• Title/Summary/Keyword: 유효열전도율

검색결과 37건 처리시간 0.022초

복합 단열 매트 보강 폴리우레탄 폼의 열적 성능 및 내충격성 평가 (Thermal Performance and Impact Resistance Evaluations of Composite Insulation Mat Reinforced Polyurethane Foam)

  • 황병관;배진호;이제명
    • Composites Research
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    • 제32권5호
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    • pp.290-295
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    • 2019
  • 본 연구에서는 액화 천연 가스 운반선 단열 시스템에 적용되는 폴리우레탄 폼(Polyurethane foam, PUF)의 열적 성능 및 내충격성을 향상시키기 위한 목적으로, PUF에 복합 단열 매트를 보강하였다. 복합 단열 매트는 극저온 환경에서 운용이 가능한 케블라, 에어로겔, 그리고 크라이오겔 매트를 선정하였다. 열적 성능은 $20^{\circ}C$의 상온에서 열전도율을 측정하였으며, 내충격성은 $20^{\circ}C$의 상온 및 $-163^{\circ}C$의 극저온에서 30 J의 충격에너지로 낙하 충격 시험을 수행하여 측정하였다. 측정된 열전도율은 유효 열전도율 이론 값을 통해 보강되지 않은 PUF와 비교하였으며, 내충격성은 접촉력, 접촉 시간, 그리고 흡수에너지를 평가하였다. 실험 결과 크라이오겔 복합 매트 보강 시 가장 우수한 열적 성능을 나타났으며, 내충격성은 에어로겔 복합 매트 보강 시 가장 우수하게 나타났다.

나노유체에 잠긴 가는 열선 주위의 자연대류 열전달 (Natural Convection Heat Transfer from a Heated Fine Wire in Nanofluids)

  • 이신표
    • 대한기계학회논문집B
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    • 제31권9호
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    • pp.807-813
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    • 2007
  • Recent research on nanofluids under forced convection experiment shows that there is little relationship between convective heat transfer and thermal conductivity increase of nanofluids. This kind of new findings are totally different from the traditional theory of nanofluids, which says that the higher thermal conductivity is a prerequisite for convective heat transfer enhancement. To elucidate this controversial issue in a very comprehensible manner, simple natural convection experiment has been carried out for the water- and oil-based nanofluids. ($water-Al_2O_3$, transformer $oil-Al_2O_3$) Present research shows that there exists strong dependence between natural convection performance and thermal conductivity increase of nanofluids.

창틀 공기층의 유효 열전도율(λeff) 산정방법 차이가 창 전체 열관류율(Uw) 시뮬레이션 결과에 미치는 영향에 대한 비교 분석 - 단창 창틀의 비환기 공기층에 대한 시뮬레이션을 중심으로 - (A comparative analysis of the total window thermal transmittance simulation result according to the evaluation method of effective conductivity(λeff) of frame cavity - Focused on unventilated frame cavity simulation results of single window -)

  • 이용준;오은주;김사겸;최경석;강재식
    • KIEAE Journal
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    • 제16권2호
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    • pp.79-85
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    • 2016
  • Purpose: It is difficult to calculate frame U-value because of the two reason. First is selection of air properties in cavity. Second is calculation method in window frame. For this reason, it is important to decide cavity properties in window frame. However, international standards offered different method(ISO 15099, ISO 10077) and air properties was changed according to the two methods. The aim of this study was to suggest method for deriving accurate frame U-value using international standard methods and CFD simulation. Method: First, this study conducted analysis calculation method of ISO 15099 and ISO 10077. And, CFD simulation conducted based on same condition. Finally, ISO calculation and CFD simulation results were verified through comparison with real experiment results. Result: The results show that effective conductivity of ISO 15099 was the highest value. ISO 10077 and CFD result followed. The convergent values of ISO 10077 was the highest. ISO 15099 and CFD followed. ISO calculation reflecting CFD simulation results will reduce error with experimental results.

지중유효열전도율 해석에 사용되는 선형열원 모델의 초기제외시간 결정에 관한 연구 (A Study of Determining Initial Ignoring Time of Line Source Model used in Estimating the Effective Soil Formation Thermal Conductivities)

  • 이세균;우정선;김대기
    • 에너지공학
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    • 제17권3호
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    • pp.167-174
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    • 2008
  • 지중유효열전도율 측정에서는 선형열원 모델이 열응답 시험의 자료 해석에 주로 이용되고 있는 실정이다. 이 선형열원 모델의 응용에서는 해의 신뢰도를 높이기 위하여 일정시간의 초기자료를 폐기하여야 하며 이 일정시간을 본 연구에서는 초기제외시간으로 명명한다. 그런데 이 초기제외시간의 산정에 관하여 뚜렷한 기준이 마련되어 있지 않아 선형열원 모델을 이용한 자료해석에서는 초기제외시간 선정이 다소 주관적이 되는 경향이 있으며 따라서 이 모델의 응용에는 충분한 경험이 필요하다. 무차원 시간 $\tau=5$가 초기제외시간 선정에 한 기준으로 제시되기도 하였으나 이 역시 완전한 선형열원 모델에서 도출되는 매우 이론적인 결과이며 실제 시스템은 이 이론적인 선형열원과 다른 점이 많다. 본 연구에서는 초기제외시간을 선정하는 새로운 방법을 제시한다. 이 방법에서는 먼저 오차해석을 수행하고 그 결과를 토대로 초기제외시간을 결정하게 된다. 본 연구에서는 이 방법을 2개의 현지 시험결과에 적용하여 보았으며 위에 언급한 $\tau=5$에 의한 방법보다 훨씬 더 신뢰성 높은 결과를 도출할 수 있었다(Table 2 참조).

내부에 히트파이프를 삽입한 메탈 하이드라이드 반응기의 열전달 특성에 대한 수치해석 연구 (A Numerical Study on the Heat Transfer Characteristics of a Metal Hydride Reactor with Embedded Heat Pipes)

  • 박영학;부준홍
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회B
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    • pp.2346-2351
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    • 2008
  • This study deals with heat pipes inserted into the metal hydride(MH) reactor to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. A numerical analysis was conducted to predict the effect of inserted heat pipes on the heat transfer characteristics of MH, which inherently has extremely low thermal conductivity. The numerical model was a cylindrical container of O.D. 76.3 mm and length 1 m, which is partially filled with about 60% of MH material. The heat pipe was made of copper-water combination, which is suitable for operation temperature range between $10^{\circ}C$ and $80^{\circ}C$. Both inner -and outer- heat pipes were considered in the model. Less than two hours of transient time is of concern when decreasing or increasing the temperature for absorption and discharge of hydrogen gas. FLUENT, a commercial software, was employed to predict the transient as well as steady-state temperature distribution of the MH reactor system. The numerical results were compared and analyzed from the view point of temperature uniformity and transient time up to the specified maximum or minimum temperatures.

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유효열이송거리가 고온 태양열기기용 액체금속 히트파이프의 열전달 특성에 미치는 영향 (Influence of the Effective Thermal Thansport Length on the Heat Transfer Characteristics of a Liquid-Metal Heat Pipe for High-temperature Solar Thermal Devices)

  • 박철민;부준홍;김진수;강용혁
    • 한국태양에너지학회:학술대회논문집
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    • 한국태양에너지학회 2008년도 추계학술발표대회 논문집
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    • pp.220-225
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    • 2008
  • Cylindrical stainless-steel/sodium heat pipe for a high-temperature solar thermal application was manufactured and tested for transient and steady-state operations. Two layers of stainless-steel screen mesh wick was inserted as a capillary structure. The outer diameter of the heat pipe was 12.7 mm and the total length was 250 mm. The effective heat transport length, the thermal load, and the operating temperature were varied as thermal transport conditions of the heat pipe. The thermal load was supplied by an electric furnace up to 1kW and the cooling was performed by forced convection of air The effective thermal conductivity and the thermal resistance were investigated as a function of heat flux, heat transport length, and vapor temperature. Typical range of the total effective thermal conductivity was as low as 43,500 W/m K for heat flux of 176.4 kW/$m^2$ and of operating temperature of 1000 K.

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모델 단순화에 의한 CFRP 복합 구조물의 유효 열전도율 추출 방법 연구 (STUDY ON A EFFECTIVE THERMAL CONDUCTIVITY OF THE CFRP COMPOSITE STRUCTURE BY A SIMPLIFIED MODEL)

  • 김동건;한국일;최준혁;이장준;김태국
    • 한국전산유체공학회지
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    • 제20권4호
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    • pp.63-69
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    • 2015
  • The thermal balance test in vacuum chamber for satellite structures is an essential step in the process of satellite development. However, it is technically and economically difficult to fully replicate the space environment by using the vacuum chamber. To overcome these limitations, the thermal analysis through a computer simulation technique has been conducted. The CFRP composite material has attracted attention as satellite structures since it has advantages of excellent mechanical properties and light weight. However, the nonuniform nature of the thermal conductivity of the CFRP structure should be noted at the step of thermal analysis of the satellite. Two different approaches are studied for the thermal analyses; a detailed numerical modeling and a simplified model expressed by an effective thermal conductivity. In this paper, the effective thermal conductivities of the CFRP composite structures are extracted from the detailed numerical results to provide a practical thermal design data for the satellite fabricated with the CFRP composite structure. Calculation results of the surface temperature and the thermal conductivities along x, y, z directions show fairly good agreements between the detailed modeling and the simplified model for all the cases studied here.

고온 나트륨 히트파이프에서 열이송 조건에 따른 열전달 특성에 대한 실험 연구 (An Experimental Study on the Heat Transfer Characteristics of a High-temperature Sodium Heat Pipe Depending on the Thermal Transport Conditions)

  • 박철민;부준홍;김진수
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회B
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    • pp.2340-2345
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    • 2008
  • Cylindrical stainless-steel/sodium heat pipe for a high-temperature application was manufactured and tested for transient and steady-state operations. Two layers of Stainless-steel screen mesh wick was inserted as a capillary structure. The outer diameter of the heat pipe was 12.7 mm and the total length was 250 mm. As thermal transport conditions, the effective transport length, the heat flux, the tilt angle and the operating temperature were varied. The heat was supplied by an electric furnace up to 1 kW and the cooling was performed by forced convection of air. The effective thermal conductivity and the thermal resistance were investigated as a function of heat flux, heat transport length, and vapor temperature. Typical range of the total thermal resistance was as low as $0.036^{\circ}C/W$ at $175.8\;kW/m^2$ of heat flux and $700^{\circ}C$ of operating temperature.

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고온 태양열기기용 액체금속 히트파이프의 작동조건에 따른 성능 특성 (Performance Characteristics of a Liquid-Metal Heat Pipe for igh-temperature Solar Thermal Devices Depending on the Operating Conditions)

  • 박철민;이정륜;부준홍;강용혁
    • 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.

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