• 한국대기환경학회지
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• 제28권1호
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• pp.52-58
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• 2012

In this study, the effect of standard phase difference in calibration of carbonyl compounds (CC) was evaluated by using their standards prepared in both gaseous and liquid phase. For this analysis, standards in both phases were prepared for 6 different CCs (formaldehyde (FA), acetaldehyde (AA), propionaldehyde (PA), butyraldehyde (BA), isovaleraldehyde (IA) and valeraldehyde (VA)) at similar concentration levels. Their gaseous standard was calibrated after derivatization with three types of DNPH cartridge, and their calibration results were compared against liquid-phase standards. Although there was a strong compatibility between 2 phases for CCs with lower molecular weights (e.g., formaldehyde and acetaldehyde), it was not the case for the heavier CCs. The results of our analysis indicate that the analytical bias of the heavier CCs can be significantly large (by more than a few tens of %). As a result, underestimation of hevier CCs can be significant, if their gaseous samples are quantified by liquid phase standard.

• 한국기계가공학회지
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• 제19권10호
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• pp.1-7
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• 2020

In this study, a multichannel gas-liquid microextraction system is designed by integrating the automatic elution of extraction line and multichannel gas-purging liquid phase microextraction. The system uses an injection pump and inert gas to push the extraction solvent to a sample bottle of a gas-phase color autosampler and then implements multichannel gas-liquid microextraction and gas chromatography-mass spectrometry. The system also employs a three-way integrated micro-high-temperature heater, syringe pump, and microflow controller to realize the simultaneous processing of multiple groups of samples, thus improving the sample pretreatment speed and reproducibility and reducing human error. Autoinjection experiments were implemented with polycyclic aromatic hydrocarbon standard samples. The experiments show that the average recovery rate of the system exceeds 70%, and the relative standard among the channels is less than 15%.

• 한국전산유체공학회지
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• 제8권3호
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• pp.12-20
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• 2003

A numerical procedure for the calculation of solidification and melting phase change using PISO algorithm is presented. In case of phase change problem, the coupling between velocity/pressure/temperature and liquid fraction is important. The converged temperature and liquid fraction solution which satisfies the energy balance is acquired by applying enthalpy method into inner iteration in matrix solver. And a modified PISO algorithm version is introduced to properly solve the coupling between velocity/pressure/temperature and liquid fraction. A comparison of the proposed procedure with a standard iterative method shows improvement both in terms of computing speed and robustness.

• 분석과학
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• 제26권4호
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• pp.287-297
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• 2013

본 연구는 고체 흡착관과 TD-GC/MS를 이용하여 7종의 휘발성 유기화합물에 대한 열탈착 분석조건을 최적화하였고, 기체상 및 액상 표준물질 첨가한 고체 흡착관을 사용하여 얻어진 검정곡선으로부터 휘발성 유기화합물을 비교 정량하였다. 대응표본 t-검정 결과, 스타일렌을 제외하고 벤젠, 톨루엔, 에틸벤젠, o-, m- 및 p-자일렌을 포함한 6종의 휘발성 유기화합물에 대해서는 액상 표준물질에 의한 표준 흡착관법이 기체상에 의해 제작된 표준 흡착관법이 유의수준 (${\alpha}=0.01$)에서 일치한 반면, 스타일렌에 대해서는 기체상 및 액체상으로 작성된 검정곡선에서 감응인자가 15.6% 차이가 발생하였는데 이것은 두방법 간에 유의한 차이가 있다는 것을 의미하였다. 따라서 BTEX를 포함한 스타일렌을 정량하는데 오차를 감소시키기 위해 액상 표준물질을 이용한 고체상 흡착관법을 사용하였다. 바로 그 점이 이 논문의 핵심내용임. 즉, 고가의 표준가스 대신에 저가의 액상 표준물질을 사용하여 정량하더라도 스타일렌 이외에 거의 동일한 값을 나타내기 때문임. 액체상 표준물법 조건에서 7종의 VOCs의 회수율은 $100{\pm}5%$, 재현성은 0.3~7.7%, 검출한계는 o-자일렌의 $0.01{\mu}g/m^3$에서부터 톨루엔의 $0.27{\mu}g/m^3$까지 범위를 나타내었다. 이러한 최적화된 분석방법을 신축 기숙사, 원룸 아파트 및 신차의 실내공기 중 휘발성 유기화합물을 정량하는데 적용하였다.

• 분석과학
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• 제18권3호
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• pp.224-231
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• 2005

잔류농약 분석에 전통적으로 사용되는 액체-액체 추출법과 액체-고체 추출법의 여러 가지 단점을 극복하고 기존의 낮은 정밀도와 저조한 추출효과를 보완하기위해 자동화된 장치를 이용한 액체상 극미량 추출법(Liquid Phase Microextraction : LPME)을 사용하였으며 이에 대한 최적화 조건을 설정하였다. 대상농약은 demeton-S-methyl, diazinon, parathion, fenitrothion, EPN등 5종이었으며 채소 시료 중에서 추출하여 HP 6890 GC/NPD를 사용하여 분석하였다. 자동화된 LPME를 이용한 최적의 추출조건은 pH 3, 염의 농도 $100{\mu}g/mL$이었으며 검량선을 작성하였을 때 $0.2{\sim}10{\mu}g/g$ 범위에서 $R^2=0.9921$ 이상 직선상의 상관관계를 나타내었고 $5{\mu}g/g$ 농도에서 demeton-S-methyl은 7.7%, diazinon은 9.8%, parathion은 7.8%, fenitrothion는 9.7%, EPN은 8.2%의 상대표준편차를 나타내었고 정확도는 demeton-S-methyl는 12.7%, diazinon는 7.8%, parathion는 10.4%, fenitrothion는 -6.7%, EPN은 -0.7%로 좋은 값을 나타내었다.

• Mass Spectrometry Letters
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• 제9권3호
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• pp.77-80
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• 2018

The focus of this paper is to present techniques to overcome certain difficulties in quantitative analysis with a time-of-flight mass spectrometer (TOF-MS). The method is based on conventional solid-phase extraction, followed by reversed-phase ultra high performance liquid chromatography of the extract, and mass spectrometric analysis. The target compounds included atenolol, atrazine, caffeine, carbamazepine, diclofenac, estrone, ibuprofen, naproxen, simazine, sucralose, sulfamethoxazole, and triclosan. The matrix effects caused by high concentrations of organic compounds in wastewater are especially significant in electrospray ionization mass spectroscopy. Internal-standard calibration with isotopically labeled standards corrects the results for many matrix effects, but some peculiarities were observed. The problems encountered in quantitation of carbamazepine and triclosan, due to nonlinear calibration were solved by changing the internal standard and using a narrower mass window. With simazine, the use of a quadratic calibration curve was the best solution.

• Journal of Mechanical Science and Technology
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• 제14권12호
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• pp.1365-1375
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• 2000

Two phase flows have been numerically calculated to analyze plume characteristics and liquid circulation in gas injection through a porous plug. The Eulerian approach has been for formulation of both the continuous and dispersed phases. The turbulence in the liquid phase has been modeled using the standard $textsc{k}$-$\varepsilon$ turbulence model. The interphase friction coefficient has been calculated using correlations available in the literature. The turbulent dispersion of the phase has been modeled by the "dispersion Prand시 number". The predicted mean flows is compared well with the experimental data. The plume region area and the axial velocities are increased with the gas flow rate and with the decrease in the inlet area. The turbulent intensity also shows the same trend. Also, the space-averaged turbulent kinetic energy for various gas flow rates and inlet areas has been obtained. The results are of interest in the design and operation of a wide variety of materials and chemical processing operations.

• 설비공학논문집
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• 제11권6호
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• pp.824-834
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• 1999

Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas injection system when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for both the continuous and dispersed phases. The turbulence in the liquid phase was modeled using the standard $k-\varepsilon$$\varepsilon$ turbulence model. The interphase friction and heat transfer coefficient were calculated from the correlations available in the literature. The turbulent dispersion of the phases was modeled by a "dispersion Prandtl number". In the case with heat transfer where the temperature of the injected gas is higher than the mean liquid temperature, the axial and the radial velocities are lower in comparison with the case of homogeneous temperatures. The results in the present research are of interest in the design and operation of a wide variety of material and chemical processes.

• 한국시뮬레이션학회논문지
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• 제6권2호
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• pp.1-14
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• 1997

The characteristics of the flow and energy conversion in OMACON liquid-metal MHD system are investigated. Numerical simulation of two-phase flow in the OMACON system without magnetic field was carried out by the Phoenics code and the energy conversion characteristics are studied in association with the fact that the mechanical energy loss at the nozzle of the OMACON system are to be converted into electrical energy. In this system, working fluid (gas) is injected through the mixer located at the bottom of the riser, and is mixed with hot liquid metal. Therefore in the riser two-phase flow is developed under the influence of the gravity. In this study, the interaction between the gas and liquid is considered by the use of IPSA(InterPhase Slip Algorithm) where standard drag coefficient has been used. It has been assumed that in the flow regime the liquid is continuous and the gas is dispersed. For the liquid and gas, the continuity equations, momentum equations and energy equations are solved respectively in association with void fraction in the flow field. In order to calculate the energy conversion efficiency, firstly the ratio of the mechanical energy loss of liquid metal flow at the nozzle to the input thermal energy is considered. Secondly flow pattern of liquid metal in the generator has been analyzed, and the characteristics of the conversion of the mechanical energy into the electrical energy has been investigated. For an representative case where Hartmann number is 540 and magnetic field is 0.35 T, the present analysis shows that the energy conversion efficiency is 0.653. This result is considered to be reasonable in comparison with published experimental results.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2813-2818
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• 2010

A novel method was developed for the speciation of chromium in natural water samples based on homogeneous liquid-liquid extraction and determination by flame atomic absorption spectrometry (FAAS). In this method, Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the sediment phase, whereas Cr(VI) remained in aqueous phase. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of sodium sulfite to the sample solution. Thus, separation of Cr(III) and Cr(VI) could be realized. Homogeneous liquid-liquid extraction based on the pH-independent phase-separation process was investigated using a ternary solvent system (water-tetrabutylammonium ion ($TBA^+$)-chloroform) for the preconcentration of chromium. The phase separation phenomenon occurred by an ion-pair formation of TBA and perchlorate ion. Then sedimented phase was separated using a $100\;{\mu}L$ micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH = 9.5, [ligand] = $1.0{\times}10^{-4}\;M$, [$TBA^+$] = $2.0{\times}10^{-2}\;M$, [$CHCl_3$] = $100.0\;{\mu}L$ and [$ClO_4$] = $2.0{\times}10{-2}\;M$, a preconcentration factor (Va/Vs) of 100 was obtained for only 10 mL of the sample. The relative standard deviation was 2.8% (n = 10). The limit of detection was sufficiently low and lie at ppb level. The proposed method was applied for the extraction and determination of chromium in natural water samples with satisfactory results.