• Journal of Mechanical Science and Technology
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• 제17권8호
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• pp.1185-1195
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• 2003

Heat losses from the receivers of a dish-type solar energy collecting system at the Korea Institute of Energy Research (KIER) are numerically investigated. It is assumed that a number of flat square mirrors are arranged on the parabolic dish structure to serve as a reflector. Two different types of receivers, which have conical and dome shapes, are considered for the system, and several modes of heat losses from the receivers are thoroughly studied. Using the Stine and McDonald model convective heat loss from a receiver is estimated. The Net Radiation Method is used to calculate the radiation heat transfer rate by emission from the inside surface of the cavity receiver to the environment. The Monte-Carlo Method is used to predict the radiation heat transfer rate from the reflector to the receiver. Tracing the photons generated, the reflection loss from the receivers can be estimated. The radiative heat flux distribution produced by a multifaceted parabolic concentrator on the focal plane is estimated using the cone optics method. Also, the solar radiation spillage around the aperture is calculated. Based on the results of the analysis, the performances of two different receivers with multifaceted parabolic solar energy collectors are evaluated.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1363-1370
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• 1997

Single liquid droplet combustion processes including heating, evaporation, droplet burning and flame radiation were theoretically investigated by adopting nongray gas radiation model for the radiative transfer equation (RTE). n-Heptane was chosen as a fuel and the numerical results were compared with the experimental data available in the literature. The discrete ordinate method (DOM) was employed to solve the radiative transfer equation and the weighted sum of gray gases model (WSGGM) was applied to account for nongray effect by CO$_{2}$, and H$_{2}$0. Therefore, detailed effects by nongray gas and its comparison with the gray gas model could be figured out in the results. It is found that the radiative heat flux is higher when the nongray model is used, thereby reducing the maximum gas temperature and the flame thickness, but the total burning time increases due to the deceased conductive heat flux in nongray model. Consequently, a better agreement with experimental data could be obtained by using nongray model.

• 한국환경과학회지
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• 제12권7호
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• pp.705-713
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• 2003

In mid-August 2002, under clear summer pressure patterns, we carried out an intensive meteorological observation to examine the warming effects due to artificial constructions in a large housing complex. We set an automatic weather system(AWS) at two places in a bare soil surface within a limited development district and an asphalt surface within a large apartment residence area, respectively. As a result of observation, it became clear that the difference of the surface air(ground) temperature between the bare soil surface and its peripheral asphalt area reached about 4$^{\circ}C$(13$^{\circ}C$) at the maximum from diurnal variation of surface temperatures on AWS data. Through the heat balance analysis using measurement data, it became clear that the thermal conditions at two places are dependent on the properties of surface material. The latent heat flux over the bare soil surface reached to about 300 W/㎡, which is more than a half of net radiation during the daytime. On the other hand, it was nearly zero over the asphalt surface. Hence, the sensible heat flux over the asphalt surface was far more than that of the bare soil surface. The sensible heat flux over the asphalt surface showed about 20∼30 W/㎡ during the night. It was released from asphalt surface which have far more heat capacity than that of bare soil surface.

• 한국산업융합학회 논문집
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• 제4권1호
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• pp.35-40
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• 2001

A spectral measurement system for reflection and transmission properties by using an optical fiber and an ellipsoidal mirror was newly developed. The hemispherical reflectance and transmittance spectra of several heating resisting ceramics materials were measured from visible to middle infrared region. The directional characteristics of reflection and transmission were also investigated in consideration of the absorptance. The measured data were analyzed by using a four flux model of radiation transfer, The radiation properties could be estimated by the obtained scattering and absorption coefficient spectra.

• Journal of Computational Design and Engineering
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• 제3권4호
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• pp.330-336
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• 2016

The present work is concerned with heat and mass transfer of an electrically conducting second grade MHD fluid past a semi-infinite stretching sheet with convective surface heat flux. The analysis accounts for thermophoresis and thermal radiation. A similarity transformations is used to reduce the governing equations into a dimensionless form. The local similarity equations are derived and solved using Nachtsheim-Swigert shooting iteration technique together with Runge-Kutta sixth order integration scheme. Results for various flow characteristics are presented through graphs and tables delineating the effect of various parameters characterizing the flow. Our analysis explores that the rate of heat transfer enhances with increasing the values of the surface convection parameter. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of thermal radiation parameter.

• Journal of Radiation Protection and Research
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• 제35권3호
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• pp.99-104
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• 2010

The potential ability of environmental temperature to enhance the effect of microwave radiation (7 GHz) was experimentally studied for rabbit heating after simultaneous application of both agents. The tested ambient temperatures (30 and $38^{\circ}C$) didn't exert a considerable influence upon rabbit heat homeostasis after the used duration of exposure (3 hours and 15 minutes, correspondingly). The synergistic interaction of microwave irradiation and ambient temperature was demonstrated for rabbit heating. Power flux density of microwave irradiation was shown to be a determinant of the synergistic interaction effectiveness. For the fixed ambient temperature ($30^{\circ}C$), the synergism was shown to be observed only within a definite power flux density ($0-100\;mW{\cdot}cm^{-2}$), inside of which there was an optimal intensity ($20\;mW{\cdot}cm^{-2}$), which maximized the synergistic effect. Any deviation of the power flux density from the optimal value resulted in a reduction of the synergy. It is concluded that any assessment of the health or environmental risks should take into account the synergistic interaction between ambient temperature and microwave radiation.

• 한국수산과학회지
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• 제29권1호
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• pp.84-91
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• 1996

각종 해${\cdot}$기상 자료와 위성관측에 의한 운량 자료를 이용하여 벌크법에 의해 동지나해에 있어서 대기와 해양간의 열속을 추정하였으며, 그 결과를 요약하면 다음과 같다. 1) 태양복사량은 5월에 $255Wm^{-2}$로 최대, 12월에 $111Wm^{-2}$로 최소이며, 그 분포는 동절기에는 남쪽으로 갈수록 증가하고, 하절기에는 장마전선의 영향으로 북쪽으로 갈수록 증가하는 경향이 있었다. 장파복사량의 경우, 공간적 분포의 차이는 작으나 계절에 따른 차이는 커서 최대인 2월의 값은 (약 $70Wm^{-2}$) 최소인 7월의 2배에 이른다. 2) 현열과 잠열의 공간적 분포양상은 조사해역내의 해류 분포와 비슷하였다. 겨울철에 이 두 요소에 의한 해양의 열손실량은 대단히 커서 $830Wm^{-2}$ 이상이고, 이것은 같은 기간중 순폭사량의 5배에 이른다. 3) 연평균 순열플럭스의 분포는 전역에서 부 값을 보였으며, 최대 열손실 해역은 큐슈 남단으로 1월에 $400Wm^{-2}$ 이상이었다. 4) 조사해역의 태양복사량, 장파복사량, 현열 및 잠열의 연평균치는 각각 187, -52, -30, $-137Wm^{-2}$이고, 결과적으로 연간 약 $32Wm^{-2}(2.48\times10^{13}\;W)$의 에너지를 손실하고 있는 것으로 추정되었다. 5) Fig. 1에 표시되어 있는 A 해역 (황해)은 대기와의 열교환을 통하여 오히려 연간 $10Wm^{-2}(0.4\times10^{13}\;W)$의 에너지를 얻고, B 해역 (동지나해)은 $48Wm^{-2}(2.1\times10^{13}\;W)$,그리고 C 해역 (쿠로시오역)은 $39Wm^{-2}(1.7\times10^{13}\;W)$의 열을 손실하고 있는 것으로 추정되었다.

• 한국환경과학회지
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• 제29권10호
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• pp.981-988
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• 2020

This study presents meteorological data integrity to improve environmental quality assessment in Yongdam catchment. The study examines both extreme ranges of meteorological data measurements and data reliability which include maximum and minimum temperature, relative humidity, dew point temperature, radiation, heat flux. There were some outliers and missing data from the measurements. In addition, the latent heat flux and sensible heat flux data were not reasonable and evapotranspiration data did not match at some points. The accuracy and consistency of data stored in a database for the study were secured from the data integrity. Users need to take caution when using meteorological data from the Yongdam catchment in the preparation of water resources planning, environmental impact assessment, and natural hazards analysis.

• 대기
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• 제16권2호
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• pp.111-124
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• 2006

This study examines seasonal variability of the surface energy balance at the King Sejong Station, Antarctica, using measurements and estimates of the components related to the balance for the period of 1996 to 2004. Annual average of downward shortwave radiation at the surface is 81 $Wm^{-2}$ which is 37% of the extraterrestrial value, with the monthly maximum of 188 $Wm^{-2}$ in December and the minimum of 8 $Wm^{-2}$ in June. These values are relatively smaller than those at other stations in Antarctica, which can be attributed to higher cloudy weather conditions in Antarctic front zone. Surface albedo varies between ~0.3 in the austral summer season and ~0.6 in the winter season. As a result, the net shortwave radiation ranges from 117 $Wm^{-2}$ down to 3 $Wm^{-2}$ with annual averages of 43 $Wm^{-2}$. Annual average of the downward longwave radiation shows 278 $Wm^{-2}$, ranging from 263 $Wm^{-2}$ in August to 298 $Wm^{-2}$ in January. The downward longwave radiation is verified to be dependent strongly on the air temperature and specific humidity, accounting for 74% and 79% of the total variance in the longwave radiation, respectively. The net longwave radiation varies between 25 $Wm^{-2}$ and 40 $Wm^{-2}$ with the annual averages of 30 $Wm^{-2}$. Accordingly, the annual average energy balance is dominated by radiative warming of a positive net all-wave radiation from September to next March and radiative cooling of a negative net all-wave radiation from April to August. The net all-wave radiative energy gain and loss at the surface is mostly balanced by turbulent flux of sensible and latent heat. The soil heat flux is of negligible importance in the surface energy balance.

• 대한기계학회논문집B
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• 제37권2호
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• pp.197-204
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• 2013

본 연구에서는 덕트 버너를 추가적으로 사용하는 수직형 배열회수 보일러(HRSG)에서 발생하게 되는 화염에 의한 전열면으로의 화염 복사 열전달에 의한 영향을 살펴보기 위한 해석 기법을 마련하였다. 덕트 버너 화염과 전열면은 가상의 평면으로 가정하였고, 화염 온도, 면적 및 방사율 입력정보는 간략화 하였다. 덕트버너 설치 위치 및 연료를 달리한 3 가지 해석 case 가 고려되었으며 계산된 화염 복사 열전달률과 열유속은 삼원자 가스 복사 및 대류 열전달과 비교되었다. 모든 해석 case 에서 삼원자 가스복사 열전달에 의한 영향은 미미하였고, 전열면에서 대류 열전달 대비 화염 복사 열전달률은 8~41%인 것으로 나타났다. 이 연구에서 얻은 중요한 사실은 화염 복사가 집중되는 전열면의 중앙부분에서 국부적인 열유속은 화염 복사에 의해 완전히 지배된다는 것이다.