• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.2
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• pp.95-102
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• 2001

Hafnium oxide thin films for gate dielectric were deposited at $300^{\circ}C$ on p-type Si (100) substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed in $O_2$ and $N_2$ ambient at various temperatures. The effect of hydrogen treatment in 4% $H_2$ at $350^{\circ}C$ for 30 min on the electrical properties of $HfO_2$for gate dielectric was investigated. The flat-band voltage shifts of $HfO_2$capacitors annealed in $O_2$ambient are larger than those in $N_2$ambient because samples annealed in high oxygen partial pressure produces the effective negative charges in films. The oxygen loss in $HfO_2$films was expected in forming gas annealed samples and decreased the excessive oxygen contents in films as-deposited and annealed in $O_2$ or $N_2$ambient. The CET of films after hydrogen forming gas anneal almost did not vary compared with that before hydrogen gas anneal. Hysteresis of $HfO_2$films abruptly decreased by hydrogen forming gas anneal because hysteresis in C-V characteristics depends on the bulk effect rather than $HfO_2$/Si interface. The lower trap densities of films annealed in $O_2$ambient than those in $N_2$were due to the composition of interfacial layer becoming closer to $SiO_2$with increasing oxygen partial pressure. Hydrogen forming gas anneal at $350^{\circ}C$ for samples annealed at various temperatures in $O_2$and $N_2$ambient plays critical role in decreasing interface trap densities at the Si/$SiO_2$ interface. However, effect of forming gas anneal was almost disappeared for samples annealed at high temperature (about $800^{\circ}C$) in $O_2$ or $N_2$ambient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.454-460
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• 2009

To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ${\rho}_a=5.0kg/m^3$ to ${\rho}_a=12.3kg/m^3$ with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.141-146
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• 2007

In this study, the effects of change in ambient gas viscosity on spray structure have been investigated in the high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Emissions of diesel engines can be reduced by the control of the mixture formation process. Therefore, this study examines the evaporating spray structure in the constant volume chamber. The viscosity of ambient gas was selected as the experimental parameter, is changed from 21.7 mPa s to 32.1 mPa s by changing in ambient gas temperature. In order to obtain images of the liquid and vapor-phase of injected spray, exciplex fluorescence method was used in this study. The liquid and vapor-phase images were taken with 35mm still camera and CCD camera, respectively. Consequentially, it could be confirmed that the distribution of vapor concentration is more uniform in the case of the ambient gas with high viscosity than in that of the ambient gas with low viscosity.

• Journal of ILASS-Korea
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• v.4 no.2
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• pp.40-46
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• 1999

Experimental investigation of unsteady impinging diesel spray on the flat plate have been carried out using high speed camera and Malvern system. The density ratios of ambient gas to diesel fuel were varied using $N_2$ and Ar gas in the case of 14.9, 21.2, 28.4, 35.1, 40.4, and 50.1. With the increase of gas density ratio, the radial penetration is decreased due to the resistance of the ambient gas. With the increase of the gas density ratio and the distance between nozzle tip and flat plate, the height of spray is increased due to the entrance and circulation. With the increase of gas density ratio, SMD is decreased on the nearby position at the center of flat plate, but SMD is increased on the far position. As the distance between nozzle tip and flat plate is increased, SMD is always decreased.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.6
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• pp.727-736
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• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.104-109
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• 2004

On this paper study is concentrated on the breakup and atomization characteristics of spray formed by impinging jet injectors(like-doublet) used in liquid rocket engine(LRE). On the process of breakup and atomization, injection velocity and ambient gas pressure are the main parameters, so that these are used as variables that specify the experimental condition. Injection velocity varied from 3m/s to 30m/s and ambient gas pressure changed from 0.1MPa to 4.0MPa with nitrogen gas. As results, measured physical quantities decreased with increasing injection velocity and ambient gas pressure. But the decreasing ratios are different from those of the theory.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.97-104
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• 2006

The spray and breakup characteristics of swirling liquid sheet were investigated by measuring the spray angle and breakup length as the axial Weber number Wel was increased up to 1554 and the ambient gas pressure up to 4.0MPa. As Wel and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces, and thus the liquid sheet disintegrated near from the injector exit. The measured spray angles according to the ambient gas density were different before and after the sheet breaks. Before the liquid sheet breaks, the spray angle was almost constant, but once the liquid sheet started to breakup, the spray angle decreased. And the breakup length decreased because of the increase of the aerodynamic force as the ambient gas density and Wel increased. Lastly, the measured breakup length according to the ambient gas density and Wel was compared with the result by the linear instability theory. We found that the corrected linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.9
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• pp.1784-1789
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• 2009

This paper describes the measurement technology of the dissolved hydrogen gas due to partial discharge in oil using gas sensor. For higher resolution and less error in measurement of the dissolved hydrogen gas in oil, the sensor outputs with ambient temperature which affect the sensor output characteristics should be considered. The sensor output trends with ambient temperature and the properties of the dissolved hydrogen gas in oil with partial discharge characteristic were analyzed through the test results. It was indicated that the sensor peak and the base voltage with measuring time were affected by ambient temperature and the measurement errors of the sensor output by temperature were reduced by using the difference between the peak and the base voltage rather than just the peak voltage. In addition, the hydrogen gas sensor outputs were increased with the increase of partial discharge energy.

• Analytical Science and Technology
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• v.34 no.5
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• pp.202-211
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• 2021

Volatile organic compounds (VOCs) in hazardous air pollutants (HAPs) have been regulated by the Air Pollution Control Act (1978) and their atmospheric concentrations have been monitored in 39 monitor sites in Korea. However, measurement standards of volatile organic compounds (VOCs) in HAPs at ambient levels have not been established in Korea. Primary reference gas mixtures (measurement standards) at ambient levels are required for accurately monitoring atmospheric VOCs in HAPs and managing their emissions. In this study, primary reference gas mixtures (PRMs) at 5 nmol/mol were developed in order to establish primary national standards of VOCs in HAPs at ambient levels. Primary reference gas mixtures (PRMs) were prepared in pressurized aluminum cylinders with special internal surface treatment using gravimetric method. Analytical methods using gas chromatography-flame ionization detector (GC-FID) coupled with a cryogenic preconcentrator were also developed to verify the consistency of gravimetrically prepared HAP VOCs PRMs. Three different columns installed in the GC-FID were evaluated and compared for the retention times and separation of eighteen target components in a chromatogram. Results show that the HAP VOCs PRMs at 5 nmol/mol were consistent within a relative expanded uncertainty (k=2) of less than 3 % except acrylonitrile (less than 6 %) and the 18 VOCs were stable for 1 year within their associated uncertainties.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.321-326
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• 2004

The pressure and differential pressure(DP) transmitters are used for gas flow rate calculation on the orifice gas metering system. On site, the pressure and DP transmitters are installed in a shelter to diminish the affects of environmental change such as an ambient temperature. But there has been an argument about the effectiveness of the shelter and this brought up the necessity to verify the affects of ambient temperature. These experiments were performed to verify the ambient temperature effects as observing the output of transmitters when the ambient temperature were changed from $-30^{\circ}C$ to $50^{\circ}C$. The results showed that the most of transmitters were operated in the spec range of performance criteria presented by manufacturer but the rapid change of ambient temperature could cause the larger measurement error for the DP transmitter of low span than others. Therefore the pressure and DP transmitters need to be operated and controlled within the proper range of ambient temperature.