• Journal of the Korean Solar Energy Society
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• v.30 no.1
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• pp.34-41
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• 2010

Gas hydrates are solid solutions when water molecules are linked through hydrogen bonding and create host lattice cavities that can enclose many kinds of guest(gas) molecules. There are plenty of methane(gas) hydrate in the earth and distributed widely at offshore and permafrost. Several schemes, to produce methane hydrates, have been studied. In this study, depressurization method has been utilized for the numerical model due to it's simplicity and effectiveness. IMPES method has been used for numerical analysis to get the saturation and velocity profile of each phase and pressure profile, velocity of dissociation front progress and the quantity of produced gas. The values calculated for the sample length of 10m, show that methane hydrates has been dissolved completely in approximately 223 minutes and the velocity of dissociation front progress is 3.95㎝ per minute. The volume ratio of the produced gas in the porous media is found to be about 50%. Analysing the saturation profile and the velocity profile from the numerical results, the permeability of each phase in porous media is considered to be the most important factor in the two phase flow propagation. Consequently, permeability strongly influences the productivity of gas in porous media for methane hydrates.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.32.3-33
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• 2021

We present H I gas kinematics and star formation activities of NGC 6822, a dwarf galaxy located in the Local Volume at a distance of ~ 490 kpc. We perform profile decomposition of the line-of-sight velocity profiles of the high-resolution (42.4" × 12" spatial; 1.6 km/s spectral) H I data cube taken with the Australia Telescope Compact Array (ATCA). For this, we use a new tool, the so-called BAYGAUD (BAYesian GAUssian Decompositor) which is based on Bayesian Markov Chain Monte Carlo (MCMC) techniques, allowing us to decompose a line-of-sight velocity profile into an optimal number of Gaussian components in a quantitative manner. We classify the decomposed H I gas components of NGC 6822 into bulk-narrow, bulk-broad, and non_bulk with respect to their velocity and velocity dispersion. We correlate their gas surface densities with the surface star formation rates derived using both GALEX far-ultraviolet and WISE 22 micron data to examine the impact of gas turbulence caused by stellar feedback on the Kennicutt-Schmidt (K-S) law. The bulk-narrow component that resides within r25 is likely to follow the linear extension of the Kennicutt-Schmidt (K-S) law for molecular hydrogen (H2) at the low gas surface density regime where H I is not saturated.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.61.1-61.1
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• 2020

We examine the HI gas kinematics and distribution of galaxy pairs in group or cluster environment from high-resolution Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot observations. We use 22 well-resolved galaxies in the Hydra cluster of which 4 galaxies are visually identified as pairs and others are isolated ones. We perform profile decomposition of HI velocity profiles of the galaxies using a new tool, BAYGAUD which enables us to separate a line-of-sight velocity profile into an optimal number of Gaussian components based on Bayesian MCMC techniques. All the HI velocity profiles of the galaxies are decomposed into kinematically cold or warm gas components with their velocity dispersion, 4~8 km/s or > 8 km/s, respectively. We derive the mass fraction of the kinematically cold gas with respect to the total HI gas mass, f = log10(M_cold / M_HI), of the galaxies and correlate them with their dynamical mass. The cold gas reservoir of the paired galaxies in the Hydra cluster is found to be relatively higher than that of the isolated ones which show a negative correlation with the dynamical mass in general.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.145-150
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• 2006

At the furnace top, the distribution of charging coke and ore is adjusted to control the reducing gas flow distribution in the furnace. It is necessary to predict operation condition of blast furnace according to the burden profile to judge whether charging is properly conducted In this study, We propose the model for predicting while layer structures whithin furnace when top burden profile was given. Layer structure of coke and ore could be predicted by top burden profile and solid velocity. Solid velocity is assumed as potential flow. Potential function distribution and timeline are also calculated using solid velocity field. The Calculation is conducted for different burden profile cases. As the result burden distribution and grid structure, which is deformed to match the layer structure in shaft and deadman profile. Gas flow was calculated using this grid, and calculated results are compared with each other.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2675-2685
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• 1994

A study has been conducted to provide the experimental information for the velocity and temperature profiles of steam-air mixutre and to investigate their roles on the film condensation with wavy interface. Saturated gas mixture of steam-air was made to flow through the nearly horizontal$(4.1^{\circ})$ square duct of 0.1m width and 1.56m length at atmospheric pressure, and was condensated on the bottom cold plate. The air mass fraction in the gas mixture was changed from zero(W =0, pure steam) to one(W =1, pure air), and the bulk velocity was varied from 2 to 4 m/s. Water film was injected concurrently to investigate the effect of wavy interface on the condensation. The velocity and temperature profiles were measured by LDA system and thermocouples along the three parameters ; air mass fraction, mixture velocity and film flow rate. The profiles moved toward the interface with increasing steam mass fraction, mixture velocity and film flow rate. The Prandtl and Schmidt numbers were near one in the present experimental range, however there was no complete similarity between the velocity and temperature profiles of gas mixture. And the heat transfer characteristics and interfacial structure were coupled with each other.

• Journal of the Korea Organic Resources Recycling Association
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• v.19 no.1
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• pp.93-101
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• 2011

The modeling of SDR was carried out for the application of the solid waste incineration system. To find optimum operating condition for removal of acidic gases, computation fluid dynamic(CFD) model was used. In this study, the temperature profile of SDR(spray dry reactor) and the gas velocity profile for different models were investigated. In this model, the diameter of SDR was 3 meter and the height of SDR was 9 meter. The amount of inlet combustion gas of SDR was $6,125Nm^3/hr$ and the inlet temperature of SDR was 493 K. The amount of lime injection of SDR was 151 kg/hr. When the inlet shape of SDR was changed, the temperatur of SDR was changed and the gas velocity of SDR was 0.48 m/sec to 1.17m/sec and the outlet gas velocity of SDR was 6.9 m/sec to 7.42m/sec As a result of modeling, the average velocities in SDR and outlet were 0.489 m/sec and 7.424 m/sec, respectively, in which the temperature of outlet in SDR was 448 K.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.70.2-71
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• 2021

We examine gas kinematics and star formation activities of NGC 6822, a gas-rich dwarf irregular galaxy in the Local Group at a distance of ~490 kpc. We perform profile decomposition of all the line-of-sight (LOS) HI velocity profiles of the high-resolution (42.4" × 12" spatial; 1.6 km/s spectral) HI data cube of the galaxy, taken with the Australian Telescope Compact Array (ATCA). To this end, we use a novel tool based on Bayesian Markov Chain Monte Carlo (MCMC) techniques, the so-called BAYGAUD, which allows us to decompose a velocity profile into an optimal number of Gaussian components in a quantitative manner. We group all the decomposed components into bulk-narrow, bulk-broad, and non-bulk gas components classified with respect to their velocity dispersions and the amounts of velocity offset from the global kinematics, respectively. Using the surface densities and velocity dispersions of the kinematically decomposed HI gas maps together with the rotation curve of NGC 6822, we derive Toomre-Q parameters for individual regions of the galaxy which quantify the level of local gravitational instability of the gaseous disk. We also measure the local star formation rate (SFR) of the corresponding regions in the galaxy by combining GALEX Far-ultraviolet (FUV) and WISE 22㎛ images. We then relate the gas and SFR surface densities in order to investigate the local Kennicutt-Schmidt (K-S) law of gravitationally unstable regions which are selected from the Toomre Q analysis. Of the three groups, the bulk-narrow, bulk-broad and non-bulk gas components, we find that the lower Toomre-Q values the bulk-narrow gas components have, the more consistent with the linear extension of the K-S law derived from molecular hydrogen (H2) observations.

• Journal of Hydrogen and New Energy
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• v.33 no.4
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• pp.419-429
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• 2022

Effects of operating variables on temperature profile and performance of 3 MWth chemical looping combustion system were estimated by mass and energy balance analysis based on configuration and dimension of the system determined by design tool. Air reactor gas velocity, fuel reactor gas velocity, solid circulation rate, and solid input percentage to fluidized bed heat exchanger were considered as representative operating variables. Overall heat output and oxygen concentration in the exhaust gas from the air reactor increased but temperature difference decreased as air reactor gas velocity increased. Overall heat output, required solid circulation rate, and temperature difference increased as fuel reactor gas velocity increased. However, overall heat output and temperature difference decreased as solid circulation rate increased. Temperature difference decreased as solid circulation rate through the fluidized bed heat exchanger increased. Effect of each variables on temperature profile and performance can be determined and these results will be helpful to determine operating range of each variable.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.448-453
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• 1998

An inverted, stagnation point flow OMVPE reactor was studied by laser Raman spectroscopy. Pure rotational Raman scattering by the carrier gas $(N_2; or; H_2)$ was used to determine the axial centerline temperature profile in the reactor as a function of the inlet flow velocity and the rector aspect ratio. A larger temperature gradient normal to the susceptor surface was obtained with higher gas glow velocity, larger aspect ratio, and the use of a $N_2$ carrier gas.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.147-153
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• 2011

A series of nonequilibrium molecular dynamics(NEMD) simulations are performed to investigate the kinetic energy and velocity distributions of molecules in shock waves. In the simulations, argon molecules are used as a medium gas through which shock waves are propagating. The kinetic energy distribution profiles reveals that as a strong shock wave whose Mach number is 27.1 is applied, 39.6% of argon molecules inside the shock wave have larger kinetic energy than molecular ionization energy. This indicates that an application of a strong shock wave to argon gas can give rise to an intense light. The velocity distribution profiles in z direction along which shock waves propagate clearly represent two Maxwell-Boltzmann distributions of molecular velocities in two equilibrium regions and one bimodal velocity distribution profile that is attributed to a nonequilibrium region. The peak appearing in the directional temperature in z direction is discussed on a basis of the bimodal velocity distribution in the nonequilibrium region.