• Resources Recycling
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• v.28 no.3
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• pp.15-20
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• 2019

The recovery of struvite using nitrogen and phosphorus in wastewaters is useful for prevention of eutrophication and use as fertilizer, but there are theoretical and technical issues to be resolved. Through the detailed literature review, this study discusses the possible reasonable prediction of struvite formation reaction by setting a feasible reaction equation with some theoretical considerations. In a technical aspect, the purity of struvite in solid precipitates can be promoted by excluding Ca in an effective way. As for the struvite reaction prediction issue, selection of proper equilibrium reaction as well as its reaction equilibrium coefficient is significant in the neutral and basic pH regions. The equilibrium reaction agrees well with the experimental batch test results. Considering the charge balance of the ions, the pH drop along struvite formation in a diluted solution can be predicted. Also, improvement of struvite purity through elimination of Ca can be expected by providing a highly concentrated ${NH_4}^+-N$ relative to ${HPO_4}^{2-}-P$ because ${NH_4}^+$ can enhance the thermodynamic driving force toward favorable struvite formation. Even though the phosphate reacts rapidly with Ca to form a solid precipitate, the thermodynamic driving force due to the high ${NH_4}^+$ activity can dissociate the phosphate-calcium precipitates and produce struvite.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.1
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• pp.41-53
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• 1997

Geochemical data of soil and water samples were presented in order to assess the environmental impart for drinking water sites. Microscopic observation of rock samples and physical and chemical analysis of soil and water samples were undertaken. The geology of study areas are classified into three groups such as granitic rocks, meta-sedimentary rocks and sedimentary rocks. Enrichment of heavy metals derived from those rocks is not found in this study areas. Soils were analyzed for Cu, Pb, Zn, Cd and Cr using AAS extracted by HNO$_3$+HClO$_4$ and 0.1 N HCl. Heavy metal concentrations in soils are within the range of those in uncontaminated soils. In comparison of metal contents extracted by 0.1 N HCl and HNO$_3$+HC1O$_4$, less than 10% of the heavy metals are present in the exchangeable fraction. In particular, an pollution index has been proposed to assess the degree of soil contamination. Pollution index in soils are between 0.03 and 0.47 therefore, soils are not polluted with heavy metals. Deep groundwaters within granitic rocks have been evolved into Na$\^$＋/-HCO$_3$$\^$-/ type, whereas other deep groundwaters evolved into Ca$\^$2＋/-HCO$_3$$\^$-/ type. The predominance of Na$\^$＋/ over Ca$\^$2＋/ in deep groundwaters within granitic rocks is a result of dissolution of plagioclase, but for sedimentary and meta-sedimentary rocks, dissolution of calcite is a dominant factor for their hydrogeochemistry. The pH, conductivity and contents of the most dissolved ions in the water increase with depth. Shallow groundwaters, however, are highly susceptible to pollution owing to agricultural activities, considering the fact that high contents of nitrate, chloride and potassium, and high K/Na ratio are observed in some shallow groundwaters. In a thermodynamic approach, most natural water samples are plotted within the stability fields of kaolinite and smectite. Therefore, microcline and other feldspars will alter to form clay minerals, such as kaolinite and smectite. From the modelling for water-rock interactions based on mass balance equation, models accord well with behavior of the ions and results of thermodynamic studies are derived.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.205-208
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• 2008

In numerical analysis numerical values of thermodynamic properties such as temperature, pressure, specific volume, enthalpy and entropy are required. But most of the thermodynamic properties of the steam table are determined by experiment. Therefore they are supposed to have measurement errors. In order to make noised thermodynamic properties corresponding to errors, random numbers are generated, adjusted to appropriate magnitudes and added to original thermodynamic properties. the neural networks and quadratic spline interpolation method are introduced for function approximation of these modified thermodynamic properties in the saturated water based on pressure. It was proved that the neural networks give smaller percentage error compared with quadratic spline interpolation. From this fact it was confirmed that the neural networks trace the original values of thermodynamic properties better than the quadratic interpolation method.

• Korean Journal of Materials Research
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• v.6 no.2
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• pp.133-137
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• 1996

본연구에서는 n-type 세라믹 초전도체인 Nd2-xCexCuO4상의 산소함량에 따른 \ulcorner기적저항의 변화를 고찰하고자 하였다. 일반적인 소결과 어닐링과정을 결쳐 제조된 Nd1.85Ce0.15CuO4-x 시편을 여러 온도와 산소분압의 분위기하에서 어닐링시킴으로써 산소의 함유량이 다른 시편들을 준비하였고 각각의 시편의 산소함량은 TGA(Thermogravimetric Analysis0에 의해 측정하였다. Nd1.85Ce0.15CuO4-x시편의 전기적 저항 측정은 표준 4-탐침방법을 이용하여 액체헬륨을 주입시켜 상온으로부터 4K까지 측정하였다. Nd1.85Ce0.15CuO4-x시편의 산소함량, 3.96$\leq$4-x$\leq$4.0의 범위에서 전기적저항을 측정한 결과 초전도특성이 나타나기 시작한 임계산소함량은 4-x=3.990이었고 이때의 임계온도 Tc=12K이었다. 또한 임계온도, Tc는 산소함량 4-x=3.96에서 24K로 측정되었다. 특이할 만한 현상은 CuO/Cu2O 열역학적 상전이가 일어나는 조건이 Nd1.85Ce0.15CuO4-x 시편의 초전도가 일어나는 임계와 일치하였다. 즉, Cu2O가 안정한 영역에서는 초전도특성이 나타났고 CuO가 안정한 영역에서는 초전도특성이 나타나지 않았다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.172-178
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• 1990

To predict the qualitative performance characteristics of Stirling Engines, an analytical approach to the Ideal Adiabatic Model set up by Urieli et al. has been treated. First, volume variations of both the expansion and the compression cylinders are approximated to piecewise linear function of the crank angle, which make it possible to specify the mass flow direction of each cylinder a priori to solve a set of basic equation. In consequences, an engine cycle can be considered as a combination of 4-type fundamental process. For each process, pressure is obtained as a solution of the algebraic equation. Application of the cyclic steady condition to the whole cycle completes the analysis. Further investigations result in analytical expressions for cyclic heat and work in terms of dependent variables determined from the pressure. The results are expected useful in establishing the preliminary design conditions of Stirling Engines.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1716-1720
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• 2006

침투는 지반이 충적토로 구성되어 있는 제방의 파괴를 야기하는 중요한 원인이다. 침투 해석 수치모형은 제방 침투와 관련된 문제 해석과 방지기법 설계에 있어 매우 유용한 방법이나, 각각의 수치모형은 적용상 한계와 문제점을 내포하고 있다. 실제 지하수 흐름은 간극률, 입자형상 및 크기, 포화도 등과 같은 토질특성, 내부침식과 같은 역학적 특성, 점성과 동결융해 같은 열역학적 특성, 그리고 화학적 특성 등 다양한 인자의 영향을 받는다. 이러한 물리적 인자 이외에도 침투 수치해석은 외력조건, 격자 크기(element size), 그리고 시간 간격(time step interval) 등 입력조건에 영향을 받기 때문에 이들 설정에 대한 검토를 시행하여야 한다. 본 연구에서는 침투 수치모형의 적절한 입력조건 범위를 검토하였으며, 격자크기는 계산시간과 해석결과 등 수치모의의 효율성을 고려하였을 때 홍수위 혹은 제방고의 1/10이하로 결정하면 타당할 것으로 판단된다. 그리고 침투수치모형의 시간 간격은 외력조건을 고려하여 1시간 이내로 설정하는 것이 바람직할 것으로 판단된다. 본 연구결과는 침투해석 수치모의의 유의사항을 검토하여 해석결과에 대한 불확실성과 위험요소를 제거하는데 도움이 될 것으로 판단된다.

• Resources Recycling
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• v.19 no.5
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• pp.3-12
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• 2010

Platinum group metals with high purity are important raw materials for high technology industry. Since there are no domestic ores containing PGMs, it is of importance to develop a separation process by which ultra pure PGMs can be recovered from diverse spent resources. Data on the chemical properties and dissolution behavior of PGMs were obtained from the literature. A method for the thermodynamic analysis of the HCl solution with chlorine gas was introduced. Utilizing the difference in the chemical properties and dissolution behavior of PGMs would lead to an efficient separation process to recover ultra pure PGMs.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.1078-1091
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• 1994

Thermodynamic calculations have been made from existing literature data to show that it is reasonable to expect to recover metal chlorides from the chlorination of metal sulfides with chlorine gas. The reactions between 12 metal sulfides, such as, $Ag_2S$, $As_2S_3$, CdS, CuS, $Cu_2S$, FeS, HgS, $MoS_2$, $Ni_3S_2$, PbS, $Sb_2S_3$ and chlorine gas were investigated by means of thermogravimetric method. The theorical calculation and the experimental investigation showed that chlorination of sulfide is a better alternative process for the extraction metallurgical process of sulfide ores.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.541-544
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• 2009

$SF_6$는 이산화탄소의 23,900배의 지구온난화지수를 가지는 온실가스로서 절연성이 뛰어나 산업 분야에 많이 사용되고 있다. 본 연구에서는 질소+$SF_6$로 구성된 혼합기체로 부터 $SF_6$를 효과적으로 분리/회수하기 위하여 가스 하이드레이트 형성을 이용한 방법을 제안하였다. 본 실험은 275-290 K의 온도범위와 3-30 bar의 압력범위에서 질소 + $SF_6$ (10, 30, 50, 70%)의 혼합기체를 사용하여 각 조성에 따른 하이드레이트(H)-물(LW)-기상(V)의 3상 평형점을 측정하였다. 또한, 고체의 하이드레이트 내부에 포집된 혼합기체의 조성과 포집되지 않은 기상의 조성을 분석함으로써 하이드레이트 형성을 이용한 공정에서의 기체분리효율을 파악할 수 있었다. 또한, 하이드레이트 생성반응 동안 시간에 따른 혼합기체의 조성변화를 측정하였다. 276.15 K에서 50%의 $SF_6$가 포함된 혼합기체가 하이드레이트를 형성을 경우 하이드레이트상에는 85%의 $SF_6$가 포집다는 것을 알 수 있었다. 본 실험에서 얻어진 결과는 하이드레이트를 이용한 $SF_6$ 분리 공정의 중요한 기초 자료가 되며 다른 혼합 기체의 분리 공정에도 응용될 수 있을 것이다.

• Applied Chemistry for Engineering
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• v.27 no.2
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• pp.128-134
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• 2016

Due to the great development made in converting the shale gas into the more valuable products, research and commercialization for production technology of olefins like propylene, butenes, butadiene from light alkanes have been intensively investigated. Especially the technology using oxygen like oxidative dehydrogenation or selective hydrogen combustion to overcome thermodynamic limit of direct dehydrogenation conversion has been extensively studied and some cases of applying this technology to the plant scale was reported. In this review, we have categorized the technology into two parts; gas phase oxygen utilization technology and lattice oxygen utilization technology. The trends, results and future direction of the technology are discussed.