• Journal of Welding and Joining
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• v.20 no.4
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• pp.517-524
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• 2002

An overlaying of the seating surfaces of engine valves by OAW, GTAW or PTA weldings are common practice. The OAW method of a lower torch energy density compared to GTAW and PTA methods produces smoother deposits but the pain size at the vicinity of the interface is increased remarkably up to $30~50{\mu\textrm{m}}$ (that of base metal is about $10\mu\textrm{m}$). It's grain coarsening and the solute dilution are related to the decarburizing during OAW could be minimized by reducing the preheating temperature and by maintaining the carbide precipitates in base metal prior to welding. The formation of columnar structures and carbide precipitation zone in the vicinity of the GTAW welded interface, because of the high heat concentration, causes weakened zone on the valve seat face. The width of the reaction boundary zone is about $50\mu\textrm{m}$ for PTA and GTAW overlaying, and about $150\mu\textrm{m}$ for OAW welding. The smaller width of the reaction boundary zone is the less the solute-dilution rate. Thereby PTA welding may be recommended for overlaying of the seating surfaces.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.69-73
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• 2000

We systematically analyze the influence of fracture junction, solute transfer characteristics on transport patterns in discrete, two-dimensional fracture network models. Regular lattices and random fracture networks with power-law length distributions are considered in conjunction with particle tracking methods. Solute transfer probabilities at fracture junctions are determined from analytical considerations and from simple complete mixing and streamline routing models. For regular fracture networks, mixing conditions at fracture junctions are always dominated by either complete mixing or streamline routing end member cases. Moreover bulk transport properties such as the spreading and the dilution of solute are highly sensitive to the mixing rule. However in power-law length networks there is no significant difference in bulk transport properties, as calculated by assuming either of the two extreme mixing rules. This apparent discrepancy between the effects of mixing properties at fracture junctions in regular and random fracture networks is explained by the statistics of the coordination number and of the flow conditions at fracture intersections. We suggest that the influence of mixing rules on bulk solute transport could be important in systematic orthogonal fracture networks but insignificant in random networks.

• Bulletin of the Korean Chemical Society
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• v.6 no.3
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• pp.128-131
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• 1985

A series of copolymer membranes of 2-hydroxyethylmethacrylate (HEMA) with selected hydrophobic monomers were prepared without crosslinking agents. The equilibrium water content, the partition coefficient, and the permeability of the solutes such as urea, methylurea, 1,3-di-methylurea, and acetamide via these membranes were measured. The partition coefficient data show that as the hydrophobicity of solutes increased, the partition of solutes were dictated by hydrophobic interaction between solute and polymer matrix. Diffusion coefficients obtained in these experiments decrease as the water content of polymer membrane decreases. This decrease is blunt as the excess heat capacities, ${\phi}C^0_p$ (excess) in aqueous solution at infinite dilution of solute increases. To investigate the relationship between water content and diffusion coefficient, the results of the diffusion experiments were examined in light of a free-volume model of diffusive transport. The remarkable increase of urea mobility in the polymer network containing relatively larger bulk water can be considered as water structure breaking effect.

• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.474-481
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• 1993

The infinite dilution activity coefficients(${\gamma}{\infty}$) of nonpolar and polar solutes have been determined in different solvents at temperature between 60 and $100^{\circ}C$ by using gas chromatography. The $ln{\gamma}{\infty}$ values of nonpolar solutes(alkanes, cyclohexane, benzene, toluene and $CCl_4$) were linearly increased as 1/T in the nonpolar solvent (n-octadecane) and the polar solvent(n-hexadecyl alcohol) systems and the $ln{\gamma}{\infty}$ values at the constant temperature were increased with the number of carbon atoms of solute molecule. For the polar solutes(alcohols, esters and ketones) and the weak polar solvent(di-2-ethyl adiphate and di-2-ethylhexyl sebacate) systems, the relations of $ln{\gamma}{\infty}$ vs. 1/T were found to be curved with increased slope, and the $ln{\gamma}{\infty}$ values at constant temperature were linearly diminished as increasing the number of carbon atoms of solute molecule. For the polar solutes(alcohols, esters and ketones) and the strong polar solvents(triphenyl phosphate and tricresyl phosphate)systems, the relations of $ln{\gamma}{\infty}$ vs. 1/T were found to be curved with increased slope but $ln{\gamma}{\infty}$ values at constant temperature were linearly increased as increasing the number of carbon atoms of solute molecule.

• Journal of Korean Society of Water and Wastewater
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• v.32 no.4
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• pp.357-361
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• 2018

Forward osmosis (FO) process has been attracting attention for its potential applications such as industrial wastewater treatment, wastewater reclamation and seawater desalination. Particularly, in terms of fouling reversibility and operating energy consumption, the FO process is assumed to be preferable to the reverse osmosis (RO) process. Despite these advantages, there is a difficulty in the empirical step due to the lack of separation and recovery techniques of the draw solution. Therefore, rather than using FO alone, recent developments of the FO process have adapted a hybrid system without draw solution separation/recovery systems, such as the FO-RO osmotic dilution system. In this study, we investigated the performance of the hollow fiber FO module according to various operating conditions. The change of permeate flow rate according to the flow rates of the draw and feed solutions in the process operation is a factor that increases the permeate flow rate, one of the performance factors in the positive osmosis process. Our results reveal that flow rates of draw and feed solutions affect the membrane performance, such as the water flux and the reverse solute flux. Moreover, use of hydraulic pressure on the feed side was shown to yield slightly higher flux than the case without applied pressure. Thus, optimizing the operating conditions is important in the hollow fiber FO system.

• Journal of the Korean Chemical Society
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• v.14 no.1
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• pp.51-59
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• 1970

The apparent molal volumes(${\phi}_v$) of the homologous salts $RNH_3Cl$, where R varies from methyl-($CH_{3^-}$) to n-butyl-(n-$C_4H_{9^-}$) in a series of methanol-water mixtures have been determined at 30$^{\circ}C$ by means of a float method to fifth decimal places down to 0.01 m. The values of ${\phi}_r$ extrapolated to infinite dilution give partial molal volumes $\bar{V}^{\circ}$which varies considerably in accordance with the solvent composition. that is, mole fraction of methanol. The experimental results are discussed in terms of the varying size and charge effect, hydrophobic nature of the solute species, and also the additivity relationship between successive homologous and the structure of the binary solvent. The results indicate that at 0.1 mole fraction methanol the enhanced structuredness of water cause a minimum in the partial molal volumes of cations $\bar{V}^{\circ}_+$, while at 0.4 mole fraction the solvent structure is such that the free volume is a minimum but the effect of electrostriction is a maximum.

• Journal of Life Science
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• v.29 no.5
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• pp.509-513
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• 2019

The Beer-Lambert law states that absorbance is proportional to the concentration of a solute in a solution at a given wavelength. This linearity works for an ideal or a 'sufficiently diluted' solution, so this linearity is often used as a criterion for the fidelity of the absorbance value measured. In this study, we used a chlorophyll (Chl) solution, isolated from rice leaves with 80% acetone to test the use of the Chl a/b ratio as an additional criterion for checking the fidelity of measured values using four different absorption spectrophotometers: Cary4E, UV-1650PC, Versamax (a microplate reader), and NanoDrop 1,000(which can handle a $4{\mu}l$ aliquot). We used Chl solutions of varying concentrations from $0.2{\mu}g/ml$ to $200{\mu}g/ml$ to measure absorbance values at 645 nm and 663 nm and checked the linearity first. The results indicated that the range of Chl concentrations that we can rely on based on the linearity was similar to the range in which the calculated Chl concentrations based on the measured absorbance values agreed with the known concentrations. However, some border cases or cases with very low Chl concentrations inside the fidelity range of Chl concentrations did not agree with the criterion that the Chl a/b ratio should not change after dilution of the Chl in the solution. These results suggest that the Chl a/b ratio is a better criterion for the reliability of the absorbance values measured for the determination of chlorophyll concentration than the criterion based on the linearity suggested by the Beer-Lambert law.