• Proceedings of the Korean Environmental Health Society Conference
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• 2003.06a
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• pp.123-127
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• 2003

This experiment was performed to investigate the characteristics of sonolytic reaction as the basic data for development of the ultrasonic AOP(Advanced Oxidation Process) process from which the refractory organic compounds in aqueous solution which are not readily removed by the existing conventional wastewater treatment processes can be destructed and removed. Trichloroethylene (TCE), benzene, and 2,4-dichlorophenol(DCP) were used as the samples, and their destruction efficiency were measured in terms of experimental parameters of the initial solution concentration, initial solution pH, reaction temperature, acoustic frequencies and intensities. Results showed that the destruction efficiencies of all of the sample materials were above 80% within 120 minutes of sonolytic reaction in all reaction condition. The reaction order of these three compounds was verified as Pseudo first order. From the fore-mentioned results, it can be concluded that the refractory organic compounds could be removed by the ultrasonic irradiation with radicals, such as H$.$and OH$.$causing the high increase of pressure and temperature. Finally, it appears that the new AOP technology using ultrasonic irradiation can be applied to the treatment of refractory substances which are difficult to be decomposed by the conventional methods.

• KSBB Journal
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• v.26 no.1
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• pp.69-77
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• 2011

In this study, poly (L-lactic acid) (PLLA) microparticles containing gemcitabine hydrochloride were prepared by a supercritical fluid process, called aerosol solvent extraction system (ASES), utilizing supercritical carbon dioxide as antisolvent. The influence of process parameters such as temperature, pressure, $CO_2$ and solution flow rate, solution concentration, and feed ratio of drug to polymer on the morphology and characteristics of the microparticles was studied in detail. The gemcitabine-loaded microparticles exhibited a spherical shape with a smooth surface. The entrapment efficiency of gemcitabine increased with increasing temperature, solution concentration and $CO_2$ flow rate and with decreasing drug/polymer feed ratio. The maximum drug loading obtained from the ASES process was found to be about 11%. The ASES-processed PLLA microparticles containing gemcitabine showed a relatively high initial burst due to the presence of surface pores on the microparticles and the poor affinity between drug and polymer.

• Journal of Environmental Science International
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• v.14 no.10
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• pp.919-928
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• 2005

This study introduces the development of new supercritical water oxidation(SCW)(multiple step oxidation) to destruct recalcitrant organic substances totally and safely by using sodium nitrate as an oxidant. This method has solved the problems of conventional SCW, such as precipitation of salt due to lowered permittivity, pressure increase following rapid rise of reaction temperature, and corrosion of reactor due to the generation of strong acid. Destruction condition and rate in the supercritical water were examined using Polyvinyl Chloride(PVC) and ion exchange resins as organic substances. The experiment was carried out at $450^{\circ}C$ for 30min, which is relatively lower than the temperature for supercritical water oxidation $(600-650^{\circ}C)$. The decomposition rates of various incombustible organic substances were very high [PVC$(87.5\%)$, Anion exchange resin$(98.6\%)$, Cationexchange resin$(98.0\%)$]. It was observed that hetero atoms existed in organic compounds and chlorine was neutralized by sodium (salt formation). However, relatively large amount of sodium nitrate (4 equivalent) was required to raise the decomposition ratio. For complete oxidation of PCB was intended, the amount of oxidizer was an important parameter.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.4
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• pp.336-341
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• 2008

Recently, research on a flat panel display(FPD) has focused on organic light-emitting display(OLED) which has wide angle of view, high contrast ratio and low power consumption. ITO(Indium-Tin-Oxide) films are the most widely used material as a transparent electrode of OLED and also in many other display devices like LCD or PDP. The performance and efficiency of OLED is related to the surface condition of ITO coated glass substrate. The typical surface defect of glass substrate is measured for electric characteristics and physical condition for transmittance and roughness. Since ITO coated glass substrate can be destroyed for inspection about surface roughness, sheet resistance, film thickness and transmittance, precise fabrication condition should be made based on the estimated relationship. In this paper, ITO films were prepared on the commercial glass substrate by the Ion-Plating method changing the partial pressure of gas(Ar, 02) and the chamber temperature between $200^{\circ}C$ and $300^{\circ}C$. The characteristics of films were examined by the 4-point probe, supersonic thickness measurement, transmittance measurement and AFM. We estimated the relationship between processing parameters(Ar gas, O2 gas, Temperature) and properties of ITO films (Sheet Resistance, Film Thickness, Transmittance, Surface Roughness).

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.1033-1036
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• 2003

In this paper, Si anisotropic etching characteristics of tetramethylammonium hydroxide (TMAH)/ ammonium persulfate (AP) solutions were investigated to realize the optimum structure of a diaphragm for the piezoresistive pressure sensor application. Due to its low toxicity and its high compatibility with the CMOS processing, TMAH was used as Si anisotropic etchants. The variations of Si etch rate on the etching temperature, TMAH concentration, and etching time were obtained. With increasing the etching temperature and decreasing TMAH concentrations, the Si etch rate is increased while a significant non-uniformity exists on the etched surface because of formation of hillocks on the <100> surface. With the addition of AP to TMAH solution, the Si etch rate is increased and an improvement in flatness on the etching front is observed. The Si etch rate is also maximized with increasing the number of addition of AP to TMAH solution per one hour. The Si square diaphragms of 20${\mu}{\textrm}{m}$ thickness and 100~400${\mu}{\textrm}{m}$ one-side length were fabricated successfully by applying optimum Si etching conditions of TMAH/AP solutions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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• pp.76-81
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• 2012

Ultrasonic metal welding is one of the welding methods which welds metal by applying high frequency vibrational energy into specific area at constant pressure, avaliable in room temperature and low temperature. Ultrasonic metal welder is consisted of power supply, transducer, booster, and horn. Precise designing is required since each parts' shape, length and mass can affect driving frequency and vibration mode. This paper focused to horn design, its length L was set to 62mm by calculating vibration equation. By performing modal analysis with various shape variable b times integer, when length of b is 30mm the output was 39,599Hz at 10th mode. Also by performing harmonic response analysis, the frequency response result was 39,533Hz, which was similar to modal analysis result. In order to observe the designed horn's performance, about 4,000 voltage data was obtained from a light sensor and was analyzed by FFT analysis using Origin Tool. The result RMS amplitude was approximately 8.5${\mu}m$ at 40,000Hz, and maximum amplitude was 12.3${\mu}m$. Therefore, it was verified that the ultrasonic metal welding horn was optimally designed.

• Composites Research
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• v.30 no.3
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• pp.188-192
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• 2017

The mechanical properties of composites are significantly affected by external environment. It is essential to understand the degradation of material performance and judge the material's lifetime in advance. In the current research, changes in mechanical properties of glass fiber and unsaturated polyester composite materials (GFRP, Glass fiber reinforced plastic) were investigated under different bending stress and submerged in hot water at a temperature of $80^{\circ}C$. Loading time of 100 H (hours), 200 H, 400 H, 600 H, 800 H for testing under stresses equal to 0% (stress-free state), 30%, 50% and 70% of the ultimate strength was applied on the GFRP specimens. From the values of bending stress, obtained from three-point bending test, fracture energy, failure time, and life curve were analysed. Moreover, a normalized strength degradation model for this condition was also developed. It was observed that within 100 H, the decline rate of the bending strength was proportional to the pressure.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.255-258
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• 2002

Liquid rocket engines using liquefied natural gas (LNG) or methane as a fuel is known to have several good characteristics, such as high specific impulse compared to other hydrocarbon fuels, environment-friendly exhaust gas, low production cost, and re-usability with low soot generation in the cooling channel. In this study, experimental combustion chambers capable of using LNC and $CH_{4}$ are being researched through experimental firing tests, and within easy range of eyes' inspection, there are the periodical existence of soot or discoloration in the chamber wall surface. This result means that mixture ratio of oxidizer and fuel fluctuates periodically between outer-row injectors in the mixing head in the circumferential direction. Therefore, based on this phenomenon, the variation of mixture ratio near the chamber wall caused by the spill pattern of a shear coaxial injector was analyzed quantitatively and the thermal heat flux Into the cooling channel is modified. Then, the calculated and modified results are compared with the measured ones.

• Journal of Mechanical Science and Technology
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• v.16 no.5
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• pp.683-695
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• 2002

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.

• Journal of ILASS-Korea
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• v.5 no.1
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• pp.13-22
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• 2000

The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.