• 신재생에너지
• /
• 제6권3호
• /
• pp.22-29
• /
• 2010

The concept of Ocean Thermal Energy Conversion (OTEC) is simple and various types of OTEC have been proposed and tried. However the location of OTEC is limited because OTEC requires $20^{\circ}C$ of temperature difference as a minimum, so most of OTEC plants were constructed and experimented in tropical oceans. To solve this we proposed the modified OTEC which uses condenser discharged thermal energy of existing fossil or nuclear power plants. We call this system CTEC (Condenser Thermal Energy Conversion) as this system directly uses $32^{\circ}C$ partially saturated steam in condenser instead of $20{\sim}25^{\circ}C$ surface sea water as heat source. Increased temperature difference can improve thermal efficiency of Rankine cycle, but CTEC should be located near existing plant condenser and the length of cold water pipe between CTEC and deep cold sea water also increase. So friction loss also increases. Calculated result shows the change of efficiency, pumping power, net power and other parameters of modeled 7.9 MW CTEC at given condition. The calculated efficiency of CTEC is little larger than that of typical OTEC as expected. By proper location and optimization, CTEC could be considered another competitive renewable energy system.

• 대한기계학회논문집B
• /
• 제26권3호
• /
• pp.474-481
• /
• 2002

Fouling deposits due to surface-coated particles have been calculated using CFD techniques. The sticking probabilities of the surface-coated particles are also evaluated on the basis of an energy balance. The sticking probabilities of the deposit surface are also included in the prediction of the deposition occurring through the multiple impaction of particles with the deposit surface. The sticking probability of an impacting particle is expressed in terms of such parameters as particle viscosity, surface tension, impact velocity, impact angle and the thickness of the sticky layer on a particle. Particulate behavior around a tube in cross flow was studied using the Lagrangian approach. Three important parameters i.e. impact velocity, impact angle, and particulate concentration, were used in the prediction of deposition rate. The computational predictions were found to be in good agreement with the experimental data.

• 한국지리정보학회지
• /
• 제18권1호
• /
• pp.90-104
• /
• 2015

본 연구의 목적은 위성영상을 이용해 시공간 증발산량을 모의할 수 있는 증발산량 산정 모형을 구축하고, 플럭스 타워 실측 증발산량과 비교를 통해 적용성을 평가하는데 있다. 증발산량 산정 모형은 SEBAL(Surface Energy Balance Algorithm for Land)을 구축하였으며, 모형 내 일부 알고리즘을 수정하여 적용하였다. SEBAL 모형의 위성 입력 자료로는 2개년(2012-2013)의 MODIS Normal Distribution Vegetation Index(NDVI), Albedo, Land Surface Temperature(LST) 영상을 500m의 공간해상도로 구축하였으며, 유역주변 기상청 기상관측소(5개 지점)의 풍속, 풍속측정높이, 일사량 자료를 내삽(Interpolation)하여 활용하였다. 모형의 적용성 평가를 위하여 금강유역의 용담댐을 대상으로 공간 증발산량을 산정하여 유역 내에 위치한 덕유산 플럭스 타워의 산림 증발산량과 비교분석하였다. 모형 매개변수 중 Albedo와 NDVI, 지표 거칠기(Surface roughness) 순으로 민감한 것으로 분석되었으며, 모형의 보정을 위해 최종적으로 Albedo와 NDVI는 월별 평균값을 적용하였다. 모의 기간 동안의 결정계수($R^2$)는 0.45이었다. SEBAL 모형은 특히 지형적 특성을 반영하므로 유역내에서 고지대에 비해 저지대에서 증발산량이 높게 산정되는 경향을 보였다.

• 대한원격탐사학회지
• /
• 제32권3호
• /
• pp.201-220
• /
• 2016

본 연구에서는 대기 상단에서 반사된 복사와 지표면에서 흡수된 복사에너지가 서로 선형 관계임을 보인 기존의 알고리즘을 MODerate resolution Imaging Spectroradiometer (MODIS) 관측 자료에 적용시킬 수 있도록 개선하여 하향 및 순 태양 복사에너지를 산출하였다. 비교 검증을 수행하기 위해 Clouds and the Earth's Radiant Energy System (CERES) 센서와 강릉원주대학교(GWNU), 미국의 Atmospheric Radiation Measurement (ARM) 관측소의 지상 일사계 자료를 사용하였다. 지구 에너지 수지와 관련하여 지표면에서의 복사에너지를 비교하기에 앞서 알고리즘을 통한 산출 결과와 CERES 자료의 대기 상단 복사에너지를 비교한 결과, 결정계수가 0.9이상을 보여 상당히 유사함을 보였지만 Root-Mean-Square-Deviation (RMSD) 값이 다소 차이가 있는 것으로 나타났고 하향과 순 태양 복사에너지도 비슷한 결과를 얻었다. 강릉원주대학교 자료와 비교한 결과, 본 연구의 알고리즘을 통해 산출된 결과가 CERES 자료보다 작은 RMSD를 보임으로서 더 높은 정확도를 보였다. 한편, ARM 관측소의 경우 하향 태양 복사에너지의 평균적인 RMSD가 CERES 자료에 비해 다소 크게 산출되었지만 순 태양 복사에너지의 경우 비슷한 결과가 나타났으며 시 공간 해상도를 고려하였을 때 상당히 유사한 경향을 보이고 있음을 확인하였다. 본 연구에서 파악된 문제점에 대한 개선을 통해 향후 지상 관측을 대신하여 위성 관측으로부터 지표면에서의 하향 및 순 태양 복사에너지 자료를 고해상도로 제공하는데 유용하게 활용될 수 있을 것으로 기대된다.

• 한국수소및신에너지학회논문집
• /
• 제23권4호
• /
• pp.300-309
• /
• 2012

Long endurance is a key issue in the application of unmanned aerial vehicles. This study presents feasibility test results when fuel cell system as an alternative to the conventional engine is applied for the power of the UAV after the 150W fuel cell system is developed and packaged to the 1/4 scale super cub airplane. Fuel cell system is operated by dead-end method in the anode part and periodically purged to remove the water droplet in flow field during the operation. Oxygen in the air is supplied to the stack by the two air blowers. And fuel cell stack is water cooled by cooling circuit to dissipate the heat generated during the fuel cell operation. Weight balance is considered to integrate the stack and balance of plant (BOP) in package layout. In flight performance test, we demonstrated 4 times standalone take-off and landing. In the laboratory test simulating the flight condition to quantify the energy flow, the system is analyzed in detail. Sankey diagram shows that electric efficiency of the fuel cell system is 39.2%, heat loss 50.1%, parasitic loss 8.96%, and unreacted purged gas 1.67%, respectively compared to the total hydrogen input energy. Feasibility test results show that fuel cell system is high efficient and appropriate for the power of UAV.

• 한국습지학회지
• /
• 제11권1호
• /
• pp.105-113
• /
• 2009

연안습지 생태계에서 열에너지 교환 과정은 매우 중요하다. 지표 열에너지 평형을 이루는 요소인 순복사플럭스, 현열 플럭스, 잠열 플럭스 그리고 토양열 플럭스를 전라남도 고흥에 위치한 수평적으로 균질하다고 판단되는 지역인 고흥만 간척지에서 관측하고 분석하였다. 열의 수송을 평가하기 위해서 5회의 집중관측 기간에 대기 난류를 측정하였고, 특히 갈대로 덮여있는 간척지에서 지표층 열에너지 수지를 분석하기 위해서는 물과 매우 미세한 입자로 구성된 토양 그리고 계절에 따라 색깔과 밀도가 변하는 식생캐노피를 고려하였다. 순복사 플럭스, 현열 플럭스, 잠열 플럭스, 토양열 플럭스를 기존의 에너지 수지방정식에 적용하여 식생과 토양과 같은 지표면 특성에 따른 열 플럭스의 특징을 조사하여 습지의 기온조절 효과에 대해 알아보았다. 에너지 수지비로 식생 성장기에는 주로 잠열 플럭스에 의해 열이 대기로 전달되는 것을 알 수 있었다. 또한 식생층은 열을 저장하여 기온의 일교차를 줄이는 역할을 한다. 여름철에 집중관측지의 기온이 주변 지역의 기온보다 보다 낮고 겨울철에는 다소높게 나타난 결과는 식생층을 포함하는 연안습지가 열환경을 조절함을 보여주었다.

• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
• /
• pp.81-114
• /
• 1999

The strain, surface and inerfacial energies of III-V ternary systems were calculated for three kinds of structure modes: the Frank-van der Merwe (FM) mode, the Stranski-Krastanov (SK) mode an the Volmer-Wever (VW) mode. The free energy for each mode was estimated as functions of the thickness and composition or lattice misfit. Through comparison of the free energy of each mode, it was found that the thickness-composition phase diagrams of III-V ternary systems can be determined only by considering the balance of the free energy and three kinds of structure modes appear in the phase diagrams. The SK mode appears only when the lattice misfit is large and/or the lattice layer is thick. The most stable structure of the SK mode is a cluster with four lattice layers or minimum thickness on a wetting layer of increasing lattice layers. The VW mode appears when the lattice misfit is large and the lattice layer is thin and only in the InPSb/InP and GaPSb/GaP systems which have the largest lattice misfit of III-V ternary systems. The stable region of the SK mode in the GaPSb/GaP and InPSb/InP phase diagrams is largest of all because the composition dependence of the strain energy of these systems is stronger than that of the other systems. The critical number of lattice layers below which tow-dimensional (2D) layers precede the three-dimensional (3D) nucleation in the SK mode at x=1.0 depnds on the lattice misfit.

• 한국대기환경학회지
• /
• 제19권3호
• /
• pp.285-296
• /
• 2003

The measurement of the radiation energy, trunk temperature, leaf area index (LAI), air temperature, vapor pres-sure, and precipitation has been conducted under a mixed forest at Kwangneung Arboretum during the period of 2001. Characteristics of the diurnal and seasonal variation of the radiative energy were investigated. The aerodynamic roughness length was determined as about 1.6 m and the mean albedo was about 0.1 The downward short-wave radiation was linearly correlated with the net radiation and its correlation coefficient was about 0.96. From this linear relation, the heating coefficient was calculated and its annual mean value was about 0.21 The albedo and heating coefficient was varied with season, surface characteristics, and meteorological conditions. The diurnal and seasonal variations of radiation energy were discussed in terms of the surface characteristics and meteorological conditions. In the daytime, during clear skies, net radiation was dominated by the shortwave radiation. In presence of clouds and fog, the radiation energy was diminished. At night, the net radiation was entirely dominated due to the net longwave radiation. There was no distinct diurnal variation in net radiation flux during the overcast or rainy days. The net radiation was strongest in spring and weakest in winter. The seasonal development in leaf area was also reflected in a strong seasonal pattern of the radiation energy balance. The timing, duration, and maximum leaf area and trunk temperature were found to be an important control on radiation energy budget. The trunk temperature was either equal or warmer than air temperature during most of the growing season because the canopy could absorb a substantial amount of sunlight. After autumn (after the middle of October), the trunk temperature was consistently cooler than air temperature.

• 한국인쇄학회지
• /
• 제18권1호
• /
• pp.71-81
• /
• 2000

The water-based ink has lately attracted considerable attention because of problems of energy and population. Carbon blacks have been widely utilized in water-based systems to provide pigmentation. One of the most important factors in the successful formulation of an aqueous system containing carbon black is the dispersion and the selection and proper utilization of the dispersing agent. This is similar to water-based ink. This paper discusses dispersion of carbon black with the factors affecting the dispersing agent requirement (DAR) and describes a laboratory method for determining it. Variables that affect the dispersion, such as structure, surface area, and oxidation level of the carbon black are examined through test data. Anionic and nonionic dispersing agents are evaluated using the DAR method. From this study, the increased surface area, the increased DAR is indicated. DAR is indicated to depend on HLB(Hydrophilic Lipophilic Balance) of dispersing agent and pH of dispersing system.

• 대한기계학회논문집B
• /
• 제23권11호
• /
• pp.1481-1489
• /
• 1999

The sliding-belt concept introduced by Bechert et al. (AIAA J., Vol. 34, pp. 1072~1074) is numerically applied to a turbulent boundary layer flow for the skin-friction reduction. The sliding belt is moved by the shear force exerted on the exposed surface of the belt without other dynamic energy input. The boundary condition at the sliding belt is developed from the force balance. Direct numerical simulations are performed for a few cases of belt configuration. In the ideal case where the mechanical losses associated with the belt can be ignored, the belt velocity increases until the integration of the shear stress over the belt surface becomes zero, resulting in zero skin friction on the belt. From practical consideration of losses occurred In the belt device, a few different belt velocities are given to the sliding belt. It is found that the amount of drag reduction is proportional to the belt velocity.