• Proceedings of the KSME Conference
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• 2001.06d
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• pp.79-84
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• 2001

The effect of spray characteristics on desulfurization yield was evaluated by performing experiments with pilot spray drying sorber (SDS). Among the variables of operating conditions, the slurry-spraying conditions were chosen as major parameters; Stoichiometric ratio and Sauter mean diameter of slurry droplet were varied for the different gas temperatures and $SO_{2}$ concentrations in the inlet gas flow. From the experimental results, we proposed semi-empirical models of desulfurization yield for both Stoichiometric ratio and Sauter mean diameter of droplets. The optimal condition of spray can be determined based on these results, which might be applied to the design or scale-up of SDS systems.

• International Journal of Automotive Technology
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• v.8 no.3
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• pp.283-288
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• 2007

This paper presents the static characteristics of a urea-SCR system. The static characterization of the urea-SCR system was generated by sweeping urea flow rates at common engine torque/speed operating points. Several experiments were performed using engine operating points at different raw NOx emission levels, space velocities, and SCR catalyst temperatures. The recorded NOx emissions from the engine exhaust outlet and engine tailpipe are then compared. The urea-SCR static system results indicated that a $50{\sim}60%$ NOx conversion is achievable at most engine operating points using the stoichiometric $NH_3/NOx$ ratio, and a high 98% NOx conversion is possible by exceeding the stoichiometric $NH_3/NOx$ ratio. The effect of the pre-oxidation catalyst volume was also investigated and found to have a profound impact on experimental results, particularly the static NOx conversion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.207-214
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• 2009

Crossover of nitrogen from cathode to anode is inevitable in typical membranes used in PEM fuel cells. This crossovered nitrogen normally accumulates in the hydrogen recirculation system at anode side channels. Excessive buildup of nitrogen in the anode side lowers the relative hydrogen concentration and finally affects the performance of fuel cell stack. So it is very important to analysis the nitrogen gas crossover at various operating conditions. In this study, characterization of nitrogen gas crossover in PEM fuel cell stack was investigated. The mass spectroscopy (MS) has been applied to measure the amount of the crossovered nitrogen gas at the anode exit. Results show that nitrogen gas crossover rate was affected by current density, anode and cathode stoichiometric ratio and operating pressure. Current density, anode stoichiometric ratio and anode operating pressure do not affect nitrogen crossover rate but anode exit concentration of nitrogen. Cathode pressure and stoichiometric ratio largely affect the nitrogen crossover rate.

• Journal of the Korean Society of Combustion
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• v.7 no.2
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• pp.1-6
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• 2002

Characteristics of laminar lifted flames of propane highly-diluted with nitrogen have been investigated at various temperatures of coflow air. At various fuel mole fractions, the base of laminar lifted flames has the structure of tribrachial (or triple) flame. The liftoff heights are correlated well with the stoichiometric laminar burning velocity considering initial temperature at a given coflow velocity. It shows that lifted flames are stabilized on the basis of the balance mechanism between local flow velocity and the propagation speed of tribrachial flame, regardless of the temperature of coflow and fuel mole fraction. Lifted flames exist for a jet velocity even smaller than the stoichiometric laminar burning velocity, and liftoff velocity increases more rapidly than stoichiometric laminar burning velocity as coflow temperature increases. These can be attributed to the buoyancy effect due to the density difference.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.228-229
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• 2003

The quasi-phase matching (QPM) technique has dramatically changed the guidelines in developing nonlinear optical materials, which doesn't require birefringence and off-diagonal components for efficient wavelength conversion. Minimum requirement for QPM is the modulation of nonlinearity and ferroelectric materials with low coercive field has become fascinating in periodical poling. Stoichiometric lithium tantalate (SLT) has attractive advantages of low coercive field (∼l .5 KV/mm), high nonlinearity, high optical damage resistance and low thermo-optic coefficients, leading to a large aperture QPM devices for high power operation. (omitted)

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1145-1152
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• 2013

The rate constant of alkaline fading of methyl green ($ME^{2+}$) was measured in the presence of non ionic (TX-100), cationic (DTAB) and anionic (SDS) surfactants. $ME^{2+}$ hydrolyses and fades in neutral water and in this work we search the effects of surfactants on its fading rate. The rate of reaction showed remarkable dependence on the electrical charge of the used surfactants. It was observed that the reaction rate constant decreased in the presence of DTAB and SDS and increased in the presence of TX-100. Binding constants of $ME^{2+}$ to TX-100, DTAB and SDS and the related thermodynamic parameters were obtained by classical (or stoichiometric) model. The results show that binding of $ME^{2+}$ to TX-100 and DTAB are two-region and that of SDS is three-region. Also, the binding constants of $ME^{2+}$ to surfactant molecules in DTAB/TX-100 and SDS/TX-100 mixed solutions and their stoichiometric ratios were obtained.

• Journal of the Korean Ceramic Society
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• v.28 no.12
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• pp.981-988
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• 1991

Various crystal defects such as voids, inclusions dislocations, stacking faults and precipitates were observed in the Czochralski-grown Bi12GeO20 crystals. Particularly, precipitates were found in the whole crystals. The phase of these precipitates was identified as Bi4Ge3O12 by EPMA and transmission electron microscopy. The precipitates were produced by pulling rapidly from a non-stoichiometric charge. During the pulling of Bi12GeO20 crystals, the melt composition of stoichiometric charge was changed Bi-deficent with gradual volatilization of Bi2O3. Precipition of the second phase may have been affected by an abrube thermal stress. By adding excess Bi2O3 into the stoichiometric batch, the precipitation of Bi4Ge3O12 was suppressed. At a pulling speed of 2 mm/hr, clear and precipitate from crystals of Bi12GeO20 were grown from the melt of the Bi2O3 excess charge.

• Journal of the Korean Vacuum Society
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• v.9 no.1
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• pp.24-29
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• 2000

MgO thin films were deposited on soda lime glass substrates by rf magnetron sputtering using a MgO target at various oxygen flow ratios in order to probe the relationship between MgO film properties and discharge characteristics. MgO films have a tendency to form microstructures with a preferred growth orientation of (200) with increasing oxygen flo ration up to 0.1 $O_2$/(Ar+$O_2$). MgO film obtained at 0.1[$O_2$/(Ar+$O_2$)] was found to be fully stoichiometric. The stoichiometric MgO film was observed to have relatively very clean surface and grains of large size and contain almost no hydroxyl group. The AC PDP with fully stoichiometric MgO film showed lower firing and sustain voltages than those with magnesium-rich or oxygen-rich MgO films, being largely attributed to the larger grain size and the minimized hydroxyl group.

• Bulletin of the Korean Chemical Society
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• v.21 no.10
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• pp.955-956
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• 2000

Solvolyses of methanesulfonyl chloride in water, $D^2O$, $CH^3OD$, and in aqueous binary mixtures of acetone, eth-anol and methanol are investigated at 25, 35 and $45^{\circ}C.$ The Grunwald-Winstein plot of first-order rate con-stants for the solvolytic react ion of methanesulfonyl chloride with YCl (based on 2-adamantyl chloride) shows marked dispersions into three separate lines for three aqueous mixtures with a small m value (m < 0.30), and shows a rate maximum for aqueous alcoholic solvents. Stoichiometric third-order rate constants, kww and kaa were calculated from the observed first-order rate constants and (kaw + kwa) was calculated from the kww and kaa values. The kinetic solvent isotope effects determined in water and methanol are consistent with the proposed mechanism of the general base catalyzed and/or SAN/SN2 reaction mechanism for methanesulfonyl chloride solvolyses based on mass law and stoichiometric solvation effect studies.

• Bulletin of the Korean Chemical Society
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• v.18 no.6
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• pp.579-584
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• 1997

A series of ferrocene-containing chelating bidentate nitrogen ligands (1 & 2) and polyazamacrocycles (3 & 4) were prepared in high yields from the reaction of ferrocenecarboxaldehydes with corresponding diamines under various catalytic and stoichiometric reaction conditions. The stoichiometric condensation to form Schiff bases required the presence of MgSO₄in the reaction mixture as a water-absorbent. Employment of cyclic diamines such as 1,2-diaminocyclohexane and p-phenylenediamine in the reaction with 1,1'-ferrocenedicarboxaldehyde resulted in the formation of polymers in stead of the expected macrocycles. All these compounds were characterized by microanalytical and spectroscopic techniques. In one case, the structure of 3a was confirmed by X-ray crystallography.