• Title, Summary, Keyword: thermal radiation

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CFD Simulations of the Ground Surface Temperature and Air Temperature, Air flow Coupled with Solar Radiation (태양복사열에 따른 지표면 온도와 열, 기류 환경 시뮬레이션 연구)

  • Lee, JuHee;Kim, JaeGwon;Yoon, JaeOck
    • KIEAE Journal
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    • v.14 no.3
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    • pp.65-70
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    • 2014
  • The thermal environment in a small city rapidly deteriorates due to the urbanization and overpopulation. It is important to understand and predict the thermal environment in a city area. The thermal environment is highly affected by the solar radiation and temperature distributions changing over time periodically. To predict the thermal environment precisely, the solar radiation calculation including radiation strength, incidence angle, and thermal radiation between building surface and ground should be considered. In this study, the computational domain includes various artificial structures such as building, ground, asphalt, brick and grass. To consider the solar radiation, the unsteady state numerical calculation is performed from sun rise to mid-day (2:00pm). The numerical methods consist of solar load and one dimensional heat conduction through the boundaries to reduce the computational load and improve the flexibility of the calculation.

Design Optimization of Thermal Radiation Shield Cooled by Cryocooler (냉동기에 의해 냉각되는 복사열차폐 최적설계)

  • Choi, Y.S.;Tang, Hongming;Kim, D.L.;Yang, H.S.;Lee, B.S.
    • Proceedings of the KSME Conference
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    • pp.2171-2174
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    • 2008
  • The design of thermal radiation shield cooled by a cryocooler is presented. This study is motivated mainly by our recent development of prototype superconducting magnet system for the Cyclotron K120. The superconducting magnet system is composed of the magnet cryostat, transfer line and supply cryostat. In order to minimize thermal radiation load, the superconducting coil form in the magnet cryostat is enclosed by the thermal radiation shield which is thermally connected to the first-stage cold head of a two-stage cryocooler in the supply cryostat. Since the supply cryostat is located far from the magnet cryostat large temperature gradient along the thermal shield is unavoidable. In this paper, the thermal radiation shield is optimized to minimize temperature gradient with taking into account the cryogenic load, system structure and electrical load. The effect of heat source from thermal conduction through mechanical supports on the temperature distribution of thermal radiation shield is also discussed.

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Process monitoring of laser welding using chromatic filtering of thermal radiation (열복사의 색수차 공간여과를 이용한 레이저용접 감시기술)

  • 백성훈;박승규;김민석;정진만;김철중
    • Journal of Korean Society of Laser Processing
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    • v.2 no.2
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    • pp.18-26
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    • 1999
  • An innovative real-time weld monitoring technique using chromatic filtering of the thermal radiation from a weld pool is developed. The thermal radiation from the weld pool is focused on an aperture and the transmitted thermal radiation is monitored at two wavelengths with high-speed single-element detectors. Due to the chromatic aberration introduced in the focusing optics, the transmittance curve of thermal radiation varies by the wavelength. Owing to this difference in the transmittance, the local variation of thermal radiation from the weld pool can be monitored by processing the two spectroscopic signals from two detectors. In this paper, the algorithms to monitor the laser power on the weld specimen and the focus shift we investigated and the performances of laser power and focus monitoring are shown for a pulsed Nd:YAG laser welding. The monitoring of the weld pool size variation is also discussed.

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Analysis of the Thermal Dome Effect from Global Solar Radiation Observed with a Modified Pyranometer

  • Zo, Ilsung;Jee, Joonbum;Kim, Buyo;Lee, Kyutae
    • Current Optics and Photonics
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    • v.1 no.4
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    • pp.263-270
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    • 2017
  • Solar radiation data measured by pyranometers is of fundamental use in various fields. In the field of atmospheric optics, the measurement of solar energy must be precise, and the equipment needs to be maintained frequently. However, there seem to be many errors with the existing type of pyranometer, which is an element of the solar-energy observation apparatus. In particular, the error caused by the thermal dome effect occurs because of the thermal offset generated from a temperature difference between outer dome and inner casing. To resolve the thermal dome effect, intensive observation was conducted using the method and instrument designed by Ji and Tsay. The characteristics of the observed global solar radiation were analyzed by classifying the observation period into clear, cloudy, and rainy cases. For the clear-weather case, the temperature difference between the pyranometer's case and dome was highest, and the thermal dome effect was $0.88MJ\;m^{-2}\;day^{-1}$. Meanwhile, the thermal dome effect in the cloudy case was $0.69MJ\;m^{-2}\;day^{-1}$, because the reduced global solar radiation thus reduced the temperature difference between case and dome. In addition, the rainy case had the smallest temperature difference of $0.21MJ\;m^{-2}\;day^{-1}$. The quantification of this thermal dome effect with respect to the daily accumulated global solar radiation gives calculated errors in the cloudy, rainy, and clear cases of 6.53%, 6.38%, and 5.41% respectively.

Study on assessment of outdoor thermal environment with coupled simulation of convection and radiation (대류.복사 연성시뮬레이션을 통한 옥외 온열환경 평가 기법)

  • Ryu, Min-Kyung;Lim, Jong-Yeon;Hwang, Hyo-Keun;Song, Doo-Sam
    • Proceedings of the SAREK Conference
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    • pp.565-572
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    • 2009
  • Deterioration of the outdoor thermal environment in urban areas such as heat island has become worse due to urbanization and overpopulation, etc. In this study, a new method which is coupled simulation of convection and radiation to evaluate outdoor thermal environment in urban area will be proposed. Because the solar radiation affects on outdoor thermal environment massively, therefore the radiation calculation is very important in outdoor thermal environment prediction. The coupled simulation proposed in this study can assess the outdoor thermal environment with accurate.

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PRELAUNCH THERMAL ANALYSIS OF KSLV-I PAYLOAD FAIRING

  • Choi Sang-Ho;Kim Seong-Lyong;Kim Insun
    • Bulletin of the Korean Space Science Society
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    • pp.356-359
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    • 2004
  • Prelaunch thermal analysis of the KSLV (Korea Space Launch Vehicle)-I PLF (Payload Fairing) was performed to predict maximum/minimum liftoff temperatures and to evaluate of air conditioning performance. Prelaunch thermal analysis includes internal air conditioning effect, external convective heating/cooling, radiation exchange with the ground and sky, radiation between spacecraft and PLF, and solar radiation incident on PLF. Analysis was performed at two extreme conditions, hot day condition and cold day condition. The results showed that the maximum liftoff temperature was $53^{\circ}C$ and the minimum liftoff temperature was $-3.8^{\circ}C$. It was also found that conditioned air supplying, in $20{\pm}2^{\circ}C\;and\;1200\;m^3/hr$, is sufficient to keep the internal air in required temperature range.

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A Development of Thermal Radiation Plume Modelling for Heat Transfer to KSLV-II Engine Base (한국형 발사체 기저부 열전달 해석을 위한 플룸 복사 모델링 개념 개발)

  • Kim, Seong-Lyong;Ko, Ju-Yong;Kim, In-Sun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.507-514
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    • 2012
  • In the present research, NASA LRB plume radiation models are reconstructed with Thermal Desktop software, where the radiation to vehicle base environment can be calculated. The calculation shows the similar radiation heat compared to NASA prediction. Based on LRB plume radiation model, a KSLV-II thermal radiation model is proposed.

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A Study of the Thermal Characteristics of Flooring Materials, Wood, Rock, Aluminum through Observation of its Radiant Environment in the Summer (하절기 복사환경 관측을 통한 석재, 목재, 알루미늄 바닥재의 열특성 평가)

  • Choi, Dong-Ho;Lee, Bu-Yong
    • Journal of the Korean Solar Energy Society
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    • v.28 no.3
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    • pp.35-44
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    • 2008
  • In this study, the experiment of the measuring of four different types of flooring materials' thermal characteristics was conducted and examined during the summer. The experimental materials were arranged on the existing slab of the roof, and then its thermal characteristics were examined from the point of view of thermal radiation analysis. The aim of this study is ultimately to draw the fundamental data for improvements in a building's thermal function and reduce the urban heat island phenomena through optimizing the thermal characteristics of the surface covering materials of a building. The results from this study are as follows; 1) Each experimental material's albedo was calculated as 0.83 on the aluminum panel, 0.40 on the rock block, 0.37 on the wood deck and 0.21 on the concrete. It shows that the concrete material, which has the lowest short wave reflective rate, absorbed the most radiation energy and the aluminium panel has absorbed the lowest radiation energy. 2) From the each experimental object's value of the long wave radiation, the concrete material measured the highest, at $628W/m^2$, and the aluminium panel measured the lowest at $412W/m^2$. Therefore, it verifies that the experimental objects' own radiation rate determines the amount of the long wave radiation. 3) The degree of energy absorbency of a building's surface covering materials is greatly influenced by its own albedo and radiation rate, Therefore, it needs to be considered for the improvements in a building's thermal function and reducing the urban heat island phenomena. 4) According to the evaluation result of the each experimental object's overall heat transmission screening function on the roof of a building, the wooden deck is proven to be an excellent material for excluding the outside temperature differences effectively with its characteristic of low heat capacity and conduction. Also its surface temperature on the roof slab and the temperature difference during the day were both measured at low.

Study on Improvement of Heat Dissipation Characteristics of TIM Material Using Radiant Energy (복사에너지를 이용한 TIM소재의 방열 특성 향상을 위한 연구)

  • Hwang, Myungwon;Kim, Dohyung;Jung, Uoo-Chang;Chung, Wonsub
    • Journal of the Korean institute of surface engineering
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    • v.52 no.2
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    • pp.58-61
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    • 2019
  • The aim of this study is to quantitatively demonstrate the possibility of heat transfer by thermal radiation by comparing heat transfer by conventional heat transfer and radiation by radiation. 1) The heat transfer was measured by using filler of TIM material with low thermal conductivity (CuS). As a result, heat transfer was easier than ceramic with high thermal conductivity ($Al_2O_3$ and $Si_3N_4$). 2) The reason for this is thought to be that the infrared wave due to radiation of the air diaphragm has moved easily. 3) From the above results, the heat dissipation of the TIM material indicates the possibility of heat transfer by thermal radiation.

Natural Convection Coupled with Thermal Radiation within Partially Open Enclosure (복사열과 부분열림이 자연대류에 미치는 영향에 관한 연구)

  • 노승균;김광선;이재효
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.11
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    • pp.2999-3007
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    • 1994
  • The unsteady numerical simulations have been presented for the laminar natural convection in a partially open compartment. Computations were performed within the domain of the compartment in order to show the thermal radiation and the partially opening effects on the flow fields and heat transfer characteristics. The results were shown for different Planck numbers(0.05~5) and opening ratios(0.25~0.75) being fixed with Ra=$10^5$ and Pr=0.71. Considering the flow which is buoyancy driven from the heated wall, and the buoyancy is not much affected by the further outside region from the opening, the numerical computations have been performed without an outer region by the particular boundary treatments on the flow velocity and temperature at the different partial openings. The confined numerical domain reduced the CPU time and the memory of computer. P-1 approximation of radiative transfer equation was employed with Marshak type boundary conditions along with the pseudo-black body approximation at the partial openings. The numerical results clearly show that the natural convective flow and heat transfer are much affected by increase of thermal radiation particularly from the initial state. When thermal radiation is not much affecting the flow ($PL{\le}1$), it was found that thermal radiation effects are almost negligible.