• 한국건축시공학회지
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• 제11권5호
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• pp.452-458
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• 2011

활성탄을 혼입한 모르타르의 특성을 분석한 결과 유동성 측면에서는 무치환과 참나무 숯 모두 큰 차이를 보이지 않았고, 강도적인 측면에서는 활성탄을 혼입한 모르타르의 강도가 참나무 숯과 무치환 모르타르에 비해 높게 나타났다. 열적 특성은 치환율이 증가할수록 두 혼화재 모두열전도율이 감소하는 경향을 보여 단열성능이 우수함을 입증하였다. 결과적으로 활성탄을 혼입한 모르타르가 강도와 단열성능이 우수함을 증명하여 기존의 활성탄이 가지고 있는 오염물질 흡착성능과 함께 우수한 건축 마감재로서의 여러 성능이 검증되었다.

• Journal of Ceramic Processing Research
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• 제20권1호
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• pp.48-53
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• 2019

Carbon fiber reinforced SiC composites (C/SiC) have high-temperature stability and excellent thermal shock resistance, and are currently being applied in extreme environments, for example, as aerospace propulsion parts or in high-performance brake systems. However, their low thermal conductivity, compared to metallic materials, are an obstacle to energy efficiency improvements via utilization of regenerative cooling systems. In order to solve this problem, the present study investigated the bonding strength between carbon fiber and matrix material within ceramic matrix composite (CMC) materials, demonstrating the relation between the microstructure and bonding, and showing that the mechanical properties and thermal conductivity may be improved by treatment of the carbon fibers. When fiber surface was treated with a nitric acid solution, the observed segment crack areas within the subsequently generated CMC increased from 6 to 10%; moreover, it was possible to enhance the thermal conductivity from 10.5 to 14 W/m·K, via the same approach. However, fiber surface treatment tends to cause mechanical damage of the final composite material by fiber etching.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.46-49
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• 2006

Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction have been examined previously, with and emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.

• Journal of Biosystems Engineering
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• 제23권1호
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• pp.21-30
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• 1998

A theoretical model was developed to evaluate the effects of soil and airflow characteristics on the soil-air heat exchanger performances. The model, which includes three-dimensional transient energy and mass equilibrium-equation, was solved by using a computer program that uses Finite Difference Methods and Gauss-Seidel iteration computation. Energy gains, heat exchange efficiencies, and outlet air temperature are presented including the effects of soil moisture content, soil conductivity, soil thermal diffusivity, and soil initial temperature. Also, data related to the effects of airflow rate and inlet air temperature on the thermal performance of the system are presented. The results indicated that energy gains depend on soil conductivity, soil thermal diffusivity, and soil initial temperature. Heat exchange efficiencies relied on air mass flow rate and soil moisture content.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.247-250
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• 2009

Sodium heat pipe for high-temperature solar thermal application was manufactured and tested for transient and steady-state operations. Total length of the heat pipe was 650 mm and the outer diameter was 12.7 mm. Thermal performance was compared experimentally for two different cooling methods of the forced and the natural convection cooling in the heat pipe condenser. During the experiment, the maximum temperature was about 1300K, and different cooling methods were applied to the condenser region to charge the operating temperature. The effective thermal conductivity and the thermal resistance were investigated as a function of heat flux, heat transport length, and operating temperature.

• 한국지열·수열에너지학회논문집
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• 제13권1호
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• pp.14-20
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• 2017

Groundwater heat pump (GWHP) system can achieve higher performance of the system by utilizing heat source of the annual constant groundwater temperature. The performance of GWHP system depends on the ground thermal environment such as groundwater temperature, groundwater flow rate and hydraulic conductivity. In this study, the geothermal environment was analyzed by using numerical simulation for develop the two-well geothermal system. As the result, this paper shows the change of the groundwater level and underground temperature around wells according to the conditions of flow rate and hydraulic conductivity.

• 한국세라믹학회지
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• 제56권3호
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• pp.325-330
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• 2019

Band convergence is known to be effective in improving thermoelectric performance by increasing the Seebeck coefficient without significantly reducing electrical conductivity. Decoupling of the Seebeck coefficient and electrical conductivity in converged bands is the key requirement. Yet, the degree of decoupling depends on the band parameters of the converging bands. Herein, we report theoretical transport properties of two valence bands as their energy difference changes from 0.25 eV to 0 eV. In order to demonstrate the effect of band parameters in transport, we first conducted calculations for the case where the two bands have the same parameters. Then, we conducted the same calculation by doubling the density-of-states effective mass of one valence band. Given that there are two bands, each band's effective mass was doubled one at a time while the other band's effective mass remained constant. We found that the decoupling was strongest when the bands participating in convergence had the same band parameters.

• 한국수소및신에너지학회논문집
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• 제34권6호
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• pp.650-656
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• 2023

In order to efficiently control boil-off rate of a liquefied hydrogen tank, the important thing is to maintain an appropriate vacuum level. however, compared to small and medium-sized storage tank, it is very difficult to create and maintain vacuum in large-capacity storage tanks. In this study, we aim to determine the target level of future large-capacity storage tank technology development and secure basic data on performance test methods by analyzing the corelation between evaporation gas and thermal conductivity of liquefied hydrogen storage tanks.

• 전기화학회지
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• 제9권2호
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• pp.89-94
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• 2006

Nafion/poly(ether(amino sulfone)) acid-base 블렌드 고분자 전해질 막을 제조하여 이온전도도, 디메틸 에테르(DME) 투과도를 측정하였으며 이를 이용하여 직접 DME 연료전지 특성을 연구하였다. Poly(ether(amino sulfone)) (PEAS)는 아민기의 치환도가 $0.6\sim2.0$인 것을 합성하였다. Nafion/PEAS 블렌드 전해질 막은 Nafion과 PEAS를 DMF에 용해시켜서 캐스팅하는 방법으로 제조하였다. 블렌드 전해질막은 $100^{\circ}C$ 이상에서도 이온전도도가 계속 증가하였다. Nafion/PEAS-0.6(85:15) 블렌드 전해질막은 $50^{\circ}C$ 이상에서의 수소 이온전도도가 recast Nafion보다 더 높게 나타났으며 $120^{\circ}C$에서의 수소 이온전도도는 $1.42\times10^{-1}S/cm$로 측정되었다. PEAS의 아민기가 많이 치환될수록 블렌드 전해질막의 DME 투과도와 이온전도도는 비례적으로 감소하는 것을 확인할 수 있었다. $100^{\circ}C$ 이상 가압 조건에서 Nafion/PEAS 블렌드 전해질막을 사용한 직접 DME 연료전지(DDMEFC)의 최대 전력밀도가 같은 조건에서 Nafion 115를 사용한 것보다 약 50%증가하였다. 이와 같은 DDMEFC의 성능 향상은 블렌드 전해질막이 Nafion과 비교하여 고온에서의 이온전도도가 향상되었고 DME투과도가 감소하였기 때문인것으로 해석된다.

• Journal of the Korean Wood Science and Technology
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• 제41권6호
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• pp.515-527
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• 2013

국내에서 주로 사용되고 있는 건물에너지 성능평가 시뮬레이션 마다 상이한 재료의 열전도율로 평가 되고 있음이 파악되었다. 시뮬레이션을 통한 정확한 건물에너지부하를 평가하기 위하여, 각 시뮬레이션에서 목조건축물의 스터드로 사용되고 있는 목재의 열전도율을 확인하고, 이에 따른 벽체의 열관류율과 부재 접합부위에서의 선형열교 차이를 연구하였다. 각 시뮬레이션은 동일 수종에 대해 상이한 열전도율을 채택 후, 각 시뮬레이션에서 추출한 열전도율 간의 차이가 가장 상이한 소나무의 열전도율을 스터드에 적용하였다. 시뮬레이션 간 지붕, 벽체, 지면 슬래브의 열관류율 중 최대오차는 $0.023W/m^2{\cdot}K$이었으며, 지붕의 서까래 접합부, 지붕-벽체 접합부, 지면슬래브-벽체 접합부 중 최대 선형열교 오차는 $0.025W/m{\cdot}K$이었다. 또한, HEAT2 정상상태전열해석 프로그램을 활용하여 선형열교 및 벽체의 온도변화에 대한 전열해석 이미지를 분석하였다. 구조체에 온도 분포를 선으로 표시하여 단열이 부족한 곳에서는 온도선이 급격하게 변하는 것이 확인되었고, 온도선이 급격하게 변하는 부위에서는 다른 곳보다 온도가 낮으며, 다른 구조체 부분보다 더 많은 열류가 손실됨이 확인되었다.