• Title/Summary/Keyword: Ambient gas

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A Study on Propulsion Performance of Underwater Ram-Jet with Optimized Nozzle Configuration (최적 노즐형상을 갖는 수중램제트의 추진성능에 관한 연구)

  • Kang, H.K.;Kim, Y.T.;Lee, Y.H.
    • Journal of the Society of Naval Architects of Korea
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    • v.34 no.4
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    • pp.42-52
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    • 1997
  • The basic principle of underwater ram-jet as a unique marine propulsion concept showing vary high cruise speed range(e. g. 80-100 knots) is the thrust production by the transfer of the potential energy of compressed gas to the operating liquid through kinetic mixing process. This paper is aimed to investigate the propulsive efficiency of the nozzle flow in underwater ram-jet at the speed of 80 knots for the buried type vessel. The basic assumption of the theoretical analysis is that mixture of water and air can be treated as incompressible gas. For an optimized nozzle configuration obtained from the performance analysis, preliminary data for performance evaluation are obtained and effects of nozzle inner wall friction, ambient temperature, ambient pressure, water density, gas velocity, bubble radius, flow velocity, diffuser area ratio, mass flow ratio and water velocity gradient are investigated.

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Study on the Comparison of Heat Exchange Performance of Liquefied Gas Vaporizer at Super Low Temperature (초저온 액화가스 기화기의 열 교환성능 비교에 관한 연구)

  • Kim, Pil-Hwan;Kim, Chul-Pyo;Jeong, Hyo-Min;Chung, Han-Shik;Lee, Yong-Hun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.10
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    • pp.679-688
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    • 2008
  • Air-heating vaporizer usually is used to regasify LNG at satellite areas because of the small demand of natural gas there. The common type of air heating vaporizer which exists in the market is the longitudinally finned type with 8 fins, 55 mm fin length and 2mm fin thickness. To contribute in developing an efficient air-heating vaporizer, experiment on finned type air-heating vaporizer using 8 fins, 50mm(fin length) with 2 mm(fin thickness) which exist in the market and 4 fins, 75 mm(fin length) with 2 mm(fin thickness), which is proposed, were conducted. Then, both types of vaporizers are compared. The experiments were conducted in one hour by varying the ambient condition and the length of the vaporizer. The ambient air was controlled so that it has the same temperature, humidity and air velocity with air condition in every season available and the length was varied 4000 mm, 6000 mm and 8000 mm for each type of vaporizer. Additional experiment with longer duration, i.e. In this experiment, the main aspects in analyzing the characteristics of the air heating vaporizer the inlet-outlet enthalpy difference and the outlet temperature of the working fluid. $LN_2$ is used to substitute LNG because of safety reason. The results show that the characteristics of the finned type 4fin75le vaporizer are comparable to finned type 8fin50le vaporizer.

A Study on Performance Change of Gas Injector with Ambient Temperature Environment (주변 온도환경 변화에 따른 가스 인젝터 성능 변화에 대한 연구)

  • Kim, Ji-Yoon;Yang, Jeong-Jik;Kim, Jin-Ho;Seo, Ii-Won;Lim, Jong-Wan
    • Journal of the Korean Institute of Gas
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    • v.22 no.5
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    • pp.18-23
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    • 2018
  • This study tries to analyze the injection amount of injector according to the external environment temperature of CNG vehicle. Especially, We investigated the effect of low temperature environment on gas injector performance by measuring the variation of injection amount under the same conditions as in coldstart condition. This experimental compared two products with different spring characteristics. The experimental device consist of a fuel supply unit, a flowrate measurement unit, a temperature chamber, and an injector control unit (ECU). According to the test result, the initial injection amount of the injector is increased in the low temperature environment and the needle opening time is delayed according to the change of the spring length.

Fabrication and characteristics of La1-xSrxMO3(M = Fe, Co, Mn) formaldehyde gas sensors (La1-xSrxMO3(M = Fe, Co, Mn) 물질을 이용한 포름알데히드 가스센서의 제조와 특성)

  • Kim, H.J.;Choi, J.B.;Kim, S.D.;Yoo, K.S.
    • Journal of Sensor Science and Technology
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    • v.17 no.3
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    • pp.203-209
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    • 2008
  • Thick film formaldehyde (HCHO) gas sensors were fabricated by using $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramics. The powders of $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) were synthesized by conventional solid-state reaction method. By using the $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) paste, the thick-film formaldehyde sensors were prepared on the alumina substrate by silkscreen printing method. The experimental results revealed that $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramic powder has a perovskite structure and the thick-film sensor shows excellent gas-sensing characteristics to formaldehyde gas (sensitivity of $La_{0.8}Sr_{0.2}FeO_3$, S= 14.7 at operating temperature of $150^{\circ}C$ in 50 ppm HCHO ambient).

Seasonal Variation of Atmospheric Polycyclic Aromatic Hydrocarbons (PAHs) on Anmyeon Island (안면도에서 대기 중 가스상 PAHs의 계절적 변동)

  • An, Joon-Geon;Yim, Un-Hyuk;Shim, Won-Joon;Kim, Gi-Beum;Kim, Seung-Kyu;Yi, Hi-Il
    • Ocean and Polar Research
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    • v.31 no.2
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    • pp.189-198
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    • 2009
  • Passive air samplers with polyurethane foam (PUF) disks were employed to determine seasonal gas phase variation of polycyclic aromatic hydrocarbons (PAHs) in ambient air on Anmyeon island from March 2007 to January 2008. Sum of 13 PAHs ranged between $3.5\;ng/m^3$ and $27.6\;ng/m^3$. Total PAHs during the heating season was 6.2 times higher than non-heating season. The dominant PAHs components during sampling periods were low and middle molecular weight PAHs including phenanthrene, fluoranthene, pyrene and chrysene. Gas exchange fluxes of PAHs across the air-water interface of the Yellow Sea were calculated using a modified two-film exchange model. PAHs fluxes ranged from $196\;ng/m^2/d$ net volatilization during summer to $3830\;ng/m^2/d$ net absorption during winter. Passive air sampler provides a convenient and cost-effective tool for measuring averaged gas phase PAHs, which was successfully used for calculation of gas exchange flux of PAHs in the Yellow Sea.

Sensing Characteristics of ZnO-based Ethanol Gas Sensor on Ga-doped Nanowires by Hot Walled Pulsed Laser Deposition (온벽 펄스 레이저 증착법을 이용해 합성한 Ga 도핑된 산화아연계 나노선 에탄올 가스 센서의 특성)

  • Jung, Da-Woon;Kim, Kyoung-Won;Lee, Deuk-Hee;Debnath, Pulak Chandra;Kim, Sang-Sig;Lee, Sang-Yeol
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.7
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    • pp.594-598
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    • 2011
  • We have investigated the sensing properties of ethanol gas sensor with pure ZnO and Ga-doped ZnO nanowires on Au coated (0001) sapphire substrates grown by hot walled pulsed laser deposition. Randomly aligned ZnO nanowires arrays were grown on a Au-electrode patterned under ambient conditions. ZnO nanowires have various sizes and shapes with a different substrate position inside a furnace. The average of length and diameter of the ZnO nanowires were $8\;{\mu}m$ and 100 nm respectively, and confirmed by field emission scanning electron microscopy. Sensitivity chanege characterization of the gas sensor was found that measured sensitivities of the ethanol gas sensors were 83.3% and 68.3% at $300^{\circ}C$ respectively.

Analytical Study on the Gas-Solid Suspension Flows through Sonic and Supersonic Nozzles (음속 및 초음속 노즐을 통한 Gas-Solid Suspension 유동에 대한 해석적 연구)

  • Sun, JianGuo;Rajesh, G.;Kim, Heuydong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.1
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    • pp.9-17
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    • 2013
  • A considerable deal of work has been carried out to get an insight into the gas-solid suspension flows and to specify the particle motion and its influence on the gas flow field. In this paper an attempt is made to develop an analytical model to study the effect of nozzle inlet/exit pressure ratio, particle/gas loading and the particle diameter effect on gas-solid suspension flow. The effect of the particle/gas loading on the mass flow, Mach number, thrust coefficient and static pressure variation through the nozzle is analyzed. The results obtained show that the presence of particles seems to reduce the strength of the shock wave. It is also found that smaller the particle diameter is, bigger will be the velocity as bigger particle will have larger slip velocity. The suspension flow of smaller diameter particles has almost same trend as that of single phase flow with ideal gas as working fluid. Depending on the ambient pressure, the thrust coefficient is found to be higher for larger particle/gas loading or back pressure ratio.

Measurement of Volatile Organic Sulfur Compounds in Ambient Air by Canister and Tedlar-bag Sampling Method (캐니스터와 Tedlar-bag 시료채집법을 이용한 대기 중의 휘발성유기황화합물의 측정)

  • 전선주;허귀석
    • Journal of Korean Society for Atmospheric Environment
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    • v.15 no.4
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    • pp.417-428
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    • 1999
  • The measurement of VOSCs(volatile organic sulfur compounds) in the air is nowadays a very important environmental research field. It is, however, very difficult because the concentration of the VOSC in ambient air is usually very low and the high reactivity makes it difficult to keep in container without loss of recovery. In this study, sampling method with cryogenic preconcentration is evaluated for analysis of atmospheric VOSC such as $CH_3SH,\;CH_3CH_2SH,\;CH_3SCH_3,\;CS_2,\;CH_3SSCH_3,\;CH_3SCH_2SCHA_3,\;and\;C_2H_5SSC_2H_5$ analyzed by GC-MS or GC-FID. Repeatabilities of measurement accompanied with preconcentration for 3-successive runs were in the range of 0.2~1.0% as a relative standard deviation. Stabilities up to 13 days were measured in 6 L canister and 10 L tedlar bag filled with VOSCs in ppb level. Higher stability was observed in tedlar bag as compared to canister with glass coated inner walls, and thiol compounds show dramatic losses in canister within 2~3 days. It is found that recovery over 70% was obtained in a week for all tested VOSCs when the compounds from ambient air matrix were stored in tedlar bag. It is also found that the stabilities of VOSCs are depending on humidity and coexisting compounds in matrix gas due to sample adsorption onto inner surface and reactivity. The results indicate the possibility and limitations of VOSC analysis in ambient air using container sampling method with cryogenic preconcentration.

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Characteristics of Contamination and Fate for PCDD/Fs in Ambient Air, Cheongju (청주지역 대기 중 PCDD/Fs 오염특성 및 거동)

  • Kim, Kyoung-Soo
    • Journal of Korean Society of Environmental Engineers
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    • v.31 no.4
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    • pp.294-299
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    • 2009
  • To investigate the pollution levels and behavior of PCDD/Fs in ambient air, gaseous and particulate phase concentrations were measured at Cheongju city in 2008. The samples were collected at 3 sites (industrial, residential/commercial and rural region) by season (winter, spring and summer). The concentrations and TEQ concentrations of PCDD/DFs ranged from 0.73 to 2.43 pg/$m^3$ and from 0.007 to 0.122 pg TEQ/$m^3$, respectively. These levels were similar or lower than that of other domestic researches (from n.d. to 2.149 pg TEQ/$m^3$). The concentration of PCDD/Fs in particulate phase (from 54% to 98% against total concentration) were higher than that of gas phase. As a results of comparison of congener patterns and statistical analysis, PCDD/Fs was mainly influenced by a combustion process in ambient air, Cheongju city.

Structural and electrical characteristics of IZO thin films deposited under different ambient gases (분위기 가스에 따른 IZO 박막의 구조적 및 전기적 특성)

  • Lee, Yu-Lim;Lee, Kyu-Mann
    • Journal of the Semiconductor & Display Technology
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    • v.9 no.3
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    • pp.53-58
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    • 2010
  • In this study, we have investigated the effect of the ambient gases on the characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering under various ambient gases (Ar, $Ar+O_2$ and $Ar+H_2$) at $150^{\circ}C$. In order to investigate the influences of the oxygen and hydrogen, the flow rate of oxygen and hydrogen in argon mixing gas has been changed from 0.1sccm to 0.5sccm, respectively. All the samples show amorphous structure regardless of ambient gases. The electrical resistivity of IZO film increased with increasing flow rate of $O_2$ under $Ar+O_2$ while under $Ar+H_2$ atmosphere the electrical resistivity showed minimum value near 0.5sccm of $H_2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO substrates made by configuration of IZO/${\alpha}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current densityvoltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.