• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.479-487
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• 1987

In order to predict the effects of droplets distributions such as number density and droplets size on group combustion characteristics and flame structure for liquid fuel sprays, modifications of group combustions model were made by changing the droplets distributions from uniform to non-uniform. Various droplets distribution models were adopted in this analysis to examine the effect of number density distribution on combustion characteristics and the difference between uniform and non-uniform droplets size distributions for a spherical droplets cloud. As results of present study, hollow droplets could with outer concentrating distribution has shorter total combustion time compare with the case of solid droplets cloud with inner concentrating distribution. Uniform droplets size distribution model predicts the shorter total combustion time compare with non-uniform droplets size distribution model, and the uniform droplets size distribution model may be used to predict the total combustion time for the droplets cloud containing larger initial size of droplets.

• Journal of Information Display
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• v.9 no.4
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• pp.1-5
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• 2008

This paper investigates the effect of the electrode edge of a patterned vertical alignment (PVA) liquid crystal (LC) device on the viewing angle characteristics. In general, a transmissive LCD applies an LC layer with half-wave retardation for a bright state and with zero retardation for a dark state. The retardation of the LC layer would be distorted in each point, however, when a voltage is applied because of the non-uniform voltage distribution in the electrode edge effect. In this paper, the feasibility of the full effect of the electrode edge on the viewing angle property is considered, and the optical viewing angles of the VA LCD with a uniform half-wave LC layer and the PVA LCD with a practical non-uniform LC layer are compared.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2376-2384
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• 1992

A theoretical analysis is carried out to predict the characteristics of transient ignition phenomena for the spherical fuel droplets cloud with non-uniform droplet size and number density distribution. Numerical calculations are performed for various cases depending on the combinations of the major parameters such as ambient temperature and initial distributions of droplet size and number density. The results of present study show that the ignition delay decreases for higher ambient temperature and smaller droplet size. Droplets cloud of hollow type with outer concentrated distribution ignites most rapidly.

• Journal of Magnetics
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• v.22 no.2
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• pp.299-305
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• 2017

Magnetic fluid, a new type of magnetic material, is a colloidal liquid constituted of nano-scale ferromagnetic particles suspended in carrier fluid. Magnetic fluid sealing is one of the most successful applications of magnetic fluid. As a new type of seal offering the advantages of no leakage, long life and high reliability, the magnetic fluid seal has been widely utilized under vacuum- and low-pressure-differential conditions. In practical applications, for improved pressure capacity, a multistage sealing structure is always used. However, in engineering applications, a uniform distribution of magnetic fluid under each tooth often cannot be achieved, which problem weakens the overall pressure capacity of the seals. In order to improve the pressure capacity of magnetic fluid seals and broaden their applications, the present study theoretically and experimentally analyzed the degree of non-uniform distribution of multistage magnetic fluid seals. A mathematical model reflecting the relationship between the pressure capacity and the distribution of magnetic fluid under a single tooth was constructed, and a formula showing the relationship between the volume of magnetic fluid and its contact width with the shaft was derived. Furthermore, the relationship of magnetic fluid volume to capacity was analyzed. Thereby, the causes of non-uniform distribution could be verified: injection of magnetic fluid; the assembly of magnetic fluid seals; the change of magnetic fluid silhouette under pressure loading; the magnetic fluid sealing mechanism of pressure transmission, and seal failure. In consideration of these causes, methods to improve the pressure capacity of magnetic fluid seals was devised (and is herein proposed).

• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.314-319
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• 2011

In this study, the flow behavior of Newtonian and non-Newtonian coating liquids inside slot die has been scrutinized for the purpose of optimal internal die design in slot coating system from three-dimensional computations by CFD Fluent solver. A hybrid slot die could be optimally designed by changing the chamber or manifold structure to guarantee the uniform velocity distribution of coating liquids at die exit. Especially, for the non-Newtonian coating liquids, the length of coat-hanger for the uniform coating has been properly chosen, according to the degree of their shearthinning properties.

• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.5
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• pp.171-176
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• 2003

For practical electrical insulation design of high temperature superconducting (HTS) power apparatuses, knowledge of the dielectric behavior of both liquid nitrogen (L$N_2$) and subcooled liquid nitrogen (SL$N_2$) are essential. To achieve SL$N_2$ at atmospheric pressure, cryostat was designed and constructed. By pumping up the L$N_2$ in the outer dewar, the temperature of L$N_2$ in the inner dewar at atmospheric pressure can be controlled. The breakdown characteristics of L$N_2$ in quasi-uniform and non-uniform electrical fields for temperatures ranging from 77 K to 65 K at atmospheric pressure and pressure ranging from 0.1 to 0.5 MPa were investigated experimentally. The experimental data suggested that the breakdown voltage (BDV) of L$N_2$ is both highly temperature and pressure dependent. We also carried out statistical analysis of the experimental results using the Weibull distribution. The Weibull shape parameter m for the sphere-to-plane electrodes in SL$N_2$ was estimated to be 11 to 18.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.4
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• pp.72-79
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• 1994

In an automotive spark ignition, it is important to form the proper mixture(air/fuel) on each driving condition for developing the stabilizing combustion and exhaust characteristics. Since most of supply fuel is attached on the inside wall of the intake manifold for unadequate atomization by fuel injection system, it brings a bad effect on combustion and exhaust caused by nonuniformity of fuel distribution to each cylinder and mixture variation. Also it affects engine performance variation and causes noises and vibration. In this study, we verified the effect of the mixture variation which is caused by fuel liquid film in an intake manifold on combustion characteristics and engine performance.

• Applied Science and Convergence Technology
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• v.25 no.3
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• pp.47-50
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• 2016

Low temperature test for half-wave resonator (HWR) cryomodule is performed at the superfluid helium temperature of 2 K. The effective temperature is defined for non-uniform temperature distribution. Helium leak detection techniques are introduced for cryogenic system. Experimental set up is shown to make the low temperature test for the HWR cryomodule. The cooldown procedure of the HWR cryomodule is shown from room temperature to 2 K. The cryomodules is precooled with liquid nitrogen and then liquid helium is supplied to the helium reservoirs and cavities. The pressure of cavity and chamber are monitored as a function of time. The vacuum pressure of the cryomodule is not increased at 2 K, which shows leak-tight in the superfluid helium environment. Static heat load is also measured for the cryomodule at 2.5 K.

• Progress in Superconductivity
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• v.12 no.1
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• pp.6-11
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• 2010

The milling effects of a precursor $Y_2BaCuO_5$ (Y211) powder having 1 wt.% $CeO_2$ on the microstructure and critical current density ($J_c$) of liquid infiltration growth (LIG) processed $YBa_2Cu_3O_{7-y}$ (Y-123) bulk superconductors were investigated. The microstructure analysis revealed that the Y211 size in the final Y-123 products decreased with increasing the milling time and a relatively high density and uniform distribution of Y211 inclusions were observed in the sample prepared using 8 h milled powder. However, the unexpected Y211 particles coarsening was observed from the 4 h milled sample which was further increased for 10 h milled sample. Critical current density ($J_c$) of the LIG processed Y-123 bulk superconductors was found to be dependent on the milling time of the Y211 precursor powder. The $J_c$ increased with the increase of milling time and reached up to a maximum at 8 h in the self field while 10 h milled sample showed lower $J_c$ at the same field which might be due to the exaggerated growth and non-uniform distribution of Y211 particles.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.485-490
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• 2010

In our previous studies, continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by two different slurry infiltration methods: vacuum infiltration and electrophoretic deposition (EPD). 12 wt% of $Al_2O_3-Y_2O_3$-MgO with respect to SiC powder was used as additives for liquid-phase assisted sintering. After hot pressing at $1750^{\circ}C$ under 20 MPa for 2 h in Ar atmosphere, a high composite density could be achieved for both cases, whereas the problems such as large grain size and non-uniform distribution of liquid phase were observed, which was resulted in the relatively poor mechanical properties of composites. Therefore, efforts have been made to reduce the grain growth during the sintering, including the optimization for hot pressing condition and utilization of spark plasma sintering using a SiC monolith. Based on the results, spark plasma sintering was found to be effective method in decreasing the amount of sintering additive, time and grain growth, which will be explained in comparison to the results of hot pressing in this paper.