• Journal of Advanced Marine Engineering and Technology
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• 제34권4호
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• pp.477-484
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• 2010

현재 국내 수산건조제품의 대부분은 천일(태양)건조에 의하는 실정으로 보관과 유통상의 위생안전성과 품질면에서 심각한 문제점을 안고 있다. 본 논문은 생산 현장에서 운용이 쉽고, 경제적이면서도 최고 건조품질을 유지할 수 있는 현장 지향적 저온진공 건조시스템의 설계 개발을 목표로 건조시간 경과에 따른 무게 감소율과 온도변동에 관한 실험적 결과를 요약하여 보고한 것이다.

• 대한기계학회논문집A
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• 제33권11호
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• pp.1233-1238
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• 2009

This study analyzed the characterization of high temperature strength of $Si_3N_4$ composite ceramics additive based on variations in the amount of nano colloidal $SiO_2$ added. Semi-elliptical cracks about 100 ${\mu}m$ length were obtained from a Vickers indenter using a load of 24.5 N. The results showed that the heat-treated smooth specimens with $SiO_2$ nano colloidal coating exhibited the highest bending strength at 0.0 wt% $SiO_2$ nano colloidal added, which is amounted to a 187 % increase over that of smooth specimen. Limiting temperature for bending strength of crack-healed zone for bending strength was about 1273 K. However, the bending strength of SSTS-3 and SSTS-4 was considerably increased while that of SSTS-1 and SSTS-2 was decreased at a temperature of 1,573K.

• 한국화재소방학회논문지
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• 제22권2호
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• pp.38-43
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• 2008

최근에 양방향 도로터널에서 배연효율의 증가가 요구됨에 따라 대배기에 의한 횡류식 양방향터널 배연시스템 적용이 증가되었다. 본 연구에서는 FDS Ver4.0을 사용한 수치해석을 통해 배연량과 화재강도를 변화시켜 최적배연조건을 도출하였다. 결과로, 터널 내부로 외부기류가 유입되는 경우에는 배연량을 증가시켜야 하는 것으로 나타났으며 화재지점으로 2.5m/s의 속도로 외기가 불어올 때 연기가 250m 이내로 제어되는 대배기구의 배연용량은 $244.8m^3/s$의 값으로 제어되어야 한다.

• 에너지공학
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• 제12권2호
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• pp.74-83
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• 2003

APR1400과 같은 차세대 원자력발전소에서는 원자로 안전성을 증진시키기 위하여 SDVS와 같은 계통을 도입하고 있다. 완전급수상실사고와 같은 경우는 POSRV가 개방되어 수조내 Sparger를 통하여 증기가 방출·응축되게 된다 증기가 응축함에 있어서 설계에서 고려해야 될 사항은 하중과 수조 혼합이며 증기제트 응축의 물리적 현상 이해를 통하여 적절한 대처를 마련할 수 있다. 수조내 Sparger를 통하여 분사되는 증기 응축에 대하여 하중과 수조 혼합 검토에 도움이 될 수 있도록 증기제트 응축의 물리적 현상 이해에 대한 검토와 평가를 수행하였다.

• 한국수소및신에너지학회논문집
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• 제24권2호
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• pp.99-106
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• 2013

The variations of performance and metabolites at an early stage were investigated for the successful start-up technology in continuous fermentative hydrogen production. Unsuccessful start-up was observed when the operation mode was changed from batch to continuous mode after the yield was reached to 0.5 mol $H_2$/mol $hexose_{added}$ by batch mode. $H_2$ production continued till 12 hours accompanied by butyrate production, but did not last with propionate production increase. It was suspected that the failure was due to the regrowth of propionic acid bacteria during batch mode which were inhibited by heat-shock but not completely killed. Thus, successful start-up was tried by early switchover from batch to continuous operation; continuous operation was started after the $H_2$ yield was reached to 0.2 mol $H_2$/mol $hexose_{added}$ by batch mode. Although $H_2$ production rate decreased at an early stage, stable $H_2$ yield of 0.8 mol $H_2$/mol $hexose_{added}$ was achieved after 10 days by lowering down propionate production. And it was also concluded that the reason for $H_2$ production decrease at an early stage was due to alcohol production by self detoxification mechanism against VFAs accumulation.

• 대한기계학회논문집B
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• 제32권4호
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• pp.307-316
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• 2008

The objective of this study is to provide numerical and experimental data that can be used to investigate the performance characteristics of a flat plate fin-tube evaporator in household and commercial refrigerators under frosting conditions. Computer simulations with variations of operating conditions such as air inlet temperature, relative humidity, and geometries were performed to find out optimal design parameters of a fin-tube evaporator for household and commercial refrigerators. The tube-by-tube method was used in the simulation and the frost growth model was considered under frosting conditions. The developed analytical model predicted the decreasing rates of heat transfer capacity and air flow rate ratio within ${\pm}$10% compared to the experimental results for a refrigerator under real operating conditions. As a result, the frost thickness at $3^{\circ}C$ & 80% is increased 40% than that of $-3^{\circ}C$ & 80%, and the frost thickness at $3^{\circ}C$ & 90% is increased 30% than that of $3^{\circ}C$ & 60%. Accordingly, the operating time of the evaporator in the refrigerator was reduced with the increase of the decreasing rate of air flow rate ratio at each condition.

• 한국환경과학회지
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• 제25권12호
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• pp.1597-1611
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• 2016

A numerical assessment using mesoscale-CFD (computational fluid dynamics) coupled A2C (atmosphere to CFD) model was carried out to analyze the variation of microscopic air flow pattern due to the construction of the Chilgok barrage in the Nakdong River. Scenarios with air flow patterns were classified into pre- and post-construction. The increased width of the river due to the construction of the Chilgok barrage induced obvious changes in moisture and the thermal environment around the river. However, air temperature variation was restricted within an area along the windward side in the numerical assessment. The impact of barrage construction on air temperature tends to be stronger during the nighttime than the daytime. It also stronger during the winter than the summer. In the simulation, the convergence of mesoscale wind is more pronounced after barrage construction than before. This is caused by the change of heat flux pattern induced by the widening of the river. Although this work is a case study with restricted atmospheric stability conditions that has several limitations in the numerical simulations, the impacts of the land-use changes brought about by the construction of the barrage in the river acceptable.

• Tribology and Lubricants
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• 제25권4호
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• pp.225-230
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• 2009

Seals are very useful machine components in protection of leakage of lubricant or working fluid, and incoming of debris from outside. Various elastomer are widely used as sealing materials and the shaft surfaces are generally coated with high hardness material after heat treatment. It is generally known that the foreign debris and wear particles get stuck into sealing surface, the steel shaft surface can be damaged and worn by mainly abrasive wear. In this paper, using MARC, contact analysis are conducted to show the hard coated steel shaft surface can be fatigue failed by very small elastic particle intervened between seal and steel surface. Variations of contact and von-Mises stress distributions and contact half-widths with interference and coating thickness are presented. The maximum von-Mises stress occurs always in the coating layer or between coated layer/substrate interface. Therefore the coated sealing surface can be fatigued and then failed by very small particles. The results can be used in design of sealing surface and further studies are required.

• Journal of Welding and Joining
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• 제19권4호
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• pp.391-398
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• 2001

MIAB welding method uses a rotating arc as its heat source and is known to be efficient in pipe butt welding. The arc is rotated around the weld line by the electro-magnetic force resulting from the interaction of arc current and magnetic field. This paper is concerned with the experiment of initial stage for process control, monitoring for weld quality, and the design of coil system which is efficient of flux generation and concentration. A coil system for the generation of magnetic flux was designed and constructed. Magnetic flux density and arc rotating behavior are important factors in MIAB welding, so the relations between these factors and process parameters were investigated. Various experiments were performed for the steel pipes(48.1mm O.D and 2.0mm thickness). The magnetic flux density is increased by increasing exciting current and decreasing gap size. The maximum of arc rotating frequency is affected by exciting current and gap size. However, the variations of arc rotating frequency during welding and then the melting process are mainly influenced by welding current. Thus, it is considered that the results of this study can be used as important data on the monitoring for weld quality and the design of efficient coil system.

• 한국대기환경학회지
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• 제18권6호
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• pp.453-463
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• 2002

Prognostic meteorological model, MM5V3 (Mesoscale Model 5 Version 3) was used to assess the effects of the land-use modifications on spatial variations of temperature and wind fields in Busan during the selected period of summer season in 2000. We first examined sensitivity analysis for temperature between MM5V3 predictions and meteorological data observed at 4 AWS (Automatic Weather System) stations in Busan, which exhibited low structural and accurate errors (Mean Bias Error, MBE: 0.73, Root Mean Square Error, RMSE: 1.18 on maximum). The second part of this paper, MMSV3 simulations for the modification of land-use was performed with 1 km resolution in target domain, 46$\times$46 $\textrm{km}^2$ area around city of Busan. It was found that modification result from change of surface land-use in central urban area altered spatial distributions of temperature and wind. In particular, heat island core moved slightly to the seaward at 1300 LST. This results may imply that modification of surface land-use leads to change the thermal environments; in addition, it has a significant effect on local wind circulations and dispersions of air pollutants.