• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.275-281
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• 2016

In this study, we investigate the pool boiling enhancement caused by perforated plates on top of a smooth surface. We conduct tests using R-123 at atmospheric pressure. It was shown that perforated plates significantly enhanced the pool boiling of the smooth surface. The reason may be attributed to the increased bubble contact area between the plates. The results showed that the enhancement ratio was dependent on the heat flux. At high heat flux, the enhancement ratio increased as the porosity increased. However, at low heat flux, the enhancement ratio decreased as the porosity increased. For the present investigation, the optimum configuration had a pore diameter of 2.0 mm, pore pitch of $2.5mm{\times}5.0mm$ or $5.0mm{\times}5.0mm$, and a gap width of 0.5 mm, which yielded heat-transfer coefficients that are close to those of GEWA-T. The optimum porosity for R-123 was significantly larger than that of water or ethanol. The reason for this may be the large liquid-to-vapor density ratio along with the small latent heat of vaporization of R-123. The perforated plates yielded smaller boiling hysteresis compared with that of the smooth surface.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3637-3641
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• 2014

In this study, we analyzed the toxicity of mixtures of dimethylformamide (DMF) and methyl ethyl ketone (MEK) or DMF and toluene (TOL) and predicted their toxicity using quantitative structure-activity relationships (QSAR). A QSAR model for single substances and mixtures was analyzed using multiple linear regression (MLR) by taking into account the statistical parameters between the observed and predicted $EC_{50}$. After preprocessing, the best subsets of descriptors in the learning methods were determined using a 5-fold cross-validation method. Significant differences in physico-chemical properties such as boiling point (BP), specific gravity (SG), Reid vapor pressure (rVP), flash point (FP), low explosion limit (LEL), and octanol/water partition coefficient (Pow) were observed between the single substances and the mixtures. The $EC_{50}$ of the mixture of DMF and TOL was significantly lower than that of DMF. The mixture toxicity was directly related to the mixing ratio of TOL and MEK (MLR $EC_{50}$ equation = $1.76997-1.12249{\times}TOL+1.21045{\times}MEK$), as well as to SG, VP, and LEL (MLR equation $EC_{50}=15.44388-19.84549{\times}SG+0.05091{\times}VP+1.85846{\times}LEL$). These results show that QSAR-based models can be used to quantitatively predict the toxicity of mixtures used in manufacturing industries.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.233-238
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• 2000

t-$ZrO_2/Al_2O_3$composites having a superior biocompatability and phase stability were prepared by adding 0~4 mol% of $Eu_2O_3$and sintered for 1 h at $1600^{\circ}C$ to evaluate phase stability, chromaticity and mechanical properties of the composites. No tetragonal to monoclinic phase transformation was observed for the composites containing $Eu_2O_3$after heat treatment for 20 h at $180^{\circ}C$ under 3.5 MPa water vapor pressure condition. As $Eu_2O_3$content increased, the color of the composites was changed from a slight white ivory to a light pink. The strength and the fracture toughness of the composites containing $Eu_2O_3$were above 620 MPa and 7.6 MPa.$m^{1/2}$, respectively, when $Eu_2O_3$was added up to 3 mol%.

• KSBB Journal
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• v.20 no.3
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• pp.183-191
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• 2005

Ionic liquids, composed of organic cations and either organic or inorganic anions remain liquid over a wide range of temperature. ionic liquids are a new group of solvents or extractants of great interest as a potential 'green solvent'. Ionic liquids are gaining wide recognition as novel solvents in many research fields, such as chemistry, chemical engineering, electrochemitry, etc. However, not much researches have been done related to biotechnology using ionic liquids, while a lot of researches have been performed in chemistry. The merits of ionic liquids in bioseparation technology are originated from some unique properties of ionic liquids, such as negligible vapor pressure, good thermal stability, controllable viscosity and miscibility with water and organic solvents. An appropriate selection of ionic liquid for bioprocesses requires basic knowledge on physicochemical properties of ionic liquids. This review gives a brief overview on the application of ionic liquids in biotechnology, including bioconversion and bioseparation.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.304-308
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• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.

• Clean Technology
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• v.14 no.4
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• pp.287-292
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• 2008

In this study, computer simulation works have been performed for the capture process of the $CO_2$ and $H_{2}S$ gases contained in the effluent stream using methanol aqueous solution. In order to increase the solubilities of the $CO_2$ and $H_{2}S$ in the methanol aqueous stream, the operating pressure of the absorber was raised to 30 bar and the feeding temperature of the solvent was lowered to $-20^{\circ}C$ by using refrigeration cycle. NRTL liquid activity coefficient model was used to estimate the liquid phase nonidealities for methanol and water. Soave-Redlich-Kwong equation of state was used for the vapor phase nonidealities. Henry's law option was also used to calculate the solubilities of the supercritical noncondensible gases into the methanol aqueous solvent stream.

• Journal of the Korean Society of Tobacco Science
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• v.12 no.2
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• pp.59-65
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• 1990

In order to predict the shelf-life of cigarettes packaged in typical flexible film under conditions of various temperature, relative humidity and sealing degree, a computer iterative technique was used. Although there were some significant differences at initial equilibrium relative humidity(55%), the experimental results agree fairly well with predictions following the student's t test($\alpha$=0.01) in most cases. Essentially, the higher the storage temperature, the shorter the shelf-life of the cigarette product. The bigger the differences from the initial equilibrium relative humidity, the shorter the storage period of the cigarette. Moisture transfer through the film at relatively high temperature gave higher confidence. The sealing degree, one of the storage parameters, appeared to be a major influencing factor to shelf-life. Slopes($\beta$) of the temp., sealing degree and %rh of the dependent variable to shelf life were 0.49, -0.39 and -0, 28 respectively, when analysed by multiple regression of SPSS software. Below 600m1/min sealing decree of the packed cigarette through the sealing Position at 30mmH20 differential pressure, the shelf-life could be increased by more than six months.

• Journal of Environmental Science International
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• v.29 no.11
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• pp.1065-1078
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• 2020

The statistical characteristics of aerosol-cloud interactions over East Asia were investigated using Moderate Resolution Imaging Spectroradiometer satellite data. The long-term relationship between various aerosol and cloud parameters was estimated using correlation analysis, principle component analysis, and Aerosol Indirect Effect (AIE) estimation. In correlation analysis, Aerosol Optical Depth (AOD) was positively Correlated with Cloud Condensation Nuclei (CCN) and Cloud Fraction (CF), but negatively correlated with Cloud Top Temperature (CTT) and Cloud Top Pressure (CTP). Fine Mode Fraction (FMF) and CCN were positively correlated over the ocean because of sea spray. In principle component analysis, AOD and FMF were influenced by water vapor. In particular, AOD was positively influenced by CF, and negatively by CTT and CTP over the ocean. In AIE estimation, the AIE value in each cloud layer and type was mostly negative (Twomey effect) but sometimes positive (anti-Twomey effect). This is related to regional, environmental, seasonal, and meteorological effects. Rigorous and extensive studies on aerosol-cloud interactions over East Asia should be conducted via micro- and macro-scale investigations, to determine chemical characteristics using various meteorological instruments.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.808-814
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• 2010

Activities of nanostructure HZSM-5 and Co-ZSM-5 catalysts (with different Co-loading) for catalytic conversion of ethyl acetate and toluene were studied. The catalysts were prepared by wet impregnation method and were characterized by XRD, BET, SEM, TEM and ICP-AES techniques. Catalytic studies were carried out inside a U-shaped fixed bed reactor under atmospheric pressure and different temperatures. Toluene showed lower reactivity than ethyl acetate for conversion on Co-ZSM-5 catalysts. The effect of Co loading on conversion was prominent at temperatures below $400^{\circ}C$ and $450^{\circ}C$ for ethyl acetate and toluene respectively. In a binary mixture of organic compounds, toluene and ethyl acetate showed an inhibition and promotional behaviors respectively, in which the conversion of toluene was decreased at temperatures above $350^{\circ}C$. Inhibition effect of water vapor was negligible at temperatures above $400^{\circ}C$. An artificial neural networks model was developed to predict the conversion efficiency of ethyl acetate on Co-ZSM-5 catalysts based on experimental data. Predicted results showed a good agreement with experimental results. ANN modeling predicted the order of studied variable effects on ethyl acetate conversion, which was as follows: reaction temperature (50%) > ethyl acetate inlet concentration (25.085%) > content of Co loading (24.915%).

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.203-211
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• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.