• 산업경영시스템학회지
• /
• 제45권3호
• /
• pp.104-114
• /
• 2022

The purpose of using coolant in machining is both to increase a tool life and also to prevent product deformation and thus, stabilize the surface quality by lubricating and cooling the tool and the machining surface. However, a very small amount of cutting mist should be used because chlorine-based extreme pressure additives are used to generate environmental pollutants in the production process and cause occupational diseases of workers. In this study, medical titanium alloy (Ti-6Al-7Nb) was subjected to a processing experiment by selecting factors and levels affecting cutting power in the processing of the Aerosol Dry Lubrication (ADL) method using vegetable oil. The machining shape was a slot to sufficiently reflect the effect of the cutting depth. As for the measurement of cutting force, the trend of cutting characteristics was identified through complete factor analysis. The factors affecting the cutting force of ADL slot processing were identified using the reaction surface analysis method, and the characteristics of the cutting force according to the change in factor level were analyzed. As the cutting speed increased, the cutting force decreased and then increased again. The cutting force continued to increase as the feed speed increased. The increase in the cutting depth increased the cutting force more significantly than the increase in the cutting speed and the feed speed. Through the reaction surface analysis method, the regression equation for predicting cutting force was identified, and the optimal processing conditions were proposed. The cutting force was predicted from the secondary regression equation and compared with the experimental value.

• 한국추진공학회지
• /
• 제27권1호
• /
• pp.37-48
• /
• 2023

본 연구에서는 정상 상태 및 천이 상태에 따른 항공기용 터보팬 엔진의 성능해석 모델링을 수행하였다. 대상 엔진은 Pratt & Whitney 사의 F100-PW-229으로 선정하여 팬, 고압 압축기, 연소기, 고압터빈, 저압 터빈, Mixer, 수축-확산형 노즐 등의 구성품을 모델링하였다. 또한, 이차 유로를 통한 터빈에서의 냉각 효과를 적용하였다. Simulink를 이용하여 터보팬 엔진 성능해석 프로그램을 자체 개발함에 따라 해석의 자유도가 높으며, 엔진 제어기 설계에 활용이 용이한 구성의 성능해석 프로그램을 개발하였다. 개발된 성능해석 프로그램은 상용 프로그램인 GASTURB 해석 결과와의 비교를 통하여 검증하였다.

• 청정기술
• /
• 제15권4호
• /
• pp.245-252
• /
• 2009

Poly(lactic acid) (PLA) 용융방사공정의 속도, 직경, 온도, 인장응력 분포를 구하기 위해 수치모사를 실시하였다. 유한차분법을 이용하여 반지름 방향으로의 온도분포곡선을 구하였다. 방사속도 1 km/min에서 5 km/min까지 방사속도에 따른 PLA 방사공정의 변화와 poly(ethylene terephthalate) (PET)와의 거동을 비교해 보았고, 방사공정변수가 섬유 중심부와 표면과의 온도차에 미치는 영향을 살펴보았다. PLA는 용융온도가 PET에 비해 낮음에도 불구하고 동일 방사조건에서 더딘 냉각속도를 보였고 방사거리에 따른 방사속도의 증가도 PET가 더 빠른 양상을 나타내었다. PLA의 섬유중심부와 섬유표면과의 온도차는 약 4.6 K에 이르렀는데, 이는 PET의 10.4 K에 비하여 낮은 값이다. PLA 섬유중심부와 표면과의 온도차는 냉각풍속도와 방사온도가 증가할수록 증가하였고, 냉각풍 온도가 감소할수록 증가하는 경향을 나타내었다.

• 한국건설순환자원학회논문집
• /
• 제11권1호
• /
• pp.1-8
• /
• 2023

본 연구에서는 시멘트 제조 공정 CO₂ 배출을 저감하기 위해 철강 슬래그로 시멘트 원료로 사용되는 석회석 사용량을 대체할수 있는 수준을 시뮬레이션 방법을 이용하여 평가하였다. 이를 위해 석회석을 비롯한 시멘트 각 원료와 석회석 대체원료로서 고로 서냉 슬래그, 전로 슬래그, KR 슬래그의 화학성분을 바탕으로 최적 시멘트 원료 배합을 도출하는 시뮬레이션 분석을 수행하였다. 분석 결과, 슬래그 대체원료는 일정 수준의 CaO를 함유해 석회석 사용량을 일부 저감하는 비탄산염 대체원료로 사용할 수 있음을 확인하였다. 동시에 각 원료의 최대 사용 가능 수준을 도출하였는데. 특히 이들 원료를 각기 사용하는 경우보다 혼합해서 사용하면 석회석 저감 효과를 증대해 탈탄산 반응에 의한 CO₂ 배출을 저감하는데 기여할 수 있는 것으로 평가되었다.

• Nuclear Engineering and Technology
• /
• 제55권2호
• /
• pp.696-706
• /
• 2023

Consequences of an anticipated Beyond Design Basis Accident (BDBA) Long-Term Station Blackout (LTSBO) event with complete loss of grid power in the VVER-1200 reactor of Rooppur Nuclear Power Plant (NPP) of Unit-1 are assessed using the RASCAL 4.3 code. This study estimated the released radionuclides, received public radiological dose, and ground surface concentration considering 3 accident scenarios of International Nuclear and Radiological Event Scale (INES) level 7 and two meteorological conditions. Atmospheric transport, dispersion, and deposition processes of released radionuclides are simulated using a straight-line trajectory Gaussian plume model for short distances and a Gaussian puff model for long distances. Total Effective Dose Equivalent (TEDE) to the public within 40 km and radionuclides contribution for three-dose pathways of inhalation, cloudshine, and groundshine owing to airborne releases are evaluated considering with and without passive safety Emergency Core Cooling System (ECCS) in dry (winter) and wet (monsoon) seasons. Source term and their release rates are varied with the functional duration of passive safety ECCS. In three accident scenarios, the TEDE of 10 mSv and above are confined to 8 km and 2 km for the wet and dry seasons, respectively in the downwind direction. The groundshine dose is the most dominating in the wet season while the inhalation dose is in the dry season. Total received doses and surface concentration in the wet season near the plant are higher than those in the dry season due to the deposition effect of rain on the radioactive substances.

• 소성∙가공
• /
• 제31권3호
• /
• pp.160-166
• /
• 2022

The purpose of this study is to investigate the effects of combined addition of Ca and Y on the precipitation and age-hardening behavior of an extruded AZ91 alloy by conducting the aging treatment at 200 ℃ for hot-extruded AZ91 and AZ91-0.3Ca-0.2Y alloys. In the AZ91 alloy, many Mg₁₇Al₁₂ discontinuous precipitate (DP) bands formed during air cooling immediately after extrusion are present, whereas in the AZ91-0.3Ca-0.2Y alloy, a few DP bands and numerous Al₂Y, Al₈Mn₄Y, and Al₂Ca phase particles are distributed along the extrusion direction. The peak-aging time of the AZ91-0.3Ca-0.2Y alloy is 16 hours, twice that of the AZ91 alloy. Although both alloys have similar hardness before aging treatment, the hardness after peak-aging treatment (i.e., peak hardness) of the AZ91-0.3Ca-0.2Y alloy is higher than that of the AZ91 alloy, as 93.1 and 88.7 Hv, respectively. The microstructures of both peak-aged alloys comprise DPs and continuous precipitates (CPs). However, the peak-aged AZ91-0.3Ca-0.2Y alloy has a smaller amount of DPs and a larger amount of CPs than the peak-aged AZ91 alloy. Additionally, the inter-particle spacings of DPs and CPs in the former are significantly narrower than those in the latter. These results demonstrate that the addition of small amounts of Ca and Y to a commercial AZ91 alloy considerably affects the formation rate, size, and amount of CPs and DPs during aging and resultant age-hardening behavior.

• Nuclear Engineering and Technology
• /
• 제55권6호
• /
• pp.2315-2324
• /
• 2023

Space nuclear reactors are becoming popular in deep space exploration owing to their advantages of high-power density and stability. Following the fourth-generation nuclear reactor technology, a conceptual design of the dual drum-controlled space molten salt reactor (D²-SMSR) is proposed. The reactor concept uses molten salt as fuel and heat pipes for cooling. A new reactivity control strategy that combines control drums and safety drums was adopted. Critical physical characteristics such as neutron energy spectrum, neutron flux distribution, power distribution and burnup depth were calculated. Flow and heat transfer characteristics such as natural convection, velocity and temperature distribution of the D²-SMSR under low gravity conditions were analyzed. The reactivity control effect of the dual-drums strategy was evaluated. Results showed that the D²-SMSR with a fast spectrum could operate for 10 years at the full power of 40 kWth. The D²-SMSR has a high heat transfer coefficient between molten salt and heat pipe, which means that the core has a good heat-exchange performance. The new reactivity control strategy can achieve shutdown with one safety drum or three control drums, ensuring high-security standards. The present study can provide a theoretical reference for the design of space nuclear reactors.

• 마이크로전자및패키징학회지
• /
• 제30권3호
• /
• pp.35-39
• /
• 2023

ESG는 많은 기업에게 기업 가치를 향상시키고, 지속 경영이 가능하게 하는 큰 지침이 되고 있다. 그 중에서도 환경(Environment)은 기술적 관점의 접근이 필요하다. 환경 오염을 줄이거나 방지하고, 에너지를 절감하는 것은 기술적인 해법이 필요하기 때문이다. 반도체 패키지 기술은 반도체 패키지의 본연의 역할인 칩의 보호, 전기/기계적 연결, 열 방출 등을 잘 하기 위해 개발 및 발전해 왔는데, 이에 따라 열 방출 효과 향상, 전기적/기계적 특성 향상, 칩을 보호하는 신뢰성 향상, 적층 및 소형화, 그러면서 비용절감을 위한 기술들이 개발되고 발전해 왔다. 그 중에서도 열 방출 기술은 열효율을 높이고, 냉각을 위한 에너지 소모를 작게 하며, 전기적 특성 향상 기술도 저전력 사용과 에너지 소모를 줄이는 효과를 만들어서 환경에도 영향을 주었다. 또한 재사용이나 재료 소모를 줄이는 기술은 환경 오염을 줄이게 되며, 특히 환경에 유해한 물질들에 대해 대체하는 기술들은 환경 개선에 기여하게 된다. 본 논문에서는 이러한 환경 오염 방지 및 개선을 위한 반도체 패키지 기술들의 트렌드를 정리하였다.

• 한국분말재료학회지
• /
• 제31권2호
• /
• pp.152-162
• /
• 2024

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150℃ under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10^-2/m²) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

• 한국전자통신학회논문지
• /
• 제19권3호
• /
• pp.589-602
• /
• 2024

열전 발전기(TEG)는 일반적으로 열 변환 효율이 높지 않다. 열전 발전기 모듈의 성능은 재료의 특성, 다리의 개수 외에도 다리의 형상에 따라 달라진다. 본 연구에서는 폐열을 효율적으로 수확할 수 있도록 열전소자의 다리 형상을 원통형, 큐브형 등 다양한 기하학적 구조로 모델링하여 전기적 특성을 수치상으로 비교하였다. 다리 형상에 따른 온도분포 및 발전량을 비교하였고 기존 Cube 모양이 가장 높게 나타났다. 냉각효과를 적용한 발전량을 비교한 결과 자연대류에서는 Cone, 강제대류에서는 Hourglass 모양이 가장 높았다. 본 연구 결과에 따르면 기하학적 구조가 열전 발전기의 효율에 영향을 미칠 수 있음을 확인하였다