• Journal of computational fluids engineering
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• v.21 no.2
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• pp.12-24
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• 2016

The standard ${\kappa}-{\varepsilon}$ and realizable ${\kappa}-{\varepsilon}$ models are adopted to improve the prediction performance on the recirculating flow. In this paper, the backward facing step flows are used to assess the prediction performance of the recirculation zone. The model constants of turbulence model are obtained by the experimental results and they have a different value according to the flow. In the case of an isotropic flow situation, decaying of turbulent kinetic energy should follow a power law behavior. In accordance with the power law, the coefficients for the dissipation rate of turbulent kinetic energy are not universal. Also, the other coefficients as well as the dissipation coefficient are not constant. As a result, a suitable coefficients can be varied according to each of the flow. The changes of flow over the backward facing step in accordance with model constants of the ${\kappa}-{\varepsilon}$ models show that the reattachment length is dependent on the growth rate(${\lambda}$) and the ${\kappa}-{\varepsilon}$ models can be improved the prediction performance by changing the model constants about the recirculating flow. In addition, it was investigated for the curvature correction effect of the ${\kappa}-{\varepsilon}$ models in the recirculating flow. Overall, the curvature corrected ${\kappa}-{\varepsilon}$ models showed an excellent prediction performance.

• Applied Chemistry for Engineering
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• v.26 no.2
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• pp.184-192
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• 2015

Characteristics of Char-$CO_2$ gasification for petroleum coke, biomass and mixed fuels were compared in the temperature range of $1,100{\sim}1,400^{\circ}C$ using TGA (Thermogravimetric analyzer). Kinetic constants with respect to reaction temperature were determined by using different gas-solid reaction models. Also activation energy (Ea) and pre-exponential factors ($K_0$) in each models were calculated by using Arrhenius equation and then were compared with experimental values to determine reaction rate equation for char-$CO_2$ gasification. Reaction time for $CO_2$ gasification decreased with an increase of reaction temperature. Also, the activation energy of $CO_2$ gasification reaction for mixture with petroleum coke and biomass decreased with increasing biomass contents. This indicates that mixing with biomass could bring synergy effects on $CO_2$ gasification reaction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.12
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• pp.830-842
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• 2015

This paper aims to develop a SI(structural identification) technique using the kinetic energy optimization technique(KEOT) and the direct matrix updating method(DMUM) to decide on optimal location of sensors and to update FE model respectively, which ultimately contributes to a composition of more effective SHM. Owing to the characteristic structural flexing behavior of cable bridges, which makes them vulnerable to any vibration, systematic and continuous structural health monitoring (SHM) is pivotal for them. Since it is necessary to select optimal measurement locations with the fewest possible measurements and also to accurately assess the structural state of a bridge for the development of an effective SHM, a SI technique is as much important to accurately determine the modal parameters of the current structure based on the data optimally obtained. In this study, the KEOT was utilized to determine the optimal measurement locations, while the DMUM was utilized for FE model updating. As a result of experiment, the required number of measurement locations derived from KEOT based on the target mode was reduced by approximately 80 % compared to the initial number of measurement locations. Moreover, compared to the eigenvalue of the modal experiment, an improved FE model with a margin of error of less than 1 % was derived from DMUM. Finally, the SI technique for long-span bridges proposed in this study, which utilizes both KEOT and DMUM, is proven effective in minimizing the number of sensors while accurately determining the structural dynamic characteristics.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.11
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• pp.941-946
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• 2009

Two types of synthetic zeolites, commercially used (Z-WK) and synthesized by coal fly ash (Z-C1), and raw coal fly ash(F-C1) were examined for its kinetics and adsorption capacities of cobalt. Experimental data are fitted with kinetic models, Lagergen $1^{st}$ and $2^{nd}$ order models, and four types of adsorption isotherm models, Langmuir, Freundlich, Redlich-Peterson, and Koble-Corrigan. Synthesized zeolite (Z-C1) which had 1.51 of Si/Al ratio was synthesized by raw coal fly ash from a thermal power plant. Adsorption capacities with three types of adsorbents, Z-WK, Z-C1, and F-C1, were in the order of Z-C1 (94.15 mg/g) > F-C1 (92.94 mg/g) > Z-WK (88.56mg/g). The adsorption kinetics of Z-WK and Z-C1 with cobalt could be accurately described by a pseudo-second-order rate equation. The adsorption isotherms of Z-WK and Z-C1 with cobalt were well fitted by the Langmuir and Redlich-Peterson equation. Z-C1 will be used to remove cobalt in water as a more efficient absorbent.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.356-367
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• 2019

This study evaluates the variation characteristics of irregular wave fields for two-dimensional Low-Crested Structure (LCS) by olaFlow model based on the two-phases flow by numerical analysis. The numerical results of olaFlow model are verified by comparing irregular wave profile of target wave spectrum and measured one, and their spectra. In addition, spacial variation of irregular wave spectrum, wave transmission ratio, root-mean square wave height, time-averaged velocity and time-averaged turbulent kinetic energy by two-dimensional LCS are discussed numerically. The time-averaged velocity, one of the most important numerical results is formed counterclockwise circulating cell and clockwise nearshore current on the front of LCS, and strong uni-directional flow directing onshore side around still water level.

• Korean Chemical Engineering Research
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• v.55 no.6
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• pp.771-777
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• 2017

Adsorption characteristics of Eosin Y dye by carbon nano tubes (CNTs) were examined through batch experiments. CNTs used in the study had specific surface area of $106.9m^2/g$, porosity volume of $1.806cm^3/g$, and porosity diameter of $163.2{\AA}$, respectively. Adsorption experiments were carried out as function of contact time, initial solution pH (2~10), dye concentration (100, 150 and 200 mg/L), adsorbent dose (0.05~1.0 g) and temperature (293, 313 and 333 K). The adsorption was favoured at lower pHs and temperatures. Adsorption data were well described by the Langmuir model. The adsorption process followed the pseudo-second order kinetic model. The adsorption capacity decreased with increase in temperature. The results of the intraparticle diffusion model suggested that film diffusion and particle diffusion were simultaneously occured during the adsorption process. Thermodynamic studies suggested the spontaneous and endothermic nature of adsorption of Eosin Y dye onto CNTs.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.6
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• pp.1055-1061
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• 2000

The kinetics of tar formation has been studied experimentally and modeled mathematically for waste lubricating oil after pyrolyzed at batch reactor. And stabilization of pyrolyzed oil has been studied. A combination of series and parallel reaction was assumed for the mechanism of tar formation. From the proposed kinetic model, pyrolyzed oil to tar was found to be rate limiting step for tar formation. It was found that the fly ash and coke had the ability to remove materials of tar formation and to protect oxidation of pyrolyzed oil.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.294-304
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• 2019

This study evaluates the variation characteristics of wave fields (transmission ratio, wave height, time-averaged velocity and time-averaged turbulent kinetic energy) for two-dimensional low-crested structure by olaFlow model based on the two-phases flow numerically. In addition, the present numerical results are verified by comparing with the existing experimental results. The time-averaged velocity, one of various numerical results is formed counterclockwise circulating cell on the front of structure and is occurred strong uni-directional flow on onshore side. It is shown that these are closely related to the factors such as overtopping, etc.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.66-71
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• 2018

The evaluation of the shelf-life of energetic materials is important. However, there are several difficulties associated with the evaluation. First, aging experiments require a considerable amount of time. Second, treating highly energetic materials is dangerous. For these reasons, many evaluation methods have been developed. Because most energetic materials decompose with the evolution of heat, it is important to analyze the thermal properties of energetic materials in order to understand decomposition and aging properties. In this paper, we describe the estimation of thermal aging properties and develop a kinetic model from spot data set of mechanical properties and estimate aging properties for mechanical results.

• New & Renewable Energy
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• v.18 no.4
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• pp.12-21
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• 2022

The pyrolysis characteristics of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) were analyzed numerically using a 1D plug flow reactor (PFR) model. A lumped kinetic model was selected to simplify the pyrolysis products as wax, oil, and gas. The simulation was performed in the 400-600℃ range, and the plastic pyrolysis and product generation characteristics with respect to time were compared at various temperatures. It was found that plastic pyrolysis accelerates rapidly as the temperature rises. The amounts of the pyrolysis products wax and oil increase and then decrease with time, whereas the amount of gas produced increases continuously. In LDPE pyrolysis, the pyrolysis time was longer than that observed for other plastics at a specified temperature, and the amount of wax generated was the greatest. The maximum mass fraction of oil was obtained in the order of HDPE, PP, and LDPE at a specified temperature, and it decreased with temperature. Although the 1D model adopted in this study has a limitation in that it does not include material transport and heat transfer phenomena, the qualitative results presented herein could provide base data regarding various types of plastic pyrolysis to predict the product characteristics. These results can in turn be used when designing pyrolysis reactors.