• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.104-107
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• 2000

Evaporative heat transfer characteristics of carbon dioxide has been investigated. Experiment has been carried out for seamless stainless steel tube with outer diameter of 9.55 mm and inner diameter of 7.75 mm. Direct heating method is used for supplying heat to the refrigerant was uniformly heated by electric current which was applied to the tube wall. The saturation temperature of refrigerant is calculated from the measured saturation pressure by using an equation of state. Inner wall temperature was calculated from measured outer wall temperature, accounting for heat generation in the tube and heat conduction through the tube wall. Mass Quality of refrigerant was calculated by considering energy balance in the preheater and the test section. Heat fluxes were set at 12, 16, 20, 23, and $27kW/m^2$, mass fluxes were controlled at 212, 318, 424, and $530 kg/m^2s$, and saturation temperature of refrigerant were adjusted at 0, 3.4, 6.7 and $10.5^{\circ}C$. From this study, heat transfer coefficients of carbon dioxide have been provided with respect to quality for several mass fluxes, heat fluxes. Finally, the experimental results in this study are compared with the correaltion by Gungor and Winterton(1987).

• 한국환경과학회지
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• 제4권2호
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• pp.139-150
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• 1995

한국남해 연안에 위치한 득량만에 있어서 하계의 태양복사, 바람, 조류에 의한 해양의 연적성층 및 연적혼합현상의 시간적 변동특성을 밝히기 위한 연구를 수행하였따. 이를 위하여 27개 정점에서 관측된 수온, 염분, 밀도값을 분석하였고. Simpson과 Hunter(1974)가 제안한 위치에너지 개념을 도입한 에너지 방정식을 이용하여 태양복사, 바람, 조류에너지를 각각 계산하였다. 그 결과 하계 득량만 해양의 연직 성층 및 혼합현상은 태양복사에너지가 일정하다고 할때 바람보다는 조류에 의해 크게 좌우됨을 알 수 있었고, 조류에너지에 의한 수괴의 연직합에너지이여율 $epsilon$의 값은 약 0.010 ~ 0.014사이를 나타내고 있었다.

• 한국수소및신에너지학회논문집
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• 제30권2호
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• pp.136-146
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• 2019

A solid oxide fuel cell (SOFC) based hybrid desiccant cooling system model is developed to study the effect of fuel utilization rate of the SOFC on the reduction of energy consumption and $CO_2$ emission. The SOFC-based hybrid desiccant cooling system consists of an SOFC system and a Hybrid desiccant cooling system (HDCS). The SOFC system includes a stack and balance of plant (BOP), and HDCS. The HDCS consists of desiccant rotor, indirect evaporative cooler, electric heat pump (EHP), and heat exchangers. In this study, using energy load data of a commercial office building and SOFC-based HDCS model, the amount of ton of oil equivalent (TOE) and ton of $CO_2$ ($tCO_2$) are calculated and compared with the TOE and $tCO_2$ generation of the EHP using grid electricity.

• 한국수소및신에너지학회논문집
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• 제20권5호
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• pp.384-389
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• 2009

KEPRI (Korea Electric Power Research Institute) has studied planar type solid oxide fuel cell (SOFC) stacks using anode-supported cells and kW class co-generation systems for residential power generation. In this work, a 1 kW SOFC system consisted of a hot box part, a cold BOP (balance of plant) part, and a hot water reservoir. The hot box part contained a SOFC stack made up of 48 cells, a fuel reformer, a catalytic combustor, and heat exchangers. Thermal management and insulation system were especially designed for self-sustainable operation in that system. A cold BOP part was composed of blowers, pumps, a water trap, and system control units. When the 1 kW SOFC stack was tested using hydrogen at $750^{\circ}C$, the stack power was about $1.2\;kW_e$ at 30 A and $1.6\;kW_e$ at 50 A. Turning off an electric furnace, the SOFC system was operated using hydrogen and city gas without any external heat source. Under self-sustainable operation conditions, the stack power was about $1.3\;kW_e$ with hydrogen and $1.2\;kW_e$ with city gas respectively. The system also recuperated heat of about $1.1\;kW_{th}$ by making hot water.

• 대한공간정보학회지
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• 제19권4호
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• pp.145-151
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• 2011

증발산(Evapotranspiration)은 생태학 수문학적으로 지표 특성을 표현하는 변수로서 지구 물 순환과 에너지 수지에 중요한 역할을 한다. 본 연구에서는 높은 지표거칠기를 고려하여 에너지 수지식을 기반으로 실제 증발산량을 산출하였다. 2009년 한반도를 대상으로 다양한 위성 자료와 관측 자료를 이용하여 연구를 수행하였다. 실제 증발산량 산출에 있어 중요한 변수인 현열은 다양한 입력 변수가 사용되어 계산 과정이 복잡하므로 본 연구에서는 경험적 계수인 B를 사용하여 현열 산출을 단순화하였다. 또한 본 연구에서는 현열 산출 시 중요한 변수인 공기역학적 저항을 고려하여 높은 지표거칠기를 반영한 실제 증발산량 모델을 제시하였다. 산출된 실제 증발산량은 Priestley-Taylor 가능 증발산량을 통한 검증(RMSE 1.0179mm/day, BIAS 0.4516mm/day)을 수행하였으며 높은 지표거칠기를 고려한 실제 증발산량이전반적으로 잘 산출되었음을 알 수 있었다.

• 대기
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• 제34권1호
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• pp.69-81
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• 2024

In this paper, Annual flux variations in the Boseong Tall Tower (BTT) from 2016 to 2020 were analyzed using data from three levels (2.5 m, 60 m, and 300 m). BTT was installed in Boseong-gun, Jeollanam-do in February 2014 and continued to conduct energy exchange observations such as CO2, sensible heat, and latent heat using the eddy covariance method until March 2023. The BTT was located in a very flat and uniform paddy field, and flux observations were conducted at four levels: 2.5 m, 60 m, 140 m, and 300 m above ground. Surface energy balance was confirmed from observed data of net radiation flux, soil heat flux, sensible heat flux, and latent heat flux. Additionally, 2.5 m height surface fluxes, which are most influenced by agricultural land, were compared with data from Local Data Assimilation and Prediction System (LDAPS) of the Korea Meteorological Administration to evaluate the accuracy of LDAPS flux data. The correlation coefficient between LDAPS flux data and observed values was 0.95 or higher. Excluding summer latent heat flux data, there was a general tendency for LDAPS data to be higher than observed values. The footprint areas estimated below 60 m height mainly covered agricultural land, and flux observations at 2.5 m and 60 m heights showed typical agricultural characteristics. In contrast, the footprint estimated at 300 m height did not show agricultural characteristics, indicating that observations at this height encompassed a wide range, including mountains, sea, and roads. The analysis results of long-term flux observations can contribute to understanding the energy and carbon dioxide fluxes in agricultural fields. Furthermore, these results can be utilized as essential data for validating and improving numerical models related to such fluxes.

• 한국토양비료학회지
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• 제23권2호
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• pp.94-99
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• 1990

콩군낙(群落)(팔달(八達)콩 ; 재식밀도(栽植密度) $45{\times}10cm$)에서의 열수지성분(熱收支成分) 변화(變化)를 계절별(季節別)로 관측(觀測)하고 열수지법(熱收支法)으로 증발산량(蒸發散量)을 계산(計算)하여 건물생산량(乾物生産量)과의 관계(關係)를 구한 결과(結果)는 다음과 같다. 1. 맑은날의 전단파복사량(全短波輻射量)에 대한 순복사량(純輻射量)의 비율(比率)은 59~76%로 흐린날의 63~83%보다 낮았다. 2. 순복사량(純輻射量)에 대한 잠열전달량(潛熱傳達量)의 비율(比率)은 흐린날에 100%를 넘는 경우가 있어 때때로 이류(移流)에 의한 열복사(熱輻射)의 수평전도(水平傳導)가 있었다. 3. 1시간(時間)마다 적산(積算)한 일적산순복사량(日積算純輻射量)(Rn)과 증발잠열(蒸發潛熱)($LE_{(+)}$) 및 화간순복사량(畵間純輻射量)($Rn_{(+)}$)과 증발잠열(蒸發潛熱)과의 관계(關係)는 각각(各各) 다음과 같은 직선관계(直線關係)가 성립(成立)하였다. $$LE_{(+)}=0.971\;Rn+1.122\;R^2=0.9017$$ $$LE_{(+)}=0.882\;Rn_{(+)}+1.945\;R^2=0.8836$$ 4. 열수지계산(熱收支計算)에 의한 군낙증발산량(群落蒸發散量)(ETa)과 대형(大型) pan 증발량(蒸發量)(Epan)과의 관계(關係)는 다음과 같았다. ETa = 1.049 Epan + 1.657 $$R^2=0.6589$$ 5. 생육초기(生育初期)를 제외(除外)한 생육기간중(生育期間中) 건물(乾物)로의 물이용효율(利用效率)은 $2.31g{\cdot}DM{\cdot}kg^{-1}\;H_2O$이었으며, 평균일증발산량(平均日蒸發散量)은 5.29mm, 일사량중(日射量中) 군낙(群落)의 증발산(蒸發散)으로 소비(消費)된 열량(熱量)의 비율(比率)은 85%이었다.

• 한국자동차공학회논문집
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• 제19권6호
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• pp.53-60
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• 2011

The effect of exhaust heat recovery system can be evaluated by two well known method. First method is to measure the time duration from engine start under cold coolant temperature till coolant get warmed. By this methodology coolant warming duration can be index of warm-up effect. Second method is to analyze heat balance of the engine during warm-up phase under steady engine operation so that wasted energy by losses such as cooling and exhaust can be index of warm-up effect. This study focused on evaluation of warming-up effect by both methodology above mentioned using 2L SI engine under from idle to 2000rpm steady condition. Results, idle operation showed low heat recovery efficiency but under higher engine speed condition, remarkable heat recovery efficiency improvement was observed. In 2000rpm steady condition, warm-up duration of engine is decreased by exhaust heat recovery system.

• 설비공학논문집
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• 제3권2호
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• pp.114-122
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• 1991

A thermal analysis method taking into account energy balance in each elements of heat exchanger was introduced. This method has a merit in predicting the temperature field over the heat exchanger in detail. To verify this method, the results were compared with the published ones. The thermal analysis of the radiator in vehicles was also conducted and the results were compared with experimental ones. It is concluded that this method can be used in thermal analysis with relatively small error. When the velocity profile of inlet air is not uniform, the outlet temperature of cooling water is higher than that of uniform velocity profile.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1201-1212
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• 1999

A numerical analysis is performed to predict the thermal response and ablation rate for charring or non-charring material which is designed to be used as thermal protection system (TPS). The numerical program composed of in-depth energy balance equation and the aerotherm chemical equilibrium (ACE) program. The ACE program calculates various thermochemical state from ablation products. The developed numerical program is verified by comparing the reported results from literature. The sensitivity tests for input parameters are performed. The thermal behavior of ablating material is mainly affected by density of ablating material, convective heat transfer coefficient and recovery enthalpy of flow field.