• Title/Summary/Keyword: 복사형상계수

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A New Simple Technique for View Factor Computation (간단한 복사 형상계수 계산 방법)

  • Cho, S. H.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.7 no.1
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    • pp.96-102
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    • 1983
  • 복사 형상계수를 계산하는 새롭고도 간단한 수치적 방법이 개발되었다. 유한선분 적분법은 윤 곽적분을 이용하며, 윤곽은 유한한 수의 선분으로 구성된 것으로 가정한다. 미소면적으로부터 유한면적까지의 복사 형상계수는 적분로 상의 절점의 좌표값에만 관계되며, 전자 계산기에 쉽게 프로그램 될 수 있다. 가우스의 적분을 이용하여 두 유한 면적사이의 복사 형상계수를 구한다. 미소 면적에서 원판까지, 두 개의 평행원판 사이, 및 두 개의 직사각형 사이의 복사 형상계수를 구하여 엄밀해와 비교하여 유한선분 적분법의 정확성이 우수함을 보였다. 단위구와 단위 정사 각형에서 타원체까지의 보가 형상계수의 값도 구하였다.

Studies of Parallelism and Performance Enhancements of Computing View Factor for Satellite Thermal Analysis (인공위성 열해석을 위한 복사형상계수 계산기법의 병렬화 및 성능향상 기법 연구)

  • Kim, Min-Ki
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.43 no.12
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    • pp.1079-1088
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    • 2015
  • Parallelism and performance enhancement of calculating view factors in KSDS developed by KARI is introduced in this paper. View factor is an essential parameters of radiation thermal analysis for a spacecraft, and the amount of computation of them is not negligible. Especially, independent integration of view factors at each position of the orbit because the relative displace between solar panel and main body of a satellite varies with the position on the orbit. This paper introduces a range of parallelism of computing view factor and their performance, detection of obstructions by spatial search algorithm based on KD-Tree, and the reduction of the calculation of view factors of a satellite with relative motion between solar panel and main body, called updating fractional view factor matrix, for satellite thermal analysis.

Development of Optimal Control of Heliostat System Using Configuration Factor and Solar Tracking Device (형상계수와 태양추적장치를 이용한 헬리오스타트 제어 시스템 개발)

  • Lee, Dong Il;Jeon, Woo Jin;Baek, Seung Wook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.12
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    • pp.1177-1183
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    • 2012
  • This study aims to develop a system that maximizes the radiative heat transfer from the heliostat to the receiver by using the configuration factor and a solar tracking device. As the heat transfer from the heliostat to the receiver is delivered by solar radiation, the configuration factor commonly utilized for radiation is applied to control the heliostat. Tracking the sun and calculating its position are possible by using an illuminance sensor (CdS) and Simulink. By applying optimized algorithms programmed using Simulink that maximize the configuration factors among the heliostat, receiver, and sun in real time, the solar absorption efficiency of the receiver can be maximized. Simulations were performed on how to change the angle required to control the elevation and azimuthal angle of the heliostat during the daytime with respect to various distances.

The radiation heat transfer among surface elements at initial stage of crystal growth in Czochralski system (Czochralski 법에 의한 단결정 성장 초기 단계에서 표면 요소 사이의 열전달)

  • 정형태;이경우
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.2 no.1
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    • pp.1-9
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    • 1992
  • Radiation heat transfer was calculated for initial stage of crystal growth in Czochralski crystal growth system. View factors among surface elements were calculated for the estimation of heat evolution and all the surfaces were assumed to be diffuse-gray. The values of view factors were greatly different along the position of surface elements. The dissipated amounts of heat flux from the melt surface were 3.6 times larger than those from the crystal surface at the initial stage of crystal growth and this amounts were greater when the surface elements were not considered. The trijunction part of the crystal was greatly affected by the melt surface near the crystal. Consequently radiation heat transfer between surface elements must be considered in order to correctly simulate the initial crystal growth.

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Numerical Analysis of Natural Convection and Surface Radiation in a Square Enclosure (정사각형 밀폐공간내에서의 자연대류와 표면복사의 수치해석)

  • 권용일;권순석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.5
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    • pp.983-991
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    • 1992
  • This investigation is carried out numerically for the two dimensional natural convection and surface radiation heat transfer in a square enclosure. The bottom and top walls are isothermal at hot and cold temperatures respectively whereas the left and right side walls are adiabatic except a transparent window on the right side partially. The exchange of radiant energy is obtained by the net radiation method and the shape factor by the crossed string method. The changes in temperature and Nusselt number distributions of the walls due to the surface radiation and insolation are also investigated.

STUDY ON VIEW FACTOR CALCULATION FOR RADIATIVE HEAT TRANSFER BY USING THE MESH SUBDIVISION METHOD (격자 세분화 방법을 고려한 복사열전달 형상계수 계산 기법 연구)

  • Kim, D.G.;Han, K.I.;Choi, J.H.;Lee, J.J.;Kim, T.K.
    • Journal of computational fluids engineering
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    • v.19 no.1
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    • pp.1-6
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    • 2014
  • Since experiments on the actual operational status are said to be very impractical because of their economic and repeatability problems, it is difficult to understand the thermal profiles of aerospace or military equipments. Thus, the CFD codes with considering the radiation heat transfer are used to compensate the defect. In case, analyzing the radiation exchanges between the object surfaces are very important. Because the temperature and the IR signal distributions of the object surface are significantly affected by the radiative heat transfer. To achieve accurate thermal radiation exchange between surfaces, it is important to calculate the radiation view factor precisely. Finer subdivision of meshes can be used to increase the accuracy of radiation view factor, but if the mesh is subdivided infinitely, the time required for calculation increases significantly and thus decreasing the efficiency. If the subdivision is not sufficient, assurance of accuracy is not guaranteed. In this paper, optimal mesh subdivision method using the solid angle has been successfully tested and found to be useful in increasing the efficiency of calculating the shape factors.

Experimental Study of Emissivity with the Variation of Temperature and Shape Factor Using the Radiation Apparatus (복사 장치를 이용한 온도와 형상계수의 변화에 따른 방사율에 관한 실험적 연구)

  • Kim, Chung-Rae;Jeong, Byung-Cheol;Kang, Hyung-Suk
    • Journal of Industrial Technology
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    • v.25 no.B
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    • pp.135-140
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    • 2005
  • Voltage of radiometer is measured experimentally using the radiation apparatus in each case of iron- and copper-plates as specimen heating device. The length between radiometer and conical shield and the temperature of specimen heating device are considered as variables. The length between radiometer and conical shield controls the amount of radiation from the specimen heating device. Emissivity for both iron-and copper-plates are calculated by using Stefan-Boltzmann equation. One of results shows that emissivity for both materials increases as the length between radiometer and conical shield increases.

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Numerical Study on the Thermal Design of Lunar Terrain Imager System Loaded on the Korea Pathfinder Lunar Orbiter (시험용 달 궤도선의 광학탑재체 시스템 열설계에 대한 수치해석적 연구)

  • Kim, Taig Young;Chang, Su-Young;Heo, Haeng-Pal
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.4
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    • pp.309-318
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    • 2019
  • The thermal design of the Lunar Terrain Imager (LUTI) on the Korean Pathfinder Lunar Orbiter (KPLO) was performed and the soundness of the thermal design was verified by thermal analysis. The thermal environment of the lunar mission orbit should be reflected in the thermal design because the IR radiation of the lunar surface is important, unlike the earth orbit. The components or modules exposed to the outside of the satellite are insulated with MLI as much as possible, but the camera tube and the radiator are functionally exposed, so the thermal shield using the concept of radiation shape factor is mounted on the front to mitigate IR radiation. The IR emissivity is important in the front side of the radiator that receives little solar radiation, and components that are susceptible to thermal deformation such as the tube use a radiation heater to minimize the temperature gradient. Through the investigation of computational results, it was confirmed that the thermal design of LUTI is stable in various situations.

An Investigation of Radiation Heat Transfer on The Horizontal Fin of An External Fuel Tank by Flame of a Flying Flare (날아가는 섬광탄이 연료탱크 수평핀에 미치는 복사열전달 연구)

  • Jung, Daehan;Kang, Chihang;Kim, Sitae
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.2
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    • pp.197-203
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    • 2014
  • In this paper, the effect of unsteady radiation on the horizontal fin of an external fuel tank by flame of a flying flare was analysed to see the temperature increase of the fin and the thermal impact on the fin. Radiation between two surfaces was calculated using the concept of radiation resistance of surface and space including radiation, irradiation and shape factor for two flying trajectories of a flare, maximum temperature of 2200 K, emissivity of 0.95, flying velocity of 30 m/s, and thermal surface area of $0.01m^2$. The result shows that the temperature increase of the fin is 0.236 K, and the thermal effect on the fin is ignorable. And it was found that temperature is increased a little because small amount of heat energy can be radiated due to the short exposure time to the heat source.

Radiative Heat Transfer in Radiatively Particpating Finite Cylindrical Media - Exact and P-N Solutions - (복사에 관여하는 유한 원통형 매질에서의 복사열 전달)

  • 서인수;손종관;임승욱;이준식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.6
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    • pp.1428-1437
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    • 1988
  • An analysis of radiative heat transfer has been conducted on axisymmetric finite cylindrical media. It is assumed that the temperature in the media is uniformly distributed and the boundaries are diffusely emitting and reflecting at a constant temperature. The scattering phase function is represented by the delta-Eddington approximation to account for highly forward scattering by particulates just as in the combustion system. Exact numerical solutions are obtained by Gaussian quadrature method and compared with P-1 and P-3 approximation solutions to verify their engineering application limit. The effects of optical thickness, scattering albedo, wall emissivity and aspect ratio are investigated. The results show that P-3 approximation is found to be in good agreement with the exact solution.