• 동력기계공학회지
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• 제21권1호
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• pp.24-29
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• 2017

Studies in liquid-vapor ejector, which performs a great efficiency in refrigeration cycle is highly concerned. This paper is based on basic refrigeration cycle and three ejector refrigeration cycles and the comparison and contrasts about when 6 different refrigerants are applied to such refrigeration cycles. All cycles had a percentage increase of COP from 4 to 74% when ejector was applied, and the source of increasement was the decrease of total work done due to ejector's pressure recovery function. When R-245fa is applied to cycle (d), results showed that COP was the most superior in such cycle, R-245fa showed high volume entrainment ratio in all cycles. Future studies in refrigeration cycles will require more knowledge and experiments on ejector's appliance to refrigeration cycles and the actuation of such functions.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.10-17
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• 2000

This work presents an investigation of aerodynamic characteristics of fuel spray injected from a high pressure hollow cone swirl injector into a constant volume chamber. Laser tomography visualization was used to interrogate the fuel and air mixing characteristics and the effect of chamber pressure and temperature increase was analyzed, Preliminary results on spray development showed that mixing effect tends to increase with the increase of injection pressure and chamber gas pressure yielding a decrease of spray penetration and an attenuation of well-defined vortex structure. Topological analysis of the spray structure has been performed to initiate the understanding of mixing and vaporization process. For the present experimental conditions fuel injection pressure and chamber gas pressure appear as the dominant factors which govern the transient mixing characteristics. Moreover spray atmixation characteristics are improved by increasing chamber gas temperature.

• 대한조선학회논문집
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• 제40권4호
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• pp.22-29
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• 2003

New high-speed depressurized circulating water channel was designed by using the CFD code. Flow in the channel has free surface and pressure in the test section can be depressed. In this study, Flow separation and bubble occurrence were considered in designing the contraction nozzle shape for better flow uniformity Tn the test section. To supplement velocity defect due to the free surface, nozzle injection system more effective in high-speed flow was installed instead of drum system. Necessary power and injection techniques were proposed. And guide vane arrangement was analyzed to reduce the flow resistance and keep quiet free surface from ´surging´. Wave absorber was devised to reduce the wave resistance and to prevent the entrainment of air to the diffuser.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.755-760
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• 1998

In the present, we have developed high strength concrete for the sleepers of high speed rail and verified its applicability by in-situ applications. Concrete for sleepers is manufactured by steam curing at low temperature(below 55$^{\circ}C$), and should be finished its manufacturing process such as placing, curing, demolding and prestressing in 24 hours. The sleepers need its compressive strength above 350kg/$\textrm{cm}^2$ in 15 hours, air-entrainment for durability and nominal design strength of 600kg/$\textrm{cm}^2$, considering its quality variation at factory. We performed the optimum mix design of concrete and verified the rightness of the use of TYPE III cement. Finally, we have confirmed the manufactured sleepers satisfy the required material properties through in-situ application.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.254-259
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• 1996

Phase Doppler particle analyze. (PDPA) is a instrument which can be used to obtain simultaneous size and velocity measurements in a multiphase flow. In this study, the size of the water droplets entrained from a bubbling surface of a stagnant liquid column is measured by PDPA with a specially designed transmitter of long focal length and large beam diameter. The test section tube is made of acryle with 18 mm I.D. and 900 mm length. The experimental data are obtained for the air superficial velocity between 0.7 m/s to 3.4 m/s at atmospheric pressure. The experimental results show that there exists large difference in the entrainment mechanism between the churn-turbulent flow and annular flow. Through the present study, the phase Doppler analyzer system is shown to be successfully applied to measure particle sizes larger than $2,000\mu\textrm{m}$ if a transmitter of long focal length is utilized.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.1159-1162
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• 1995

In the continuous process systems, traction between a moving web and rollers is one of key mechanisms for the study of major issues including the distributed control of tension, guiding, wrinkling, and scratching. Energy is transferred from the driven rollers to the web and from the web to the idle rollers through traction. The characteristics of friction plays a major role in the determination of the traction force between the moving web and the rollers. In this paper, a procedure to determine the frcition coefficient between the moving web and rollers is devoloped. An experimental setup to validate the procedure is devised. Experimental results showed that the value of traction coefficient decreases as the operating web speed increases and increases as the operating web tension and wrap alngle increase.

• 한국연소학회지
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• 제7권1호
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• pp.44-51
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• 2002

This paper presents an atomization model for sprays under flash boiling conditions. The atomization is represented by the secondary breakup of a bubble/droplet system, and the breakup is considered as the results of two competing mechanisms, aerodynamic force and bubble growth. The model was applied to predict the atomization of a hollow-cone spray from pintle injector under flash boiling conditions. In the regimes this study considered, sprays are atomized by bubble growth, which produces smaller SMD#s than aerodynamic forces alone. With decreasing ambient pressures, the spray thickness, fuel vaporization rate and vapor radial penetration increases, and the drop size decreases. With increasing the fuel and ambient temperatures to some extent, the effect of flash boiling and air entrainment completely change the spray pattern.

• Bulletin of the Korean Chemical Society
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• 제26권9호
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• pp.1415-1420
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• 2005

The spectral interferences of OH from aqueous solvents in ICP-AES have been studied and eliminated using a cryogenic argon trap. The prominent lines of Bi I 306.772 nm, Al I 309.271 nm, and V II 310.230 nm, which are very seriously overlapped with the OH band, were examined. With an extended torch and high tangential flow of 20 L/min, water vapor from air entrainment was prevented. The combination of a condenser and argon cryogenic trap was able to eliminated most of water vapor carried by the argon sample gas. Removal of OH spectral interference could extend the linearity of the calibration curve 5-10 times on the lower concentration for ICP-AES. Interference Equivalent Concentration (IEC) has been reduced to 5.6, 5.9, and 12.4 times for Bi, Al and V, respectively.

• 한국분무공학회지
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• 제11권4호
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• pp.244-250
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• 2006

Of the macroscopic spray characteristics of non-reacting diesel fuel sprays, the spray angle reflects directly the atomization and air entrainment processes downstream the nozzle. In addition, spray angle is important because it will be closely related to the spray penetration. The existing definitions for the measurement of spray angle as well as the correlations for the prediction of spray angle are, therefore, summarized and reviewed. The existing definition of spray angle can be classified into four groups: distance based on orifice diameter, distance based on spray tip penetration, definition based on surface wave, and definition based on atomization. It is strongly required to specify the definition and measurement method when the data for spray angle is reported. The existing correlations for spray angle can be classified into two groups: theoretical and empirical correlations. The study on the evaluation of the existing correlations fer spray angle is required.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.865-876
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• 2004

A new concept of reduced quasi-dimensional combustion model for a direct injection diesel engine is developed based on the previously developed quasi-dimensional multi-zone model to improve the computational efficiency. In the reduced model, spray penetration and air entrainment are calculated for a number of zones within the spray while three zones with aggregated spray zone concept are used for the calculation of spray combustion and emission formation processes. It is also assumed that liquid phase fuel appears only near the nozzle exit during the breakup period and that spray vaporization is immediate in order to reduce the computational time. Validation of the reduced model with experimental data demonstrated that the new model can predict engine performance and NO and soot emissions reasonably well compared to the original model. With the new concept of reduced model, computational efficiency is significantly improved as much as 200 times compared to the original model.