• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.456-461
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• 1995

The concept of hyperbolicity breaking is applied to predict the flow regime transition from inverted annular flow (IAF) to agitated inverted annular flow (AIAF). The resultant correlation has the similar form to Takenaka's empirical one. To validate the proposed model, it is applied to predict Takenaka's experimental results using R-113 refrigerant with four different tube diameters of 3, 5, 7 and 10 mm. The proposed model gives accurate predictions for the tube diameters of 7 and 10 min. As the tube diameter decreases, the differences between the predictions and the experimental results increase slightly. The flow regime transition from AIAF to dispersed flow (DF) is described by the drift flux model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.766-774
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• 2017

When a plume flow exhausted from a lunar lander descent engine impinges on the lunar surface, regolith particles on the lunar surface will be dispersed due to a plume-surface interaction. If the dispersed particles collide with the lunar lander, some adverse effects such as a performance degradation can be caused. Thus, this study tried to predict the plume flow behaviors using the CFD methods. A nozzle inside region was analyzed by a continuum flow model based on the Navier-Stokes equations while the plume behaviors of the outside nozzle was performed by comparing and analyzing the individual results using the continuum flow model and the DSMC method. As a result, it was possible to establish an optimum procedure of the plume analysis for the lunar lander descent engine in the vacuum condition. In the future, it is expected to utilize the present results for the development of the Korean lunar lander.

• Elastomers and Composites
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• v.39 no.3
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• pp.193-208
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• 2004

Morphology of injection molded polymer blend was investigated by experimental and theoretical approach. In experiments, the effects of injection speed and injection temperature on the morphology of injection molded MPPO/Nylon 6 blend were investigated. The morphology distribution across the part thickness was clearly observed in injection molded blend. We could observe several distinct regions across the thickness of molded part: skin layer, subskin layer and core region. The skin layer where the dispersed phase is fine and highly deformed to the flow direction is observed to be located near the part surface. The subskin layer located at inner region of the skin layer also observed. In the subskin layer, the dispersed phase is coarser than that of skin layer and deforms to the flow direction. Based on the experimental results, the calculation scheme to predict the morphology of injection molded polymer blend was suggested. The morphology of injection molded polymer blend could be predicted in corporation with the result of flow analysis obtained from commercial software for injection molding process and the theory of drop behavior under the flow. The suggested calculation scheme could predict the effect of injection conditions on the morphology of injection molded parts.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.174-181
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• 2001

The Gird is a communication service that collaborates dispersed high performance computers, large-scale databases and modern equipments so that those can be shared and worked together. In this paper. CFD research based on National Grid project is discussed. To validate the Grid technology, the flow past ONERA M6 wing and the flow past infinite wing are simulated on the National Grid testbed.

• Korea-Australia Rheology Journal
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• v.20 no.1
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• pp.35-42
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• 2008

An inverse ferrofluid composed of micron sized polymethylmethacrylate particles dispersed in ferrofluid was used to investigate the effects of test duration times on determining the flow curves of these materials under constant magnetic field. The results showed that flow curves determined using low duration times were most likely not measuring the steady state rheological response. However, at longer duration times, which are expected to correspond more to steady state behaviour, we noticed the occurrence of plateau and decreasing flow curves in the shear rate range of $0.004\;s^{-1}$ to ${\sim}20\;s^{-1}$, which suggest the presence of nonhomogeneities and shear localization in the material. This behaviour was also reflected in the steady state results from shear start up tests performed over the same range of shear rates. The results indicate that care is required when interpreting flow curves obtained for inverse ferrofluids.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.714-724
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• 1985

Two-phase(air-solid, air-liquid droplet) turbulent round jet has been analyzed numerically using two equation turbulence model. The mean motion of suspending particles in air has been treated as the secondary fluid with virtual density and eddy viscosity. In this paper, the local mean velocity of secondary fluid is not assumed to be the same as that of the primary one. Dissipation rate of turbulent kinetic energy which arises because the particles can not catch up with the turbulent fluctuations of the primary fluid has been modelled by using the concept of Kolmogorov's spectral energy transfer. Numerical computations were performed for flows with different volume fraction of the dispersed phase and the diameter of particle. Results show that the total rate of turbulent energy dissipation, turbulent intensities and spreading rate of jets are reduced by the increase of volume fraction of dispersed phase. However it does not show consistent tendency with increasing the particle diameter. This investigation also shows that presence of particles in the fluid modifies the structure of the primary fluid flow significantly. Predicted velocity profiles and turbulence properties qualitatively agree with available data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.1-10
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• 1991

The purpose of this study is to lay groundwork for a complete analysis of two component flow by analyzing a single component flow made of continuous fluid without dispersed phase. In order to achieve uniform velocity distributions which are desirable in designing an optimum spray column direct contact heat exchanger, the influence of injection nozzle orientation has been investigated for axial and radial injections. The results that radial injection ensures more uniform velocity distributions compared to the axial case. The flow characteristics in a spray column have been investigated with various L/D values and inlet velocities, the most uniform internal velocity distributions have been obtained for the case of L/D=10 and 0.1m/sec. In the present investigation, it is shown that radial injection method for the continuous flow is advantageous in obtaining desirable uniform velocity distributions in a spray column. It is also found that as the value of L/D increases and the inlet velocity decreases, the flow improves to be better uniform velocity distributions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.25-32
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• 1988

Vehicle platoons starting a stopline are dispersed while travelling along the street and the delay at the next intersection depends on the arrival pattern of dispersed traffic flow. In this paper, the platoon dispersion charactiristics of our country, especially the time gap between passenger cars and buses caused by the dwell time at bus stops, were investigated through travel time surveys. Based on the survey results, on improved analysis method of intersection delay is proposed.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.533-535
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• 2002

In Korea, power requirement has been increasing. But the large generation unit is hardly installed because of economic and environment problem. Therefore, the concern of dispersed generation system(DGS) is growing. The power distribution system is generally operated with radial type. The protection system is composed of one directive source. But power distribution system inserted DGS changes it to two directive source system. Therefore, the insertion of DGS has the problem of protection coordination. In this paper, we argue fault current affected by interconnected DGS. We analyze fault current flow affected by DGS placement. Then, we find protective coordination problem. Consequently, we study advance point for protection scheme of power system interconnected DGS.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.123-130
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• 1993

Dispersed type Al2O3-SiC composite powders were synthesized from Al-isopropoxide (Al(i-OC3H7)3) and Si(OC2H5)4 precursors by hydrolysis of mixed alkoxides and carbothermal reaction method. The characteristics of the synthesized (dispersed type) Al2O3-SiC composite powders were investigated using XRD, SEM, TEM, BET and particle size analyzer. Carbothermal reaction to produce Al2O3-SiC composite was completed in 10h at 135$0^{\circ}C$ on 3~4㎤/s (0.21~0.28cm/s) of H2 flow rate and about 1/1 of carbon/oxides(=SiO2＋Al2O3) molar ratio. The synthesized powders were observed to have the mean particle size range of 0.4~1.26${\mu}{\textrm}{m}$ and showed finer particle size with increasing SiC content.