• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1870-1875
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• 2007

The microchannel heat sink is promising heat dissipation method for high heat flux source. Contrary to conventional circular channel, MEMS based microchannel had rectangular or trapezoidal cross-sectional shape. In our study, we conducted three dimensional conjugate heat transfer calculation for rectangular shape microchannel. First, we simulated that channel was completely drained with known heating power. As a result we obtained calibration line, which indicates heat loss was function of temperature. Second, we simulated single phase heat transfer with various mass flux, 100-400 $kg/m^2s$. In conclusion, the single phase test verified that the present heat loss evaluation method is applicable to micro scale heat transfer devices. Heat fluxes from each side wall shows difference due to non-uniform heating. However those ratios were correlated with supplied total heat. Finally, we proposed effective area correction factor to evaluate appropriate heat flux.

• Nuclear Engineering and Technology
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• 제53권8호
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• pp.2488-2498
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• 2021

The wall film-wise condensation plays an important role in the heat transfer processes of heat exchangers, refrigerators, and air conditioner. In the field of nuclear engineering, steam condensation is often utilized in safety systems to remove the core decay heat under both transient and accident conditions. In particular, passive containment cooling system (PCCS), are designed to ensure containment safety under severe accident conditions. A computational fluid dynamics (CFD) scale analysis has been conducted to calculate the heat transfer rate of the PCCS. However, despite the increase in computing power, there are challenges in the long-term transient simulation of containment using CFD scale codes. In this study, a heat structure coupling between the CFD and system analysis codes was performed to efficiently analyze PCCS. In addition, the component unstructured program for interfacial dynamics (CUPID) was improved to analyze the condensation behavior of ternary gas mixtures. Thereafter, the condensation heat transfer on the primary side was calculated using the improved CUPID and CFD code, whereas that on the secondary side was simulated using MARS. Both the coupled codes were validated against the CONAN facility database. Finally, conjugate heat transfer simulations with wall condensation in the presence of non-condensable gases were appropriately performed.

• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.1059-1067
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• 2006

In order to develop a compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled minichannel were performed in our previous research. This study was focused on the performance analysis of helically coiled heat exchangers with circular minichannels with an inner diameter=1.0 mm. The working fluid was R-22, and the properties of R-22 were estimated using the REFPROP program. Numerical simulation was performed to compare results with the experimental results of the helically coiled heat exchanger. As the heat transfer rate and pressure drop were calculated at the micro segment of the branch channels, the performance of the evaporator was evaluated. The following conclusions were obtained through the numerical simulations of the helically coiled heat exchanger. It showed good performance when the flow rate of each branch channels was suitable to heat load of air-side. The numerical simulation value agreed with experimental results within ${\pm}15%$. In this study, a numerical simulation program was developed to estimate the performance of a helically coiled evaporator. And, an optimum helically coiled minichannels evaporator was designed.

• 한국전산유체공학회지
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• 제15권2호
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• pp.1-6
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• 2010

The purpose of the present study is to investigate the flow resistance and the heat transfer characteristics of oval fin-tube heat exchanger. Six kinds of oval fin having the same fin area and different diameter ratio tested numerically. Test data for the heat transfer, pressure drop and fin temperature were shown and discussed. The pressure drop and heat transfer increased for increasing the oval fin diameter ratio(diameter of span-wise direction to diameter of longitudinal diameter) up to 50% and 45% respectively.

• Journal of Biosystems Engineering
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• 제30권3호
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• pp.185-191
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• 2005

Importance of alternative energy has been increasing due to environmental issues and lack of fossil fuels. In addition, heating cost that occupies from 30 to $40\%$ of the total production cost in the protected cultivation sector in Korea needs to be reduced for profitability and global competition. But, study on geothermal energy to solve these problems has not been activated for Korean protected cultivation. This study was conducted to develop an optimized geothermal exchange system through fundamental test of heat transfer characteristics in soil such as thermal diffusivity, changes in soil temperature during heating and cooling operations, and restorations of soil temperature after the heater was fumed off, These issues were investigated using computer simulation for different depths. The simulated characteristics were evaluated through controlled tests. Simulated characteristics of heat transfer in the soil at different depths showed a reasonable agreement with the results of the controlled tests. All of computer simulation and controlled tests, soil temperatures changed at 10cm and 20cm distance from pipe. but don't change at more than 30cm distance. It means that distances of heat transfer of the soil ranged from 20 to 30cm a day. Based on these results, the optimum spacing between adjacent heat exchange pipes and the pitch were selected as 50 and 40cm, respectively.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1802-1813
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• 2023

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor's safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Pr_t,, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal's CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k - ε turbulence model and the Manservisi k_𝜃 - ε_𝜃 heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson's experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.107-110
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• 2004

Application of aluminum alloy has been increasing for most of industry area because aluminum has a good mechanical properties and castability, especially automotive field for weight reduction. But, Furnace industry is sluggish. The purpose of this study is numerical analysis of aluminum holding furnace for reasonableness estimation when we design for new model of furnace. The numerical simulation involving fluid flow of inside air and heat transfer to fireproof material is presented in order to improve the understanding of aluminum furnace. First of all, we are carried out numerically for the two dimensional inside convection and surface radiation heat transfer in a square enclosure. Subsequently, we are established the analysis method of aluminum furnace considering natural convective heat transfer

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2094-2099
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• 2008

A numerical and experimental studies are carried out to investigate the transient heat transfer characteristics of 5kWth dish-type solar air receiver. Measured solar radiation and temperatures at several different locations are used as boundary conditions for numerical simulation. Many parameters' effects (reflectivity of the reflector, the thermal conductivity of the receiver body, transmissivity of the quartz window, etc.) on the thermal performance are investigated. Discrete Transfer Method is used to calculate the radiation heat exchange in the receiver. A transient heat transfer model is developed and the rate of radiation, convection and conduction heat transfer are calculated. Comparing the experimental and numerical results, good agreement is obtained. Using the numerical model, the transient heat transfer characteristics of volumetric air receiver for dish-type solar thermal systems are known and the transient thermal performance of the receiver can be estimated.

• 설비공학논문집
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• 제15권5호
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• pp.422-431
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• 2003

Theory of the building heat transfer is generally limited to the heat flux to the surfaces of windows and walls, which influences the indoor climate of a building, in the field of architectural environmental engineering. While the heat flux from the buildings to their environment has been considered in the viewpoint of urban climate, its conventional theory have been rarely examined. The purpose of this study is to propose a building-urban heat transfer model for defining the relation between the building and the urban climate by extending the building heat transfer model. In this study, the extended building heat transfer model, where response factor method is used, is established on the urban space and the indoor space by the boundary of building envelopes. Computer simulation (HASP/ACLD) is conducted on the subjected urban area by the established building-urban heat transfer model. As a result it is logically proved that the short waves of solar radiation, which interact with long Waves of radiation from the buildings and the earth, increase the urban air temperature ana buildings largely influence on the urban climate.

• Advances in Energy Research
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• 제5권4호
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• pp.321-339
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• 2017

Energy simulation tools can provide information on the amount of heat transfer through building envelope components, which are considered the main sources of heat loss in buildings. Therefore, it is important to improve the quality of outputs from energy simulation tools and also the process of obtaining them. In this paper, a new Building Energy Performance Assessment Tool (BEPAT) is introduced, which provides users with granular data related to heat transfer through every single wall, window, door, roof, and floor in a building and automatically saves all the related data in text files. This information can be used to identify the envelope components for thermal improvement through energy retrofit or during the design phase. The generated data can also be adopted in the design of energy smart homes, building design tools, and energy retrofit tools as a supplementary dataset. BEPAT is developed by modifying EnergyPlus source code as the energy simulation engine using C++, which only requires Input Data File (IDF) and weather file to perform the energy simulation and automatically provide detailed output. To validate the BEPAT results, a computer model is developed in Revit for use in BEPAT. Validating BEPAT's output with EnergyPlus "advanced output" shows a difference of less than 2% and thus establishing the capability of this tool to facilitate the provision of detailed output on the quantity of heat transfer through walls, fenestrations, roofs, and floors.