• 한국유체기계학회 논문집
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• 제3권3호
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• pp.12-18
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• 2000

In this study, experimental and numerical analyses are carried out to investigate the performance of centrifugal pump with various air admitting conditions. Experiments on the pump performance under air-water two-phase flow are accomplished using a centrifugal pump with semi-open type impeller having three, five and seven blades, respectively. Also, the numerical analysis of turbulent air-water two-phase flow using the finite volume method has been carried out to obtain the pressure, velocities and void fraction on the basis of a so-called bubbly flow model with the constant size and shape of cavity. The results obtained through this study show the reasonable agreements within the range of bubbly flow regime. There are promising developments concerning application of the present study for the flow in a centrifugal pump with two-phase flow conditions and efforts must be followed to improve the turbulence model and two-phase flow model for turbomachinery.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.568-573
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• 2000

In this study, experimental and numerical analyses are carried out to investigate the performance of centrifugal pump with various air admitting conditions. Experiments on pump performance under air-water two-phase flow n accomplished using a centrifugal pump with semi-open type impeller having three, five and seven blades, respectively. Also, the numerical analysis of turbulent air-water two-phase flow using finite volume method has been carried out to obtain the pressure, velocities and void fraction on the basis of a so-called bubbly flow model with the constant size and shape of cavity. The results obtained through this study show the reasonable agreements within the range of bubbly flow regime. There are promising developments concerning application of the present study for the flow in a centrifugal pump with two-phase flow conditions and efforts must be followed to improve the turbulence model and two-phase flow model for turbomachinery.

• 대한조선학회논문집
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• 제49권6호
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• pp.461-468
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• 2012

In this study, a Cartesian-grid method based on finite volume approach is applied to simulate the ship motions in large amplitude waves. Fractional step method is applied for pressure-velocity coupling and TVD limiter is used to interpolate the cell face value for the discretization of convective term. Water, air, and solid phases are identified by using the concept of volume-fraction function for each phase. In order to capture the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with weighed line interface calculation (WLIC) method which considers multidimensional information. The volume fraction of solid body embedded in the Cartesian grid system is calculated using a level-set based algorithm, and the body boundary condition is imposed by a volume weighted formula. Numerical simulations for the two-dimensional barge type model and Wigley hull in linear waves have been carried out to validate the newly developed code. To demonstrate the applicability for highly nonlinear wave-body interactions such as green water on the deck, numerical analysis on the large-amplitude motion of S175 containership is conducted and all computational results are compared with experimental data.

• 대한기계학회논문집B
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• 제28권1호
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• pp.1-8
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• 2004

An study has been performed with axisymmetric coflow diffusion flames to investigate the influence of air-side fuel side dilution and initial preheated temperature on the soot formation in methan/air flames. Soot quantities are determined by using PLII(Planar Laser Induced Incandescence), such a $C_2$H$_2$ major species(CH$_4$, $O_2$, $N_2$) and temperature are simulated by chemkin code. The numerical analysis was performed with transport properties and detailed reaction mechanisms m axisymmetric coflow diffusion flames. The study of how flame temperature and $N_2$ dilution of air and fuel side influence the soot concentrations is focused. Soot concentrations results on PLII show that preheated temperature contributes to an increase in the soot volume fraction, and soot formation Is more productive to air side dilution than to fuel side dilution. $C_2$H$_2$ concentrations have a similar tendency to soot concentrations.

• 설비공학논문집
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• 제22권10호
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• pp.710-718
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• 2010

A numerical study was performed to predict refrigerant charge amount in a mini-channel condenser for a R410A residential air-conditioning system. Multi-channel flat tubes with 12 mini-channels of 1.17 mm average hydraulic diameter for each tube were applied to the condenser. The condenser consisted of 3 passes, and the first, second, and third pass had 44, 19, and 11 tubes, respectively. Each pass was connected by a vertical header. In this study, the condenser was divided into 410 finite volumes, and analyzed by an $\varepsilon$-NTU method. With thermophysical properties and void fraction models for each volume element, the R410A amount distribution and a total charge amount in the condenser were calculated. The predicted total charge amount was compared with the experimentally measured charge amount under a standard ARI A condition. The developed model could predict the charge amount in the mini-channel condenser within prediction errors from -23.9% to -3.0%. Air velocity distribution at the condenser face was considered as non-uniform and uniform by the simulation model, and its results showed that the air velocity distribution could significantly influence the charge amount and vapor phase distribution in the condenser.

• 한국연소학회지
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• 제4권2호
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• pp.75-83
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• 1999

The effect of temperature distributions on soot volume fraction in double-concentric diffusion flames have been investigated experimentally. Using fine thermocouple wires and a rapid insertion mechanism, we have measured temperature without the effect of soot particles attached to the thermocouple junction, which can lower the temperature signal about 100 K by increasing the heat loss from the junction by radiation. The temperature at the flame axis is higher in the double-concentric diffusion flames than in normal co-flow diffusion flames because of the inverse diffusion flame. However, it is almost the same as that at the periphery of normal flames, on which the inverse flame does not have an effect. Thus, the lower soot concentration found in the double-concentric diffusion flame can be explained by the effect of nitrogen diffusion from the central air jet.

• 한국환경보건학회지
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• 제19권3호
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• pp.52-57
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• 1993

This study was carried out to investigate the air pollution in Hwasoon Nulitjae tunnel for two months, from August 1992 to September 1992. The total suspended particles were collected by high volume air sampler at inside and outside of Hwasoon Nulitjae tunnel, of which major water soluble component and heavy metalic element were analyzed. Size distribution and respirable mass fraction of aerosol at inside were measured by filters on nine stages Andersen air sampler. The average concentration of TSP at inside was 657.57 $\mu$g/m$^3$, which appeared about 9.2 times as high as that of 71.47 $\mu$g/m$^3$ at outside. The decrease effect caused by using new tunnel was 31.2%. As a result of correlation analysis between concentration of TSP at inside of Hwasoon Nulitjae tunnel and that at outside, correlation coefficient was 0.713. The average concentrations of SO$_4^{2-}$ , NO$_3^-$, CI$^-$ were 43.02 $\mu$g/m$^3$, 19.86 $\mu$g/m$^3$, 4.96 $\mu$g/m$^3$, those of NH$_4^+$, Na$^+$, K$^+$ 1.42 $\mu$g/m$^3$, 4.45 $\mu$g/m$^3$, 2.89 $\mu$g/m$^3$ and those of Ca$^{2+}$, Mg$^{2+}$, Pb$^{2+}$ 3.92 $\mu$g/m$^3$, 2.27 $\mu$g/m$^3$. 1.52 $\mu$g/m$^3$, respectively. It was estimated that mass fraction rate of respirable particle at inside was about 84.54% of aerosol. The average concentration of suspended particle to be collected by Andersen sampler was 478.90 $\mu$g/m$^3$, this was about 72.8% of that by high volume air sampler.

• Journal of Mechanical Science and Technology
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• 제16권6호
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• pp.829-838
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• 2002

A constant volume combustion chamber is used to investigate the flame kernel development of gasoline air mixtures under various ignition systems, ignition energies and spark plugs. Three kinds of ignition systems are designed and assembled, and the ignition energy is controlled by the variation of the dwell time. Several kinds of spark plugs are also tested. The velocity of flame propagation is measured by a laser deflection method, and the combustion pressure is analyzed by the heat release rate and the mass fraction burnt. The results represent that as the ignition energy is increased by enlarging either dwell time or spark plug gap, the heat release rate and the mass fraction burnt are increased. The electrodes materials and shapes influence the flame kernel development by changing he transfer efficiency of electrical energy to chemical energy. The diameter of electrodes also influences the heat release rate and the burnt mass fraction.

• 대한조선학회논문집
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• 제50권2호
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• pp.79-87
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• 2013

In this paper, an Euler equation solver based on a Cartesian-grid method and non-uniform staggered grid system is applied to predict the ship motion response and added resistance in waves. Water, air, and solid domains are identified by a volume-fraction function for each phase and in each cell. For capturing the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with a weighed line interface calculation (WLIC) method. The volume fraction of solid body embedded in a Cartesian-grid system is calculated by a level-set based algorithm, and the body boundary condition is imposed by volume weighted formula. Added resistance is calculated by direct pressure integration on the ship surface. Numerical simulations for a Wigley III hull and an S175 containership in regular waves have been carried out to validate the newly developed code, and the ship motion responses and added resistances are compared with experimental data. For S175 containership, grid convergence test has been conducted to investigate the sensitivity of grid spacing on the motion responses and added resistances.

• KIEAE Journal
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• 제15권4호
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• pp.45-52
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• 2015

Purpose: Foam concrete is the concrete that contains large amount of air voids inside. In general, the density of foam concrete depends on parameters like water/binder ratio, foam volume, aggregate and pozzolan content, etc. Method: In this study, the effect of foam volume and fly ash content on dry density is investigated intensively in order to find the relationship between each parameter and their abilities to counteract with each other. According to the above information, though there are quite a number of studies on the effect micro fiber on foam concrete at low volume fractions, there is still lack of information especially on the high fiber content side. The objective of the second study is to investigate further on the use of micro fiber at higher volume fraction and fill in the lacking information. Beside from this study, the investigation of the effect of micro-fiber (polypropylene) to enhance the properties of foam concrete is also carried out. Result: Of the two variables that are investigated in this study, the foam volume and the fly ash content, show significant effect on the properties of foam concrete. The foam volume tends to decrease the density and strength of foam concrete. In the second part of our study, a large fibre volume fraction is proved to be able to evidently increase the flexural strength of foam concrete up to about 40% due to the effect of fibre bridging over the crack and a significant number of fibres that intercepts the crack surfaces. However, the compressive strength is found to decrease severely due to the occurrence of large pores as the result of fibre being added into concrete mixture.