• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.983-989
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• 2013

The current research reviewed the design conditions that would maximize the efficiency of the hybrid collector that combines in one unit "cyclone-inertial impaction-bag filter". The computational analysis for the shape of cyclone entry predicts that a design that installs the guide vane at the entry of the tangential type cyclone brings a high-rpm and powerful vortex, very effective in promoting the deflection of coarse particles from the streamline at the cyclone. As the lower part of the cyclone is venturi-shaped, however, a strong flow downward of 4 to 5 m/sec persists through the lower part of the hopper, revealing the likely reentrainment of collected dust. And the removal of the venturi at the lower part of the cyclone would solve the problem of the reentrainment of collected dust. The acceleration of the flow velocity through the adjustment of the gap of the collision baffle would increase the effect of collision, but as the interference with the dust separation is expected, the original design should be kept for the baffle.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.8
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• pp.1076-1083
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• 2009

The physicochemical properties of rice flour produced by 3 different grinding methods using various steeping times (3, 6, 9, and 12 hrs) were investigated. Roller mill gave coarse rice flour; the pin mill, intermediate flour; and mixed when both (roller & pin mills) were used. With the increase of steeping times, the rice flours became finer and the contents of crude protein, crude fat and crude ash decreased. Damaged starch was noticeably high in rice flour by roller & pin mills compared to those by roller or pin mills alone. Amylose contents, solubility and swelling power increased as the steeping times increased. Water binding capacity was the highest in roller & pin mills, followed by pin mill. In scanning electron microscope (SEM), pin mill showed distribution of separated fine particles of rice flours. The physicochemical properties of rice flours showed many differences by steeping times of rice and grinding methods. With sufficient steeping times, the rice flours obtained from pin mill were relatively fine having less damaged starch.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1C
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• pp.39-51
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• 2011

A large number of small particles may surround large gravels which are non-contact and dispersed within the ground. The strength of such soil may be influenced by the mechanical properties of a few coarse gravels. A specimen or gravel size can impact the shear characteristics of sand with dispersed gravels. In this study, the size of gravel and specimen varies and its effect on shear characteristics of a granular soil was evaluated. Five sizes of gravels with 7, 12, 15, 18, and 22 mm were used repeatedly and inserted in the middle of each compacted layer. A specimen consists of five or ten equal layers depending on gravel size, which is 5 cm or 10 cm in diameter and 10 cm or 20 cm in height. An embedded gravel ratio by weight is 3% and constant for all cases with gravel. After consolidation, a series of undrained triaxial compression tests under three confining pressures was performed on sand with dispersed gravels. The maximum deviator stress of a specimen with 10 cm in diameter was at average 30% higher than that with 5 cm in diameter and increased up to 90% for a specimen with gravel. When a gravel size of 7 and 12 mm used, the maximum deviator stress of a specimen with 10 cm in diameter was higher than that of one without gravel, whereas the maximum deviator stress of a specimen with 5 cm was higher or lower than that without gravel. The gravel size and specimen diameter influenced the undrained behavior of sand. The maximum deviator stress of a specimen with gravel either increased or decreased compared to that without gravel, depending on the ratio of gravel size to specimen diameter, 1/5.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.2
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• pp.49-55
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• 2011

The failure of electronic instruments is mostly caused by heat and shock. This shock causes the crack initiation at the solder joint interface of PCB component which is closely related with the formation of intermetallic compound(IMC). The Ag content in Pb-free Sn-xAg-0.5Cu solder alloy used in this study was 1.0, 1.2 and 3.0 wt.%, respectively. After soldering with PCB component, isothermal aging was performed to 1000 hrs. The growth of IMC layer was observed during isothermal aging. The drop impact property of solder joint was evaluated by impact bending test method. The solder joint made with the solder containing lower Ag content showed better impact bending property compared with that with higher Ag content. On the contrary to this result, the solder joint made with solder containing higher Ag content showed better impact bending property after aging. It should be caused by the formation of fine $Ag_3Sn$, which relieved the impact. It showed consequently the different effect of fine $Ag_3Sn$ and coarse $Cu_6Sn_5$ particles formed in the IMC layer on the impact bending property.

• Journal of the Korean earth science society
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• v.22 no.6
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• pp.480-490
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• 2001

The soil-air exchange processes of Hg were investigated from the Hari area of Kang Hwa Island during the late March 2001. In the course of our study, we determined the concentration gradients of Hg and combined these gradient data with micrometeorological components to derive its fluxes. Results of our study indicate that the concentration levels of Hg in the study area are notably lower than those typically found in urbanized areas of Korea. However, the computed fluxes were seen to be significantly larger for relatively remote areas, reaching over 200 ng/m$^2$/hr. Comparison of environmental conditions shows that the concentrations of most pollutant species including NO$_X$ and PM were significantly higher during emission, while meteorological conditions were characterized by high temperature and low humidity. Results of correlation analysis also indicate that such pollutants as hydrocarbons, nitrogen oxides, and PM generally exhibit strong positive correlations with Hg-related parameters during emission events, while such relationships were reversed during dry deposition events. The results of our present study suggest the possibility that the concentrations and fluxes of total gaseous Hg observed during deposition events can be influenced by the processes that are also important for the fine, rather than coarse, size fraction of particles.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.337-343
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• 2009

To apply to novel two-interconnected fluidized beds system for selective solid circulation, a solid separator and a solid circulation system were developed. The solid separation rate increased as the gas velocity through the solid injection nozzle, solid height, and diameter of solid injection nozzle increased. However, the effect of the fluidization velocity was negligible. Coarse($212{\sim}300{\mu}m$) and fine($63{\sim}106{\mu}m$) particles were separated using the solid separator and the solid separation rate was ranged from 66 to 453 g/min. The solid circulation rate increased as the gas velocity through the solid injection nozzle, solid height, and the number of solid intake holes increased. However, the effect of the fluidization velocity was negligible. Fine particle was circulated using the solid circulation system and the solid circulation rate was ranged from 65 to 390 g/min. We also proposed two interconnenced fluidized beds system for selective solid circulation equipped with the developed solid separator and the solid circulation system. Long-term operation of continuous solid circulation up to 20 hours has been performed to check feasibility of stable operation. The pressure drop profiles in two beds and the solid separation rate were maintained steadily, and therefore, we could conclude that solid circulation was smooth and stable.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.5
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• pp.590-603
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• 2006

Size-and time-resolved aerosol samples were collected using an eight-stage Davis rotating unit for monitoring (DRUM) sampler from 23 March to 29 April 2001 at Gosan, Jeju Island, Korea, which is one of the super sites of Asia-Pacific Regional Aerosol Characterization Experiment(ACE-Asia). These samples were analyzed using synchrotron X-ray fluorescence for 3-hr average concentrations of 19 elements including Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb, and Pb. The size-resolved data sets were then analyzed using the positive matrix factorization(PMF) technique to identify possible sources and estimate their contributions to particulate matter mass. PMF analysis uses the uncertainty of the measured data to provide an optimal weighting. Twelve sources were resolved in eight size ranges($0.09{\sim}12{\mu}m$) and included continental soil, local soil, sea salt, biomass/biofuel burning, coal combustion, oil combustion, municipal incineration, nonferrous metal source, ferrous metal source, gasoline vehicle, diesel vehicle, and volcanic emission. The PMF result of size-resolved source contributions showed that natural sources represented by local soil, sea salt, continental soil, and volcanic emission contributed about 79% to the predicted primary particulate matter(PM) mass in the coarse size range ($1.15{\sim}12{\mu}m$) while anthropogenic sources such as coal combustion and biomass/biofuel burning contributed about 58% in the fine size range($0.56{\sim}2.5{\mu}m$). The diesel vehicle source contributed mostly in ultra-fine size range($0.09{\sim}0.56{\mu}m$) and was responsible for about 56% of the primary PM mass.

• Journal of the Korea Institute of Building Construction
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• v.20 no.4
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• pp.331-338
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• 2020

The aim of the research is to evaluate the possibility of using coal gasification slag (CGS) as a combined aggregate for concrete mixture. To achieve this goal, the fundamental properties and the durability of concrete were analyzed depending on various combining ratio of CGS into both fine aggregate with favorable gradation and relatively coarse particles. According to the results of the experiment, slump and slump flow were increased with content of CGS regardless of crushed fine aggregate with good and poor gradations while the air content was decreased. For the compressive strength of the concrete, in the case of using the crushed aggregate with good gradation, increasing CGS content decreased compressive strength of the concrete, while when the concrete used crushed aggregate with poor gradation, the compressive strength was the maximum at 50% of CGS content. As a durability assessment, drying shrinkage was decreased and carbonation resistance was improved by increasing CGS content. On the other hand, for freeze-thawing resistance, CGS influenced adverse effect on freeze-thawing resistance. Therefore, it is known that an additional air entrainer is needed to increase the freeze-thawing resistance when CGS was used as a combined aggregate for concrete.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.333-340
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• 2012

The current study prepared 9 laboratorial concrete mixes and 3 ready-mixed concrete batches to examine the size and shape effects in compression failure of lightweight aggregate concrete (LWC). The concrete mixes were classified into three groups: normal-weight, all-lightweight and sand-lightweight concrete groups. For each concrete mix, the aspect ratio of circular or square specimens was 1.0 and 2.0. The lateral dimension of specimens varied between 50 and 150 mm for each laboratorial concrete mix, whereas it ranged from 50 to 400 mm with an incremental variation of 50 mm for each ready-mixed concrete batch. Test observations revealed that the crack propagation and width of the localized failure zone developed in lightweight concrete specimens were considerably different than those of normal-weight concrete (NWC). In LWC specimens, the cracks mainly passed through the coarse aggregate particles and the crack distribution performance was very poor. As a result, a stronger size effect was developed in LWC than in NWC. Especially, this trend was more notable in specimens with aspect ratio of 2.0 than in specimens with that of 1.0. The prediction model derived by Kim et al. overestimated the size effect of LWC when lateral dimension of specimen is above 150 mm. On the other hand, the modification factors specified in ASTM and CEB-FIP provisions, which are used to compensate for the shape effect of specimen on compressive strength, were still conservative in LWC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.317-324
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• 2020

Plastic wastes generated from domestic waste are separated by mixed discharge with foreign substances, and the cost of the separation and screening process increases, so recycling is relatively low. In this study, as a fundamental study for recycling mixed plastic wastes generated from domestic waste into concrete aggregates, changes in concrete properties according to the plastic waste types and the substitution rate were evaluated experimentally. The mixed plastic waste aggregate(MPWA) was found to have a lower density and a higher absorption rate compared to the coarse aggregate with good particle size distribution. On the other hand, the single plastic waste aggregate(SPWA) was composed of particles of uniform size, and both the density and the absorption rate were lower than that of the fin e aggregate. It was found that the MPWA substitution concrete did not cause a material separation phenomenon due to a relatively good particle size distribution even with the largest amount of plastic waste substitution, and the amount of air flow increased little. The compressive strength and flexural strength of the PWA substitution concrete decreased as the amount of substitution of the PWA increased due to the low strength of the PWA, the suppression of the cement hydration reaction due to hydrophobicity, and the low adhesion between the PWA and the cement paste. It was found that the degree of deterioration in compressive strength and flexural strength of concrete substituted with MPWA having good particle size distribution was relatively small.