• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.91-93
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• 2003

A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.

• Journal of Energy Engineering
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• v.6 no.1
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• pp.58-67
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• 1997

In this study numerical computations were performed to predict reacting flow fields of gasification processes of pulverized subbituminous coal in a cylindrical coal gasifier. To check the size effects of particles on flow fields in the gasifier, simulations were performed for five cases with four sizes of particles such as 40 $\mu\textrm{m}$, 60 $\mu\textrm{m}$, 80 $\mu\textrm{m}$ and 100 $\mu\textrm{m}$. Each case has a unique size of particles with one more case that has evenly mixed four sizes of particles. Predictions showed that the gasification which uses coals of the mixed sizes reveals more preferable gas velocity and temperature distributions than that uses coals of a unique size. Predicted gas temperature at the exit of the gasifier ranged 1,400 to 1580$^{\circ}C$, 1,480 to 1,700$^{\circ}C$, 1,600 to 1740$^{\circ}C$, 1630 to 1790$^{\circ}C$ and 1500 to 1680$^{\circ}C$ for particle sizes of 40 $\mu\textrm{m}$, 60 $\mu\textrm{m}$, 80 $\mu\textrm{m}$, 100 $\mu\textrm{m}$ and the evenly mixed four sizes, respectively.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.6
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• pp.50-57
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• 2007

Pressure Sensitive Paint(PSP) means a reacting paint in pressure. PSP can measure continuous pressure field by analyzing the oxygen quantity using optical method. The surface pressure of down stream after the sonic jet that injected transversely into the supersonic freestream was measured by PSP technique. Moreover the effect of various rectangular shaped cavities in front of the jet was measured by PSP technique. A comparison of the PSP results with conventional pressure tap and CFD indicates good agreement. Until now, the results of numerical analysis were compared with the discrete points such as the results of pressure tap. In this study, the whole region pressure was measured using PSP technique and its results were similar to CFD. Therefore, the flow phenonenon of cavity downstream was clearly grasped.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.3
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• pp.149-154
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• 2017

We investigate the availability of $CO_2$ ocean storage by means of chemical conversion of $CO_2$ to the dissolved inorganic carbon (mainly the bicarbonate ion) in seawater. The accelerated weathering of limestone (AWL) technique, which is accelerating the natural $CO_2$ uptake process through the chemical conversion using limestone and seawater, was proposed as an alternative method for reducing energy-related $CO_2$ emission. The method presented in this paper is slightly different from the AWL method. It involves reacting $CO_2$ with seawater and quicklime obtained from alkaline wastes to produce the bicarbonate-rich solution over 100 times more than seawater, which could be released and diluted into the ocean. The released dense bicarbonate-enriched water mass could subside into the deeper layer because of the density flow, and could be sequestrated stably in the ocean.

• Journal of the Korean Society of Safety
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• v.9 no.1
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• pp.100-109
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• 1994

In this study, it is investigated that the possibility of the numerical simulation for the incineration of the hazardous material, crbon tetrachloride($CCl_4$). A 3-dimensional numerical technology is applied for turbulent reacting flows of the full-scale Dow Chemical incinerator. The calculations are made by a CRAY-2S, super computer. The major parameters considered in this study are kiln revolution rate (rpm), filling ratio of the solid waste(f), burner Injection velocity and angle, and turbulent air jets for swirl. And the employed turbulent reaction model is the eddy break-up model which is a kind of fast chemistry model assuming general equilibrium and used for a premixed flame. The calculated flow fields are presented and discussed. 1) The presence of turbulent air nozzles for swirl gives rise to visible increase of the convective motion over the region of the solid waste. This implies the possibility to enhance the mixing of the waste with the surrounding all and thereby to reduce thermal and species stratification, which were reported in a large rotary kiln operation. 2) Considering that the location of the recirculation region has a strong relation with the heating rate of the solid waste, the control of the recirculation region by the burner injection angle Is quite desirable in the sense of the flexible design of the rotary kiln incinerator for a carbon tetrachloride. 3) Finally, it is found that the eddy break-up model Is not suitable for carbon tetrachloride($CCl_4$) because this model is not incorporated the flame inhibition trend due to the presence $CCl_4$compound.

• The Journal of the Korea Contents Association
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• v.16 no.10
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• pp.766-779
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• 2016

This study was designed to look at a gap between what is reported and what is real, based on 'virtuality' shown in the media coverage of the Sewol ferry disaster. The way the Korean media reported the disaster raised serious concern in describing realities as the coverage was dotted with omitted, diluted, misleading, false and biased information, dubbed as the sinking of journalism by the Special Committee of the Korea Broadcasting Journalist Association. Virtuality can be problematic in journalism since users, when frequently exposed to 'mediated reality' or mediated presentment, often consider it actual and respond to it, rather than reacting to 'actual reality'. Many studies have found that media users tend to perceive mediated reality as an actual outside world. This paper aimed to explain signification of media reporting and limitations of user perception by reviewing major discussions and arguments on virtuality in previous research and history of thoughts. It was easy to link virtuality of mediated reality to the role of the media, which impact public opinion and change the flow of an event, and to other concepts such as the socialization of power, social control and social hegemony.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.473-485
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• 1997

Detailed experimental study has been made of air blast kerosene spray flames with and without swirl in combustion air flow. Phase-Doppler detect technique is used to measure Sauter mean diameter, axial component mean and rms velocity, size-velocity correlation, and number density. These measurements are obtained for both nonreacting and reacting cases under several stable flame conditions. The results show that the introduction of swirl to the combustion air modifies the spatial distribution of droplet size, velocity, and number density, and thus alters the flame structure. However, due to the weak swirl intensity, the overall structure of swirling flames are essentially same as that of nonswirling flames. Physical model of structure of air blast atomized spray flames is projected to show that spray flames are composed of three distinct regions: the two-phase mixture region, the main reaction and the intermittent combustion region. Near the atomizer, two phase mixture of droplet and air is formed in the core region. This dense spray region is characterized by high droplet number density and the strong convective effect. There follows the main combustion region where the main flame penetrates within the spray boundary. Main reaction region of these flames are governed by internal group combustion mode. Finally there exists the intermittent combustion region where local group burning or isolated droplet burning occurs.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.18-28
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• 2016

Numerical analysis was conducted as a preliminary study for evaluating the dual bell nozzle. For future parametric studies, a dual bell nozzle was designed, and thereafter inlet condition, turbulence model, and the number of optimum grids were determined. Dual bell nozzle was designed based on the KSLV-II first stage nozzle. Inlet condition was determined to frozen flow model of non-reacting eight species by comparing with the design values. SST $k-{\omega}$ model turned out to be suitable as turbulence model. About 150 thousand of the grids were selected after grid sensitivity tests. Based on the results determined in this study, we plan to investigate performance gain of the KSLV-II by adopting a proposed dual bell nozzle.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.133-138
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• 2002

A 3-D axisymmetric computer program is developed to predict the NO behavior in SNCR system for the stoker incinerator with the waste treatment capacity, 200ton/day. To this end a turbulent reacting flow field calculation is made using proper assumption and empiricism. The stoker bed is assumed to be a homogeneous waste-volatilized gaseous state. The initial composition or reactants are assumed based on the data of the ultimate analysis. Turbulent is resolved by k-e model and turbulent reaction is handled by eddy-breakup model harmonized with empirical chemistry data for gaseous combustion, NO and urea reaction. The liquid droplet is traced by Lagrangian method incorporated by aerodynamic drag, Coriolis and crntrifugal forces. Radiation is treated by sensible heat loss model. Calculation results are in good agreement with experimental data at the outlet of post combustion chamber in Daejon 4th industrial complex. The flue gas shows the temperature range of $900\sim1000^{\circ}C$, velocity of 5m/s and NO concentration of 140ppm at the exit while the measured temperature, flue gas velocity and NO concentration are $967^{\circ}C$, $3\sim4m/s$ and $100\sim200ppm$respectively. Using the developed computer program a parametric study has been made with the variation of heat content of waste, castable length and SNCR variables for the determination of proper injector location. In general, the calculated results are consistent and physically acceptable.

• Journal of the Semiconductor & Display Technology
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• v.21 no.3
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• pp.101-104
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• 2022

Mist-CVD is known to have advantages of low cost and high productivity compared to ALD and PECVD methods. It is capable of reacting to the substrate by misting an aqueous solution using ultrasonic waves under vacuum-free conditions of atmospheric pressure. In particular, Ga₂O₃ is regarded as advanced power semiconductor material because of its high quality of transmittance, and excellent electrical conductivity through N-type doping. In this study, Computational Fluid Dynamics were used to predict the uniformity of the thin film on a large-area substrate. And also the deposition pattern and uniformity were analyzed using the flow velocity and particle tracking method. The uniformity was confirmed by quantifying the deposition cross section with an FIB-SEM, and the consistency of the uniformity prediction was secured through the analysis of the CFD distribution. With the analysis and experimental results, the match rate of deposition area was 80.14% and the match rate of deposition thickness was 55.32%. As the experimental and analysis results were consistent, it was confirmed that it is possible to predict the deposition thickness uniformity of Mist-CVD.