• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.80-89
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• 2002

The flame structure and soot formation in Acetylene-Air nonpremixed jet flame are numerically analyzed. We employed two variable approach to investigate the soot formation and oxidation processes. The present soot reaction mechanism involves nucleation, surface growth, particle coagulation, and oxidation steps. The gas phase chemistry and the soot nucleation, surface growth reactions are coupled by assuming that the nucleation and soot mass growth has the certain relationship with the concentration of pyrene and acetylene. We also employed laminar flamelet model to calculate the thermo-chemical properties and the proper soot source terms from the information of detailed chemical kinetic model. The numerical and physical model used in this study successfully predict the essential features of the combustion processes and soot formation characteristics in the reaction flow field.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.1-8
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• 1998

Waste combustion above a grate is the core process of incineration systems, stability of which should be guaranteed for emission minimization. However, complicated reactions and heat and mass transfer phenomena make understanding the process difficult. One dimensional bed combustor with a numerical combustion model is utilized to investigate the combustion process of the bed, using cubic wood particles as a simulated fuel. Bed combustion behavior is characterized with apparent flame propagation speed, which has close relationship with air supply rate and chemical and physical characteristics of the fuel. Base on the availability of oxygen, two distinct reaction zone is identified; the oxygen-limited and the reaction-limited zone leading to the extinction by excessive convection cooling. The numerical modeling shows good agreement with the experimental results. The transient bed combustion behavior of local temperature and oxygen consumption rate is adequately reproduced. The numerical model is extended to model the waste bed combustion of a commercial incineration plant, which shows meaningful results as well.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1160-1165
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• 2004

The purpose of this study was to calculate three dimensional angular displacements, moments and joint reaction forces of the ankle joint during the waist pulling, and to assess the ankle joint reaction forces according to different perturbation modes and different levels of perturbation magnitude. Ankle joint model was assumed 3-D ball and socket joint which is capable of three rotational movements. We used 6 cameras, force plate and waist pulling system. Two different waist pulling systems were adopted for forward sway with three magnitudes each. From motion data and ground reaction forces, we could calculate 3-D angular displacements, moments and joint reaction forces during the recovery of postural balance control. From the experiment using falling mass perturbation, joint moments were larger than those from the experiment using air cylinder pulling system with milder perturbation. However, JRF were similar nevertheless the difference in joint moment. From this finding, we could conjecture that the human body employs different strategies to protect joints by decreasing joint reaction forces, like using the joint movement of flexion or extension or compensating joint reaction force with surrounding soft tissues. Therefore, biomechanical analysis of human ankle joint presented in this study is considered useful for understanding balance control and ankle injury mechanism.

• Bulletin of the Korean Chemical Society
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• v.9 no.5
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• pp.298-303
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• 1988

Kinetic studies on cupric ion ($Cu^{2+}$) oxidation of 1-benzyl- and 1-aryl-1,4-dihydronicotinamides (XNAH) in aqueous solution were performed. In the presence of dioxygen ($O_2$), the reaction followed first order kinetics with respect to both XNAH and $Cu^{2+}$. The oxidation reaction was found to be independent and parallel to the acid-catalyzed hydration reaction of XNAH. The catalytic role of $Cu^{2+}$ for the oxidation of XNAH in the presence of $O_2$ was attributed to $Cu^{2+}/Cu^+$ redox cycle by the reactions with XNAH and $O_2$. The second order rate constants of the Cu2+ oxidation reaction kCu, and acid-catalyzed hydration reaction $k_H$ were strongly dependent on the nature of the substituents in 1-aryl moiety. The slopes of log $k_{Cu}$ vs log $K_H$ and log $k_{Cu}$ vs ${\sigma}_p$ of the substituents plots were 1.64 and -2.2, respectively. This revealed the greater sensitivity of the oxidation reaction rate to the electron density on the ring nitrogen than the hydration reaction rate. A concerted two-electron transfer route involving XNAH-$Cu^{2+}$ complex was proposed for mechanism of the oxidation reaction.

• Journal of Environmental Science International
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• v.26 no.7
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• pp.859-868
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• 2017

In this study, the reductive dechlorination of triclosan using zero-valent iron (ZVI, $Fe^0$) and modified zero-valent iron (i.e., acid-washed iron (Aw/Fe) and palladium-coated iron (Pd/Fe)) was experimentally investigated, and the reduction characteristics were evaluated by analyzing the reaction kinetics. Triclosan could be reductively decomposed using zero-valent iron. The degradation rates of triclosan were about 50% and 67% when $Fe^0$ and Aw/Fe were used as reductants, respectively, after 8 h of reaction. For the Pd/Fe system, the degradation rate was about 57% after 1 h of reaction. Thus, Pd/Fe exhibited remarkable performance in the reductive degradation of triclosan. Several dechlorinated intermediates were predicted by GC-MS spectrum, and 2-phenoxyphenol was detected as the by-product of the decomposition reaction of triclosan, indicating that reductive dechlorination occurred continuously. As the reaction proceeded, the pH of the solution increased steadily; the pH increase for the Pd/Fe system was smaller than that for the $Fe^0$ and Aw/Fe system. Further, zero-order, first-order, and second-order kinetic models were used to analyze the reaction kinetics. The first-order kinetic model was found to be the best with good correlation for the $Fe^0$ and Aw/Fe system. However, for the Pd/Fe system, the experimental data were evaluated to be well fitted to the second-order kinetic model. The reaction rate constants (k) were in the order of Pd/Fe > Aw/Fe > $Fe^0$, with the rate constant of Pd/Fe being much higher than that of the other two reductants.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.467-479
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• 2021

Abstract: A kinetic model was developed for the dehydration of ethanol to ethylene based on two parallel reaction pathways. Kinetic parameters were estimated by fitting experimental data of powder catalysts in a lab-scale test, and the effectiveness factor was determined using data from pellet-type catalysts in bench-scale experiments. The developed model was used to design a multitubular fixed-bed reactor (MTR) and an adiabatic reactor (AR) at a 10 ton per day scale. The two different reactor types resulted in different process configurations: the MTR consumed the ethanol completely and did not produce the reaction intermediate, diethyl ether (DEE), resulting in simple separation trains at the expense of high equipment cost for the reactor, whereas the AR required azeotropic distillation and cryogenic distillation to recycle the unreacted ethanol and to separate the undesired DEE, respectively. Quantitative analysis based on the equipment and annual energy costs showed that, despite high equipment cost of the reactor, the MTR process had the advantages of high productivity and simple separation trains, whereas the use of additional separation trains in the AR process increased both the total equipment cost and the annual energy cost per unit production rate.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.137-138
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• 2012

The two-equation soot model based on the transient laminar flamelet model is implemented for soot formation of laminar non-premixed $CH_4/Air$ flame with detailed chemical reaction mechanism and complex thermodynamic properties. The soot model represents nucleation, growth and oxidation with gas-phase chemistry. This represented unsteady flamelet soot model has been tested and compared using well verified reference calculation result obtained solving the Full Transport Equations method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.778-787
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• 1999

In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

• Journal of the Korean Ceramic Society
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• v.45 no.8
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• pp.439-442
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• 2008

A series of reaction-sintered SiC was fabricated from preforms with varying volume fractions of two resin-coated SiC particles of different sizes (63 and $18{\mu}m$). The electrical resistivity and mechanical strength were eventually optimized at the small particle volume fraction of $0.3{\sim}0.4$, at which point the porosity of the preform was minimized. This study experimentally proves that additional processes after the formation of the preform, such as silicon infiltration and reaction sintering, do not apparently alter the optimum volume fraction of the preform packing, predicted by an existing analytical model based on solid packing. Thus, the volume fraction of particles of different sizes can be determined practically through the solid packing model to fabricate RSSCs with optimal properties.

• Journal of Ginseng Research
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• v.28 no.3
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• pp.136-142
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• 2004

During our investigations on the relationship between the browning reaction of ginseng root and two compounds (arginyl-fructosyl-glucose and arginyl-fructose) in the model system of steaming and heat-drying processes for the preparation of red ginseng, the preheating treatment of main roots of raw ginseng at 60∼70$^{\circ}C$ prior to the steaming and heat-drying processes was found to bring about the gelatinization of starch granules. The enzymatic hydrolysis of gelatinized starch to maltose, a marked formation of maltose, and the increase of both free arginine and total amino acids, resulting the acceleration of the Maillard type-browning reaction of ginseng root during the steaming and heat-drying processes, and the rise of brown color intensity of red ginseng. These results show that the preheating treatment may be effective for the decrease of inside white of red ginseng.