• Journal of Advanced Marine Engineering and Technology
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• 제31권3호
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• pp.263-271
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• 2007

The heat transfer coefficient and pressure drop during 9as cooling process of $CO_2$ (R744) in a helically coiled copper tube with the inner diameter of 4.55 mm and outer diameter of 6.35 mm were investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter a pre-heater and a helically coiled type gas cooler (test section). The refrigerant mass fluxes are varied from 200 to $800kg/m^2s$ and the inlet pressures of gas cooler are 7.5 to 10.0 MPa. The heat transfer coefficients of $CO_2$ in a helically coiled tube are higher than those in a horizontal tube. The Pressure drop of $CO_2$ in the gas cooler shows a relatively good agreement with those predicted by Ito's correlation developed for single-phase in a helically coiled tube. The local heat transfer coefficient of $CO_2$ agrees well with the correlation by Pitla et al. However. at the region near pseudo-critical temperature. the experiments indicate higher values than the Pitla et al correlation. Therefore, various experiments in helically coiled tubes have to be conducted and it is necessary to develop the reliable and accurate prediction determining the heat transfer and pressure drop of $CO_2$ in a helically coiled tube.

• 설비공학논문집
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• 제19권12호
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• pp.842-849
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• 2007

For a $CO_2$ two-stage twin rotary compressor used for heat pump water heater system, changes of $CO_2$ solubility in PAG oil were investigated along the gas passages from the first stage suction to final discharge. Only slight changes in solubility took place in suction chambers for both of the first and second stages, but for compression chambers, solubility variation ranged from 0.115 to 0.136, and from 0.133 to 0.182, respectively for the first and second stages. Calculation of gas flashing in parts of leakage oil flows and of oil contained in control volumes due to solubility changes was conducted and included in gas pressure calculation. For the second stage, gas flashing amounts to around $5%\sim6%$ for most leakage flows. Cooling capacity, compressor input, and COP obtained by calculation were well compared to the experimental results. Effects of operation speed on the compressor performance was also studied: as the shaft speed increased, adiabatic efficiency decreased rapidly due to increased over-compression loss.

• 한국정밀공학회지
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• 제29권1호
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• pp.121-125
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• 2012

This paper presents the friction and anti-wear characteristics of nano-oil with a mixture of a refrigerant oil and carbon nano-particles in the thrust slide-bearing of scroll compressors. Frictional loss in the thrust slide-bearing occupies a large part of total mechanical loss in scroll compressors. The characteristics of friction and anti-wear using nano-oil is evaluated using the thrust bearing experimental apparatus for measuring friction surface temperature and the coefficient of friction at the thrust slide-bearing as a function of normal loads up to 4,000 N and rotating speed up to 3,200 rpm. It is found that the coefficient of friction increases with decreasing rotating speed and normal force. The friction coefficient of carbon nano-oil is 0.023, while that of pure oil is 0.03 under the conditions of refrigerant gas R-22 at the pressure of 5 bars. It is believed that carbon nano-particles can be coated on the friction surfaces and the interaction of nano-particles between surfaces can be improved the lubrication in the friction surfaces. Carbon nano-oil enhances the characteristics of the anti-wear and friction at the thrust slide-bearing of scroll compressors.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.76-76
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• 2008

갈륨-질화물(GaN) 기반의 고속전자이동도 트랜지스터(high electron mobility transistor, HEMT)는 최근 마이크로파 또는 밀리미터파 등의 고주파 대역의 통신시스템에 널리 사용되는 전자소자이자, 차세대 고주파용 전력 소자로 각광받고 있다. AlGaN/GaN HEMT에서 AlGaN층과 GaN층의 이종접합 구조(heterostructure)는 두 물질 간의 큰 전도대의 불연속성으로 인해 발생하는 이차원 전자가스(two-dimensional electron gas, 2DEG) 채널을 이용하여 높은 전자이동도, 높은 항복전압 및 우수한 고출력 특성을 얻는 것이 가능하다. 그러나 이린 이론적인 우수한 특성에도 불구하고 실제 AlGaN/GaN HEMT 소자에서는 AlGaN 표면과 AlGaN과 GaN 층 사이 접합면, AlGaN과 GaN 벌크층에 존재하는 트랩의 영향으로 이론보다 낮은 DC 출력 특성을 갖는다. 본 논문에서는 표면, 접합면, 벌크 층에 존재하는 트랩들을 각각의 존재 유무에 따라 시뮬레이션 함으로써 각각의 트랩이 DC 특성에 미치는 영향에 대해서 알아본다. 또한 소스와 게이트, 드레인과 게이트간의 거리에 따라 표면 트랩에 따른 영향과 AlGaN층과 GaN 층의 두께를 변화시켜가면서 각 층의 두께에 따라 벌크 트랩이 DC 특성에 미치는 영향을 알아보았다. 본 논문에서 트랩에 따른 특성의 파악을 위해서 $ATLAS^{TM}$를 이용하여 전산모사 하였다.

• Bulletin of the Korean Chemical Society
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• 제30권11호
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• pp.2589-2594
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• 2009

Aging phenomena of plasma polymer films were studied by using the surface analysis techniques of contact angle measurement, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), and atomic force microscopy (AFM). The polymer films were grown on an aluminum substrate by using a plasma polymerization method from a gas mixture of acetylene and helium, and the films were subsequently modified to have a hydrophilic surface by oxygen plasma treatment. Aging of the polymer films was examined by exposing the samples to water and air environments. The aging process increased the hydrophobicity of the surface, as revealed by an increase in the advancing contact angle of water. XPS analysis showed that the population of oxygen-containing polar groups increased due to the uptake of oxygen during the aging, whereas TOF-SIMS analysis revealed a decrease in the polar group population in the uppermost surface layer. The results suggest that the change in surface property from hydrophilic to hydrophobic nature results from the restructuring of polymer chains near the surface, rather than compositional change of the surface. Oxidative degradation may enhance the mobility and the restructuring process of polymer chains.

• Journal of Mechanical Science and Technology
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• 제14권6호
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• pp.597-604
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• 2000

Low noise of air-conditioners is one of the most important issues because of the users' strong demand. The main source of noise in an air-conditioner is the compressor. Therefore, noise reduction in a compressor is quite significant as an element technology in the air-conditioner field. Recently, scroll compressors are widely used, because they feature low noise, due to less pulsation of gas pressure, than that of rotary compressors. For reduction of noise, the source of noise must be identified. This paper presents a detailed analysis to identify the noise source and shows the dominant factors of noise of the scroll compressor, which will make it possible to design a scroll compressor with low noise.

• 연구논문집
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• 통권27호
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• pp.109-118
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• 1997

Kerosene Burner has widely used in domestic heating appliance. Higher combustion efficiency is required to save fuel and clean exhaust gas. The combustion characteristics in kerosene burner highly depends on the performance of evaporating liquid kerosene. And performance of evaporating effect on generation of tar. In this study, flow and heat transfer of kerosene burner is simulated by FLUENT/UNS using unstructured mesh system and discrete phase model to analyze performance of evaporating kerosene liquid. The simulated results show very complicated flow pattern and back flow at the exit of burner.

• 한국수소및신에너지학회논문집
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• 제7권2호
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• pp.193-206
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• 1996

The simplest and lightest element-hydrogen is an alternative fuel which provides a clean and renewable energy source. Hydrogen can be used to power gas-type appliance and modified automobiles with water vapor as the only byproduct of combustion. Historically, production of hydrogen from coal was one of the mass production technology of hydrogen. In this paper, the status of hydrogen production process from coal was investigated to review the current situation of hydrogen production and utilization.

• 한국안전학회지
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• 제31권6호
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• pp.25-31
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• 2016

This paper has analyzed the structure, applicable regulations and the resistance characteristics of insulation ring type of CSST (Corrugated Stainless Steel Tubing for Gas). With the flammability test conducted in accordance with KS C IEC 60811-1-1, the evaluation of insulation resistance, temperature characteristics, and reliability has been conducted. An insulation ring type CSST consists of protective coating, tube, nut, insulation ring, packing, socket, and ball valve. Connecting an insulation ring type CSST to gas tubings for gas appliance is not permitted, moreover, the product shall be installed inside a sleeve pipe in case of buried installation such as the ceiling. Damages on protective coating and tube were detected when fire was applied to the test sample with a portable torch for 60 seconds. The insulation resistance of a normal product was $49.59M{\Omega}$, while that of the product completed the flammability test reduced to $9.21M{\Omega}$. The mean insulation resistance within the confidence Interval of 95% using the mini tap program 17 was $49.59M{\Omega}$ and the mean insulation resistance within the confidence interval reduced to $9.21M{\Omega}$. In the normal distribution analysis of 95% confidence interval, the value-P of the normal product was stable at 0.075 and AD(Anderson-Darling) statistic value was turned out to be 0.063, which is very normal, and the standard deviation was analyzed as 0.2586. The value P of the product completed the flammability test resulted in 0.005, the AD was 1.355 and the standard deviation reduced to 0.07908.

• 한국식생활문화학회지
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• 제21권3호
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• pp.319-324
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• 2006

묵은 배추김치의 휘발성 성분들을 고진공승화법을 이용하여 분리, 농축하였으며, GC-MS로 분석하였다. 총 62가지의 휘발성 성분들이 검출되었으며, 7개의 sulfur-containing compounds, 8개의 terpenes, 5개의 esters, 8개의 acids, 15개의 alcohols, 2개의 nitriles, 2개의 ketones, 11개의 aliphatic hydrocarbons, 4개의 miscellaneous compounds등으로 구성되어 있었다. 이 중 특히, acids인 acetic acid와 butanoic acid가 높은 함량을 나타내었다. 묵은 배추김치에서 향기활성성분을 규명하기 위해 고진공승화법을 이용하여 휘발성 성분들을 분리 및 농축 후 향 추출물 희석분석법으로 flavor dilution(FD) factor($Log_3FD$)를 구하였으며, GC-MS 및 GC-Olfactometry(GC-O)법으로 휘발성 성분들을 동정하였다. 이 결과 묵은 배추김치에서 총 16종의 화합물이 검출되었다. 이중 시큼한 냄새, 군덕내의 특성을 지닌 acetic acid, butanoic acid가 높은 FD factor를 보였으며, acids외에 높은 (FD > 9)를 나타내는 성분들로는 linalool, 2-vinyl-4H-1,3-dithin 등이 있었다.