• 한국주조공학회지
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• 제29권6호
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• pp.265-269
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• 2009

The optimum RRA heat treating conditions and SCC (stress corrosion cracking) resistance of semi-solid Al-Zn-Mg-Cu alloy fabricated by inclined cooling plate were compared with those of conventional mould cast alloys. The non-stirring method characterized by using a cooling plate can effectively eliminate dendritic structure and form a fine globular semisolid microstructure in as-cast Al-Zn-Mg-Cu alloy and the SCC resistance of semi-solid Al-Zn-Mg-Cu alloy was higher than that of conventional mold cast alloy. Also, after retrogressed treatment at RRA heat treatment of semi-solid Al-Zn-Mg-Cu alloy, retrogressed treatment time has increased more than 10 minutes at $180^{\circ}C$ to recovery the T6 heat treatment strength.

• 열처리공학회지
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• 제11권1호
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• pp.46-53
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• 1998

The variation of the mechanical properties, microstructures and the formation of retained austenite with heat treatment conditions in austempered ductile cast iron has been investigated. In the case of austempered ductile cast iron below 25mm diameter, it has been found that a pearlite structure are not obtained under a super cooled condition at range of $0.05^{\circ}C/sec{\sim}10^{\circ}C/sec$, and the matrix is precipitated in graphite, bainite and retained austenite. After austempering treatment the retained austenite is increased with decreasing cooling rate. The elongation increases with decreasing super cooling rate, and the optimum result has been shown to be the elongation of 15.6% at super cooling rate of $0.05^{\circ}C/sec$. The optimum result has been shown to be the tensile strength-elongation balance of $1656kgf/mm^2.%$ and it is more than doubled to as the casting state and continuous cooling condition.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.143.2-143.2
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• 2011

Energy foundations and other thermo-active ground structure, energy wells, energy slab, and pavement heating and cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. This paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Pipes, energy slabs, filled with a heat carrier fluid are installed under conventional structural elements, forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and heat sink in summer season. The system represented very high heating and cooling performance due to the stability of EWT from energy slab. Maximum heat pump unit COP and system COP were 4.9 and 4.3.

• 한국재료학회지
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• 제12권5호
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• pp.398-406
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• 2002

VAR process is required to control its various operating parameters. Heat transfer simulation has been accomplished to understand development of solidification micro and macro-structures during VAR process in Ti alloys. Optimum VAR process parameters could be also estimated in this study. It was found that macro-structures were closely related to the shape and depth of liquid pool, and solidification parameters, such as temperature gradient, heat flux, solid fraction. The cooling rates were higher at bottom, top, and center part respectively. As cooling rates increased, the $\alpha$ phase decreased in length, width and fraction. In order to evaluate which parameter affects the result of heat transfer calculation most sensitively, the sensitivities of input parameters to the simulation result were examined. The pool depth and cooling rate showed more sensitive to the temperature of the molten metal, heat transfer coefficient, and liquidus respectively. Also, these thermal properties became more sensitive at higher temperatures.

• Journal of Biosystems Engineering
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• 제25권5호
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• pp.385-390
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• 2000

The heat pump is one of heating and cooling systems driven by electricity using natural energy as a heat source. The heat pump system was mainly adopted to a cooling system or a refrigeration system. In regions with a large amount of electricity, it is used as a heating system or a heating and cooling system of houses, buildings and agricultural facilities. During cold weather, air source heat pumps do not work well because of some technical problems, such as frosting on evaporator coil when outside air temperature is below -5$^{\circ}C$. In this research, the heat regenerative technology was employed to eliminate the frosting on evaporator coil and improve the COP of the heat pump system. This fiber belt heat regeneration system(FBHRS) has very simple structure consisting of a geared motor and a porous fiber belt passing through alternatively between cold and warm air duct. The laboratory test showed that the heat pump system with a FBHRS yielded an impressive COP higher than 3.5 at the outside air temperature of -7$^{\circ}C$ in heating mode.

• 한국산학기술학회논문지
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• 제16권5호
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• pp.3511-3517
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• 2015

본 지하매설 구조물용 콘크리트는 보수가 어려워 내구성을 극대화할 필요가 있는데, 콘크리트의 건조수축에 의한 균열은 재료의 특성상 발생하는 열화현상으로 대안이 필요하다. 본 연구에서는 건조수축 저감방안의 하나로써 급냉 슬래그 잔골재의 반응에 의한 팽창을 활용하여 콘크리트의 건조수축 발생량을 저감시키고자 하였는데, 실험결과 초기 재령에서 발생되는 수축을 효과적으로 억제하는 것으로 확인되었으며, 급냉 슬래그 잔골재의 치환사용량과 비례하여 전 재령에 거쳐 압축강도가 상승하는 것을 확인할 수 있었다.

• 설비공학논문집
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• 제12권3호
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• pp.227-234
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• 2000

An experimental study was performed for understanding the limiting power and heat transfer characteristics of an MHP having the diameter of 3 or 4 mm which could be applied to cooling of miniature electronic equipment such as the notebook PC CPU etc. The experimental parameters which are inclination, structure of the wick, the length of the condenser and the total heat pipe were considered. The MHP with a woven-wired wick has the advantages of the improvement in capillary limit, the effective attachment tightly toward wall and the convenience in construction of wick. Cooling performance of the present MHP was compared with that of MHP with grooved, fine fiber and sintered type wick which were applied by existing enterprises. With respect to the inclination of$ -5^{\circ}$ , an MHP having the diameter of 3 or 4 mm shows the limiting power of 6~14 W. Therefore, it is expected that the MHP of the present study has sufficient applicability of cooling of notebook PC of which the amount of heat generated is about 12 W.

• 대한건축학회논문집:구조계
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• 제35권9호
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• pp.207-214
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• 2019

Natural ventilation through openings such as windows in school buildings is an efficient resource for natural cooling during the intermediate season of the year. Because the natural ventilation uses the wind outside the building, the amount of ventilation will depend not only on the wind speed and wind direction but also on the window layout and open window ratio. Therefore, in this study, the natural ventilation plans of school classroom windows are divided into 4 types and 8 cases as shown in Table 1. The characteristics of cooling effect by natural ventilation are simulated by applying Energyplus's Airflow Network Model and the comfort of the occupants is evaluated by the number of hours included in the 80% acceptability range of the ASHRAE Standard 55-2010 adaptive comfort model for the weekdays (Monday-Friday) and the class hours (08: 00-19: 00). Based on the analysis results of the above, this study presents basic data related to classroom cooling plan using intermediate season natural ventilation.

• 한국재난정보학회 논문집
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• 제18권1호
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• pp.163-172
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• 2022

연구목적: Li-ion 배터리의 효율적인 열관리 기술을 확보하기 위하여 Single&-phase 침지 냉각 기술을 적용한 시스템의 실험을 통하여 적용가능성을 확인하고자 하였다. 연구방법: LG-Chem에서 생산된 JH3 파우치 셀을 사용하여 14S2P 모듈을 제조하여 미국 카길사에서 생산된 식물성계 냉각유체에 침지한 후 0.3C~1C 속도로 충방전을 시행하여 열분포를 확인하였다. 연구결과: 침지냉각 기술로 배터리 모듈을 40℃ 이하의 온도로 관리할 수 있으며, 침지액의 분자구조 변화가 없다는 결과를 도출하였다. 결론: 침지냉각 방식이 Li-ion 배터리 열관리에 적용 가능함을 확인하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.65-68
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• 2009

The Stirling cryocoolers have been widely used for the cooling of the infrared detector(InSb, HgCdTe, and etc,) and HTS(High Temperature Superconductor) to the cryogenic temperature. The monobloc Stirling cryocoolers with the rotary compressor are applicable to the cooling device for the compact mobile thermal imaging system, because the cryocoolers have the compact structure and light weight. The typical performance factors of the Stirling cryocooler are the cool-down time, cooling capacity at the desired temperature (80 K), the electric input power and COP. The above performance factors depend on the operating conditions such as the charging pressure of the helium gas, the thermal environment and etc.. In this study, the effects of the thermal environment (temperature of 241, 293, and 333 K) on the performance of the cryocooler were investigated by experiments. The results show the effects of the temperature of the thermal environment on the cooling capacity and input power.