Hyuksang Chang
Yeungnam University, Environmental Engineering, Faculty Member
− Using a premixed flat flame aerosol reactor, the experimental study on the morphological evolution of the aggregates was done. With the objectives to understand the morphological process of SiO 2 and TiO2 particle that matches to the... more
− Using a premixed flat flame aerosol reactor, the experimental study on the morphological evolution of the aggregates was done. With the objectives to understand the morphological process of SiO 2 and TiO2 particle that matches to the cases of the reaction-limited aggregation process and the diffusion-limited aggregation process respectively, the difference in chemical reaction rate of SiCl 4 and TiCl 4 was utilized under given flame temperatures. To evaluate the morphological evolution of the aggregates, the light scattering measurement and electron microscopy coupled with thermophoretic sampling method were used. In the case of SiCl 4 oxidation that produces SiO 2 particles, the microscopic observation obtained with respect to the axial position in the reactor showed that the diffusion-limited aggregation was the dominant mechanism in the aggregation process because that the very low reaction rates was maintained excepted the earlier reaction stage in the given reactor temperatur...
UV-TiO2 광촉매를 이용한 공기 정화 시스템에 운전조건에 대한 연구가 수행되었다. 이 연구에서 시스템의 운영 조건이 바뀜에 따른 오염물질 제거 특성을 관찰하기 위해 덕트 형태의 반응기를 제작하고, 스테인레스 격자망에 TiO2를 코팅하였다. 또한 benzene을 이용하여 UV/TiO2 공정으로 유입농도를 변화시키고, 반응기로 들어오는 유량을 조절하여 TiO2를 코팅한 스테인레스 격자망을 부착한 평판에서의 유속을... more
UV-TiO2 광촉매를 이용한 공기 정화 시스템에 운전조건에 대한 연구가 수행되었다. 이 연구에서 시스템의 운영 조건이 바뀜에 따른 오염물질 제거 특성을 관찰하기 위해 덕트 형태의 반응기를 제작하고, 스테인레스 격자망에 TiO2를 코팅하였다. 또한 benzene을 이용하여 UV/TiO2 공정으로 유입농도를 변화시키고, 반응기로 들어오는 유량을 조절하여 TiO2를 코팅한 스테인레스 격자망을 부착한 평판에서의 유속을 변화시켰으며, 코팅한 TiO2 광촉매량을 변화시키고, 일정한 양의 TiO2 광촉매를 코팅한 면적을 변화시켰으며, UV light intensity를 변화시켜 그에 따른 영향을 관찰하였다. 모든 실험에서의 상대습도는 55%, 반응기 온도는 45℃를 유지하였다. 실험의 결과를 살펴보면, benzene의 유입농도가 증가할수록 제거효율이 감소하였고, 유속이 느려질수록, 즉 농도 경계층 두께(concentration boundary layer thickness)가 증가할수록, 코팅한 광촉매량, 광촉매를 코팅한 면적, 조사한 UV 램프의 intensity가 증가할수록 benzene 제거효율이 증가하였다. 본 연구 자료를 바탕으로 실내 공기 중 저농도의 VOCs를 대상으로 공기 정화 시스템을 설계할 경우 유용하게 적용할 수 있는 자료를 제시할 수 있다고 판단된다.
: A study on the operational variables of the UV-TiO 2 based photocatalytic air cleaning system was tried. In this study, toexamine effects as various air cleaning system conditions, a duct-type reactor was made, and TiO 2 was immobilized... more
: A study on the operational variables of the UV-TiO 2 based photocatalytic air cleaning system was tried. In this study, toexamine effects as various air cleaning system conditions, a duct-type reactor was made, and TiO 2 was immobilized on a stainless mesh.Benzene was chosen as a target compound. Removal experiments for benzene were done under different initial benzene concentration, air velocity, TiO 2 loading, area coated TiO 2 as the same TiO 2 loading, and UV light intensity conditions. During the experiments, rela-tive humidity was 55%, and reactor temperature was 45. As a result, the photocatalytic degradation of benzene decreased as the inletconcentration increased. But the photocatalytic degradation increased as the concentration boundary layer thickness, amount of TiO 2 , areacoated TiO 2 as the same amount of TiO 2 , and UV light intensity increased. Based on results of current study, they can be applied to thedesign of air cleaning system over low level VOCs in the ind...
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Effects of the electric conductivity of particles were studied for the aggregation process of charged particles with a Brownian dynamic simulation in the free molecular regime. A periodic boundary condition was used for the calculation of... more
Effects of the electric conductivity of particles were studied for the aggregation process of charged particles with a Brownian dynamic simulation in the free molecular regime. A periodic boundary condition was used for the calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered two extreme cases, a perfect conductor and a perfect nonconductor. The electrostatic force on a particle in the simulation cell was considered as a sum of electrostatic forces from other particles in the original cell and its replicate cells. We assumed that aggregates were only charged with pre-charged primary particles. The morphological shape of aggregates was described in terms of the fractal dimension. The fractal dimension for the uncharged aggregate was D
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Using a premixed flat flame, the aggregation process of thermally stable particles was studied. Based on the theoretical descriptions of the reaction limited aggregation process (RLAP) and the diffusion limited aggregation process (DLAP),... more
Using a premixed flat flame, the aggregation process of thermally stable particles was studied. Based on the theoretical descriptions of the reaction limited aggregation process (RLAP) and the diffusion limited aggregation process (DLAP), the entire aggregation process was explained by a combination of the RLAP and the DLAP. Experiments were done to test the possibility of this explanation for the dynamic aggregation processes in terms of the parameters that are used in a normal chemical conversion process. By defining the primary particle as the basic unit of the aggregates, the aggregation process was divided into the early stage--when the primary particles are formed--and the stage of aggregation thereafter. Changing the combustion equivalence ratio of the premixed flat flame from 0.7 to 0.98 controlled the sizes of the primary particles. The deficiency of the oxygen in the combustion process controlled the final size of the primary particles in the aggregate. The morphological evolution of particles was well defined due to the stable condition in the flow. Titania and silica that were formed in the flame by the oxidation of TiCl 4 and SiCl 4 were used as the simulation materials of the aggregation process. Depending on the residence time and temperature history in the oxidation process, the aggregates were formed in various fractal dimensions. The thermophoretic sampling and image analysis techniques were used to evaluate the aggregation in the flame region. The coalescence effect on the particle morphology was estimated by using the tubular aerosol reactor.
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Various technical methods are applied for removing water from the water-retaining media, and the energy efficiency is the main concern in those methods. The electroosmotic process is studied as an efficient way for dewatering. An... more
Various technical methods are applied for removing water from the water-retaining media, and the energy efficiency is the main concern in those methods. The electroosmotic process is studied as an efficient way for dewatering. An experimental electroosmotic reactor is designed and used for evaluating the effects of operational variables. The operational variables such as the electrical fields and the structure of water-retaining medias were studied. Three different shapes of polarized electric fields in ranges of 0-100 V/cm and 0-10 kHz are used as the source of electric voltage. The effect of electroosmotic process with respect to the structural variation is estimated by filling the electroosmotic reactor with the glass beads in 0.18 mm, 0.35 mm and 1.2 mm in diameters. 6% of water removal is obtained in the simulating electroosmotic reactor of glass beads. The estimated energy consumption in the simulating electroosmotic was 330~490 cal/g-water.
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Abstract A light scattering system using angular dissymmetry is used to map out the evolution of the size distribution of a nonabsorbing aerosol in a controlled methane—air flat flame. Silicon tetrachloride vapor is generated by bubbling... more
Abstract A light scattering system using angular dissymmetry is used to map out the evolution of the size distribution of a nonabsorbing aerosol in a controlled methane—air flat flame. Silicon tetrachloride vapor is generated by bubbling argon through a pool of silicon tetrachloride (SiCl 4 ) liquid and fed in controlled amounts into the flame, wherein silica (SiO 2 ) particles are formed by oxidation of the SiCl 4 vapor. A fractal analysis of light scattering data indicates that the particles are close to spherical. The scattered light intensity data at three different angular positions is inverted using the Mie light scattering expressions to determine the effective spherical aerosol size distribution assuming that the distribution can be described by a lognormal function. The results are compared to monodisperse inversion techniques and the predictions of a 1—D lognormal model.