• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1175-1184
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• 2000

Effects of porous wind fences on the wind erosion of particles from a triangular sand pile were investigated experimentally. The porous fence and sand pile were installed in a simulated atmospheric boundary layer. The mean velocity and turbulent intensity profiles measured at the sand pile location were well fitted to the atmospheric boundary layer over the open terrain. Flow visualization was carried out to investigate the motion of windblown sand particles qualitatively. In addition, the threshold velocity were measured using a light sensitive video camera with varying the particle size, fence porosity $\varepsilon$ and the height of sand pile. As a result, various types of particle motion were observed according to the fence porosity. The porous wind fence having porosity $\varepsilon$=30% was revealed to have the maximum threshold velocity, indicating good shelter effect for abating windblown dust particles. With increasing the sand particle diamter, the threshold velocity was also increased. When the height of sand pile is lower than the fence height, threshold velocity is enhanced.

• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.99-105
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• 2001

For the design of selective catalytic reactors of NOx by $NH_3$, engineering approach can be performed to determine the reactor shape, mixing device and $NH_3$ injection system. This study shows the optimization of guide vanes to improve the flow pattern near the catalyst layer of SCR in a untility boiler. By varying their spacings and shapes, flow performance of guide vanes was analyzed to achieve an uniform velocity distribution which increases the NOx convesion efficiency, and a flow direction normal to the layer which minimises the erosion by the dust in the flue gas. Including these results, experimental and numerical studies for the SCR design were discussed.

• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.146-153
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• 2006

A performance test of the stainless steel based sintered metal filter was conducted on the low and intermediate level radioactive waste (LILW) vitrification process. The applicability of the metal filter was based on the test results as well. The baseline pressure drop of the metal filter was evaluated similar to the ceramic filter. During the test, when the flow rate of off-gas was $110Nm^{3}/h$, the total baseline pressure drop was shown as $92mmH_{2}O$. The total pressure drop was attributed to the filter media and the residual dust layer and the value of each was $25mmH_{2}O\;and\;67mmH_{2}O$ respectively. The SEM-EDS spectrum and micrograph of the metal filter specimen showed, no corrosion and no physical damage both at the skin membrane and at the support layer. And most of the baseline pressure drop was caused by the deposition of dust on the surface of the membrane. In conclusion, even though the filter exposure time was short at the test, the performance of the stainless steel based metal filter was acceptable for the treatment of LILW vitrification process.

• Journal of the Optical Society of Korea
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• v.14 no.3
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• pp.215-220
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• 2010

Aerosol observation with Raman LIDAR in NIES (National Institute for Environmental Studies, Japan) LIDAR network was conducted from 17 April to 12 June 2008 over Beijing, China. The aerosol optical properties derived from Raman LIDAR were compared with the retrieved data from sun photometer and sky radiometer observations in the Aerosol Robotic Network (AERONET). The comparison provided the complete knowledge of aerosol optical and physical properties in Beijing, especially in pollution and Asian dust events. The averaged aerosol optical depth (AOD) at 675 nm was 0.81 and the Angstrom exponent between 440 nm and 675 nm was 0.99 during experiment. The LIDAR derived AOD at 532 nm in the planetary boundary layer (PBL) was 0.48, which implied that half of the total AOD was contributed by the aerosol in PBL. The corresponding averaged LIDAR ratio and total depolarization ratio (TDR) were 48.5sr and 8.1%. The negative correlation between LIDAR ratio and TDR indicated the LIDAR ratio decreased with aerosol size because of the high TDR associated with nonspherical and large aerosols. The typical volume size distribution of the aerosol clearly demonstrated that the coarse mode radius located near 3 ${\mu}m$ in dust case, a bi-mode with fine particle centered at 0.2 ${\mu}m$ and coarse particle at 2 ${\mu}m$ was the characteristic size distribution in the pollution and clean cases. The different size distributions of aerosol resulted in its different optical properties. The retrieved LIDAR ratio and TDR were 41.1sr and 19.5% for a dust event, 53.8sr and 6.6% for a pollution event as well as 57.3sr and 7.2% for a clean event. In conjunction with the observed surface wind field near the LIDAR site, most of the pollution aerosols were produced locally or transported from the southeast of Beijing, whereas the dust aerosols associated with the clean air mass were transported by the northwesterly or southwesterly winds.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.38.2-38.2
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• 2012

We use two-dimensional high-resolution MHD simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures as well as on the mass inflow rates to the galaxy center. We find that there exists an outermost x1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks and leads to a smaller and more centrally distributed ring, resulting in the mass inflow rates larger, by more than two orders of magnitude, than in the unmagnetized counterparts. Outside the outermost x1-orbit, on the other hand, an MHD dynamo operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms have a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density which propagate along the arms to turn the outer disk into a highly chaotic state.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.526-532
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• 2000

Recent studies have been directed toward obtaining a better understanding of the application of electrostatic precipitators to collect fly ash particles produced in a coal-fired power plant. Electrical resistivity can be described as the resistance of the collected dust layer to the flow of electrical current and is an important property for the collection efficiency in the electrostatic precipitator. In this paper, fly ash resistivity as a function of temperature up to $450^{\circ}C$ has been experimentally investigated using the resistivity meter consisted of the movable electrode, dust cup, and furnace. Resistivity was found to increase with increased temperature up to $200^{\circ}C$ due to the reduction of water concentration and then gradually decrease with increased temperature due to the activation of electrons. As the resistivity of fly ash in the flue gas temperature of $150^{\circ}C$ was measured >$10^{10}$ ohm cm, the efficiency of fly ash removal in the electrostatic precipitator might be expected to be low due to back-corona phenomenon. Flue gas conditioning in the electrostatic precipitator to reduce the resistivity of fly ash as required.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.67.2-67.2
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• 2014

Comet nucleus is a solid body consisting of dark dust grains and ice. Cometary volatiles sublimate from subsurface layer by solar heating, leaving behind large dust grains on the surface. Eventually, the appearance could turn into asteroidal rather than cometary. It is, therefore, expected that there would be "dormant comets" in the list of known asteroids. Our research group has undertaken the research on the population of dormant comets. We applied a brand-new asteroidal catalog compiled from data garnered by three infrared astronomical observatories, AKARI, IRAS and WISE. We extracted objects which have comet-like orbits on the basis of their orbital properties (Tisserand parameters with respect to Jupiter, TJ, and aphelion distance, Q). We found that (1) there are a considerable number (>100) of asteroids in comet-like orbits, and (2) 80% of them have low albedo consistent with comets. This result suggest that these low albedo objects could be dormant comets. One unanticipated finding is that 20% of asteroids in comet-like orbit have high albedo similar to S-type asteroids. It is difficult to explain the population of S-type asteroids in comet-like orbits by the classical mechanics theory. We further found that these high-albedo objects are small (D < 2 km) bodies distributed in near-Earth space. We suggest that such high-albedo, small, near-Earth asteroids are susceptible to Yarkovsky effect and injected into comet-like orbits.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.85-95
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• 2019

The internal environment in pig house is closely related to the animal productivity. In addition, it is important to consider a working environment inside the pig house due to high gas and dust concentrations. The poor working environment inside the pig house can cause health problems including respiratory diseases. To analyze the working environment, it is important to evaluate the ventilation efficiency to effectively remove harmful gases and dust. The purpose of this study is to develop a 3D CFD model to analyze the working environment in the pig house. CFD model was validated by comparing air temperature distributions between CFD computed and field measured data. The average air flow rate at the pig height was 40.1 % lower than the working height when incoming air was concentrated on upper layer by the installed ventilation system on the experimental pig house. Using the validated CFD model, the regional ventilation efficiency was computed by the TGD(tracer gas decay) method at the pig and working heights. There was a difference of ventilation efficiency on 14 % between the air stagnated section and the rest sections. Stagnated gas concentration can be effected by animal and human health.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.51-54
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• 2003

We analyzed radiative properties of aerosols, $CO^{2}$ and clouds using Optical Properties of Aerosols and Clouds(OPAC) and the Column Radiation Model (CRM). From OPAC, if the soot component is disregarded, dust-like components depict the highest extinction values in the solar spectral range and the lowest. single scattering albedoes, which are attributable to the presence of large particles. In the dust aerosol, the high absorptivity in the infrared may induce a warming of the lower atmospheric layer in the nighttime. The radiative properties of aerosols, clouds and double $CO^{2}$ using the CRM model at Seoul (37N, 127.4 E) on 3 April 2003 were calculated. The solar zenith angle is 65˚ and the surface albedo is 0.1836 during the clear day. The aerosol optical depth change 0.14 to 1.7, which is derived during Asian dust days in Korea. At this time, abedo by aerosols is considered as 0.3. In cloudy condition, the short wave cloud forcing on both the TOA and the surface is -193.89 $Wm^{-2}$ and -195.03 $Wm^{-2}$, respectively, and the long wave cloud forcing is 19.58 $Wm^{-2}$ and 62.08 $Wm^{-2}$, respectively. As a result, the net radiative cloud forcing is -174.31 $Wm^{-2}$ and -132.95 $Wm^{-2}$, respectively. We calculate also radiative heating rates by double $CO^{2}$ during the clear day. The $CO^{2}$ volumn mixing ratio is 3.55E-4.

• Textile Coloration and Finishing
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• v.34 no.1
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• pp.20-26
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• 2022

Centrifugal spinning is an emerging technique for fabricating micro-to-nano-fibers in recent years. To obtain fibers with the desired size and morphology, it is necessary to configure and optimize the parameters used in centrifugal spinning. In this study, it was controlled by changing the solution's concentration (7.5, 10, and 12.5 wt.%) and disk's rotational velocity (6,000, 8,000, and 10,000 rpm) to prepare centrifugal spun nano-filter. The morphological property, air permeability, and dust collection efficiency of the PVA/PP bi-layer nanoweb prepared by centrifugal spun PVA on the PP micron nonwoven substrate are studied using a field emission scanning electron microscope, an air permeability tester, and a filter tester equipment, and the analysis results indicate that it is suitable as a nano-filter when the concentration of PVA solution is 10 wt.% and the rotational velocity of the disk is 8,000 rpm. The resultant reduced diameter and uniform fibers also proved that an excellent dust collection efficiency filter could be made.