• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.7-13
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• 2010

To satisfy the needs on fuel economy and engine performance, continuous variable valve lift systems are applying to engines. In the CVVL system, fuel economy can be improved by reducing pumping loss during the induction process, and engine performance can be also improved by controlling volumetric efficiency and the residual gas fraction. Because the residual gas fraction directly affects volumetric efficiency, engine performance, combustion efficiency and emissions in SI engines, controlling residual gas fraction is one of the important things in engine development process. This analysis investigates the residual gas fraction and volumetric efficiency with changes of intake valve lifts and intake valve timings. In this study, unsteady state solutions were solved during exhaust and induction processes. Results show variation of the residual gas fraction and volumetric efficiency by changing intake valve timing and lift. Decreasing intake valve lift leads to increase the residual gas fraction and to decrease volumetric efficiency.

• Journal of the Korean Institute of Gas
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• v.23 no.4
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• pp.65-73
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• 2019

A spiral steel pipe has been more used widely as a structural member as well as transport pipeline because the pipe can be manufactured continuously, consequently more economical than the conventional UOE pipe. As improved pipe manufacture technology makes spiral pipes to have high strength and to have larger diameters, the spiral pipes have been recently used as long distance transport pipeline with a large diameter and strain-based design is thus required to keep structural integrity and cost effectiveness of the spiral pipe. However, design codes of spiral pipe have not been completely established yet, and structural behaviors of a spiral pipe are not clearly understood for strain-based design. In this paper, the effects of residual stresses due to the spiral pipe manufacture process are investigated on the flexural behavior of the spiral pipe. Finite element analyses were conducted to estimate residual stresses due to the manufacturing process for the pipes which have different forming angle, thickness, and strength, respectively. After that, the results were used as initial conditions for flexural analysis of the pipe to numerically investigate its flexural behaviors.

• Journal of Energy Engineering
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• v.12 no.1
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• pp.1-10
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• 2003

Pressurized fluidized bed combustion unit is operated at pressures of 1~1.5 MPa with combustion temperatures of 850~87$0^{\circ}C$. The pressurized coal combustion system heats steam, in conventional heat transfer tubing, and produces a hot gas supplied to a gas turbine. Gas cleaning is a vital aspect of the system, as is the ability of the turbine to cope with some residual solids. The need to pressurize the feed coal, limestone and combustion air, and to depressurize the flue gases and the ash removal system introduces some significant operating complications. The proportion of power coming from the steam : gas turbines is approximately 80:20%. Pressurized fluidized bed combustion and generation by the combined cycle route involves unique control considerations, as the combustor and gas turbine have to be properly matched through the whole operating range. The gas turbines are rather special, in that the maximum gas temperature available from the FBC is limited by ash fusion characteristics. As no ash softening should take place, the maximum gas temperature is around 90$0^{\circ}C$. As a result a high pressure ratio gas turbine with compression intercooling is used. This is to offset the effects of the relatively low temperature at the turbine inlet.

• The Korean Journal of Nuclear Medicine Technology
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• v.14 no.1
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• pp.8-12
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• 2010

Purpose: In $^{18}F$-FDG automated synthesizer, deliver is done in automated mode after synthesis until the dispenser. After the delivery, the yield is calculated from the radioactivity which was read by the dose calibrator located in the dispenser. However, when the distance between the automated synthesizer and the dispenser is far, there are $^{18}F$-FDG residues, which results in loss of the amount of $^{18}F$-FDG. This study investigated the usefulness of a method that minimizes $^{18}F$-FDG residues. Materials and Methods: The structure of the tubing between the (TRACERlab Mx FDG; GE.) and the dispenser is that the distance is 8 m and the internal diameter is 1/16 inch. The synthesis process of The module goes through the synthesis process of trap, synthesis, delivery in the automated module. The time taken for synthesis is about 25 to 26 minutes, after which rinsing is done. However, after rinsing, as the distance of the tubing increased, there were 10~13% of $^{18}F$-FDG residues. Therefore, a method of using push syringe and $N_2$ gas in manual mode to minimize $^{18}F$-FDG residues is analyzed. Results: In manual mode, there were $^{18}F$-FDG residues of 4~5% for the push syringe, and there were $^{18}F$-FDG residues of less than 1% for the $N_2$ gas, which showed that the method using $N_2$ gas had superior usefulness. Also, there were no $^{18}F$-FDG residues in the cleaning the next day. Conclusion: The distance between the synthesizer and the dispenser needs to be reduced as much as possible, to reduce the rate of loss of $^{18}F$-FDG resulting from the distance of the tubing. However, in case the distance between the synthesizer and the dispenser has to be increased due to the system structure, using push syringe and $N_2$ gas simultaneously is a useful method for minimizing $^{18}F$-FDG residues.

• Journal of the Korean Institute of Gas
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• v.17 no.6
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• pp.46-51
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• 2013

Composite cylinder is used by hydrogen fuel cell vehicles and natural gas vehicles because of high specific modulus, specific strength and fatigue resistance. composite cylinder has a seamless integrated liner and it is fully overwrapped with structural fibers of high strength carbon fibers in an epoxy matrix. In this study, filament winding pattern and autofrettage pressure design technique are presented considering structural weakness of knuckle and compressive residual stress. Presented methodology is verified by pressure cycling test of composite cylinders.

• Journal of the Korean Vacuum Society
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• v.4 no.1
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• pp.77-84
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• 1995

LCD용 다결정 실리콘 TFT의 제조에 요구되는 고품위의 다결정 실리콘 박막을 60미만의 저온 공정으로 제조하는 기술로 비정질 박막의 고상 결정화(solid phase crystallization) 가 유망하다. 본 연구에서는 고진공 화학증착기를 이용하여 증착된 비정질 실리콘 막의 고상결정거동에 대해 연구하였다. 고상 결정화 속도 및 결정화 후의 결정성(결정립 크기 및 결함 밀도) 화학증착시의 증착가스의 종류(SiH4 혹은 Si2H6), 공정 압력, 증착 온도 등에 민감한 영향을 받으며 Si2H6가스의 사용, 증착 압력의 증가, 증착온도의 감소는 최종 결정립의 크기를 현저히 증가시킨다. 또한 증착전의 기초 진공도를 높임으로써 반응기 잔류 가스에 의한 산소나 탄소 등의 막내 유입이 감소되어 결정화 속도가 증가하고 결정성이 향상되었다.

• The Korean Journal of Rheology
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• v.8 no.3_4
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• pp.207-214
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• 1996

사출성형은 많은 장점과 유용성에도 불구하고 싱크마크나 휨과 같은 변형문제를 피 하기 어렵다. 이것은 성형품의 부위별 온도분포 및 냉각속도 차이에 의한 잔류응력에 기인 하는 것으로 구조가 복잡하거나 크기가 쿤 경우에 더욱 더 문제가 되기 쉽다. 이와 같은 문 제를 해결하기 위하여 성형품의 내부에 기포를 형성시켜 수지의 수축분을 기포의 성장으로 보상하여 주는 가스사출성형이 개발되어 많이 활용되고 있는 실정이다. 한편 일반 가스성형 과 달리 수지를 완전히 채운후 저압의 공기를 이용하여 기포를 발생시켜 수지의 체적수축분 을 보상해주는 PFP성형기술은 가스사출의 나점인 공기의 유동조절문제를 해결하고 비용이 저렴한 등의 잇점을 가지고 있다. 이 과정은 가스성형공정의 2차 침투과정과 매우 유사하나 아직까지 이에대한 이해나 연구는 매우 부족한 실정이다 본 연구는 기포의 성장이 수지의 체적수축에 의한 것이라는 가정에 근거하여 기포성장길이에 관한 모델링을 수행한 것이다. 실험결과와의 비교를 통하여 기본 가정에 대한 타당성을 검증하고 여러 인자들의 영향을 살 펴보았다. 본 연구는 PFP성형공정에 대한 이해를 증진시켜 금형설계 및 성형조건 설정에 대한 가이드라인을 제시하며 아울러 PFP공정에 대한 보다 체계적인 이해 및 일반가스성형 의 2차 침투과정 등의 관련 현상에 대한 이해 및 연구에 도움이 될것으로 기대된다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.1
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• pp.15-22
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• 2014

Multiple devices have been installed to reduce exhaust emissions and to increase thermal efficiency. Those devices reduce the exhaust pipe opening area and increase the exhaust gas pressure. The pressure increase disturbs a gas flow and has a bad effect on the engine performance. However there is some study that NOx can be reduced with exhaust gas pressure increase. In this study an engine performance is tested with various opening ratios. The result shows that the fuel consumption rate is reduced in case of little amount of the pressure increase, and NOx is reduced with the pressure increase, while the concentration of the toxic exhaust gases are increased in the case of high back-pressure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.45-51
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• 2015

In order to meet the enforced emission regulations and reduce fuel consumption, various new technologies are employed in engines. The problem of NOx emissions under a lean mixture condition should be solved, because a lean-burn direct-injection engine can realize stable lean combustion with a stratified mixture, which results in improvements in fuel economy and emissions. This study investigated the effects of intake and exhaust valve timing changes on the performance and emission characteristics of a lean-burn LPG direct-injection engine. Under a partial-load operating condition without throttling, an increase in the intake valve opening led to an increase in NOx emissions due to an increase in the amount of excess air. The fuel consumption deteriorated with an increase in the exhaust valve opening due to a decrease in the expansion work and an increase in the pumping loss.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.179-179
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• 2016

희토류계 영구자석은 높은 보자력과 잔류 자화을 가지고 있어 자기기록저장매체, MEMS(엑츄에이터), 센서 등의 응용 분야에 적용시키기 위해 다양한 연구들이 진행되고 있다. 하지만 희토류계 원소의 수급 및 가격의 문제점으로 친환경자석으로의 전환 및 희토류나 중희토류를 사용하지 않는 비희토류계 영구자석을 개발하는 연구에 대한 필요성이 대두되고 있다. 이 중 Fe-N 계 자성 물질인 $Fe_{16}N_2$는 포화 자화 값이 현재까지의 자성물질 중 가장 높은 값(240emu/g)을 나타내며 상대적으로 높은 결정자기이방성 상수를 가지고 있어 비희토류계 영구자석 물질 중 하나로 주목받고 있다. 본 연구에서는 $Fe_{16}N_2$ 박막을 얻기 위해 DC Magnetron Sputtering 방법을 이용하여 Si wafer 위에 박막을 증착하고 증착공정 조건 중 질소 유량 및 Sputtering Power를 변수로 따른 박막의 성장, 조직변화, 자성 특성을 관찰을 통해 최적의 공정 조건을 찾고자 하였다. $N_2$ 가스 유량 변화에 따른 박막의 성장 속도는 거의 변화가 없었으며 $N_2$ 가스 유량의 증가에 따라 박막 내 Fe의 함유량은 감소하였다. 모든 공정 조건에서 $Fe_3N$, $Fe_4N$, $Fe_{16}N_2$ 상들이 섞여 성장하였으며 XRD를 통한 상분석과 더불어 VSM을 통한 자성 특성을 분석해본 결과 $Fe_{16}N_2$의 분율이 가장 높게 성장된 공정 조건은 Power는 200W, $N_2$ 가스 유량은 20sccm이었으며 이 조건에서 2.45T의 포화 자화 값과 1.4T의 잔류 자화 값을 얻을 수 있었다.