• Title, Summary, Keyword: Heat radiation

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A Study on the Radiation and Convection Component Separated from Surface Combined Heat Transfer Coefficient on Dynamic Heat Load Simulation (표면 열전달율의 복사.대류성분 분리와 비정상 열부하 계산에 관한 연구)

  • Kim, Young-Tag;Choi, Chang-Ho
    • Journal of the Korean Solar Energy Society
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    • v.25 no.3
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    • pp.1-9
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    • 2005
  • The purpose of this paper was to analyze the influence of radiation and convection component separated from surface heat combined transfer coefficient on dynamic Heat load simulation. In general, it was not considered the mutual radiation of walls that heat load simulation calculated by surface combined heat transfer coefficient. In order to solve this problem, we had developed new simulation program to calculate radiation heat transfer and convection heat transfer respectively, and verified the influence of radiation component with this new program, in indoor heat transfer process.

Numerical Analysis of Natural Convection-Radiation Heat Transfer in an Enclosure Containing Absorbing, emitting and Linear Anisotropic Scattering Medium (흡수,방사 및 선형비등방 산란 매질을 포함하는 밀폐공간내의 자연대류- 복사열전달에 대한 수치해석)

  • 차상명;김종열;박희용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.5
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    • pp.952-964
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    • 1992
  • The interaction of natural convection and radiation heat transfer in a two dimensional square enclosure containing absorbing, emitting and linear anisotropically scattering gray medium is numerically analyzed. P-1 and P-3 approximation is introduced to calculate radiation heat transfer. The effects of scattering albedo, wall emissivity, scattering anisotropy, and optical thickness on the characteristics of the flow and temperature field and heat transfer are investigated. Temperature and velocity profiles depend a great deal on the scattering albedo, and the importance of this effect increases with decrease in albelo. Planck number is another important parameter in radiation heat transfer. The increase in scattering albedo increases convection heat transfer and decreases radiation heat transfer at hot wall. However, the increase in scattering albedo decreases both convection and radiation heat transfer at cold wall. The increase in optical thickness decreases radiation heat transfer. The scattering anisotropy has important effects on the radiation heat transfer only. The highly forward scattering leads to an increase of radiation heat transfer whereas the highly backward scattering leads to an decrease of radiation heat transfer. The effect of scattering anisotropy decreases when reducing the wall emissivity.

Experimental Study of Radiation Heat Flux for the Pool and Spill Fire in Petroleum Storage Tanks (석유류 저장 탱크에서의 액면 및 유츌화재에 대한 복사열의 실험적 연구)

  • Kim, Hong;Park, Hyung-Ju
    • Journal of the Korean Society of Safety
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    • v.19 no.1
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    • pp.88-93
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    • 2004
  • This experimental study was carried out to evaluate effect of the radiation heat flux for the pool and spill fire in petroleum storage tanks, which were made form steel. Each of them had the capacity of 250, 2500 and 25000 liter, respectively. The effects of the radiation heat flux are as follows; 1) The intensity of radiation heat flux from a flame decreased exponentially with increasing distance from outside wall of tanks, and increased significantly with surface area of tank and dyke. 2) In the case of 25000L tank, the radiation heat flux was about max. 98.9kW/$m^2$ in 1m from wall of tank. 3) The distance, that was able to ignite wood or plastics by radiation heat flux of approximately 12.5kW/$m^2$, was about 3.14m from wall of 25000L tank.

Analysis of Radiative-Convective Heat Transfer about a Circular Cylinder in Crossflow Using Finite Volume Radiation Solution Method (유한체적 복사전달해석법을 이용한 주유동중에 놓인 원형실린더 주위에서의 복사-대류 열전달해석)

  • Lee, Gong-Hun;Lee, Jun-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.1
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    • pp.346-358
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    • 1996
  • A finite volume radiation solution method was applied to a non- orthogonal coordinate system for the analysis of radiative-convective heat transfer about a circular cylinder in crossflow. The crossflow Reynolds number based on the cylinder radius was 20, and the fluid Prandtl number was 0.7. The radiative heat transfer coupled with convection was reasonably predicted by the finite volume radiation solution method. The investigation includes the effects of conduction- to-radiation parameter, optical thickness, scattering albedo and cylinder wall-emissivity on heat transfer about the cylinder. As the conduction- to-radiation parameter decreases, the radiative heat transfer rate increases and conduction rate as well due to the increase in temperature gradient on the cylinder wall which is caused by radiation enhancement. With an increase in the optical thickness, the Nusselt number increases significantly and the temperature gradient shows similar behavior. Though the radiative heat transfer increases with the scattering albedo, the total heat transfer decreases. This is because the decrease in the conduction heat transfer exceeds the increase in the radiation heat transfer. As the wall- emissivity increases, the radiation absorbed in the vicinity of the cylinder wall increases and thereby the total heat transfer increases, even though the conduction heat transfer decreases.

A Study on the Radiation Heat Transfer Effect near a Refrigerator Gasket (냉장고 가스켓 주위의 복사열전달 효과에 관한 연구)

  • Ha, Ji-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.3
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    • pp.1605-1610
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    • 2015
  • The present study has been accomplished to elucidate the effect of radiation heat transfer in the heat transfer analysis of refrigerator gasket, which has near 30% of refrigerator heat loss. The numerical heat transfer analysis has been conducted with the simplified modeling of refrigerator gasket. From the present CFD analysis, heat loss at the gasket is $25.6W/m^2$ for the case without radiation effect and that for the case with radiation effect is $55.0W/m^2$, which is 2.2 times greater heat loss. The radiation protection layers were installed in the gasket from 0 to 7 and the case with 7 layers has 33% reduction effect of heat loss compared with the case without any radiation protection layer. Additionally, it is better effect of radiation heat loss reduction that the radiation protection layers would be placed to the outer or inner side of gasket rather than placing to the center of gasket.

Analysis of Variations in Soil Heat Flux and Air Temperature by Net Radiation at a Mud Flat in Hampyeong Bay (함평만 갯벌에서 순복사에 의한 토양열 플럭스와 기온의 변동 분석)

  • Park, Ho-seon;Kwon, Byung Hyuk;Kim, Il-Kyu;So, Yoon Hwan;Oh, Se Bong;Kang, Dong-hwan
    • Journal of Environmental Science International
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    • v.26 no.9
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    • pp.1101-1110
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    • 2017
  • In this study, we analyze changes in soil heat flux and air temperature in August (summer) and January (winter) according to net radiation, at a mud flat in Hampyeong Bay. Net radiation was observed as $-84.2{\sim}696.2W/m^2$ in August and $-79.4{\sim}352.5W/m^2$ in January. Soil heat flux was observed as $-80.7{\sim}139.5Wm^{-2}$ in August and $-49.09{\sim}137W/m^2$ in January. Air temperature was observed as $24.2{\sim}32.9^{\circ}C$ in August and $-1.5{\sim}11.1^{\circ}C$ in January. The rate of soil heat flux for net radiation ($H_G/R_N$) was 0.17 in August and 0.34 in January. Because the seasonal fluctuation in net radiation was bigger than the soil heat flux, net radiation in August was bigger than in January. We estimated a linear regression function to analyze variations in soil heat flux and air temperature by net radiation. The linear regression function and coefficient of determination for the soil heat flux by net radiation was y=0.19x-7.94, 0.51 in August, and y=0.39x-11.69, 0.81 in January. The time lag of the soil heat flux by net radiation was estimated to be within ten minutes in August 2012 and January 2013. The time lag of air temperature by net radiation was estimated at 160 minutes in August, and 190 minutes in January.

Estimating the urban radiation heat flux distribution and the reduction effect of building and tree shade (건물과 수목의 그림자에 의한 도시의 열 분포 산정 및 저감효과 연구)

  • Park, Chae-Yeon;Lee, Dong-Kun;Yoon, June-Ha
    • Journal of the Korean Society of Environmental Restoration Technology
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    • v.21 no.6
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    • pp.1-13
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    • 2018
  • Mapping radiation heat flux of urban area is essential for urban design and landscape planning. Because controlling urban geometry and generating green space are important urban design strategies for reducing urban heat, urban planner and designer need to recognize the micro urban heat distribution for adequate urban planning. This study suggests a new methodology for mapping urban radiation heat flux in a micro scale considering buildings and trees' shade. For doing that, firstly, we calculate net radiation for each urban surfaces (building, road (not shaded, building shaded, tree shaded), ground (not shaded, building shaded, tree shaded), tree (not shaded, building shaded)). Then, by multiplying the area ratio of surfaces to the net radiation, we can obtain the radiation heat flux in micro-scale. The estimated net radiation results were found to be robust with a $R^2$ of 90%, which indicates a strong explanatory power of the model. The radiation heat flux map for 12h $17^{th}$ August explains that areas under the building and tree have lower net radiation heat flux, indicating that shading is a good strategy for reducing incident radiation. This method can be used for developing thermal friendly urban plan.

An Analysis of Heat Losses from Receivers for a Multifaceted Parabolic Solar Collector (접시형 태양열 집광시스템용 흡수기의 열손실 해석)

  • Ryu, S.Y.;Seo, T.B.;Kang, Y.H.
    • Solar Energy
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    • v.20 no.3
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    • pp.61-73
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    • 2000
  • Heat losses from receivers for a dish-type solar energy collecting system are numerically investigated. The analytical method for predicting conductive heat loss from a cavity receiver is used. The Stine and McDonald Model is used to estimate convective heat loss. Two kinds of techniques for the radiation analysis are used. The Net Radiation Method that is based on the radiation heat balance on the surface is used to calculate the radiation heat transfer rate from the inside surface of the cavity receiver to the environment. The Monte-Carlo Method that is the statistical approach is adopted to predict the radiation heat transfer rate from the reflector to the receiver. Based on the heat loss analysis, the performance of two different receivers for multifaceted parabolic solar collectors with several flat facets can be estimated, and the optimal facet size is obtained.

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Thermal analysis inside a small chamber including radiation (미소 챔버 내 복사열전달을 수반한 열유동 해석)

  • Lee, Hyung-Sik;Do, Gi-Jung;Lee, Sang-Ho
    • Proceedings of the SAREK Conference
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    • pp.194-198
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    • 2006
  • In this study, numerical modeling was performed to analyze air flow including radiation heat transfer inside a small chamber. Characteristics of heat transfer between source plate and target through glass are investigated for various surface temperature of heat source plate with buoyancy effect due to gravity force. Conduction heat transfer through the glass is considered and heat source plate is assumed to be a black body. Target surface temperature is largely affected by the radiation heat transfer. It can also be seen that as the source temperature increases target surface is dominated by radiation rather than convective heat transfer by air.

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