• Korean Chemical Engineering Research
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• v.49 no.2
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• pp.200-205
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• 2011

Axial and radial distributions of bubble holdup were investigated in a slurry bubble column with pilot plant scale(D=1.0 m). Effects of gas velocity, surface tension of continuous liquid medium and solid fraction in the slurry phase on the axial and radial distributions of bubble holdup were examined. The bubble holdup decreased with increasing radial dimensionless distance from the center of the column, while it increased with increasing dimensionless distance in the axial direction from the distributor, in all the cases studied. The radial non-uniformity of bubble holdup increased with increasing gas velocity but decreasing surface tension of liquid medium, while it was not dependent upon the solid fraction in the slurry phase. The axial non-uniformity of bubble holdup increased with increasing gas velocity, but it does not change considerably with variations of liquid surface tension or solid fraction in the slurry phase . The axial and radial distributions of bubble holdup were well correlated in terms of operating variables within this experimental conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.8-14
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• 2003

The particle dispersion in the turbulent mixing layer has been numerically investigated to clarify the effect of the velocity ratio in the large-scale vortical structures. In this study the LES with subgrid-scale model is employed. The Lagrangian method to predict the particle motion is applied. The particles of 10, 50, 150, 200${\mu}m$ in mean diameter were loaded into the origin of the mixing layer. It is shown that the characteristics of flow and growth rate are strongly dependent on the variation of the velocity ratio. It is also shown the relationship between the Stokes number and the particle dispersion. As a result, in the case of St~1 the particle dispersion is faster than the diffustion of the flow field while in the cases of both St<<1 and St>>1 it is shown that the particle dispersion in lower than the diffusion of the flow filed.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.61.1-61.1
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• 2013

Turbulence is a common phenomenon in astrophysical fluids such as the interstellar medium (ISM) and the intracluster medium (ICM). In turbulence studies it is customary to assume that fluid powered by an energy injection on a single scale. However, in astrophysical fluids, there can be many different driving mechanisms that act on different scales simultaneously. In this work, we assume multiple energy injection scale (2${\surd}$12 and 15

• 한국연소학회:학술대회논문집
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• 1997.06a
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• pp.163-173
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• 1997

This article presents an application of a large-scale structural mixing model (Broadwell et al. 1984) to the blowout of turbulent reacting jets discharging perpendicularly into an unconfined cross air-flow. In an analysis of a common stability curve, a plausible explanation can be made that the phenomenon of blowout is related only to the mixing time scale of the two flows. The most notable observation is that the blowout distance is traced at fixed positions at all times according to the velocity ratio R. Measurements of the lower blowout limits in the liftable flame agree qualitatively with the blowout parameter ${\varepsilon}$, proposed by Broadwell et al. Good agreement between the results calculated by a modified blowout parameter ${\varepsilon}^'$ and experimental results confirms the important effect of a large-scale structure in specifying the stabilization feature of blowouts.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1592-1597
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• 2004

Experimental studies were carried out to confirm the turbulent enhancement of the cooling system of nuclear reactor by large scale vortex generation in nuclear fuel rod bundle. The large scale vortex motions were generated by rearranging the inclination angles of mixing vanes to the coordinate directions. Experimental studies were carried out at Reynolds Number 60,000 with hydraulic condition. Normal variations of mean velocity and turbulent intensity in the rod bundle subchannel were measured by the 2-color LDV measurement system. The turbulence generated by split mixing vanes has small length scales so that they maintain only about 10DH after the spacer grid. On the other hand, the turbulences generated by the large scale vortex continue more and remain up $25D_{H}$ after the spacer grid.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.1 no.1
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• pp.45-50
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• 1997

Understanding the nonlinear flow caused by orographic effects can be valuable in siting of new businesses, industries, and transportation facilities. In spite of recent work on large-amplitude waves and wave breaking, the studies of flow around large scale mountains have just begun. The generative mechanism of lee vortices in the lee of large scale mountain is investigated by Ertel's theorem. The CSU RAMS is used as a numerical model. According to the numerical results, the isentropes are depressed behind the large scale mountains. This means the vortex lines must run upward and downward along the depression surface because vortex lines adhere to isentropic surfaces. Therefore, the vertically oriented vorticity can be formed in the lee of the large scale mountain. This vorticity plays an important role for orographic precipitation, because strong vertical velocity and cloud bands are developed along isothermal deformation surface.

• Journal of Environmental Science International
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• v.1 no.1
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• pp.45-50
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• 1992

Understanding the nonlinear flow caused by orographic effects can be valuable in siting of new businesses, industries, and transportation facilities. In spite of recent work on large-amplitude waves and wave breaking, the studies of flow around large scale mountains have just begun. The generative mechanism of lee vortices in the lee of large scale mountain Is investigated by Ertel's theorem. The CSU RAMS is used as a numerical model. According to the numerical results, the isentropes are depressed behind the large scale mountains. This means the vortex lines must run upward and downward along the depression surface because vortex lines adhere to isentropic surfaces. Therefore, the vertically oriented vorticity can be formed in the lee of the large scale mountain. This vorticity plays an important role for orographic Precipitation, because strong vertical velocity and cloud bandy are developed along isothermal deformation surface.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.249-252
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• 2005

We present results of the velocity-resolved spectroscopy of the [Fe II] $\lambda$1.644${\mu}m$ emission toward outflow sources with the Subaru Telescope at the angular resolution of 0.apos;16 ${\~}$ 0.apos;5 arcseconds. The observed sources are L1551 IRS 5, DG Tau, HL Tau and RW Aur, which are located in the Taurus-Aurigae Molecular Cloud, one of the closest star forming regions (0.apos;1 = 14 AU). We were able to resolve outflow structure in the vicinity of the sources at a scale of a few tens of AU. The position-velocity diagram of each object shows two velocity components: the high velocity component (HVC: 200 - 400 km $s^{-l}$) and the low velocity component (LVC: 50 - 150 km $s^{-l}$), which are clearly distinct in space and velocity. The HVC may be a highly collimated jet presumed from its narrow velocity width and high velocity. The LVC, on the other hand, may be a widely opened disk wind inferred from its broad velocity width and low velocity. The spectrum taken perpendicular to the L1551 IRS 5 outflow at its base shows that the LVC has a spatially wide subcomponent, supporting the above interpretation. We demonstrated that the [Fe II] 1.644 $\mu$ spectroscopy is a very powerful tool for the studies of fast jets and winds that directly emanate from star-disk systems.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.540-545
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• 2001

Many previous researches on the premixed flame in a tube have treated the unsteady flame behaviors in which the shape, position and intensity of the flame varied, but more detail and fundamental research has been necessary. The flame stabilization condition in a tube, a unique steady state, and the unsteady behaviors, using the stabilization condition as an initial condition, were carried out in recent years. In this paper, propane-air premixed flame was stabilized in a tube and the flame behavior was observed when the mean velocity variation was imposed into the opposite direction of the initial mean velocity. The velocity variation is larger than the burning velocity and longer than the reaction time scale. During the period of the velocity variation flame is not extinguished. But after the period of the mean velocity variation the flame could be re-stabilized or be extinguished depending on the experimental conditions: equivalence ratio, period of velocity variation and magnitude of velocity variation. The extinction mechanisms were classified into the two cases, one is caused by the flame stretch in the shear layer near the wall, and the other is caused by the vortices and vortexes, which are generted by the acoustic waves.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.2
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• pp.29-38
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• 2010

The experimental study on paraffin wax/LDPE blended fuel for hybrid rocket was performed. Various combustion characteristics of blended fuel were compared with pure paraffin, HTPB, HDPE and SP-1a fuel in order to evaluate the performance of blended fuel. The regression rate of lab-scale and large-scale motor using pure paraffin fuel was increased by 10.2 and 9.8 factor when respectively compared to that of HDPE. The regression rate factor of blended fuel was 3.4 in which the regression rate of blended fuel was higher than that of HTPB and HDPE, but lower than that of pure paraffin, SP-1a fuel. The values of characteristic velocity and specific impulse of blended fuel was higher than those of pure paraffin, HTPB and HDPE, and almost the same as SP-1a fuel. As these results, it was confirmed that blended fuel can be an effective solid fuel for hybrid rocket.