• 한국약용작물학회지
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• 제28권2호
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• pp.111-118
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• 2020

Background: Cnidium officinale is a medicinal crop sensitive to high temperature. It is necessary to develop environment control technology that can reduce environmental stresses such as high temperature. This study was conducted to develop technology for stable production of Cnidium officinale by reducing damage owing to high temperature by applying shading treatment of varying duration, and structure. Methods and Results: Black shading nets were used from May to September or November; shading structures such as pillar, flat roof, and tunnel type structures were installed. Environmental changes, rate of photosynthesis, and growth characteristics were investigated. The shading treatment reduced temperature by 3℃. The rate of photosynthesis and yield with shading treatment were higher by 134% and 127%, respectively, than those with full sunlight. The ratio of shading area ranged from 50% to 71% according to the type of shading structure. The effect of environmental control on growth varied depending on the type of shading structure. Conclusions: The shading treatment reduced damage owing to high temperature, shading rate of 55% - 75% was recorded between the period May - September, and the flat roof type shading structure was considered the most suitable among shading methods.

• 한국분무공학회지
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• 제16권3호
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• pp.126-133
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• 2011

In HCCI Engine, combustion is affected by change of compression speed corresponding to engine speed. The purpose of this study is to investigate the mechanism of influence of engine speed on HCCI combustion characteristics by using numerical analysis. At first, the influence of engine speed was shown. And then, in order to clarify the mechanism of influence of engine speed, results of kinetics computations were analyzed to investigate the elementary reaction path for heat release at transient temperatures by using contribution matrix. In results, as engine speed increased, in-cylinder gas temperature and pressure at ignition start increased. And ignition start timing was retarded and combustion duration was lengthened on crank angle basis. On time basis, ignition start timing was advanced and combustion duration was shortened. High engine speed showed higher robustness to change of initial temperature than low engine speed. Because of its high robustness, selecting high engine speed was efficient for keeping stable operation in real engine which include variation of initial temperature by various factors. The variation of engine speed did not change the reaction path. But, as engine speed increased, the temperature that each elementary reaction would be active became high and reaction speed quicken. Rising the in-cylinder gas temperature of combustion start was caused by these gaps of temperature.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.359-365
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• 2002

The fatigue crack growth behavior of the SA516/60 steel which is used for pressure vessels was examined experimentally at room temperature $25^{\circ}C,\;-30^{\circ}C,\;-60^{\circ}C,\;-80^{\circ}C,\;-100^{\circ}C$ and $-120^{\circ}C$ with stress ratio of R=0.05, 0.1 and 0.3. Fatigue crack propagation rate da/dN related with stress intensity factor range ${\Delta}K$ was influenced by stress ratio in stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. The resistance of fatigue crack growth at low temperature is higher compared with that at room temperature, which is attributed to tile extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperatures are mainly explained by the crack closure and the strengthening due to the plasticity induced and roughness induced.

• 한국표면공학회지
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• 제25권5호
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• pp.235-252
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• 1992

(Ti, Al)N films were deposited on 304 stainless steel sheet by D.C. magnetron sputtering using Al target and Ti plate. The high temperature oxidation of (T, Al)N films with the variation of composition has been investigated. The chemical composition of (Ti, Al)N films with the variation of composition has been investigated. The chemical composition of (Ti, Al)N films was similar to the sputter area ratio of titanium to aluminum target by means of EDS and AES survey. The high temperature oxidation test of (Ti, Al)N showed that (Ti, Al)N has better high temperature resistance than TiN and TiC films. TiC films were cracked at 40$0^{\circ}C$ in air TiN films quickly were oxidised at $600^{\circ}C$, were spalled more than $700^{\circ}C$. But (Ti, Al)N films are relatively stable to$ 900^{\circ}C$. The good resistance to high temperature oxida-tion of (Ti, Al)N films are due to the formation of dense Al2O3 and TiO2 oxide layer. Especially, Al2O3 oxide layer is more important. The results obtained from this study show, it is believe that the (Ti, Al)N film by D.C. magnetron sputtering is promising for the use of high temperature and wear resistance mate-rials.

• 한국전기전자재료학회논문지
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• 제36권6호
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• pp.603-608
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• 2023

Carbon black with high purity and excellent conductivity is used as a conductive filler in the semiconductive compound for EHV (Extra High Voltage) power cables of 345 kV or higher. When carbon black and CNT (carbon nanotube) are applied together as a conductive filler of a semiconductive compound, stable electrical properties of the semiconductive compound can be maintained even though the amount of conductive filler is significantly reduced. In EHV power cables, since the semi-conductive layer is close to the conductor, stable electrical characteristics are required even under high-temperature conditions caused by heat generated from the conductor. In this study, the theoretical principle that a semiconductive compound applied with carbon black and CNT can maintain excellent electrical properties even under high-temperature conditions was studied. Basically, the conductive fillers dispersed in the matrix form an electrical network. The base polymer and the matrix of the composite, expands by heat under high temperature conditions. Because of this, the electrical network connected by the conductive fillers is weakened. In particular, since the conductive filler has high thermal conductivity, the semiconductive compound causes more thermal expansion. Therefore, the effect of CNT as a conductive filler on the thermal conductivity, thermal expansion coefficient, and volume resistivity of the semiconductive compound was studied. From this result, thermal expansion and composition of the electrical network under high temperature conditions are explained.

• 대한기계학회논문집B
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• 제23권2호
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• 대한기계학회논문집B
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• 제27권4호
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• pp.447-457
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• 2003

An experiment in a turbulent non-premixed flat flame was carried out in order to investigate the effect of swirl number on the flow and combustion characteristics. First. stream lines and velocity distribution in the flow field were obtained using PIV method. In contrast with the axial flow without swirl, highly swirled air induced stream lines along the burner tile. and backward flow was caused by recirculation in the center zone of the flow field. In the combustion. the flame with swirled air also became flat and stable along the burner tile with increment of the swirl number. Flame structure by measuring OH and CH radicals intensity and by calculating Damkohler number(Da) and turbulence Reynolds number(Re$_{T}$) was examined. It appeared to be comprised in the wrinkled laminar-flame regime. Backward flow by recirculation of the burned gas decreased the flame temperature and emissions concentrations as NO and CO. Consequently, the stable flat flame with low NO concentration was achieved.d.

• 한국연소학회지
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• 제17권4호
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• pp.5-10
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• 2012

The reformer system is a chemical device that drives the conversion of hydrocarbon to hydrogen rich gas under high temperature environment($600-1,000^{\circ}C$). Generally, NG(Natural Gas) or AOG(Anode Off Gas) is used as fuel of fuel cell reformer combustion system. The experimental study to analyze the combustion characteristics of a premixed ceramic burner used for 0.5-1.0 kW fuel cell reformer was performed. Ceramic burner experiments using NG and AOG were carried out to investigate the flame stability characteristics by heating capacity, equivalence ratio and different fuels respectively. The results show that surface flames can be classified into green, red, blue and lift-off flames as the equivalence ratio of methane-air mixture decreases. And the stable flames can be established using NG and AOG as reformer fuel in the perforated ceramic burner. In particular, the blue flame is found to be stable at a lean equivalence ratio under different mixture conditions of NG and AOG for the 0.5 to 1.0 kW fuel cell system power range. NOx emission is under 60 ppm between 0.70 to 0.78 of equivalence ratio and CO emission is under 50 ppm between 0.70 to 0.84 of equivalence ratio.

• 한국군사과학기술학회지
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• 제22권2호
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• pp.249-254
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• 2019

A Digital Transmitter/Receiver Module(DTRM), which is an essential part in active phased-array radar systems, generates a high heat density, and needs to be properly cooled for stable operation. A tile-type DTRM that is a stacking structure of multi-layer components was modeled with simplification and heat dissipation characteristics of the DTRM model were studied using computational fluid dynamics(CFD) simulations. Most of the heat was dissipated by the heat conduction through the cold plate, but the heat transfer by the forced convection on top of the DTRM also was found to play an important role in the thermal management. Under the given conjugated heat transfer environment, the DTRM was confirmed to secure a stable operating temperature range.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1989-1991
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• 1999

This paper presents characteristics of CrN thin-film strain gauges, which were deposited on glass by DC reactive magnetron sputtering in an argon-nitrogen atmosphere(Ar-$(5{\sim}25%)N_2$). The physical and electrical characteristics of these films investigated with the thickness range $3500{\AA}$ of CrN thin films, annealing temperature $(100{\sim}300^{\circ}C)$ and annealing $(24{\sim}72hr)$. The optimized condition of CrN thin-film strain gauges were thickness range of $3500{\AA}$ and annealing condition($300^{\circ}C$, 48 hr) in Ar-10 %$N_2$ deposition atmosphere. Under optimum conditions, the CrN thin-films for strain gauge is obtained a high resistivity, ${\rho}=1147.65{\mu}{\Omega}cm$, a low temperature coefficient of resistance, TCR=$-186ppm/^{\circ}C$ and a high temporal stability with a good longitudinal, 11.17. And change in resistance after annealing for the CrN thin-films were quitely linear and stable.