• Title/Summary/Keyword: 유효열전도율

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

  • Hwang, Byeong-Kwan;Bae, Jin-Ho;Lee, Jae-Myung
    • Composites Research
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    • v.32 no.5
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    • pp.290-295
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    • 2019
  • In the present study, composite insulation mat was reinforced over polyurethane foam (PUF) to improve the thermal performance and impact resistance of the PUF applied to the liquefied natural gas carrier insulation system. The composite insulation mat used Kevlar, aerogel, and cryogel composite mat that can be applied in a cryogenic environment. The thermal conductivity was measured at $20^{\circ}C$ to investigate the thermal performance, and the drop impact test was carried out under impact energy of 30 J at $20^{\circ}C$, $-163^{\circ}C$ to investigate the impact resistance. The measured thermal performance was compared with neat PUF through effective thermal conductivity theoretical value. The shock resistance was evaluated of contact force, contact time, and absorb energy. In experimental results, cryogel composite mat was the best performance in terms of thermal performance, and aerogel composite mat was the best performance in terms of impact resistance.

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

  • Lee, Shin-Pyo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.9
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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.

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 - (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 -)

  • Lee, Yong-jun;Oh, Eun-joo;Kim, Sa-kyum;Choi, Gyeong-seok;Kang, Jae-sik
    • KIEAE Journal
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    • v.16 no.2
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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.

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

  • Lee, Se-Kyoun;Woo, Joung-Son;Kim, Dae-Ki
    • Journal of Energy Engineering
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    • v.17 no.3
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    • pp.167-174
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    • 2008
  • Line source model is commonly used in analyzing the data obtained from thermal response test to estimate the effective soil formation thermal conductivity. In the application of line source model some part of initial data must be ignored in order to achieve more accurate result. The period of time for this initial data is called initial ignoring time(IIT) in this paper. However there has been no definite rule in determining this initial ignoring time. Therefore line source model requires experienced analyzer to select the useful data, which is somewhat subjective. One method often suggested is the calculation of IIT with non dimensional time $\tau=5$. However, this is a very theoretical result derived from a system of perfect line source model, which is somewhat different from the real system. A new method to determine IIT is presented in this study. This method requires error estimation first and IIT can be decided from the results of error estimation. This method is applied in the analysis of field test data and shows better result than the one obtained from the method using non dimensional time mentioned above as shown in Table 2.

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

  • Park, Young-Hark;Boo, Joon-Hong
    • Proceedings of the KSME Conference
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    • 2008.11b
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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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Influence of the Effective Thermal Thansport Length on the Heat Transfer Characteristics of a Liquid-Metal Heat Pipe for High-temperature Solar Thermal Devices (유효열이송거리가 고온 태양열기기용 액체금속 히트파이프의 열전달 특성에 미치는 영향)

  • Park, Cheol-Min;Boo, Joon-Hong;Kim, Jin-Soo;Kang, Yong-Heack
    • 한국태양에너지학회:학술대회논문집
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    • 2008.11a
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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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STUDY ON A EFFECTIVE THERMAL CONDUCTIVITY OF THE CFRP COMPOSITE STRUCTURE BY A SIMPLIFIED MODEL (모델 단순화에 의한 CFRP 복합 구조물의 유효 열전도율 추출 방법 연구)

  • Kim, D.G.;Han, K.I.;Choi, J.H.;Lee, J.J.;Kim, T.K.
    • Journal of computational fluids engineering
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    • v.20 no.4
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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.

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

  • Park, C.M.;Boo, J.H.;Kim, J.S.
    • Proceedings of the KSME Conference
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    • 2008.11b
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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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Performance Characteristics of a Liquid-Metal Heat Pipe for igh-temperature Solar Thermal Devices Depending on the Operating Conditions (고온 태양열기기용 액체금속 히트파이프의 작동조건에 따른 성능 특성)

  • Park, Cheol-Min;Lee, Jung-Ryun;Boo, Joon-Hong;Kang, Yong-Heack
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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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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