• New & Renewable Energy
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• v.8 no.2
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• pp.24-32
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• 2012

Natural gas hydrates have a high potential as the 21st century new energy resource, because it have a large amount of deposits in many deep-water and permafrost regions of the world widely. Natural gas hydrate is formed by physical binding between water molecule and gas mainly composed of methane, which is captured in the cavities of water molecules under the specific temperature and pressure. $1m^3$ methane hydrate can be decomposed to the methane gas of $172m^3$ and water of $0.8m^3$ at standard condition. Therefore, there are a lot of practical applications such as separation processes, natural gas storage transportation and carbon dioxide sequestration. For the industrial utilization of methane hydrate, it is very important to rapidly manufacture hydrate. However, when methane hydrate is artificially formed, its reaction time may be too long and the gas consumption in water becomes relatively low, because the reaction rate between water and gas is low. So in this study, hydrate formation was experimented by adding natural zeolite and Synthetic zeolite 5A in distilled water, respectively. The results show that when the Synthetic zeolite 5A of 0.01 wt% was, the amount of gas consumed during the formation of methane hydrate was higher than that in the natural zeolite. Also, the natural zeolite and Synthetic zeolite 5A decreased the hydrate formation time to a greater extent than the distilled water at the same subcooling temperature.

• Journal of the korean society of oceanography
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• v.35 no.1
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• pp.16-33
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• 2000

In order to measure the vertical fluxes of particles and reactive radionuclides such as thorium and polonium isotopes, Dunbar-type sediment traps were freely deployed at the Ulleung Basin and in warm and cold water masses around the polar front of the East Sea. We estimated the ratios of the catched (F) to the predicted $^234$Th fluxes (P) using natural tracers pair $^234$Th-$^238$U. The F/P ratios are decreased with increasing water depth. Whereas the concentrations of suspended particles are homogeneous in water column, the mass fluxes are also decreased with increasing water depth like the F/P ratios. These facts indicate that organic matters of settling particles are destructed within the euphotic layer due to decomposition. Whereas regenerations of sinking particles are negligible in the cold water mass, about 80% of them are regenerated in the warm water mass during falling of large particles. These downward mass fluxes are closely correlated with their primary productions in euphotic zone. The activities of $^234$Th, $^228$Th and $^210$Po in the sinking material were increased with water depth. Because $^234$Th steadily produced in the water column are cumulatively adsorbed on the surface of sinking particles, vertical $^234$Th fluxes were observed to increase with water depth. Therefore, these sinking particles play important roles in transporting the particle reactive elements like thorium from surface to the deep sea. The scavenging processes including adsorption and settling reactions generate radio-disequilibrium between daughter and parent nuclides in water column. The activity ratios of $^234$Th/$^238$U and $^228$Th/$^228$Ra were observed to be < 1.0 in the surface water and approached to be equilibrium below the thermocline. The extent of the deficiency of daughter nuclides compared to the parents nuclide was highly correlated with the vertical particle flux. Because most of the $^210$Po in the surface water are scavenged on a labile phase and are recycled at sub-surface depths (< 200 m), the $^210$Po are always observed to be excess activities compared to $^226$Ra in surface water.

• Journal of Environmental Science International
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• v.9 no.3
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• pp.241-252
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• 2000

Twenty-two water samples(fifteen groundwater and seven geothermal water samples) were collected to elucidate chemical characteristics of the ground and geothermal waters in the Haeundae hot spring area and its vicinity. Major and honor elements were analyzed for ground and geothermal water samples. The concentrations of $K^+$, Na+$, $Ca^{2+}$, $SO_4^{2-}$, $Cl^-$, ^F^-$ and $SiO_2$ were higher in the geothermal water samples than the groundwater samples except $HCO_3^- and Mg^{2+}$ ions. Based on the contents of Fe, Zn, Cu, Al, Mn and Pb, some of the ground and geothermal water samples are contaminated by anthropogenic sources. The ground waters shown on the Piper diagram belong to $Ca-HCO_3$ type, while the geothermal waters Na-Cl type. The graphs of $Cl^-$ versus $Na^+$, $Ca^{2+}, Mg^{2+}, K^+, SO_4^{2-} and HCO_3^-$ indicate that the groundwater is related partly with mineral-water reaction and partly with anthropogenic contamination, while the geothermal water is related with saline water. On the phase stability diagram, groundwater and thermal water mostly fall in the field of stability of kaolinite. This indicates that the ground and geothermal waters proceed with forming kaolinite. Factor and correlation analyses were carried out to simplify the physicochemical data into grouping some factors and to find interaction between them. Based on the Na-K, Na-K-Ca and Na-K-Ca-Mg geothermometers and silica geothermometers, the geothermal reservoir is estimated to have equilibrium temperature between 125${$\mid$circ}C$ and 160${$\mid$circ}C$.

• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.67-75
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• 2014

Methane gas hydrate which is considered energy source for the next generation has an urgent need to develop reliable numerical simulator for coupled THM phenomena in the porous media, to minimize problems arising during the production and optimize production procedures. International collaborations to improve previous numerical codes are in progress, but they still have mismatch in the predicted value and unstable convergence. In this paper, FEM code for fully coupled THM phenomena is developed to analyze methane hydrate dissociation in the porous media. Coupled partial differential equations are derived from four mass balance equations (methane hydrate, soil, water, and hydrate gas), energy balance equation, and force equilibrium equation. Five main variables (displacement, gas saturation, fluid pressure, temperature, and hydrate saturation) are chosen to give higher numerical convergence through trial combinations of variables, and they can analyze the whole region of a phase change in hydrate bearing porous media. The kinetic model is used to predict dissociation of methane hydrate. Developed THM FEM code is applied to the comparative study on a Masuda's laboratory experiment for the hydrate production, and verified for the stability and convergence.

• Steel and Composite Structures
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• v.8 no.1
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• pp.1-18
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• 2008

Observations from experiments and real fire indicate that restrained steel beams have better fire-resistant capability than isolated beams. Due to the effects of restraints, a steel beam in fire condition can undergo very large deflections and the run away damage may be avoided. In addition, axial forces will be induced with temperature increasing and play an important role on the behaviour of the restrained beam. The factors influencing the behavior of a restrained beam subjected to fire include the stiffness of axial and rotational restraints, the load type on the beam and the distribution of temperature in the cross-section of the beam, etc. In this paper, a simplified model is proposed to analyze the performance of restrained steel beams in fire condition. Based on an assumption of the deflection curve of the beam, the axial force, together with the strain and stress distributions in the beam, can be determined. By integrating the stress, the combined moment and force in the cross-section of the beam can be obtained. Then, through substituting the moment and axial force into the equilibrium equation, the behavior of the restrained beam in fire condition can be worked out. Furthermore, for the safety evaluation and repair after a fire, the behaviour of restrained beams during cooling should be understood. For a restrained beam experiencing very high temperatures, the strength of the steel will recover when temperature decreases, but the contraction force, which is produced by thermal contraction, will aggravate the tensile stresses in the beam. In this paper, the behaviour of the restrained beam in cooling phase is analyzed, and the effect of the contraction force is discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.283.2-283.2
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• 2014

열필라멘트 화학증착공정(Hot Wire Chemical Vapor Deposition)에서 기상 에서 생성되는 하전된 실리콘 나노입자와 저온결정성 실리콘박막 증착의 연관성을 압력의 변화에 따른 상호비교를 통해 조사하였다. 필라멘트 온도는 $1800^{\circ}C$로 고정시키고 0.3~2 torr의 범위에서 공정 압력을 변화시키면서 증착하였다. 압력이 증가함에 따라 증착된 실리콘 박막의 결정화도는 증가하였으며, 증착속도는 감소하였다. 반응기 압력에 따른 기상에서 생성되는 나노입자의 크기분포의 변화를 조사하기 위하여 탄소막이 코팅된 투과전자현미경(Transmission Electron Microscopy) 그리드 위에 실리콘 나노입자를 포획하고 관찰하였다. 포획된 실리콘 나노입자의 크기분포와 개수농도는 압력이 증가함에 따라 감소하였다. 투과전자현미경을 이용하여 분석한 결과, 나노입자는 결정성 구조를 보였다. 압력이 증가함에 따라 나노입자의 크기가 감소하고 개수농도가 감소하는 것은 증착속도의 감소와 관련됨을 알 수 있다. 한편, 공정압력 증가에 따른 나노입자의 크기분포 및 개수농도 감소와 증착속도의 감소는 일반적으로 알려진 기상에서 석출하는 고상의 평형석출량(equilibrium amount of precipitation)이 압력의 증가함에 따라 증가한다는 사실과 일치하지 않는다. 이러한 압력경향성은 Si-H 시스템이 0.3~2 torr의 압력 영역에서 retrograde solubility를 갖는 것을 의미한다. 나노입자의 하전여부, 크기분포 및 개수농도를 측정하기 위하여 입자빔질량분석장비(Particle Beam Mass Spectroscopy)를 이용하였다. 그 결과, 실리콘 나노입자는 양 또는 음의 극성을 가진 하전된 상태임을 확인하였고, 투과전자현미경(TEM) grid에 포획한 실리콘 나노입자의 크기와 경향성이 일치하였다. 이는 나노입자가 저온의 기판에서 핵생성되어 성장하여 생성된 것이 아니라 열필라멘트 주위의 고온영역에서 생성된 것을 의미한다.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.4
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• pp.203-209
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• 1998

The quality of groundwater used for natural mineral water should be strictly regulated on international level by hydrogeology experts and officials because groundwater is greatly subjected to contaminations and its aquifer system may be easily destroyed by external reasons. A total of 18 natural mineral water plants exist in Precambrian metamorphic terrains of the Gyunggi massif and Yeungam massif. The g개undwater quality for the natural mineral water investigated in hydrochemical aspects shows that pH ranges from 6.85 to 8.02 with an average of 7.52. The electric conductivity (EC) and hardness average 134.1 $\mu$S/cm and 43.5, respectively, which are relatively low to the total average (151.4 $\mu$S/cm and 57.9). The contents of major cations and anions are in the order of $Ca^{2＋}$＞$Na^{＋}$＞Mg$^{2＋}$＞K$^{＋}$ and HCO$_3$$^{-}$ ＞SO$_4$$^{2－}$ ＞Cl$^{-}$ ＞F$^{-}$ , respectively. The dominant water types determined by Piper diagram are $Ca^{2＋}$－$Na^{＋}$－HCO$^{-}$ $_3$and $Ca^{2＋}$-HCO$^{-}$ $_3$, mainly due to the dissolution of plagioclase in the host rocks. Representative correlation coefficients between chemical species are $Ca^{2＋}$－HCO$^{-}$ $_3$(0.92), $Ca^{2＋}$－Cl$^{-}$ (0.63), $Na^{＋}$－F$^{-}$ (0.67), HCO$^{-}$ $_3$－Cl$^{-}$ (0.66), and $Na^{＋}$－HCO$^{-}$ $_3$(0.63). The determinative. coefficients between $Ca^{2＋}$ and HCO$^{-}$ $_3$, and (Ca$^{2＋}$＋$Na^{＋}$＋K$^{＋}$ and EC art highest among the elements. According to the saturation index, most chemical species are undersaturated with respect to major minerals, except for some silica phases. In viewpoint of phase equilibrium, the chemical evolution of the groundwater may continue to proceed with increasing pH because the groundwater is undersaturated with respect to feldspars.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.123.1-123.1
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• 2011

본 연구에서는 THF(Tetrahydrofuran)와 산화탄소나노튜브를 혼합한 유체가 메탄 하이드레이트 생성에 어떠한 영향을 미치는지 알아보기 위해 하이드레이트 생성실험을 수행하고 비교분석하였다. 먼저 하이드레이트 생성 시 정확히 큰 동공에 하나의 THF 분자를 위치시킬 수 있는 5.56 mol%의 THF 혼합유체와 0.003 wt%의 산화 탄소나노튜브를 첨가한 산화탄소나노유체에서 하이드레이트 생성실험을 수행한 결과 같은 과냉도에서 상평형은 THF가 우수하였으며, 하이드레이트 생성에 소모되는 가스소모량은 산화탄소나노튜브가 월등히 우수한 효과를 보였다. 따라서 이 두 종류 촉진제의 단점을 보완하고, 우수한 효과를 이끌어 내기 위해 THF와 산화탄소나노튜브를 혼합하였다. 0.003 wt%의 산화탄소나노유체에 5.56 mol%의 THF를 혼합하였으며, 하이드레이트 상평형, 가스소모량, 생성시간을 측정하여 증류수와 THF, 산화탄소나노유체와 비교하였다. 그 결과, THF+산화탄소나노튜브 혼합유체의 상평형은 THF의 상평형과 비슷하였으고, 과냉도 3.4K에서의 가스소모량은 산화나노유체가 증류수의 3.6배, THF가 증류수의 1.7배, THF+산화탄소나노튜브 혼합유체가 증류수의 5.2배로 THF+산화탄소나노튜브 혼합유체에서 가스소모량이 가장 높음을 알 수 있었다. 또한 하이드레이트 생성시간은 같은 과냉도에서 THF+산화탄소나노튜브 혼합유체가 THF보다 빠르며, 산화탄소나노유체의 하이드레이트 생성시간과 비슷함을 보였다. 따라서 THF+산화탄소나노튜브 혼합유체는 THF의 우수한 상평형 효과와 탄소나노튜브의 높은 가스소모량 효과를 같이 가지고 있음을 확인하였다.

• Journal of Soil and Groundwater Environment
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• v.20 no.4
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• pp.73-82
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• 2015

Despite significant effects on macroscopic migration and distribution of CO₂ injected during geological sequestration, only limited information is available on wettability in microscopic scCO₂-brine-mineral systems due to difficulties in pore-scale observation. In this study, a micromodel had been developed to improve our understanding of how scCO₂ flooding and residual characteristics of porewater are affected by the wettability in scCO₂-water-glass bead systems. The micromodel (a transparent pore structure made of glass beads and glass plates) in a pressurized chamber provided the opportunity to visualize scCO₂ spreading and porewater displacement. CO₂ flooding followed by fingering migration and dewatering followed by formation of residual water were observed through an imaging system. Measurement of contact angles of residual porewater in micromodels were conducted to estimate wettability in a scCO₂-water-glass bead system. The measurement revealed that the brine-3M NaCl solution-is a wetting fluid and the surface of glass beads is water-wet. It is also found that the contact angle at equilibrium decreases as the pressure decreases, whereas it increases as the salinity increases. Such changes in wettability may significantly affect the patterns of scCO₂ migration and porewater residence during the process of CO₂ injection into a saline aquifer at high pressures.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.539-546
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• 2008

A study on the selection of an optimal entrainer as the third component among water, aniline, 1,3-diethylbenzene, furfural, and MEK, for the extractive distillation of an azeotropic acetone/methanol system was performed using both the entrainer effect vapor-liquid equilibrium (VLE) and the relative volatility. In the case of water as the entrainer, a VLE curve without azeotropic point in the range of water composition from 0.3 up to 0.7 mole fraction could be obtained by both the experiment and the calculation using modified-UNIFAC model. For aniline and 1,3-diethylbenzene, however, VLE curve without azeotropic point could be obtained only at compositions above 0.7 mole fraction, which exhibited that they could be hardly utilized as the entrainer. Moreover, both furfural and MEK were verified to be improper entrainer since they formed an azeotropic phase. Relative volatility of water showed greater than 1.0 and increased with compositions, while those of the others decreased non-linearly, exhibiting that only water could be utilized as the proper entrainer for the extractive distillation of azeotropic acetone/methanol system.