• 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.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1555-1562
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• 2023

Natural circulation phenomena have been nowadays largely revisited aiming to investigate the performances of passive safety systems in carrying-out heat removal under accidental conditions. For this purpose, assessment studies using CFD (Computational Fluid Dynamics) and also 3D thermal-hydraulic system codes are considered at different levels of the design and safety demonstration issues. However, these tools have not being extensively validated for specific natural circulation flow regimes involving flow mixing, temperature stratification, flow recirculation and instabilities. In the present study, an experimental test case based on a small-scale pool test rig experiment performed by Korea Atomic Energy Research Institute, is considered for code-to-code and code-to-experimental data comparison. The test simulation is carried out using the FLUENT and the 3D thermal-hydraulic system CATHARE-2 codes. The objective is to evaluate and compare their prediction capabilities with respect to the test conditions of the experiment. It was observed that, notwithstanding their numerical and modelling differences, similar agreement results are obtained. Nevertheless, additional investigations efforts are still needed for a better representation of the considered phenomena.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.235-236
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• 2022

In the present study, the effect of horizontal vent position on fire phenomena in the enclosure with vertical and horizontal vents was examined using numerical simulation. Case 1 indicates the condition that the horizontal vent is in the center of the ceiling. Case 3 indicates the condition that the horizontal vent is far away from the vertical vent. Case 2 indicates the condition that the horizontal vent is installed between Case 1 and Case 3. The temperature distribution, smoke layer temperature, velocity distribution, and mass flow rate of horizontal vent flow were analyzed. In Case 2, the temperatures were lowest and the mass flow rate through the horizontal vent was largest. This is because the flame is inclined by the inflow through the vertical vent. Hence, to determine the proper horizontal vent location for the high smoke ventilation performance, the inflow through the vertical vent and its effect on flame behavior should be considered.

• Nuclear Engineering and Technology
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• v.47 no.5
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• pp.523-533
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• 2015

Three-dimensional flow phenomena in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor, Monju, were investigated with a numerical analysis using a general-purpose commercial computational fluid dynamics code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-averaged Navier-Stokes flow simulation using a shear stress transport turbulence model. The main purpose of the current study is to understand the three-dimensional complex flow phenomena in a wire-wrapped fuel assembly to support the license issue for the core design. Computational fluid dynamics results show good agreement with friction factor correlation models. The secondary flow in the corner and edge subchannels is much stronger than that in an interior subchannel. The axial velocity averaged in the corner and edge subchannels is higher than that averaged in the interior subchannels. Three-dimensional multiscale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Behavior of the large-scale vortex structures in the corner and edge subchannels is closely related to the relative position between the hexagonal duct wall and the helically wrapped wire spacer. The small-scale vortex is axially developed in the interior subchannels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and the wire spacer.

• Journal of the Korean Society of Industry Convergence
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• v.21 no.5
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• pp.191-195
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• 2018

By using an ANSYS product suite (CFX, Ansys Multiphysics), which is a powerful tool for multiphysics analysis of complicated physical phenomena, we performed a structural stress analysis based on fluid flow and heat transfer phenomena within a quick connect/disconnect (QC/DC) bellows system. Considering the extremely low temperatures in the QC/DC environment, an approach to the problem based on complex multi-physics phenomena, where different phenomena interact with each other, is crucial. Therefore, we use a numerical analysis technique where fluid-thermal-structural interactions are combined. In conclusion, when low temperature fluids flow inside bellows, the expected service life is conspicuously reduced due to the thermal stress caused by heat transfer. Therefore, in future research, a structure with considerably reduced thermal stress by robust design optimization will be derived.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.6
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• pp.81-90
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• 1992

This paper deals with an experimental study on the initial condition of liquid film surface waves disintegration and investigation on the behavior of liquid film surface waves formed by the high speed air flow on the solid plane surface. The authors conducted the qualitative and quantitative study to in vestigate the liquid film flow phenomena, the liquid film disintegration mechanism, and droplet formation process with breaking the liquid film surface wave. The newly devised transparent rectangular test section which has semi-two-dimensional flow at the center of the bottom was introduced to perform the experimental study, and it can generate the uniform thickness liquid film at the bottom. The strobo streak camera was used to obtain the instantaneously transformed photographs. The electronic measuring device was also used to measure the liquid film thickness variation in order to perform the easy and effective analysis of complex flow phenomena in the air-water cocurrent flow.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.145-150
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• 2004

In this study the numerical analysis on staging flow with forward ejector is conducted. The forward ejector plays a vital role in staging, which jets out from aftbody. This staging environment needs careful flow analysis for securing staging safety Present study investigates the steady inviscid staging flow phenomena with variation of separation distance. The performance index is forebody base pressure coefficients. The three dominant flow phenomena are observed according to separation distance which could be told as impinging stage, cavity vortex dominancy stage, and pure base flow characteristics stage. Impinging stage shows high thrust for forebody as one might think. However, important point is that cavity vortex dominancy stage can be more favorable for separation than impinging stage as one simply think in certain separation distance.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.526-529
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• 2008

Air Conditioner has become a popular comfort providing device since two decades, whether in an office or home especially for warm and wet climate countries. The RAC (Room Air Conditioner) is widely used in various working spaces and residences. It composed of heat exchager, cross-flow fan, stabilizer, rearguider and blade of diffuser region, etc. In this study, numerical analyses based on the prediction of transient phenomena were carried out to investigate the flow characteristics in the RAC, including the impeller, the rearguider, the stabilizer and the blade of the diffuser region. Using a commercial code, FLUENT, the velocity, pressure and streamlines were obtained with unsteady, turbulent flow and no-slip condition. The angular velocities of impeller are located in the 900 rpm. Turbulent closure was achieved using a standard k-${\varepsilon}$ model. A moving reference frame (MRF) approach was adopted to simulate the flow field generated by impeller in the RAC. Results were graphically depicted with various geometrical configurations and operating conditions.

• Journal of Power System Engineering
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• v.7 no.3
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• pp.35-39
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• 2003

In this paper, the heat transfer phenomena in the sensor tube of a mass flow controller(MFC) were studied by experiments. In the sensor tube of MFC, the difference of temperature between inlet and outlet was necessary for calculating the mass flow rate. Therefore, the relations of flow rate, generated heat by heating wire, sensor location and tube thickness were investigated to find the optimized condition. Based on this study, static and dynamic characteristics of sensor can be used for mass flow controller.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.108-113
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• 1999

In a scroll compressor it is generally accepted that a check valve is necessary to prevent reverse rotation of the scrolls. The check valve is subjected to discharge pulsations and their resultant forces. The flow phenomena around the check valve may affect the efficiency and the noise level significantly. The motivation of this study is to understand the flow phenomena and the unstable motion of the check valve on operating conditions in order to identify reasons raising noise and improve the performance of the check valve. In this study, unsteady flow simulation was performed using CFD and the pressure distribution around the check valve was obtained. This paper also shows that unstable motion of the check valve on standard operating conditions through theoretical analysis and flow visualization.