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정사각형 밀폐공간내에서 수평격판에 의한 자연대류의 진동현상
김점수,정인기,송동주,Kim, J.S.,Chung, I.K.,Song, D.J. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.4
An oscillatory motion of natural convection in a two-dimensional square enclosure fitted with a horizontal partition is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was positioned perpendicularly at the mid-height of one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were carried out with the variations of the partition length and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). As the results, an oscillatory motion of natural convection has perfectly shown the periodicity with the decrease of Rayleigh number, and the stability was reduced to a chaotic state with the increase of Rayleigh number. The period of oscillation gets shorten with the decrease of the partition length and the increase of Rayleigh number. The frequency of oscillation obtained by the variations of stream function is more similar to the experimental results than that of the average Nusselt number. The stability of oscillation grows worse with the increase of Rayleigh number. The transition Rayleigh number for the chaos is gradually decreased with the increase of the partition length.
수평격판을 갖는 상부가 부분 개방된 밀폐공간내의 자연대류
김점수,정인기,송동주,Kim, J.S.,Chung, I.K.,Song, D.J. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.3
Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.
수평격판으로 분리된 정사각형 밀폐공간내의 층류 자연대류 해석
김점수,정인기,Kim, J.S.,Chung, I.K. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
The natural convective flow in a two-dimensional square enclosure with horizontal partitions is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and two identical partitions were positioned perpendicularly at the mid-height of the right and left walls, respectively. The governing equations are solved by using the finite element method with Galerkin method. Calculations are made for different partition lengths, partition conductivites, and Rayleigh numbers based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). An oscillatory motion of the natural convective flow is affected significantly by the variation of the gap width and Rayleigh number. When the gap width is comparatively short, the heat transfer rate is raised with the increase of the thermal conductivity of partitions. However, for sufficiently large gap widths at higher Rayleigh numbers, the average Nusselt numbers of the conductive partitions are smaller than those of the adiabatic partitions.
격판을 가진 밀폐공간내의 자연대류 열전달에 공간 및 격판의 경사가 미치는 영향
정인기,송동주,김점수,Chung, I.K.,Song, D.J.,Kim, J.S. 대한설비공학회 1994 설비공학 논문집 Vol.6 No.3
The effects of the inclination of enclosure and partition on natural convective flow and heat transfer were investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was positioned perpendicularly at the mid-height of one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were performed with the variations of the partition length and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). The effects of the inclination angle of enclosure and partition on the heat transfer within an enclosure were also studied. As the results, the increase of the inclination angle of enclosure rapidly raised the heat transfer rate, while the inclination angle for the maximum Nusselt number was retarded with the increase of the partition length and the decrease of the heat transfer rate became larger in proportion to the increase of the partition length. The Nusselt number obtained by the inclination of partition was smaller than that of the inclination of enclosure. However, the difference of the heat transfer rates was considerably decreased at the longer partition lengths and the trends for the variation of the average Nusselt number were more similar with that of the inclination of enclosure. The upward oriented partition increases the convective heat transfer distinctly in contrast to that of the inclination of enclosure as the partition length increases.
Energy Exchanges and Inversion Temperatures in Electron Emission at High Fields and Temperatures
정문성(M. S. Chung),김일원(I. W. Kim),최점수(J. S. Choi),박지모(J. M. Park) 한국진공학회(ASCT) 1994 Applied Science and Convergence Technology Vol.3 No.1
전자방출에서 에너지 교환과 역온도를 새롭게 계산하였다. 전자방출에서 대체전자들에 유용한 빈상태들을 만드는 요소로 터널링 효과를 이 계산에서 고려하였다. 그것은 방출부분에서 일어나는 대체과정을 설명하기 위해서는 빈상태를 만드는데 터널링 기여가 필수적이기 때문이다. 이렇게 계산하여 온도와 전장의 함수로 얻어진 전자당 에너지 교환은 실험결과와 잘 일치하였다. 또한 전장의 함수로 얻어진 역온도도 실험치와 만족할 만한 일치를 보여주었다. 이 결과는 대체전자들의 평균에너지에 대한 노팅햄-플레밍과 헨더슨의 논쟁에서 후자의 견해를 지지하는 것이다. A new calculation of energy exchanges and inversion temperatures in electron emission is presented. In this calculation, we introduce the tunnelling state contribution as a mechanism to vacate levels available for replacement electrons in field emission. It is found that the tunnelling contribution to the availability of vacant states is necessary to explain the replacement process occurring in the emitter region. The net energy exchange △ε per electron obtained as a function of both temperature and field shows much improved agreement with experimental data. The inversion temperature T_i as a function of field is now in good quantitative agreement with existing experimental data. The present results favor the argument of Fleming and Henderson in the Nottingham-Fleming and Henderson controversy concerning the average energy of the replacement electrons.