• Korean Chemical Engineering Research
• /
• v.59 no.4
• /
• pp.542-547
• /
• 2021

Glass lined impellers are corrosion resistant to most chemicals, including strong acids, and also have a smooth, non-stick surface, easy to clean and free from impurities in the process. Glass lined home base impeller is a multi-purpose impeller designed to stir a wide viscosity range of liquids from low viscosity fluids to high viscosity fluids, among others, cell culture, yeast culture, and beer fermentation pots, especially used for air-water system breathable stirring. The glass lining for HB impellers, which are simple in structure and competitive in performance, is essential to have upper and lower division in order to make the joint area between the impeller and shaft as small as possible. The upper and lower division of the impeller hardly affects the mixing performance, but the aeration performance. In this study, in order to optimize the shape of the Glass Lining HB impeller, a study was conducted on the effect of the angle between the upper and lower impellers, the clearance between the impellers, and the number of baffles on the aeration power. The optimal shape and baffle plate conditions for the Glass lined HB impeller were derived through the study results that the angle and the clearance between the upper and lower impellers decreased the ration of the power consumption with aeration P_g and that without aeration P₀, P_g/P₀.

• Korean Chemical Engineering Research
• /
• v.59 no.4
• /
• pp.565-573
• /
• 2021

Isotherms, kinetics and thermodynamic properties for adsorption of Brilliant Green(BG), Quinoline Yellow(QY) dyes by activated carbon were carried out using variables such as dose of adsorbent, pH, initial concentration, contact time, temperature and competitive. BG showed the highest adsorption rate of 92.4% at pH 11, and QY was adsorbed at 90.9% at pH 3. BG was in good agreement with the Freundlich isothermal model, and QY was well matched with Langmuir model. The separation coefficients of isotherm model indicated that these dyes could be effectively treated by activated carbon. Estimated adsorption energy by Temkin isotherm model indicated that the adsorption of BG and QY by activated carbon is a physical adsorption. The kinetic experimental results showed that the pseudo second order model had a better fit than the pseudo first order model with a smaller in the equilibrium adsorption amount. It was confirmed that surface diffusion was a rate controlling step by the intraparticle diffusion model. The activation energy and enthalpy change of the adsorption process indicated that the adsorption process was a relatively easy endothermic reaction. The entropy change indicated that the disorder of the adsorption system increased as the adsorption of BG and QY dyes to activated carbon proceeded. Gibbs free energy was found that the adsorption reaction became more spontaneous with increasing temperature. As a result of competitive adsorption of the mixed solution, it was found that QY was disturbed by BG and the adsorption reduced.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.33 no.5
• /
• pp.203-216
• /
• 2021

Analyzing various wave interactions with oscillating wave surge converters (OWSC) is essential because they must be operated efficiently under a wide range of wave conditions and designed to extract optimal wave energy. In the conceptual design and development stage of OWSC, numerical analysis can be a good alternative as a design tool. This study performed a numerical analysis on the behavioral characteristics of the inverted triangle flap against the incident waves using open source CFD to examine the essential behavioral attributes of OWSC. Specifically, the behavioral characteristics of the structure were studied by calculating the free water surface displacement and the flap rotation angle near the inverted triangular flap according to the change of the period under the regular wave conditions. By comparing and examining the numerical analysis results with the hydraulic model experiments, the validity of the analysis performed and the applicability in analyzing the wave-structure interactions related to OWSC was verified. The numerical analysis result confirmed that the hydrodynamic behavior characteristic due to the interactions of the wave and the inverted triangle flap was well reproduced.

• Clean Technology
• /
• v.27 no.2
• /
• pp.182-189
• /
• 2021

The adsorption of disperse yellow 3 (DY 3) on granular activated carbon (GAC) was investigated for isothermal adsorption and kinetic and thermodynamic parameters by experimenting with initial concentration, contact time, temperature, and pH of the dye as adsorption parameters. In the pH change experiment, the adsorption percent of DY 3 on activated carbon was highest in the acidic region, pH 3 due to electrostatic attraction between the surface of the activated carbon with positive charge and the anion (OH^-) of DY 3. The adsorption equilibrium data of DY 3 fit the Langmuir isothermal adsorption equation best, and it was found that activated carbon can effectively remove DY 3 from the calculated separation factor (R_L). The heat of adsorption-related constant (B) from the Temkin equation did not exceed 20 J mol^-1, indicating that it is a physical adsorption process. The pseudo second order kinetic model fits well within 10.72% of the error percent in the kinetic experiments. The plots for Weber and Morris intraparticle diffusion model were divided into two straight lines. The intraparticle diffusion rate was slow because the slope of the stage 2 (intraparticle diffusion) was smaller than that of stage 1 (boundary layer diffusion). Therefore, it was confirmed that the intraparticle diffusion was rate controlling step. The free energy change of the DY 3 adsorption by activated carbon showed negative values at 298 ~ 318 K. As the temperature increased, the spontaneity increased. The enthalpy change of the adsorption reaction of DY 3 by activated carbon was 0.65 kJ mol^-1, which was an endothermic reaction, and the entropy change was 2.14 J mol^-1 K^-1.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.23 no.5
• /
• pp.281-302
• /
• 2021

Railway projects have been consistently increasing in Korea. In relation to this trend, the mechanized tunneling using Tunnel Boring Machine (TBM) is preferably applied for mining urban areas and passing under rivers. The TBM tunneling under difficult grounds like mixed faces with high water pressure could require ground improvements for stable TBM advance or safe cutter head intervention (CHI). In this study, pre-grouting works for CHI in Daegok-Sosa railway project are presented in terms of the grouting zone design, the executions and the results, the lessons learned from the experience. It should be mentioned that the grouting from inside TBM was carried out several times and turned out to be inefficient in the project. Therefore, grouting experiences from the surface are highlighted in this study. Jet grouting was implemented on CHI points on land, while permeation grouting off shore in the Han River, which mostly allow to access the cutter head of TBM in free air with stable faces. The results of CHI works have been analyzed and the lesson learned are suggested.

• Journal of the Microelectronics and Packaging Society
• /
• v.27 no.4
• /
• pp.135-141
• /
• 2020

The silica aerogels with benzene-bridged were designed to have uniform network structure, ordered pore structure, improved mechanical properties and excellent textural properties. Adding organic to enhance the mechanical properties of silica aerogels is a common method, but textural properties of aerogels with organic are reduced due to the organic-inorganic phase separation. In this paper, we use a simple and low-cost method to increase mechanical properties while maintaining textural properties of SiO2 aerogels. Two types of benzene-bridged precursors were prepared to study the effect of the number of hydroxyl band on the textural and mechanical properties. The porous silica aerogel was prepared by a simple, cost effective and pollution-free sol-gel method. This method does not require additional silylating reagents. The benzene-bridged silica aerogel samples prepared had excellent textural properties, high specific surface area (1,326 ㎡/g), porous structure and hydrophobicity (>140°). The mechanical strength of 2T4 is more than 5 times that of pure silica aerogel.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.3
• /
• pp.13-19
• /
• 2021

This study examined the effects of stacking faults on the thermoelectric properties for n-type SiC semiconductors. Porous SiC semiconductors with 30~42 % porosity were fabricated by the heat treatment of pressed ��-SiC powder compacts at 1600~2100 ℃ for 20~120 min in an N2 atmosphere. XRD was performed to examine the stacking faults, lattice strain, and precise lattice parameters of the specimens. The porosity and surface area were analyzed, and SEM, TEM, and HRTEM were carried out to examine the microstructure. The electrical conductivity and the Seebeck coefficient were measured at 550~900 ℃ in an Ar atmosphere. The electrical conductivity increased with increasing heat treatment temperature and time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The Seebeck coefficients were negative due to nitrogen behaving as a donor, and their absolute values also increased with increasing heat treatment temperature and time. This might be due to a decrease in stacking fault density, i.e., a decrease in stacking fault density accompanied by grain growth and crystallite growth must have increased the phonon mean free path, enhancing the phonon-drag effect, leading to a larger Seebeck coefficient.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.7
• /
• pp.445-454
• /
• 2022

Ice accretion on the aircraft components, such as wings, fuselage, and empennage, can occur when the aircraft encounters a cloud zone with high humidity and low temperature. The prevention of ice accretion is important because it causes a decrease in the aerodynamic performance and flight stability, thus leading to fatal safety problems. In this study, a shape design optimization of a multi-element airfoil is performed to minimize the amount of ice accretion on the high-lift device including leading-edge slat, main element, and trailing-edge flap. The design optimization framework proposed in this paper consists of four major parts: air flow, droplet impingement and ice accretion simulations and gradient-free optimization algorithm. Reynolds-averaged Navier-Stokes (RANS) simulation is used to predict the aerodynamic performance and flow field around the multi-element airfoil at the angle of attack 8°. Droplet impingement and ice accretion simulations are conducted using the multi-physics computational analysis tool. The objective function is to minimize the total mass of ice accretion and the design variables are the deflection angle, gap, and overhang of the flap and slat. Kriging surrogate model is used to construct the response surface, providing rapid approximations of time-consuming function evaluation, and genetic algorithm is employed to find the optimal solution. As a result of optimization, the total mass of ice accretion on the optimized multielement airfoil is reduced by about 8% compared to the baseline configuration.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.24 no.5
• /
• pp.395-409
• /
• 2022

To overcome the limitation of conventional rock excavation methods, the excavation with abrasive waterjet has been actively developed. The abrasive waterjet excavation method has the effect of reducing blasting vibration and enhancing the excavation efficiency by forming a continuous free surface on the rock. However, the waterjet cutting performance varies with rock fracturing characteristics. Thus, it is necessary to analyze the cutting performance for various rocks in order to effectively utilize the waterjet excavation. In this study, cutting experiments with the high pressure waterjet system were performed for basalt and granite specimens. Water pressure, standoff distance, and traverse speed were determined as effective parameters for the abrasive waterjet cutting. The cutting depth and width of basalt specimens were analyzed to compare with granite results. The averaged cutting depth of basalt was shown in 41% deeper than granite; in addition, the averaged cutting width of basalt was formed by 18.5% narrower than granite. The results of this study are expected to be useful basic data for applying rock excavation site with low strength and high porosity such as basalt.

• Korean Journal of Food Science and Technology
• /
• v.53 no.4
• /
• pp.479-485
• /
• 2021

To improve the oxidative stability of Glycyrrhiza uralensis extract (GU), GU extraction conditions were optimized for maximal antioxidant activity, and GU-loaded nanocapsules were prepared by chitosan ionic gelation. The optimized ethanol concentration and extraction time were 83.0% and 32.6 min, respectively, using response surface methodology. The particle size of the GU-loaded nanocapsules ranged from 280 to 370 nm. A GU extract of 0.8 mg/mL and chitosan concentration of 2.0 mg/mL were selected as the optimal conditions for entrapment and loading efficiency. Both free GU and GU-loaded chitosan nanocapsules exhibited concentration-dependent antioxidant activity. However, the antioxidant protection factor of GU was effectively maintained when it was entrapped within the chitosan nanocapsules. In conclusion, chitosan nanoencapsulation is a potentially valuable technique for improving the oxidative stability of GU.