• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.221.2-221.2
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• 2015

Graphene is very interesting 2 dimensional material providing unique properties. Especially, graphene has been investigated as a stretchable and transparent conductor due to its high mobility, high optical transmittance, and outstanding mechanical properties. On the contrary, high sheet resistance of extremely thin monolayer graphene limits its application. Artificially stacked multilayer graphene is used to decrease its sheet resistance and has shown improved results. However, stacked multilayer graphene requires repetitive and unnecessary transfer processes. Recently, growth of multilayer graphene has been investigated using a chemical vapor deposition (CVD) method but the layer controlled synthesis of multilayer graphene has shown challenges. In this paper, we demonstrate controlled growth of multilayer graphene using a two-step process with multi heating zone low pressure CVD. The produced graphene samples are characterized by optical microscope (OM) and scanning electron microscopy (SEM). Raman spectroscopy is used to distinguish a number of layers in the multilayer graphene. Its optical and electrical properties are also analyzed by UV-Vis spectrophotometer and probe station, respectively. Atomic resolution images of graphene layers are observed by high resolution transmission electron microscopy (HRTEM).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.220-227
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• 2000

The purpose of this study is to develop the non-gravity fluidized dryer. In this non-gravity fluidized dryer the fluidized zone is produced by two paddles in mixer, which maximizes the surface area of materials and then heated air through the guiding panels dehumidify them. This can conduct the drying process quickly and control moisture contents to lower limits. The ventilation system is closed loop system, which can be changeable to open system, and can be used as a multi-purposed dryer in which mixing, drying, granulating and cooling process is conducted. In order to develop non-gravity fluidized dryer, in the first the fundamental experiments performed to mixing accuracy and then the other parts of dryer and control system were examined to check whether they were designed properly and operated harmoniously with mixer. Also the preparatory experiments were fulfilled to examine the efficiency and reliability of dryer. Lastly, on the basis of preparatory experiments in case the initial moisture contents, desired moisture contents, heated air velocity and heating temperature were vary, performance test for the non-gravity fluidized dryer carried out.

• Journal of Biosystems Engineering
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• 제8권2호
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• pp.39-48
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• 1983

This study was performed to obtain the basic data which could be used for the modification of the manual center-burner-type rice-husk furnace into a small scale automatic type for the multi-purpose use in the farm. For this purpose, first, the utilization feasibility of the rice-husk furnace in the farm was analyzed briefly in aspects of available amount of rice-husk for the fuel, annual operation time and replaceble amount of residential heating energy with rice-husk in the farm. For the experiment a prototype furnace geared with an automatic feeding device was fabricated, and feed rate, mold size and chimney height were changed to investigate the combustion efficiency of rice-husk and thermal efficiency of the furnace. Also, optimum and limiting operational factors were observed in each treatments. The results obtained are summarized as follows. 1. If the rice-husk is intensively used for residential heating in the farm for winter season, on an average 51 percent of the total heating energy can be replaced with the rice-husk. Therefore, development of a small scale automatic rice-husk furnace was recognized to be feasible. 2. The operational condition depending on husk-feed rates was very important factor for successive steady burning operation of the given furnace. When the feed-rate was 1.5 kg/hr, the top of the burning zone should be kept at the position about 55 cm from the bottom of the combustion chamber with the periodic removal of ash (termed as steady state position), which was 18 cm above the mold waist. When the feed rates were 2.4 kg/hr and 3.0 kg/hr, the steady state position was at about 4 cm above the mold waist. 3. The mold size affected inflow rate of air into the furnace and consequently CO content in the exhaust gas. The relatively bigger mold gave positive effect on the air-inflow rate. 4. When the husk-feed rates were 1.5 kg/hr, 2.4 kg/hr, 3.0 kg/hr, the combustion efficiencies of the rice-husk were 98.5%, 97.4% and 95.0%, the thermal efficiencies of the furnace were 93.4%, 93.2% and 87.6%, and CO content in the exhaust gas were 1.21%, 1.03%, and 2.43%, respectively. The air-inflow rates were decreased with the increase of feed rates. When the amount of excess air was 30-40%, the CO content in the exhaust gas was at the minimum level. 5. When the chimney height was lowered from 260 cm to 96 cm, the air-inflow rate was slightly decreased, but the average temperature in the combustion chamber, CO content in the exhaust gas and combustion and thermal efficiencies were not changed significantly. 6. The incidental problems associated with the protytype furnace were accumulation of the ash inside the mold, accumulation of the cinder between the outer-drum of the furnace and the combustion chamber wall, and accumulation of the cinder in the chimney.

• 한국해양공학회지
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• 제25권6호
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• pp.66-71
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• 2011

Recently, the production of shipbuilding and offshore plant industries, with a trend toward large structures, has led to an increased use of high strength ultra-thick plates. The use of ultra-thick plates increases the welding tasks, and the welding process generates distortion and residual stress in the weldment because of the rapid heating and cooling. Welding distortion and residual stress in the welded structure resulte in many troubles such as deformation and life deterioration. In particular, the welding residual stress has an important effect on welding deformation, fatigue, buckling strength, brittleness, etc. The purpose of this study was to evaluate the residual stress at a multi-pass weldment using an experimental method for EH36 high-tension steel. In this experimental method, AIS3000 was used to measure the residual stress of a welded part, HAZ, and base metal; EPMA and XRD were used to study the material properties.

• Advances in environmental research
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• 제4권3호
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• pp.143-153
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• 2015

The ventilation system is a key device to ensure both healthful indoor air quality (IAQ) and thermal comfort in buildings. The ventilation system should make the IAQ meet the standards such as ASHRAE 62. This study deals with a new approach to modeling the ventilation and IAQ requirement in residential buildings. In that approach, Elite software is used to calculate the air supply volume, and CONTAM model as a multi-zone and contaminant dispersal model is employed to estimate the contaminants' concentrations. Amongst various contaminants existing in the residential buildings, two main contaminates of carbon dioxide ($CO_2$) and carbon monoxide (CO) were considered. CO and $CO_2$ are generated mainly from combustion sources such as gas cooking and heating oven. In addition to the mentioned sources, $CO_2$ is generated from occupants' respirations. To show how that approach works, a sample house with the area of $80m^2$ located in Tehran was considered as an illustrative case study. The results showed that $CO_2$ concentration in the winter was higher than the acceptable level. Therefore, the air change rate (ACH) of 4.2 was required to lower the $CO_2$ concentration below the air quality threshold in the living room, and in the bedrooms, the rate of ventilation volume should be 11.2 ACH.

• 공업화학
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• 제31권4호
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• pp.443-451
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• 2020

본 연구에서는, 축분 고형연료의 연료적 가치를 판단하기 위해 물리화학적 특성과 열분해 동역학 분석을 수행하였다. 원소분석과 공업분석결과는 축분 고형연료는 휘발성 물질(64.94%), 탄소(44.35%) 및 수소(5.54%)의 함량이 높았다. 축분 고형연료의 저위발열량(3,880 kcal/kg) 또한 가축분뇨 고형 연료 기준(3,000 kcal/kg)보다 높았다. 열중량분석결과 축분연료는 3개의 분해온도구간을 가졌다. 첫 번째 온도구간(130~330 ℃)은 추출물의 기화, 헤미셀룰로우스 및 셀룰로우스의 분해로 구성되었다. 두 번째(330~480 ℃)와 세 번째(550~800 ℃) 온도 구간들은 리그닌의 분해와 carbonaceous materials 분해에 의한 것이었다. Friedman, FWO, KAS 같은 model free 분석방법에 의해 구해진 축분 고형연료의 열분해에 대한 활성화 에너지 값은 전환율 0.1에서 0.9 범위에서 173.98에서 525.79 kJ/mol로 나타났다. 특히, 전환율이 0.6보다 높은 구간에서 활성화에너지가 크게 증가하였다. Curve fitting 방법을 사용한 동역한 분석은 축분 고형연료가 5단계의 분해 단계로 구분될 수 있는 다단계 반응에 의해 분해됨을 제안하였다.