• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.483-488
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• 2001

In the present study a numerical simulation is performed on a natural convection inside a square cavity with a vibrating wall. The study has been conducted varying the heat transfer rate, wall excitation frequency and also the orientation of the cavity. The temperature and velocities inside the cavity was observed and also, the heat transfer coefficients on the heating wall was seen. From the results, it can be seen that the temperature inside the cavity decreases when excited with the proper frequency and the heat transfer coefficient increased with cavity inclination angle, ${\theta}$. It is also found from the results that flow resonance is occurred near the inclination angle ${\theta}=90^{\circ}$.

• 태양에너지
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• 제10권1호
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• pp.31-37
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• 1990

사각관로의 축대칭 공동부내의 흐름에 대하이 실험적으로 연구를 하였다. 공동부의 측벽과 대향벽에서 압력과 전달계수를 측정하였다. 공동부의 길이는 80mm에서 ${\infty}$로 변화시켰을때 재부착점을 지나서 공동부의 길이를 증가시킨 경우 열전달계수는 감소하였고, 재부착점 근방에서 평균 열전달계수가 최대치가 됨을 얻었다.

• 천문학회지
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• 제49권1호
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• pp.1-8
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• 2016

The aim of this study is to describe the physical processes taking place in the solar photosphere. Based on 3D hydrodynamic simulations including a detailed radiation transfer scheme, we investigate thermodynamic structures and radiation fields in solar surface convection. As a starting model, the initial stratification in the outer envelope calculated using the solar calibrations in the context of the standard stellar theory. When the numerical fluid becomes thermally relaxed, the thermodynamic structure of the steady-state turbulent flow was explicitly collected. Particularly, a non-grey radiative transfer incorporating the opacity distribution function was considered in our calculations. In addition, we evaluate the classical approximations that are usually adopted in the onedimensional stellar structure models. We numerically reconfirm that radiation fields are well represented by the asymptotic characteristics of the Eddington approximation (the diffusion limit and the streaming limit). However, this classical approximation underestimates radiation energy in the shallow layers near the surface, which implies that a reliable treatment of the non-grey line opacities is crucial for the accurate description of the photospheric convection phenomenon.

• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.664-673
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• 2005

The heat transfer characteristics of rarefied flows in a micro-actuator are studied numerically. The effect of Knudsen number (Kn) on the heat transfer of the micro-actuator flows is also examined. The Kn based on gas density and characteristic dimension is varied from near-continuum to highly rarefied conditions. Direct simulation Monte Carlo calculations have been performed to estimate the performance of the micro-actuator. The results show that the magnitude of the temperature jump at the wall increases with Kn. Also, the heat transfer to the isothermal wall is found to increase significantly with Kn.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.157-162
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• 2003

This study is analysis on the heat transfer of exhaust gas into the muffler at passenger Car. Numerical analysis with Computational fluid Dynamics(CFD) was carried out to investigate exhaust gas flow. The STAR-CD S/W used for the three dimensional steady state CFD analysis in a muffler. The Navier-Stokes Equation is solved with the SIMPLE method in a general cartesian coordinates system. Result of numerical simulation; Inlet and outlet temperature shown about ${\Delta}T=239K$, 216K, 202K at in the muffler. Heat transfer was progressed quickly by atmospheric temperature of muffler external at in the near wall.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• Journal of Magnetics
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• 제18권2호
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• pp.105-110
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• 2013

The design model and key parameters of the material design for the control of induced magnetic flux at the near-field and efficient power transfer in a modified wireless power transfer (WPT) system with a large air gap of wireless electric vehicles were investigated through analytical simulations for magnetic vector and time-domain transient analysis. Higher saturation magnetic core with low core loss induced a stronger vertical magnetic field by the W-type primary coil in the WPT system with a gap of 20 cm at 20 kHz, which is shown from the vector potentials of the magnetic induction. The transient analysis shows that the higher magnetic fluxes through the pick-up cores lead to a linear increment of the alternating voltage with a sinusoidal waveform in the non-contact energy transfer system.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.906-914
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• 2016

We investigated the heat load imposed on the lower head of a reactor vessel by the natural convection of the oxide pool in a severe accident. Mass transfer experiments using a $CuSO_4-H_2SO_4$ electroplating system were performed based on the analogy between heat and mass transfer. The $Ra^{\prime}_H$ of $10^{14}$ order was achieved with a facility height of only 0.1 m. Three different volumetric heat sources were compared; two had identical configurations to those previously reported, and the other was designed by the authors. The measured Nu's of the lower head were about 30% lower than those previously reported. The measured angular heat flux ratios were similar to those reported in existing studies except for the peaks appearing near the top. The volumetric heat sources did not affect the Nu of the lower head but affected the Nu of the top plate by obstructing the rising flow from the bottom.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 추계학술대회
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• pp.59-60
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• 2015

무선전력전송은 각종 전자기기에 필요한 전력을 전선 없이 무선으로 공급하는 기술이다. 무선전력전송 기술은 자기 코일을 이용하는 근거리 무선전력전송 기술과 안테나를 이용하는 원거리 무선전력전송 기술로 구분된다. 본 연구에서는 시설물 관리용 전원공급 문제를 해결하기 위한 방안으로 UWB를 활용하여 초정밀 측위가 가능한 RTLS 태그와 무선 충전부를 설계하였다. 무선 충전 패드는 자기 공진 방식을 이용하여 4개의 기기를 충전할 수 있는 기능을 제공한다.

• 문화기술의 융합
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• 제4권3호
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• pp.287-291
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• 2018

차세대 반도체 소자로 관심을 받고 있는 CNTFET은 소자의 소스와 드레인 사이에 CNT를 배치시켜, 기존 MOSFET보다 작은 전압으로 전자의 ballstic 혹은 near-ballastic 이동을 가능하게 만든 반도체 소자이다. CNTFET의 성능을 높이기 위해서는 많은 수의 CNT를 CNTFET 안에 높은 밀도로 배치해야 하기 때문에 CNT의 밀도를 증가시키기 위한 다양한 공정들이 개발되고 있다. 최근, 방향성 수축 전송 방법이 개발되어 CNTFET의 전류 밀도를 150uA/um까지 향상시켜줄 수 있음을 보이고 있어, CNTFET 기반 집적회로의 구현 가능성을 높이고 있다. 본 논문에서는, 방향성 수축 전송 방법으로 CNTFET 소자를 만들 경우, CNTFET 회로의 성능이 기존 MOSFET의 성능에 비해 얼마나 향상시킬 수 있는지 그 성능을 평가할 수 있는 방안을 논의하고자 한다.