulated experimental results of TEMR Test. The time-dependent temperature profiles in the fluid and pipe nil are shown with the thermal stratification occurring in the horizontal section of the pipe. The corresponding thermal stresses are also presented. The numerical result for thermal stratification by the outsurge during heatup operation of PWR shows that the maximum dimensionless temperature difference is about 0.83 between hot and cold sections of pipe well and the maximum thermal stress is calculated about 322MPa at the dimensionless time 28.5 under given conditions.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3E
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• pp.133-140
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• 2003

A time series simulation is presented by a ray approach for the simulating the received waveform of a broadband acoustical signals interacting with the ocean boundaries. The environment is assumed to be horizontally stratified, and the seafloor is described in terms of homogeneous fluid half-space. The ray approach includes the effects of reflection from the air-water, water-sediment interface and phase shifts due to boundaries interaction. To generate time series, we assume that the acoustic energy propagates from source to receiver along eigenrays and represent the action of the bottom on the incident wave by a linear filter and characterized in the frequency domain by the transfer function. As example application, the time series for an explosive source in a shallow water environment is calculated and analyzed in terms of acoustical process. good agreement with measured time series is demonstrated.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.51-54
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• 2002

When a cold HPSI (High Pressure Safety Injection) fluid associated with an design basis accident, such as LOCA (Loss of Coolant Accident), enters the cold legs of a stagnated primary coolant loop, thermal stratification phenomena will arise due to incomplete mixing. If the stratified flow enters a reactor pressure vessel downcomer, severe thermal stresses are created in a radiation embrittled vessel wall by local overcooling. Previous thermal-mixing analyses have assumed that the thermal stratification phenomena generated in stagnated loop of a partially stagnated coolant loop are neutralized in the vessel downcomer by strong flow from unstagnated loop. On the basis of these reasons, this paper presents the thermal-mixing analysis results in order to identify the fact that the cold plume generated in the vessel downcomer due to the thermal stratification phenomena of the stagnated loop is affected by the strong flow of the unstagnated loop.

• 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.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.5
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• pp.22-30
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• 1999

Optimization of in-cylinder flow is regarded as one of the most important factors to realize stable stratified charge combustion in a Spark-ignited Direct Injection(SDI) engine. Therefore, Computational Fluid Dynamic(CFD) simulation technique were used to clarify the characteristics of in-cylinder flow of a SDI engine with top entry intake port. Also, CFD results were compared to experimental results using Laser Doppler Velocimetry(LDV), Particle Image Velocimetry(PIV) and good validations were met. As the results reverse tumble flow generated during intake process was preserved by configuration of curved piston while base and reverse tumbles were diminished at the end of compression stroke in case of flat top piston. In addition, it will be needed to optimize the fuel mixture distribution based on these results.

• Proceedings of the SAREK Conference
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• 2007.06a
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• pp.229-229
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• 2007

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1645-1653
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• 2017

This investigation explores the thermally stratified stretchable flow of an Oldroyd-B material bounded by a linear stretched surface. Heat transfer characteristics are addressed through thermal stratification and heat generation/absorption. Formulation is arranged for mixed convection. Application of suitable transformations provides ordinary differential systems through partial differential systems. The homotopy concept is adopted for the solution of nonlinear differential systems. The influence of several arising variables on velocity and temperature is addressed. Besides this, the rate of heat transfer is calculated and presented in tabular form. It is noticed that velocity and Nusselt number increase when the thermal buoyancy parameter is enhanced. Moreover, temperature is found to decrease for larger values of Prandtl number and heat absorption parameter. Comparative analysis for limiting study is performed and excellent agreement is found.

• Water for future
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• v.25 no.2
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• pp.99-110
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• 1992

A problem of outlet salinity from a stratified fluid with a well developed interface thickness consisting of an upper and lower layer differing slightly in density is considered. Three kinds of apparatus were used for the experimental test and salinity differences between inlet layer and outlet discharge were estimated by the functional relationship using the dimensionless values. For the critical incipient condition of withdrawal of upper layer, Densimetric Froude number is correlated by the inlet diameter and depth ratio in the tank.

• Journal of Environmental Science International
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• v.7 no.2
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• pp.233-241
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• 1998

This study Is concerned with properties of a thermal convection in a stably stratified Boussinesq fluid caused by partial heating at the lower boundary. For thins purpose, two-dimensional, nonrotating system was employed. U the heating is very strong, convection takes the form of a turbulent plume. Othenuse, remains laminar. If the partial heating at the bottom boundary Is symmetric. the convection takes the form of a trubuient plume. Otherwise remains but beating form Is not so signiacant as to alter the vergence in the lower layer at the center of the partial heating area. The temperature perturbation is characterized by the temperature 'Cross-Over' over the partial heating area. These features are cleared ac- cording to the Increase of temperature difference between the center and side part of the bottom boundary.