• Fire Science and Engineering
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• v.30 no.4
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• pp.111-120
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• 2016

This is an experimental study to analyze the explosion and fire hazards of mobile phone batteries. Using the lithium-ion batteries currently used on smart phone as the experiment samples, the experiments were conducted by overcharging, internal and external short circuit, and thermal shock with the potential of explosion and fire caused by careless use or abnormal conditions. The experiment results showed that, in the case of overcharging and external short circuit, there was no explosion and fire hazard in the normal operation of the protection circuit module (PCM), but there were big risks when the PCM faulted conditions were assumed. In the case of the experiments by internal short circuit and thermal shock, such risks varied depending on a battery charge state. In other words, it could be verified that there were low risks of explosion and fire in a full discharge state, but there were high risks in a full charge state. These experiment results suggest that to minimize the explosion and fire hazards of mobile phone batteries, an alarm device is necessary when the PCM fault occurs. In addition, a solid battery case should be made and safety equipment, such as a cooling device to avoid high temperature, is needed.

• Korean Journal of Ecology and Environment
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• v.38 no.1 s.110
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• pp.105-117
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• 2005

During the period of heavy rain from 2002 to 2004, the characteristics of the inflow, temporal and spatial fluctuations of high turbid water according to thermal stratification were studied on the Andong Reservoir which is the largest artificial lake in the Nakdong River basin, Korea. Thermal stratification was formed in June. Its structure determined to the pathway of inflowing turbid water and has affected by the transportation of high turbid water. Regardless of the time and amount of inflow, the high turbid water showed the shape of underflow at the riverine zone, separated from the bottom at the transition zone and moved to the lacustrine zone with the shape of density current. The plunging point depended on the time and amount of inflow. The distributions of thermal stratification and DO concentrations were changed by inflowing discharge. Two thermoclines and minimum DO layers were found out existing at metalimnion in a specific time, respectively. The layer of high turbid water which formed with the thickness of 20 m at the maximum below the depth of 15 m moved toward dam. Not settled to the bottom, the newly formed layer was discharged through the intake-outlet and dispersed into all layers by the circulation in the fall.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Korean Journal of Ecology and Environment
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• v.50 no.2
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• pp.238-253
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• 2017

The sewage and wastewater (SAW) are a well-known major source of eutrophication and greentide in freshwaters and also a potential source of thermal pollution; however, there were few approaches to thermal effluent of SAW in Korea. This study was performed to understand the behavioral dynamics of the thermal effluents and their effects on the water quality of the connected streams during winter season, considering domestic sewage, industrial wastewater and hot spring wastewater from December 2015 to February 2016. Sampling stations were selected the upstream, the outlet of SAW, and the downstream in each connected stream, and the water temperature change was monitored toward the downstream from the discharging point of SAW. The temperature effect and its range of SAW on the stream were dependent not only on the effluent temperature and quantity but also on the local air temperature, water temperature and stream discharge. The SAW effects on the stream water temperature were observed with temperature increase by $2.1{\sim}5.8^{\circ}C$ in the range of 1.0 to 5.5 km downstream. Temperature effect was the greatest in the hot spring wastewater despite of small amount of effluent. The SAW was not only related to temperature but also to the increase of organic matter and nutrients in the connected stream. The industrial wastewater effluent was discharged with high concentration of nitrogen, while the hot spring wastewater was high in both phosphorus and nitrogen. The difference between these cases was due to with and without chemical T-P treatment in the industrial and the hot spring wastewater, respectively. The chlorophyll-a content of the attached algae was high at the outlet of SAW and the downstream reach, mostly in eutrophic level. These ecological results were presumably due to the high water temperature and phosphorus concentration in the stream brought by the thermal effluents of SAW. These results suggest that high temperature of the SAW needs to be emphasized when evaluating its effects on the stream water quality (water temperature, fertility) through a systematized spatial and temporal investigation.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.9-18
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• 2012

Annual power consumption of our country is positioned in the upper percentile in the world, and because the proportion of fossil power generation is high, which ranks the 10th $CO_2$ emission country. In this regard, government has established and is implementing the National Energy Basic Plan to realize to get out of fossilization in energy supply while focusing on securing the technology for renewable energy as well as its commercialization in order to reduce greenhouse gas. Resource recovery technology for deep seawater thermal energy which is one of renewable energies is newly getting attention domestically as well as in overseas for securing resources and environmental improvement as a core technology for multilateral use of marine resources for low carbon and green growth. Economic feasibility analysis was conducted for the research and development as follows on the use of ocean thermal energy conversion and seawater air conditioning. First, in the case of power generation using deep seawater and warm discharge water from ocean thermal energy conversion plant of 1MW level, it is judged that the economic feasibility is insufficient but the feasibility will be significantly improved if we consider not only power generation but also drinking water and certified emission reduction by developing the power plant to the size for commercialization. Second, the economic feasibility for the use of deep seawater as air conditioning for the power plant of 1,000RT level turned out to be very good. Especially, when we consider certified emission reduction, it will be possible to secure sufficient economic feasibility. When we use it in connection with ocean thermal energy conversion, water conversion and agricultural and fishery use, it is judged that economic ripple effect will be significant and therefore it will be necessary to conduct research and development for early commercialization, distribution and diffusion of deep seawater energy.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.4
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• pp.183-189
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• 2012

Surface treatments and their effects on high temperature properties for the Hastelloy X, which is a promising candidate alloy for high temperature heat-transport system, have been evaluated. For TiAlN and $Al_2O_3$ overlay coatings, the two different PVD (physical vapor deposition) methods using an arc discharge and a sputtering, were applied, respectively. In addition, a different surface treatment method of the diffusion coating by a pack cementation of Al (aluminiding) was also adopted in this study. To achieve enhanced thermal oxidation resistance at $1000^{\circ}C$ by suppressing the inhomogeneous formation of thick $Cr_2O_3$ crust at the surface region, a study for the surface modification methods on the morphological and structural properties of Hastelloy X substrates has been conducted. The structural and compositional properties of each sample were characterized before and after heat-treatment at $1000^{\circ}C$ under air and He environment. The results showed that the Al diffusion coating showed the more enhanced high temperature properties than the overlay coatings such as the suppressed thick $Cr_2O_3$ crust formation and lower wear loss.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.126-139
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• 1994

Best-estimate thermal-hydraulic codes, CATHARE2 V1.2 and RELAP5/MOD3, hate been assessed against the BETHSY 6.2 tc six-inch cold leg break loss-of-coolant accident (LOCA) test. Main objective is to analyze the overall capabilities of the two codes on physical phenomena of concern during the small break LOCA i.e. two-phase critical flow, depressurization, core water level de-pression, loop seal clearing, liquid holdup, etc. The calculation results show that the too codes predict well both in the occurrences and trends of major two-phase flow phenomena observed. Especially, the CATHARE2 calculations show better agreements with the experimental data. However, the two codes, in common, show some deviations in the predictions of loop seal clearing, collapsed core water level after the loop seal clearing, and accumulator injection behaviors. The discrepancies found from the comprision with the experimental data are larger in the RELAP5 results than in the CATHARE2. To analyze the deviations of the two code predictions in detail, several sensitivity calculations have been performed. In addition to the change of two-phase discharge coefficients for the break junction, fine nodalization and some corrections of the interphase drag term are made. For CATHARE2, the change of interphase drag force improves the mass distribution in the primary side. And the prediction of SG pressure is improved by the modification of boundary conditions. For RELAP5, any single input change doesn't improve the whole result and it is found that the interphase drag model has still large uncertainties.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.593-593
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• 2012

본 연구는 화력 및 원자력 발전소로 취입된 냉각수(circulating and essential service water)가 복수기로부터 온배수 형태의 개수로 흐름으로 표층배수 될 경우 수온을 저감시키기 위해 주입하는 희석수(by-pass cooling water)와의 혼합효과의 효율성을 증대시키고, 불리한 수리현상을 야기하지 않으며, 경제적인 배수로 구조물을 고찰하기 위한 목적으로 시도되었다. 배수로 구조물 내 온배수와 희석수가 혼합되는 구간을 혼합지(mixing basin)라 하는데, 본 과업에서는 ${\bigcirc}{\bigcirc}$발전소의 배수로 구간 중 혼합지를 대상으로 FLOW-3D$^{(R)}$를 이용한 3차원 수치모형을 구축하고, 총 9개에 해당하는 각 대안별 현상을 분석하고 비교하였다. 각 대안들의 차이점은 배수로에 설치되는 보조구조물들의 형상과 배열 등이며, 복수기로부터 나오는 배출수의 수온은 $42^{\circ}C$, 희석수는 $35^{\circ}C$이고, 본 과업의 주요 관심대상 물리량은 유속과 온도이다. 배수로에 아무런 보조 구조물이 없는 형태인 기본 계획안을 검토한 결과, 평균 $3.31^{\circ}C$의 수온강하가 이루어졌으나, 우안 쪽으로 강한 흐름이 발생하여 수온의 좌우편차가 $4.61^{\circ}C$ 가량 발생하는 것으로 나타났다. 기본 계획안의 검토결과를 보완하기 위한 대안으로 연직 흐름의 소산을 위해 고안된 잠형 소파블록(baffle block) 설치안은 평균 $3.06^{\circ}C$의 수온강하가 이루어지고 $4.44^{\circ}C$의 수온 좌우편차가 발생했다. 지그재그(zigzag) 형태의 흐름을 만들어 혼합효과를 올리기 위한 미로형 수제(labyrinth groin) 설치안은 평균 $5.33^{\circ}C$의 수온강하가 이루어지고, $1.43^{\circ}C$의 수온 좌우편차를 보여줘 검토했던 대안들 중 가장 좋은 결과를 보여주었다. V자 배열 소파블럭(deformed block) 설치안은 연직 및 수평방향의 소산을 기대했으나 평균 $3.00^{\circ}C$의 수온 강하와 $4.41^{\circ}C$의 수온 좌우편차를 나타냈다. 벤츄리(Venturi) 형태의 흐름을 발생시키기 위한 병목형(bottleneck) 수로안은 평균 $3.18^{\circ}C$의 수온강하와 $3.94^{\circ}C$의 수온 좌우편차, 흐름의 소산과 흐름방향을 변화시키기 위한 와형 수제(swirl groin) 설치안은 평균 $2.24^{\circ}C$의 수온강하와 $1.48^{\circ}C$의 수온좌우편차, 우안 흐름을 지연시키기 위한 물방석(water cushion) 수로안은 평균 $3.03^{\circ}C$의 수온강하와 $4.50^{\circ}C$의 수온 좌우편차, 우안의 흐름을 좌안으로 보내기 위한 분사형(injector) 수로안은 평균 $3.13^{\circ}C$의 수온강하와 $4.45^{\circ}C$의 수온 좌우편차, 우안의 흐름을 막기 위한 외팔형 수제(cantilever groin) 설치안은 평균 $3.11^{\circ}C$의 수온강하와 $3.02^{\circ}C$의 수온 좌우편차가 발생하는 것으로 나타났다.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.42-48
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• 2021

Zn and Al added LiNi0.85Co0.15O2 cathode materials were synthesized to improve electrochemical properties and thermal stability using a solid-state route. Crystal structure, particle size and surface shape of the synthesized cathode materials was measured using XRD (X-ray diffraction) and SEM (scanning electron microscopy). CV (cyclic voltammetry), first charge-discharge profiles, rate capability, and cycle life were measured using battery cycler (Maccor, series 4000). Strong binding energy of Al-O bond enhanced structure stability of cathode material. Electrochemical properties were improved by preventing cation mixing between Li+ and Ni2+. Large ion radius of Zn+ increased lattice parameter of NC cathode material, which meant unit-cell volume was expanded. NCZA25 showed 80% of capacity retention at 0.5 C-rate during 100 cycles, which was 12% higher than that of NC cathode. The discharge capacity of NCZA25 showed 104 mAh/g at 5 C-rate. NCZA25 achieved 36 mAh/g more capacity than that of NC cathod. NCZA25 cathode material showed excellent rate capability and cycling performance.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.32-38
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• 2023

In this study, the electrochemical properties of dopamine coated silicon/silicon carbide/carbon(Si/SiC/C) composite materials were investigated to improve cycle stability and rate performance of silicon-based anode active material for lithium-ion batteries. After synthesizing CTAB/SiO₂ using the Stöber method, the Si/SiC composites were prepared through the magnesium thermal reduction method with NaCl as heat absorbent. Then, carbon coated Si/SiC anode materials were synthesized through polymerization of dopamine. The physical properties of the prepared Si/SiC/C anode materials were analyzed by SEM, TEM, XRD and BET. Also the electrochemical performance were investigated by cycle stability, rate performance, cyclic voltammetry and EIS test of lithium-ion batteries in 1 M LiPF₆ (EC: DEC = 1:1 vol%) electrolyte. The prepared 1-Si/SiC showed a discharge capacity of 633 mAh/g and 1-Si/SiC/C had a discharge capacity of 877 mAh/g at 0.1 C after 100 cycles. Therefore, it was confirmed that cycle stability was improved through dopamine coating. In addition, the anode materials were obtain a high capacity of 576 mAh/g at 5 C and a capacity recovery of 99.9% at 0.1 C/0.1 C.