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수직원관 주위에서 밀도차와 자연대류를 고려한 응고과정 해석
김무근,노승탁 대한기계학회 1992 대한기계학회논문집 Vol.16 No.1
본 연구에서는 실제 빙축열 시스템의 해석을 위한 기초 모델로서 수직원관 주 위의 응고과정에 대하여 밀도차와 자연대류 효과 및 최대 밀도점을 나타내는 밀도-온 도 관계식을 도입한 수치해석과 실험을 통하여 여러가지 매개변수들이 상변화에 미치 는 영향을 알아 보았다. Numerical analysis is performed for the unsteady axisymmetric two dimensional phase change problem of freezing of water around a vertical tube. Heat conduction in the tube wall and solid phase, natural convection in liquid phase and volume expansion caused by density difference between solid and liquid phases are included in the numerical analysis. Existing correlation is used for estimating density-temperature relation of water, and the effect of volume expansion is reflected as fluid velocity at the interface and the free surface. As pure water has maximum density at 4.deg. C, it is found that there exists an initial temperature at which the flow direction reverses near the interface and by this effect the slope of interface becomes reversed depending on the initial temperature of water. By considering natural convection and solid-liquid density difference in the calculation, their effects on phase change process are studied and the effects of various parameters are also studied quantitatively.
초크랄스키법에 의한 실리콘 단결정성장에서 회전효과가 미치는 영향에 대한 연구
김무근 대한기계학회 1995 대한기계학회논문집 Vol.19 No.5
The influence of varying rotation speed of both crystal and crucible was numerically investigated for the Czochralski silicon-crystal growth. Based on a simplified model assuming flatness of free surfrae, the Navier-Stokes Boussinesq equations were employed to identify the flow pattern, temperature distribution as well as the shape of the melt/crystal interface. The present results showed that the interface shape was relatively convex with respect to the melt at lower pulling rate and tended to be concave as the pulling rate increased. In particular, the experimentally observed gull-winged shape of the interface was qualitatively in agreement with the predicted shape. The rotation of crystal alone little affected the growth system. When the rotation speed of the crucible was increased, there occurred inversion of the interface shape from convex to concave pattern. At rapid rotation of the crucible, an interesting channel formation was predictied primarily due to the assumption of laminar flow.
초크랄스키 단결정 성장에서 자기장이 용질분포에 미치는 영향
김무근,서정세,Kim, Moo Gewi,Suh, Jeong Se 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.3
Numerical simulations are carried out for the magnetic Czochralski single crystal growth system. It Is shown that a magnetic field significantly suppresses the convective flow and as the strength of magnetic field becomes to be stronger, the heat transfer in the melt is dominated by conduction rather than convection. By imposing a cusp magnetic field, the growth interface shape becomes convex toward the melt. When the axial magnetic field is imposed, there occurs an inversion of the interface shape with increase of the magnetic field strength. The oxygen concentration near the interface decreases with increasing cusp magnetic field strength while axial field causes an increase of an oxygen concentration at the central region and decrease of that at the edge of the crystal. The results show that the cusp magnetic field has advantages over an axial magnetic field In the radial uniformity of oxygen as well as in the additional degree of control.
이산화탄소 사이클에서 팽창장치의 영향에 관한 수치적 연구
김무근,김욱중,김유진 대한설비공학회 2004 설비공학 논문집 Vol.16 No.1
In order to evaluate the performance of carbon dioxide cycle, a simulation model was developed to predict the steady state performance of CO2 transcritical cycle. The expansion process is treated as an isenthalpic throttling process or isentropic expansion process. The mathematical model is based entirely on the basic energy conservation law and thermodynamic and transport properties of CO2. A parametric study has been conducted in order to investigate the effect of isentropic efficiency of expansion turbine and various operating conditions on the cycle performance. An optimal heat rejection pressure existed for the given evaporating temperature and outlet temperature of gas cooler.
자기장하에서 액막 초크랄스키 방법에 의한 단결정 성장에 관한 연구
김무근,서정세,Kim, Mu-Geun,Seo, Jeong-Se 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
Numerical simulations are carried out for the liquid encapsulant Czochralski(LEC) by imposing a magnetic field. The use of a magnetic field to the crystal growth is to suppress melt convection and to improve the homogeneity of the crystal. In the present numerical investigation, we focus on the range of 0-0.3Tesla strength for the axial and cusped magnetic field and the effect of the magnetic field on the melt-crystal interface, flow field and temperature distribution which are the major factors to determine the quality of the single crystal are of particular interest. For both axial and cusped magnetic field, increase of the magnetic field strength causes a more convex interface to the crystal. In general, the flow is weakened by the application of magnetic field so that the shape of the melt-crystal interface and the transport phenomena are affected by the change of the flow and temperature field.
김무근,홍장표 인제대학교 1994 仁濟論叢 Vol.10 No.2
A study on the application of closed diesel cycle to power underwater vehicles in deep water led to the development of a new concept for exhaust gas treatment. The totally closed cycle is based on liquefaction of combustion carbon dioxide. The characteristics of carbon dioxide liquefaction system which is provided by the evaporation and superheating of oxygen liquid was studied by numerical simulation. The results show that there exists a mass flow rate of oxygen where the compression work is minimum.