• 에너지공학
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• 제11권3호
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• pp.276-282
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• 2002

본 논문에서는 압축공기를 작동매체로 한 저압용 vortex tube에 대한 에너지분리 과정을 상세히 연구하였다. 먼저 vortex tube에서 에너지 분리되어 나오는 온공기와 냉공기의 온도변화에 대하여 실험하였고, vortex tube의 안쪽표면의 최대벽면온도 변화와 vortex tube내의 온도분포를 통하여 vortex tube내 유동장에서의 정체점의 위치에 대한 유용한 정보를 얻게되었다. 이를 바탕으로 vortex tube의 최적 길이와 throttle의 형상, sleeve에 따른 에너지분리과정 등을 실험을 통하여 알아보았다. 또한 본 연구에서는 디젤기관의 배기에 적용하기 위한 외통을 사용하였다. 이때 vortex tube에서 나오는 은공기가 180$^{\circ}$돌아 나오면서 vortex tube의 바깥쪽 벽면을 가열하게 된다. 이러한 기하학적 형상을 통하여 에너지분리효과가 증대됨으로 인하여 디젤기관의 배기가스에 적용 시 고온유동의 온도를 높이고자함에 본 연구의 목적을 두고자한다.

• 비파괴검사학회지
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• 제26권3호
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• pp.174-180
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• 2006

Steam generator (SG) tubes are expanded inside tubesheet holes by using explosive or hydraulic methods to be fixed in a tubesheet. In the tube expansion process, it is important to minimize the crevice gap between expanded tube and tube sheet. In this paper, absolute and differential signals are computed by a numerical method for several different locations of tube expansion inside and outside a tubesheet and signal variations due to tubesheet, tube expansion and operating frequencies are observed. Results show that low frequency is good for detecting tubesheet location in both types of signals and high frequency is suitable for sizing of tube diameter as well as the detection of transition region. Also learned is that the absolute signal is good for measuring tube diameter, while the differential signal is good for locating the top of tubesheet and both ends of the transition region. In the case of mingled anomaly with tube expansion and tubesheet, low frequency inspection is found to be useful to analyze the mixed signal.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.49-53
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• 2001

Recently hydroforming process became a process which is increasingly applied in the automotive industry. As the hydroforming process is a new technology, there is no abundant data to assist manufacturing the products. To investigate the effects of process parameters on the tube hydroforming process, simple bulging, circular bulging and Tee-fitting tests are performed. The optimal leading path to escape the failure modes(bursting, wrinkling) is determined and the effects of the process parameters, the internal pressure and axial feeding on the product quality, such as thickness distribution, forming height and branch dome shape are investigated.

• Korean Chemical Engineering Research
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• 제47권6호
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• pp.795-800
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• 2009

본 연구는 Vortex tube 형 이산화탄소 흡수장치에서 연소배가스 중 $CO_2$ 흡수 특성을 고찰한 것이다. 연소배가스로는 석탄(유연탄)을 연료로 하는 증기발생량 12 ton/hr 규모의 순환유동층 연소보일러에서 발생한 것을 이용하였으며 이산화탄소농도는 11~13 vol% 내외이다. 흡수 용액은 MEA 20 wt%를 기준으로 AMP, HMDA, 강염기계 KOH를 혼합하였다. 본 연구의 목적은 $CO_2$ 흡수장치를 Scrubbing 방식보다 소형화하고, 흡수용액을 절감하는 것이다. 흡수장치는 연소배가스 유량 $20Nm^3/hr$를 처리할 수 있는 직경 17 mm, 길이 250 mm의 Vortex tube 형을 사용하였다. 연소배가스와 흡수용액의 혼합 분무를 통한 $CO_2$ 제거율을 측정하였다. 실험조건은 흡수용액 농도(20~50 wt%), 흡수용액 유량(1.0, $3.0{\ell}/min$)과 연소배가스 유량($6{\sim}15Nm^3/hr$)을 변화시켰다. 결과적으로, MEA에 HMDA를 혼합한 흡수용액의 $CO_2$ 제거율이 가장 우수(약 43% 제거율)하였으며, Vortex tube 장치에서 고속유동의 기 액 접촉효과 및 기 액 분리 특성을 이용하여 $CO_2$ 흡수가 가능하였다. 그러나 $CO_2$ 흡수 효율 향상을 위한 추가적인 공정개발이 요구된다.

• Elastomers and Composites
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• 제34권4호
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• pp.315-320
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• 1999

점착성과 소수성을 제거함으로써 실리콘 EVD 튜브의 성능을 향상시키기 위하여 저온 플라스마 공정을 이용한 실리콘 고무의 표면개질을 시도하였다. 고분자를 형성하지 않는 플라스마를 이용한 표면처리와 고분자를 형성하는 플라스마를 이용한 박막코팅 방법을 시도하였다. 박막코팅을 할 경우에 점착성이 특히 크게 줄어들었으며, 결과적으로 실험실 환경에서의 오염 정도를 줄일 수 있었다. 산소를 포함한 플라스마를 이응할 경우 튜브의 외부뿐만 아니라 내부의 표면을 친수성으로 개질시킴으로써, 결과적으로 수력학적 초기 저항을 줄일 수 있었다. 대부분의 경우에 있어서, 이러한 표면개질은 실리콘 튜브의 기계적 물성에 아무런 악영향을 끼치지 않았으며 영율, 인장강도, 인장율 등의 물성은 오히려 향상되었다.

• 대한기계학회논문집A
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• 제31권8호
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• pp.833-838
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• 2007

In tube hydroforming process, several defective products could be obtained such as bursting, wrinkling, folding, buckling. Because, especially, bursting is most frequently occurred failure among the well known failures, it is mostly important to predict the onset of bursting failure on tube hydroforming process. For most sheet metal forming processes, strain based forming limit diagram(FLD) is used often as a criteria to estimate the possibility of onset of the failures proposed above. However, FLD has a shortcoming that it is dependent on strain path while stress based diagram is independent on strain history. Generally, tube hydroforming consists of three main processes such as pre-bending, pre-forming, and hydroforming and it means that the strain histories of final products are nonlinear. Therefore, forming limit stress diagram(FLSD) is more suitable to predict forming limit for hydroforming parts. In this study, FLSD is applied to estimate bursting failure for an engine cradle of an automobile part. Consequently, it is proved that application of FLSD to predict forming limit is available for tube hydroforming parts.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.239-242
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• 2005

In the roll forming, a flat strip is progressively deformed by feeding it through a series of rotating rolls. There are various layouts for the tube toll-forming stages. The process sequences are as follows: leveling, roll-forming, welding, bead removing, seam annealing, cooling, sizing and cutting. Electric resistance welded(ERW) tubes have been widely used for the machinery parts, especially for hydroformed automotive parts. However conventional ERW tubes do not have a high formability because of hardening of welded portion by rapid cooling. Moreover the decrease in thickness of the welded portion during the grinding of the inner and outer bead may reduce the formability of the tube. In case of applying the tubular parts without grinding the bead, the flow of the fluid can be prevented due to the turbulent flow induced by the inner bead. In attempt to determine the optimal bead grinding amount in the roll forming process, in the present paper, the effects of the removal depth and width of the inner beads on the hydroformability are analyzed by the finite element simulation.

• Journal of the Korean Wood Science and Technology
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• 제28권4호
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• pp.10-16
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• 2000

Two wood decay ascomycetes fungi identified as Hypoxylon mammatum and H. truncatum were isolated from backyard of Korea Research Institute of Chemical Technology (KRICT) in Korea. Hypoxylon truncatum is newly recorded as a wood degrader in Korea. Unusual germination mechanisms of ascospores in H. mammatum and H. truncatum are described and illustrated. The differences between two species were noticed on the process of germ tube formation. In the process of germ tube formation, the fast movement to pigmented ascospores activated from their perispores was termed as spore eclosion that was only found in H. mammatum. This sophisticated recognition mechanism indicated the existence of specific eclosion and germ tube formation due to the composition of cell wall layers and their preferable host derive, based on examined two species under a genus. The observation on present study postulates different composition of wall layers of ascospore and different nutrient composition for germination.

• 한국정보시스템학회지:정보시스템연구
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• 제30권4호
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• pp.173-202
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• 2021

Purpose This study explored overall phenomena in context such as YouTube channel operation, strategy, and profit generation through interviews with two research participants who started their own businesses and are recognized as influencer on YouTube and analysis of viewer responses to uploaded contents. With the explosive growth of YouTube content provision and use, previous studies on YouTube are only being conducted individually on YouTube's content, influence, and content providers, so it is need to explore YouTube channel operations and the effect of revenue generation in context from an integrated perspective. Therefore, the purpose of this study is to present an integrated model that provides a specific process by contextually linking the factors and results influencing YouTube channel operation and revenue generation phenomena to individuals and companies who are trying to operate YouTube channels for the first time. Design/methodology/approach This study systematized and structured the overall phenomena in context such as YouTube channel operation, communication strategy, effect on revenue generation, and YouTube channel operation results by selecting interview subjects and collecting data through interviews, and analyzing viewer reactions (likes, comments, etc.). Due to the lack of previous studies exploring integrated phenomena, research analysis used Strauss & Corbin (1998)'s grounded theory approach, which presented inductive research methods to discover new theories by structuring concepts and categories based on detailed observations and information provided by interviewees. Findings The academic implication of this study is that while previous studies are conducted as individual studies on YouTube's content, influence, and content providers in the current situation where YouTube content provision and use are exploding, it integrally explores and presents an integrated model throughout the process. In addition, taking into account the lack of previous studies, it can be found in the aspect of using the grounded theory approach, an inductive theory approach that establishes a new theory. The practical implications can be found in that it presented practical directions to beginners who want to start operating YouTube channels by identifying operational preparations, communication strategies with viewers, and response management strategies.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.206-209
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• 2004

In the hydroforming process the number of process can be reduced by combining pre-forming process and post-forming process such as the bending, piercing and the embedding process. Integrated studies on the embedding manufacturing technology have been performed by analyzing the deformed mode of the tubes and the optimal process parameters. In this study, a simulation model that can prove clamping force between the clamping element and tube has been investigated by FEM. The characteristics of the embedded parts, such as the shape of the screw tip, screw thread and shape of thread were investigated at various clamping element conditions.