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난류 모형에 따른 수직 평판 위 파동 액막류의 수치해석 연구
민준기(June Kee Min),박일석(Il Seouk Park) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.5
액막류는 다양한 산업분야에 적용되는 쉘-튜브 열교환기의 주요 열교환기구로 오랫동안 연구되어 왔다. 액막류의 한쪽 경계는 고정벽에 접하고 있지만 반대편에서는 기체 영역과 경계를 형성하므로 액막 레이놀즈 수가 증가함에 따라 쉽게 불안정해지는 특징을 가지고 있다. 따라서 레이놀즈 수가 증가함에 따라 자유표면 파동 현상이 나타나는데, 층류 영역에서는 큰 진폭의 고립파가, 난류 천이 이후에는 낮은 진폭의 물결파가 나타난다. 액막류의 열전달 성능은 액막의 두께에 의해 크게 지배받는데 액막류에 동반된 파동은 액막 두께의 시공간적 변화를 의미하는 것이므로 이에 대한 정보를 해석적으로 수집하는 것은 액막류 열전달 성능을 예측하는데 필수적이다. 본 연구에서는 낮은 진폭의 물결파를 동반한 난류 액막류에 대하여 여러 가지 난류 모형을 적용한 해석결과들을 실험결과와 비교함으로써 난류 모형들에 대한 평가를 실시하였다. Film flows applied to shell-and-tube heat exchangers in various industrial fields have been studied for a long time. One boundary of the film flow interfaces with a fixed wall, and the other boundary interfaces with a gaseous region. Thus, the flows become so unstable that wavy behaviors are generated on free surfaces as the film Reynolds number increases. First, high-amplitude solitary waves are detected in a low Reynolds number laminar region; then, the waves transit to a low-amplitude, high frequency ripple in a turbulent region. Film thickness is the most significant factor governing heat transfer. Since the wave accompanied in the film flow results in temporal and spatial variations in film thickness, it can be of importance for numerically predicting the film"s wavy behavior. In this study, various turbulent models are applied for predicting low-amplitude ripple flows in turbulent regions. The results are compared with existing experimental results, and finally, the applied turbulent models are appraised in from the viewpoint of wavy behaviors.
립이 있는 2차원 슬롯 형상의 가스터빈 입구측 케이싱 막냉각 장치 막냉각 특성에 대한 수치적 연구
서호진(Ho Jin Seo),민준기(June Kee Min),하만영(Man Yeong Ha) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.11
립이 있는 2차원 슬롯에 대해 분사비 0.2~1.5 범위에서 슬롯 형상의 변화가 막냉각 효율, 누셀트수에 미치는 영향을 수치 해석으로 연구하였다. 형상 변수로 립의 두께, 분사구-슬롯 면적비 및 분사 각도를 선정하였다. 립 두께의 증가는 낮은 분사비에서 막냉각 효율의 감소를 야기하는 반면, 높은 분사비에서 막냉각 효율을 증가시키는 요인임을 확인하였다. 립의 두께 및 분사구-슬롯 면적비의 증가에 따라 누셀트 수가 감소함을 확인하였다. The effects of a two-dimensional slot geometry with a lip on the film cooling effectiveness, i.e., the Nusselt number, were numerically investigated in the blowing ratio range of 0.2~1.5. For geometric parameters, the lip thickness, area ratio, and injection angle were considered. The film cooling effectiveness was found to decrease as the lip thickness increased for a low blowing ratio and increase for a high blowing ratio. As the area ratio and lip thickness increased, the Nusselt number decreased.
양방향 유체-고체 연성해석을 통한 표면 위 미세날개의 진동이 열전달에 미치는 영향 분석
박기홍(Ki-Hong Park),민준기(June Kee Min),김진규(Jin Kyu Kim),강석훈(Seok-Hoon Kang),김성진(Seong-Jin Kim),박상후(Sang-Hu Park) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.8
A microfin on a heated surface and its effects of the heat transfer has been investigated. The thickness of the fin is about 8 micrometer to allow the flexible up-down motion of the fin. Two-way complete FSI (Fluid-Structure Interaction) method has been applied for the analysis. Firstly, the deformation of a microfin due to the pulsating flow is evaluated using structure analysis. The flow and temperature patterns are predicted by CFD (Computational Fluid Dynamics) method. At each time step, using the pressure force and temperature distribution from CFD, the deformation of the wing is evaluated by FEM. Also in order to estimate the resonance probability, the natural frequency of the wing structure is calculated by modal analysis. The proposed numerical procedure was validated through experiment using a single fin. Through this work, we show that the increase of 40% in heat transfer capacity using the microfin has been compared with that of flat plate case.
무윤활 수직-수평 복합하중 조건에서 재료조합에 따른 마모특성 변화에 관한 실험적 연구
최성우(Sung-Woo Choi),민준기(June Kee Min),정일욱(Il-Wook Jeong),박상후(Sang-Hu Park) Korean Society for Precision Engineering 2009 한국정밀공학회지 Vol.26 No.11
A pair of connectors for transferring torque is widely used in various types of a mechanical system. By the repetition of mechanical contact between a pair of connector, wear occurs easily. This kind of defect sometimes can cause a serious problem of health in case of the connector is used in a refrigerator. In this work, the material combination of connectors was experimentally studied to reduce the amount of wear; for the combination of connectors, various types of engineering materials including polyacetal, polycabonate, stainless steel (STS-304), NiP coated STS-304, and STS-310 were evaluated to check each wear behavior. Also an effective method of wear test was suggested for precise controlling of wear conditions such as contact area, contact force, and relative motion speed. From the test results, it was found out that a pair of polyacetal to STS-304 and STS-310 showed the lowest specific wear rates among other pairs.