• The Journal of Engineering Geology
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• v.28 no.1
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• pp.81-99
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• 2018

Excessive groundwater discharge by tunneling and tunnel operation can lead to groundwater exhaustion and ground subsidence. Therefore, it is very important to evaluate environmental impact and to establish mitigation measures of the impact related to tunnel excavation based on hydrogeological and modeling approaches. This study examined the depletion of surface reservoirs and valley water due to tunnel excavation through field survey, water quality analysis, tracer test, and groundwater modeling. As a result of field water quality test, the concentration of chemical constituents in groundwater discharge into the tunnel is slightly higher than that of valley water. By the result of laboratory water analysis, both valley water and the groundwater belong to $Ca^{2+}+HCO_3{^-}$ type. Tracer test that was conducted between the valley at the injection point and the tunnel, indicates valley water infiltration into the ground and flowing out to the tunnel, with maximum electrical conductance changes of $70{\mu}S/cm$ in the first test and of $40{\mu}S/cm$ in the second test. By groundwater modeling, the groundwater discharge rate into the tunnel during tunnel construction is estimated as $4,942m^3/day$ and groundwater level recovers in 3 years from the tunnel completion. As a result of particle tracking modeling, the nearest particle reaches the tunnel after 6 hours and the farthest particle reaches the tunnel after 9 hours, similarly to the case of the field trace test.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.3
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• pp.245-251
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• 2014

Pyroprocess for treating spent nuclear fuels has been developed based on electrochemical principles. Process simulation is one of the important methods for process development and experimental data analysis and it is also a necessary approach for pyroprocessing. To date, process simulation of pyroprocessing has been focused on electrorefining and there have been not so many investigations on electrolytic reduction. Electrolytic reduction, unlike electrorefining, includes specific features of gas evolution and porous electrode and, thus, different equations should be considered for developing a model for the process. This study summarized required concepts and equations for electrolytic reduction model development from thermodynamic, mass transport, and reaction kinetics theories which are necessitated for analyzing an electrochemical cell. An electrolytic reduction cell was divided and equations for each section were listed and, then, boundary conditions for connecting the sections were indicated. It is expected that those equations would be used as a basis to develop a simulation model for the future and applied to determine parameters associated with experimental data.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.393-398
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• 2021

In order to optimize the performance of a lithium-ion battery, a performance prediction modeling technique that considers various degradation factors is required. In this work, mathematical modeling was carried-out to predict the change in discharging behavior and cycle life, taking into account the cycle aging of lithium-ion batteries. In order to validate the modeling, a cycling test was performed at the charge/discharge rate of 0.25C, and discharging behavior was measured through RPT (Reference Performance Test) performed at 30 cycle intervals. The accuracy of cycle life prediction was improved by considering the break-in mechanism, one of the phenomena occurring in the BOL (beginning of life), in the model for predicting the cycle life of lithium-ion batteries. The predicted change in cycle life based on the model was in good agreement with the experimental results.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.275.1-275.1
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• 2016

반전형 폴리머 태양전지는 그 구조에 의하여 훌륭한 안정성을 가질 뿐만 아니라 roll-to-roll 공정을 통한 대량생산이 가능하여 각광받고 있는 구조이다. 이런 반전형 구조에서, 금속 산화물 나노파티클에 의해 만들어지는 금속 산화물 층은 전자수송층으로서 사용된다. 이 연구에서는 표면개질 물질인 PEIE (Polyethyleneimine-ethoxylate)와 화학적으로 기능화된 산화아연/그래핀 핵/껍질 양자점을 이용하여 전기수송층의 역할을 하는 기능화된 산화아연/그래핀 단분자층을 가지는 태양전지를 제작하였다. 이는 기능화된 산화아연/그래핀 단분자층이 표면개질, 광센서, 전기수송층의 역할을 동시에 수행하는 효과로 인해 제작된 태양전지는 향상된 전자 수집능력을 보였다. 단분자층이 잘 형성되어 있는지 확인하기 위하여 집속 이온 빔 장비를 이용하여 태양전지의 내부 구조를 확인하였으며, density functional theory (DFT)을 이용한 모델링을 통하여 기능화된 산화아연/그래핀 양자점의 전자상태밀도를 분석하였다. 기능화된 산화아연 단분자층에 의한 효과적인 계면 제어 및 전하수송에 의해 약 10.3%의 높은 효율을 가지는 반전형 폴리머 태양전지를 제작할 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.49-49
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• 2009

최근 범세계적인 그린에너지 정책에 관련해 화석연료를 대체할 수 있는 수소, 풍력, 태양광 등의 대체 에너지에 대한 관심이 고조되고 있다. 이러한 여러 대체에너지 중에서도 태양광을 전기에너지로 변환하는 태양전지에 관한 연구가 집중되고 있다. 태양전지는 구조적으로 단순하고 제조 공정도 비교적 간단하지만, 보다 널리 보급되기 위해서는 경제성 향상이라는 문제점을 해결해야 한다. 이를 위해서는 기존의 실리콘 태양전지를 대체할 수 있는 신물질에 대한 연구가 필요하며, 그 중에서도 반도체 기술을 이용한 박막형 태양전지는 기존의 실리콘 태양 전지가 가지고 있는 고비용이라는 문제점을 극복할 수 있을 것으로 기대를 모으고 있다. 박막형 태양전지의 박막 재료로는 CIGS, CdTe 등이 연구되어지고 있지만, 아직까지는 기존의 실리콘 태양전지에 비해 에너지변환효율이 낮은 이유로 인해 실용화가 많이 이루어지지 못하고 있는 것이 사실이다. 이러한 박막형 태양전지의 재료들 중에서도 CdTe는 이종접합 박막형 태양전지에 흡광층으로 사용되는 것으로 상온에서 1.45eV 정도의 밴드갭(band gap) 에너지를 갖는 II-VI족 화합물반도체로써 태양광 스펙트럼과 잘 맞는 이상적인 밴드랩 에너지와 높은 광흡수도 때문에 박막형 태양전지로 가장 주목을 받고 있다. CdTe 박막의 제조 방법으로는 진공증착법(vacuum evaporation), 전착법(electrodeposition), 스퍼터링법(sputtering) 등이 있지만 본 연구에서는 스퍼터링법을 이용하여 박막을 증착하였다. 이상과 같이 증착된 CdTe 박막을 화학적기계적연마(CMP, chemical mechanical polishing) 공정을 적용시킴으로써, 태양전지의 에너지변환효율에 직접적인 영향을 끼칠 수 있는 CdTe 박막의 물리적, 전기적 특성들의 변화를 연구하기 위한 선행 연구를 진행하였다. 특히 본 연구에서는 CdTe 박막의 화학적 기계적 연마 특성을 분석하여 정규화를 통한 모델링을 수행하였다. 또한 화학적기계적연마 공정 전과 후의 표면 특성을 관찰하기 위해 SEM(scanning electron microscopy)과 AFM(atomic forced microscope)를 이용하였으며, 구조적 특성 관찰을 XRD(X-ray diffraction)를 사용하여 실험을 수행하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.907-915
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• 2008

The computational fluid dynamic analysis has been conducted for the thermo-chemical flow field in an arcjet thruster with mono-propellant Hydrazine (N2H4) as a working fluid. The Reynolds Averaged Navier-Stokes (RANS) equations are modified to analyze compressible flows with the thermal radiation and electric field. the Maxwell equation, which is loosely coupled with the fluid dynamic equations through the Ohm heating and Lorentz forces, is adopted to analyze the electric field induced by the electric arc. The chemical reactions of Hydrazine were assumed to be infinitely fast due to the high temperature field inside the arcjet thruster. The chemical and the thermal radiation models for the nitrogen-hydrogen mixture and optical thick media respectively, were incorporated with the fluid dynamic equations. The results show that performance indices of the arcjet thruster with 1kW arc heating are improved by amount of 180% in thrust and 200% in specific impulse more than frozen flow. In addition thermo-physical process inside the arcjet thruster is understood from the flow field results.

• Journal of Energy Engineering
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• v.6 no.1
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• pp.87-95
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• 1997

A chemical heat pump based on the reversible reactions between metal chlorides and ammonia gas is attractive alternative to compression system and liquid absorption systems in cooling and refrigerating fields. The advantages of chemical heat pump are no regulatory constants due to CFC refrigerants, utilization of gas, industrial waste heat, electricity, fuel oil etc. as heat sources and wide applications to energy storage system, large-scale energy managements for industrial process. The scale-up of chemical heat pump from laboratory prototype to pilot plants necessitates the interpretation of system performance and evaluation of dynamic behavior in the chemical reactor. This study contains the prediction of performance of chemical refrigerator according to operating condition, the dynamic simulations through reactor modelling, which is used for the calculation of reactive medium temperature and the conversion variation with reactor cooling temperature, and the effect survey of block parameters on the power of refrigerator.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.48-52
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• 2003

A mathematical dynamic model of fuel cell was formulated in order to design the control system which will meet the control object. The control objective is set to regulate the airflow in the load change by utilization of airflow and the pressure difference between anode and cathode is maintained below a limit range. Simulation result of 10kW polymer electrolyte membrane fuel cell (PEMFC) clearly demonstrates that response time need to be less. than 1 seconds for the control requirements. Besides, pressure difference was allowed in pressure range less than 0.01 atm.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.86-92
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• 2017

A process, which converts carbon dioxide contained in the flue gas of coal-fired power plants to sodium bicarbonate, was studied experimentally and numerically. In this process, the carbon dioxide reacts with sodium hydroxide which is produced through saline water electrolysis. A bench scale reactor system was prepared for experiments of this process and numerical process modeling was performed for the bench scale reactor system. Comparing the process modeling results with the experimental data, responsibility of the process modeling was confirmed. Using this model, commercial scale process was simulated. Mass and energy balance of this process were calculated. Temperature profile in the reactor and carbon dioxide removal rate were obtained.

• Journal of the Korean institute of surface engineering
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• v.27 no.4
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• pp.223-233
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• 1994

It is well known that compositionally modulated Cu-Ni alloy can be produced by an electrochemical method in Ni sulfate solution containing trace amount of Cu. a mathematical model is presented to describe the current distribution and weight percent of Cu in Ni layer on the rotating disk electrode. The model includes convective-diffusion equation, the Laplace's equation and various overpotentials, and is solved numerically. The thickness of Cu layer is almost uniform whereas the thickness of Ni layer as well as the Ni/Cu weight ratio are increased approaching to the edge of the disk. These results agree well with the experimental values. The ohmic potential drop is suggested as a major cause of a nonuniformity in Ni layer. The optimum plating condition for the fabrication of susperlattice is proposed based on the results of this study.