• 한국항공우주학회지
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• 제39권5호
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• pp.474-480
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• 2011

지구의 저궤도에서 운용되는 영상센서는 극저온 환경에서 태양 복사 뿐 아니라 지구의 적외선 및 알베도(Albedo)의 영향을 받는다. 극한 환경에 노출되는 영상센서는 작동/비작 동시 허용 온도를 벗어나지 않도록 열설계가 필요하며, 정상상태 에너지 평형식을 통해 필요한 방열판 면적 및 히터 예비 설계 값을 설정한다. 일반적으로 위성체 패널에 주기를 갖는 발열장비가 장착되어, 패널의 일부를 방열판 면적으로 설계한다. 본 논문에서는 위성체와 분리하여 설계하는 영상센서의 열제어를 위하여, 내부에서 항상 발열하는 장비의 열을 히트파이프를 이용하여 패널에 장착된 방열판으로 효과적으로 전달하도록 설계하였다. 예비 설계값을 기준으로 수치해석에 기반을 두는 SINDA를 이용하여 궤도 열해석을 실시하여, 방열 면적 및 히터 설계는 쉽고 빠르게 계산되어졌다. 또한, 방열 성능을 유지하면서 질량을 줄이도록 방열판을 립형상(Rib-type)으로 설계하였으며, 궤도 열해석 결과, 영상센서의 열적 요구사항을 만족함을 검증하였다.

• 신재생에너지
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• 제6권3호
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• pp.22-29
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• 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.

• 한국결정성장학회지
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• 제9권4호
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• pp.402-416
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• 1999

The thermal distributions near the growth interface of 150nm CZ crystals were measured by three thermocouples installed at the center, middle (half radius) and edge (10nm from surface) of the crystals. The results show that larger growth rates produced smaller thermal gradients. This contradicts the widely used heat flux balance equation. Using this fact, it is confirmed in CZ crystals that the type of point defects created is determined by the value of the thermal gradient(G) near the interface during growth, as already reported for FZ crystals. Although depending on the growth systems the effective length of the thermal gradient for defect generation are varied, we defined the effective length as 10n,\m from th interface in this experiment. If the G is roughly smaller than 20C/cm, vacancy rich CZ crystals are produced. If G is larger than 25C/cm, the species of point defects changes dramatically from vacancies to interstitials. The experimental results after detaching FZ and CZ crystals from the melt show that growth interfaces are filled with vacancies. We propose that large G produces shrunk lattice spacing and in order to relax such lattice excess interstitials are necessary. Such interstitials recombine with vacancies which were generated at the growth interface, nest occupy interstitial sites and residuals aggregate themselves to make stacking faults and dislocation loops during cooling. The shape of the growth interface is also determined by te distributions of G across the interface. That is, the small G and the large G in the center induce concave and convex interfaces to the melts, respectively.

• 한국지반공학회논문집
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• 제29권8호
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• pp.65-73
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• 2013

지중 열교환 시스템은 지속적인 에너지 효율의 개선으로 공간 냉난방을 위한 친환경적 에너지 기술로 주목받고 있다. 지중에 매설된 파이프는 내부 유체 순환을 통하여 인접한 지반과 열적 상호작용으로부터 직접적인 열에너지 교환을 수행한다. 하지만, 파이프의 수치모델링에서 열-수리가 연관된 난류해석과 파이프의 긴 세장비에 의한 메쉬사이즈의 부적합성은 열교환 시스템의 적절한 수치해석을 어렵게 하고 있다. 본 논문에서는 파이프 내부 유체흐름에 대한 에너지 보존의 법칙을 적용하여 지배방정식을 유도하였으며, Galerkin수식화와 시간적분을 통하여 열-수리 연동일차원 파이프 요소를 개발하였다. 그리고 제안된 파이프 요소를 기 개발된 다공질 재료를 위한 열-수리-역학(Thermo-Hydro-Mechanical) 해석을 위한 유한요소 프로그램과 결합하였다. 개발된 요소를 이용한 수치해석 결과는 열응답 시험(Thermal Response Test) 결과로부터 주위지반의 유효 열전도도를 평가하기 위하여 사용하는 선형 열원 모델이 인접 파이프간의 열적상호작용과 파이프의 단부효과에 의하여 지반의 열전도도를 과다 평가하는 것으로 보여주었다. 따라서 열응답 시험 해석 결과에 대한 역해석을 적용하여 최적의 수렴성을 보여주는 변환행렬을 제시하였다.

• 한국항공우주학회지
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• 제44권1호
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• pp.88-97
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• 2016

폐회로 열제어 시스템은 열진공 챔버의 온도를 $-150^{\circ}C{\sim}120^{\circ}C$와 같은 온도 조건으로 모사하기 위한 시스템으로, 극저온 블로워, 슈라우드, 히터, 극저온 밸브 등으로 구성된다. 본 연구는 우주 열환경 모사를 위한 폐회로 열제어 시스템의 설계 요소 정의 및 제어 변수별 실험 결과 등을 포함하고 있다. 폐회로 열제어 시스템 설계를 위해 설계 요소인 블로워 용량, 슈라우드 재질, 형태에 따른 특성 등의 분석을 수행 하였다. 폐회로 열제어 시스템의 극저온 블로워 필요 유량은 에너지 평형 방정식에 의해 결정되며, 제어는 작동 유체의 밀도 제어를 통해 제어된다. 밀도, 회전수와 같은 제어 변수별 실험을 통해 슈라우드 온도 분포 균질도 및 균일도를 측정하여 요구된 폐회로 열제어 시스템의 성능을 확인 하였다.

• 한국태양에너지학회 논문집
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• 제38권5호
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• pp.49-62
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• 2018

This study aims to analyze the performance of solar thermal system with heat pump for domestic hot water and heat supply. There are four types of system. Systems are categorized based on the existence of a heat pump and the ways of controlling the working fluid circulating from the collector. Working fluid is controlled by either temperature level (categorized as system 1 and 2) or sequential flow (system 3 and 4). Heat balance of the system, the solar fraction, hot water and heating supply rates, and performance of heat pump are analyzed using TRNSYS and TESS component programs. Technical specifications of the main facilities are as follow; the area of the collector to $25m^2$, the volumes of the main tank and the buffer tank to $0.5m^3$ and $0.8m^3$, respectively. Heating capacity of the heat pump in the heating mode is set to 30,000 kJ / hr. Hot water supply set 65 liters per person each day, total heat transfer coefficient of the building to 1,500 kJ / kg.K. Indoor temperature is kept steadily around $22^{\circ}C$. The results are as follows; 6 months average solar fraction of system 1 turns out to be 39%, which is 6.7% higher than system 2 without the heat pump, indicating a 25% increase of solar fraction compared to that of system 2. In addition, the solar fraction of system 1 is 2% higher than that of system 3. Hot water and heating supply rate of system 1 are 93% and 35%, respectively. Considering the heat balance of the system, higher heat efficiency, and solar fraction, as whole, it can be concluded that system 1 is the most suitable system for hot water and heat supply.

• 한국농공학회논문집
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• 제46권7호
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• pp.35-44
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• 2004

In this study, a ventilation model was developed to determine a ventilation rate for the balance of heat, moisture and $CO_{2}$ in a mushroom house. Internal and external temperature, relative humidity and $CO_{2}$ concentration were measured and used to validate the ventilation model. The effects of various environmental factors on physiological responses of mushroom were also investigated. The verified model was simulated under the observed ventilation rates with a difference of$ 0.001{\~}0.065\;m^{3}{\cdot}S^{-1}$ (relative error of $0.3{\~}18.9\%$) when external temperature varied 22.5 to $24.8^{circ}C$ and average ventilation rates was $0.35m^{3}{\cdot}S^{-1}$. The optimal conditions for mushroom growth (internal temperature $22 ^{circ}C$, relative humidity $80\%$, $CO_{2}$ concentration 1,000 ppm) were used for the model application with external temperature, relative humidity and $CO_{2}$ concentration of $27.5{\~}33.5^{circ}C$, $60\%$, and 355 ppm, respectively. Thermal balance was a important factor for an optimum ventilation up to the external temperature of $32^{circ}C$, while $CO_{2}$ concentration balance was more important over $32^{circ}C$. This suggests that humidification for moisture balance is required to maintain temperature and $CO_{2}$ concentration at an optimal level by ventilation in a mushroom house.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권4호
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• pp.220-228
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• 2002

The cool-down performance after soaking is very important in an automotive air-conditioning system and is considered as a key design variable. Therefore, transient characteristics of each system component are essential to the preliminary design as well as steady-state performance. The objective of this study is to develop a computer simulation model and ostinato theoretically the transient performance of an automotive air-conditioning system. To do that, the mathematical modelling of each component, such as compressor, condenser, receiver/drier, expansion valve, and evaporator, is presented first of all. The basic balance equations about mass and energy are used in modelling. For detailed calculation, condenser and evaporator are divided into many sub-sections. Each sub-section is an elemental volume for modelling. In models of expansion valve and compressor, dynamic behaviors are not considered in this analysis, but the quasisteady state ones are just considered, such as the relation between mass flow rate and pressure drop in expansion device, polytropic process in compressor, etc. Also it is assumed that there are no heat loss and no pressure drop in discharge, liquid, and suction lines. The developed simulation model is validated by comparing with the laboratory test data of an automotive air-conditioning system. The overall time-tracing properties of each component agreed well with those of test data in this case.

• 대한의용생체공학회:의공학회지
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• 제41권6호
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• pp.264-271
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• 2020

The purpose of this study was to investigate the effects of active vibration exercise of upper limb on physical capacity index (endurance, grip strength, balance, and flexibility) and vasomotor index (capillary length and body surface temperature) in middle aged women. 20 participants randomly divided into two groups: vibro-swing exercise (VSE) and non vibro-swing exercise (NVSE). Subjects in each group measured the 30 second arm curl test, hand dynamometer, one leg standing test, back scratch test, nail fold capillary microscope (NFM), and digital infrared thermal imaging (DITI) before and after exercise. The results showed that active vibration exercise of upper limb with vibro-swing equipment increased the endurance, balance ability, and the capillary length. In addition, changes in body temperature immediately after exercise were predicted to affect vasomotor. Active vibration exercise of upper limb has the advantage of being able to exercise anywhere regardless of the location by inducing different frequency changes in movement of various ranges and velocity. For this reason, the combination of vibration and active movement can be expected the physiological effects when producing exercise programs for middle aged women.

• 한국항공우주학회지
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• 제41권11호
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• pp.921-930
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• 2013

(주)쎄트렉아이는 고해상도 전자광학카메라인 EOS-D Ver.1.0의 개발 및 검증을 성공적으로 완료하였다. EOS-D Ver.1.0 시스템은 기존 EOS-C 계열 대비 향상된 공간 해상도 및 방사학적 해상도를 갖도록 설계되었다. EOS-D Ver.1.0의 열제어계는 능동 열제어 방식과 수동 열제어 방식을 혼용하여 개발되었다. 또한, 광학계 주구조물의 수분 발산 효과에 의한 비정렬 상태를 보상할 수 있도록 초점 조절장치(refocusing mechanism)를 설계하고 이를 검증하였다. 설계를 바탕으로 실제 모델을 제작, 인증 수준의 열진공 시험을 통해 설계 여유(design margin)와 작업도(workmanship)를 확인하였다. 또한 열-수치 모델(TMM)에 대한 검증 작업을 수행하여 해석 모델이 실제 모델의 열적 특성을 잘 모사하고 있음을 확인하였다.