• Title/Summary/Keyword: 1차원 열전달 모델

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KSTAR 진공용기 및 플라즈마 대향 부품에 대한 베이킹 해석

  • 이강희;임기학;허남일
    • Proceedings of the Korean Vacuum Society Conference
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    • 1999.07a
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    • pp.38-38
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    • 1999
  • KSTAR(Korea Superconducting Tokamak Advanced Research) 핵융합 실험 장치의 진공용기 및 진공용기 내부의 플라즈마 대향 부품들은 초고진공 (5$\times$10-9 Torr)의 달성을 위해 진공용기 내부의 이물질(H2, H2O, CO, CO2, CH4 등) 제거를 목적으로 SS316LN인 진공용기는 25$0^{\circ}C$, 탄소 물질인 플라즈마 대향부품은 35$0^{\circ}C$ 정도까지 가열(이하 베이킹)할 필요성이 있다. 이 가열방법으로 고온 질소가스를 진공용기 이중벽 사이로 흘려주는 방식과 코일에 저주파 교류전류를 흘려 진공용기를 유도가열하는 방식이 고려되고 있는데, 유도가열방식은 최대 유도 전력이 70kW 정도로 실제 베이킹에 필요한 열량을 공급하는데 있어 적잖이 부족하며 또 국부적인 가열 특성으로 인하여 KSTSR의 베이킹 방식은 전자의 가열방식을 우선적으로 채택하고 있다. 본 논문에서는 0-차원 해석을 통하여 진공용기와 플라즈마 대향 부품들에 대한 베이킹 계획을 결정하고 이를 만족시키기 위해 투입해야 할 열량을 직선적으로 증가하는 온도 곡선에서 각 부분의 온도 상승률을 다르게 설정한 세 경우와 F-자 형태로 변화하는 온도 곡선의 경우에 대해 각각 적용하여 시간에 따른 필요열량을 비교.검토하였으며, 이를 근거로 안정적인 베이킹 계획을 선정하였고 이 베이킹 계획의 실현을 위해 투입해야 할 고온 질소가스의 유량과 온도 도달시간까지 매 시간에서의 가스온도를 산출하였다. 토러스 형상의 토카막 진공용기와 플라즈마 대향 부품 및 다층단열재에 대한 해석 모델은 길이가 유한한 0-차원 실린더 모델로 가정하였고, 이에 대한 기하학적 성질 및 열역학적 성질은 유효계수를 고려하여 산출하였다. 진공용기 이중 벽 내부로 흐르는 질소가스의 유량과 온도의 계산은 진공용기 내벽과 외벽을 각각 독립적인 열전달 요소로 가정하여 구성한 모델을 이용하였다. 전체 해석에서 각 열전달 요소의 비열 값은 온도에 따라 변화하는 비열의 특성을 반영하였으며. 진공용기와 플라즈마 대향 부품의 방사율(emissivity)은 앞서 가정했던 각 온도 상승 곡선에 대해서 각각 0.1, 0.2, 1.3의 경우를 가정하여 계산하였다. 직선적으로 증가하는 온도 상승 곡선중 2$0^{\circ}C$/hr의 온도상승율을 갖는 경우가 다른 베이킹 시나리오 모델에 비해 효과적이라 생각되며 초대 필요 공급열량은 200kW 정도로 산출되었다. 실질적인 수치를 얻기 위해 보다 고차원 모델로의 해석이 필요하리라 생각된다. 끝으로 장기적인 관점에서 KSTAR 장치의 베이킹 계획도 살펴본다.

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An Analysis of Unsteady 2-D Heat Transfer of the Thermal Stratification Flow inside Horizontal Pipe with Electrical Heat Tracing (Heat Tracing이 있는 수평배관 내부 열성층 유동의 비정상 2차원 열전달 해석)

  • 정일석;송우영
    • Journal of Energy Engineering
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    • v.6 no.2
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    • pp.119-128
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    • 1997
  • A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external heating on the thermal stratification flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt number distributions are analyzed under heating conditions. The numerical results of this study show that the maximum dimensionless temperature difference between hot and cold sections of the inner wall of pipe is 0.424 at dimensionless time of 1,500 and the thermal stratification phenomenon disappears at about dimensionless time of 9,000.

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Numerical Analysis of Heat Transfer in Multichannel Volumetric Solar Receivers (다채널 체적식 태양열 흡수기에서 열전달 수치해석)

  • Lee, Hyun-Jin;Kim, Jong-Kyu;Lee, Sang-Nam;Kang, Yong-Heack
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.12
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    • pp.1383-1389
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    • 2011
  • The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

Performance analysis of a scroll compressor considering quasi one-dimensional leakage modeling and heat transfer loss (준 1차원 누설모델링 및 열전달 손실을 고려한 스크롤압축기의 성능해석)

  • Gang, Tae-Gyu;Park, Gyeong-U;Jeong, Yeon-Gu;Park, Hui-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.10
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    • pp.1339-1349
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    • 1997
  • A numerical method of calculating the performance of a scroll compressor for refrigerant R-22 and R-134a is presented in this paper. A series of involute curves are employed for the scroll wrap design and the compression volume is investigated geometrically. The radial leakage flow rate through tip clearance is calculated by the two-dimensional compressible flow. On the basis of the results, quasi one-dimensional leakage modeling can be applied to the performance analysis of a scroll compressor, more effectively. Furthermore, the heat transfer effect between scroll wrap and working fluid in compression chamber is considered for the performance analysis. As the results of this study, the effects of the radial and tangential leakage flow rate and heat transfer on the scroll compressor performance are derived precisely. These results may provide the guideline for the design and development of a real scroll compressor.

Kinetic Studies on the Oxidation of Copper Concentrate Particles (동정광 입자의 산화반응에 관한 속도론적 연구)

  • Sohn Ho-Sang
    • Resources Recycling
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    • v.11 no.6
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    • pp.47-54
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    • 2002
  • Copper concentrate particles were fed from the top of vertical reaction tube of 2.8 cm ID and 65 cm long with an $O_2$-$N_2$ gas mixture. The reaction tube was heated to 1000 K to 1400 K. The copper concentrate particles were very rapidly oxidized and melted down during their descent in the reaction tube. The particle temperature were calculated by combining an unreacted core model, mass transfer between gas and particles, and heat transfer between gas, particles and tube wall. The particle temperature reached its maximum at the height of 20 to 30 cm from the top of the reaction tube, and it attained about 1700 K at higher oxy-gen partial pressure. The most particles were melted at the oxygen partial pressure above 0.2 atm.

Experimental study on the heat transfer characteristics of evaporative transpiration cooling (증발분출냉각의 열전달 특성에 관한 실험적 연구)

  • 이진호;남궁규완;김홍제;주성백
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.5
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    • pp.1130-1137
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    • 1988
  • Heat transfer characteristics of evaporative transpiration cooling was investigated experimentally in the range of coolant mass flux, 0.002kg/m$^{2}$.sec~0.015m$^{2}$.sec. Glass beads, sand and copper particles were used as porous media and distilled water was used as a conant. The existence of evaporation zone was confirmed on this experimental conditions and its length increases with increasing article size and with decreasing mass flux. In order to get the low surface temperature, porous materials with high thermal conductivity is preferred when the panicle sizes are same, and small particles with low porosity is effective in case of the same material. Due to the relatively small coolant mass flux, evaporative transpiration cooling system could be stable by the capillary effect.

Study on Evaluation of Effective Thermal Conductivity of Unsaturated Soil Using Average Capillary Pressure and Network Model (평균 모세관압과 네트워크 모델을 이용한 불포화토의 유효 열전도도 산정에 관한 연구)

  • Han, Eunseon;Lee, Chulho;Choi, Hyun-Jun;Choi, Hangseok
    • Journal of the Korean Geotechnical Society
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    • v.29 no.1
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    • pp.93-107
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    • 2013
  • Thermal conduction of the particulate composites or granular materials can be widely used in porous materials and geotechnical engineering. And it has continued to develop "effective thermal conductivity" of medium by modeling energy relationship among particles in medium. This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From a series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. And an empirical correlation between the fraction of the mean radius (${\chi}$) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conductivity of the granular soils, to estimate thermal conductivity of granular soils.

A Numerical Study of 1-D Surface Flame Spread Model - Based on a Flatland Conditions - (산불 지표화의 1차원 화염전파 모델의 수치해석 연구 - 평지조건 기반에서 -)

  • Kim, Dong-Hyun;Tanaka, Takeyoshi;Himoto, Keisuke;Lee, Myung-Bo;Kim, Kwang-Il
    • Fire Science and Engineering
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    • v.22 no.2
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    • pp.63-69
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    • 2008
  • The characteristics of the spread of a forest fire are generally related to the attributes of combustibles, geographical features, and meteorological conditions, such as wind conditions. The most common methodology used to create a prediction model for the spread of forest fires, based on the numerical analysis of the development stages of a forest fire, is an analysis of heat energy transmission by the stage of heat transmission. When a forest fire breaks out, the analysis of the transmission velocity of heat energy is quantifiable by the spread velocity of flame movement through a physical and chemical analysis at every stage of the fire development from flame production and heat transmission to its termination. In this study, the formula used for the 1-D surface forest fire behavior prediction model, derived from a numerical analysis of the surface flame spread rate of solid combustibles, is introduced. The formula for the 1-D surface forest fire behavior prediction model is the estimated equation of the flame spread velocity, depending on the condition of wind velocity on the ground. Experimental and theoretical equations on flame duration, flame height, flame temperature, ignition temperature of surface fuels, etc., has been applied to the device of this formula. As a result of a comparison between the ROS(rate of spread) from this formula and ROSs from various equations of other models or experimental values, a trend suggesting an increasing curved line of the exponent function under 3m/s or less wind velocity condition was identified. As a result of a comparison between experimental values and numerically analyzed values for fallen pine tree leaves, the flame spread velocity reveals a prediction of an approximately 10% upward tendency under wind velocity conditions of 1 to 2m/s, and of an approximately 20% downward tendency under those of 3m/s.

A Study on the Estimation of Temperature Distribution in Ultrasonic Hyperthermia by 1-Dimensional FEM Model (1차원 유한요소법 모델을 이용한 초음파 Hyperthermia의 온도분포에 관한 연구)

  • Ha, Jae-Gyu;Seong, Goeng-Mo
    • The Journal of the Acoustical Society of Korea
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    • v.6 no.1
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    • pp.29-38
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    • 1987
  • In clinical applications of hyperthermia, temperatures can be measured at only a few locations, whereas accurate temperature profiles need to be known for efficient therapy. For doing this, bio-heat transfer equation was modified into 1 dimensional 2 boundary value problem for simplicity and the efficiency of time, and solved by Galerkin's method. The results were then applied to annular array transducer for both the calculation of its axial temperature distribution and the estimation of temperature profiles from a few measured temperature data.

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TRAC-PF1을 이용한 FLECHT-SEASET 평가계산

  • 이재훈;최동수;이걸우;황태석;박병서;조창석
    • Proceedings of the Korean Nuclear Society Conference
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    • 1997.10a
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    • pp.627-632
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    • 1997
  • FLECHT-SEASET 실험을 이용하여 냉각재상실사고시 Reflood에 대한 TRAC-PF1 전산코드의 예측 능력을 평가하였다. FLECHT-SEASET 실험 장치는 3.657m(12 ft) 높이 161개 전열 봉으로 이루어 져 있으며, 다양한 재관수율, 계통압력, 초기 피복재온도, 재관수온도 노심내 반경방향 출력분포 둥의 조건에 따라 수행된 실험이다. TRAC-PF1은 비균질 비평형 이상유동 열수력(Nonhomogeneous Non-equilibrium Two-Fluid Hydrodynamic)모델을 사용하고 원자로 압력용기는 3차원으로 모델할 수 있는 최적전산코드로서, 이 평가 계산에는 HP Version이 사용되었다. 본 연구에서는 재관수율 변화에 따라 달라지는 연료봉 최대 피복재온도와 Quench 시간에 대한 TRAC-PF1 전산코드의 예측 능력을 중점적으로 평가하였다. 계산 결과 TRAC-PF1은 최대 피복재온도는 약 20-100$^{\circ}$K 낮게, Quench 시간은 실험치와 비교하여 약 40-150초 정도 늦게 예측하는 것으로 나타났는데, 재관수율이 낮을수록 최대피복재 온도는 낮게, Quench 시간은 늦게 예측하는 경향을 보이고 있다. 또한 재관수율이 3 in/sec 이상에서 노심 상부가 일찍 Quenching 되는 것으로 계산되는데, 이는 노심상부 열전달 Regime의 부적절한 계산이 원인으로 보인다.

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