• Journal of Ocean Engineering and Technology
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• v.16 no.4
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• pp.1-6
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• 2002

Experimental investigation of drag reduction by adding a polymer additive(polyacrylamid, N-401P) into water is carried out in a Circular Water Channel. The effect of viscosity, surface roughness and degradation as a function of running time is also measured with varying the concentration of polymer additives(20ppm,100ppm) and Reynolds numbers. Near and far wakes past a circular cylinder are observed by LDV. Drag forces are measured with a strain-gaged device. The experimental results show that around 5%-30% of drag reduction with the polymer solution are observed. The larger effects of drag reduction can be found at low range of Reynolds number, more roughened surface cylinder. The effect of polymer solution for near wakes is larger than for far wakes.

• Journal of Korea Water Resources Association
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• v.54 no.12
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• pp.1215-1222
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• 2021

In this study, a study on how to use a fire hydrant as a heat wave reduction facility through hydraulic analysis of the water supply pipe network was conducted. Assuming that the fire hydrant installation point is open for heat wave reduction, the water pressure at each point was derived. And the reduction rate of the temperature according to the hydrant watering was compared with the watering area according to the operation of the watering truck. The watering area according to the opening of the fire hydrant was calculated by deriving the pressure value at the node where the fire hydrant was installed through hydraulic analysis of the water pipe network, and then using the watering radius relational expression according to the pressure value. As a result of applying the proposed methodology to two real city areas, the temperature reduction effect of the watering method by a fire hydrant can be derived lower than the watering method by a watering truck according to the difference in the absolute watering area. However, unlike a watering truck, a fire hydrant does not have a relative restriction on the amount of water supply and is expected to allows continuous divided spraying of the same area.

• Journal of Powder Materials
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• v.31 no.2
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• pp.163-168
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• 2024

As the demand for lithium-ion batteries for electric vehicles is increasing, it is important to recover valuable metals from waste lithium-ion batteries. In this study, the effects of gas flow rate and hydrogen partial pressure on hydrogen reduction of NCM-based lithium-ion battery cathode materials were investigated. As the gas flow rate and hydrogen partial pressure increased, the weight loss rate increased significantly from the beginning of the reaction due to the reduction of NiO and CoO by hydrogen. At 700 ℃ and hydrogen partial pressure above 0.5 atm, Ni and Li₂O were produced by hydrogen reduction. From the reduction product and Li recovery rate, the hydrogen reduction of NCM-based cathode materials was significantly affected by hydrogen partial pressure. The Li compounds recovered from the solution after water leaching of the reduction products were LiOH, LiOH·H₂O, and Li₂CO₃, with about 0.02 wt% Al as an impurity.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.7
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• pp.476-482
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• 2014

In this study, the characteristics of emulsified fuel and engine emissions were studied with engine dynamometer. Microexplosion took place in the combustion chamber. While combustion, emulsion fuel scattered to micro particles and it caused to smoke reduction. The heat produced from water vapour reduce the temperature of internal combustion chamber and it caused to inhibition of NOx production. It can be verified by the lower exhaust temperature of each ND-13 mode using emulsion fuel than that of MDO fuel. The NOx and smoke concentration were reduced by increasing water content in emulsion fuel. The power also decreased according to the increment of water content of emulsion fuel because emulsion fuel has low calorific value due to high water content than MDO. As a result of ND-13 mode test with 17% moisture content, it was achieved 24% reduction in NOx production, 76% reduction in smoke density, 11% reduction of $SO_2$ and 13% reduction in power loss.

• Journal of Korean Society on Water Environment
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• v.32 no.1
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• pp.108-114
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• 2016

Sediment-laden water leads to water quality degradation in streams; therefore, best management practices must be implemented in the source area to control nonpoint source pollution. Field monitoring was implemented to measure precipitation, direct runoff, and sediment concentrations at a control plot and straw-applied plot to examine the effect on sediment reduction in this study. A hydrology model, which employs Curve Number (CN) to estimate direct runoff and the Universal Soil Loss Equation to estimate soil loss, was selected. Twenty-five storm events from October 2010 to July 2012 were observed at the control plot, and 14 storm events from April 2011 to July 2011 at the straw-applied plot. CN was calibrated for direct runoff, and the Nash-Sutcliffe efficiency and coefficient of determination were 0.66 and 0.68 at the control plot. Direct runoff at the straw-applied plot was calibrated using the percentage direct runoff reduction. The estimated reduction in sediment load by direct runoff reduction calibration alone was acceptable. Therefore, direct runoff-sediment load behaviors in a hydrology model should be considered to estimate sediment load and the reduction thereof.

• Journal of Korean Society on Water Environment
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• v.20 no.5
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• pp.512-519
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• 2004

Hybrid barriers using reduction and immobilization were tested to remediate the groundwater contaminated with multi-pollutants in this study. Iron filings and HDTMA(hexadecyltrimethylammonium)-bentonite were simulated in columns to assess the performance of hybrid barriers for remediation of trichloroethylene(TCE)-contaminated water. TCE reduction rate for the mixture of iron filings and HDTMA-bentonite was about 7 times higher than that for iron filings, only suggesting the reduction of TCE was accelerated when HDTMA-bentonite was mixed with iron filings. TCE reduction rate for the two layers of iron and HDTMA-bentonite was nearly similar to that for iron filings alone, but the partition coefficient($K_d$) for the two layers was 4.5 times higher than for that iron filings only. TCE was immobilized in the first layer with HDTMA-bentonite, and then dechlorinated in the second layer with iron filings. HDTMA-bentonite may contribute to the increase in TCE concentration on iron surface so that more TCE can be reduced. Also, TCE removal in the hybrid barriers was not affected by chromate and naphthalene while the reduction rate of TCE with the co-existing contaminants by iron filings was significantly decreased. Significant TCE removal in this research indicates that the proposed hybrid barrier system has the potential to become the effective remediation alternative during the occurrence of oil shock. Also, if subsurface environments are contaminated with multi-pollutants that contain non-reducible compounds as well as reducible compounds such as TCE, the conventional reactive barriers cannot be applied to this subsurface environment, while the proposed hybrid system can be applied successfully.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.5
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• pp.17-27
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• 2018

The objective of this study is to identify the priority area where the nonpoint source pollution (NPS) management is required and to set up the load reduction goals for the identified priority area. In this study, the load duration curve (LDC) was first developed using the flow and water quality data observed at 286 monitoring stations. Based on the developed LDC, the priority area for the NPS pollution management was determined using a three-step method. The 24 watersheds were finally identified as the priority areas for the NPS pollution management. The water quality parameters of concern in the priority areas were the total phosphorus or chemical oxygen demand. The load reduction goals, which were calculated as the percent reduction from current loading levels needed to meet target water quality, ranged from 67.9% to 97.2% during high flows and from 40.3% to 69.5% during moist conditions, respectively. The results from this study will help to identify critical watersheds for NPS program planning purposes. In addition, the process used in this study can be effectively applied to identify the pollutant of concern as well as the load reduction target.

• Journal of Korean Society on Water Environment
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• v.34 no.6
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• pp.621-631
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• 2018

In this study, catalyst was made through incipient wetness method using palladium (Pd) as noble metal, indium (In) as secondary metal, and montmorillonite (MK10) and Al pillared montmorillonite (Al-MK10) as supporters. The nitrate reduction rate of the catalysts was measured by batch experiments where H2 gas was used as reducing agent and formic acid as pH controller. Transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were all used to determine the elemental distribution of Pd, In, Al, and Si on catalysts. It was observed that Al pillaring increased the Al/Si elemental composition ratio and point of zero charge of MK10, but decreased its BET specific surface area and pore volume. The nitrate reduction rate of Al-MK10 Pd/In was 2.0 ~ 2.5 times higher than that of MK10 Pd/In using artificial groundwater (GW) in ambient temperature and pressure. Nitrate reduction rates in GW were 1.2 ~ 1.7 times lower than those in distilled deionized water (DDW). Nitrate reduction rates in acidic conditions were higher than those in neutral condition in both GW and DDW. The amount of produced NH3-N over degraded NO3- at acid conditions was lower than that of neutral condition. Even though the leaching of Pd after reaction was measured in DDW it was not detected when both Al-MK10 Pd/In and MK10 Pd/In were used in GW. The modification of montmorillonite as a supporter significantly increased the reductive catalytic activities of nitrates. However, the ratio of producing ammonia by-products to degraded nitrates in ambient temperature and pressure was similar.

• Ecology and Resilient Infrastructure
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• v.2 no.4
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• pp.305-310
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• 2015

In 2014, the city of Seoul revised the ordinance regarding water-cycle restoration in the Seoul Metropolitan areas by incorporating the 'Low Impact Development (LID)' policy. The new ordinance plan will utilize 630 mm or almost 45 to 50% of annual rainfall until 2050 by means of providing a rainwater management system consisting of infiltration, retention and vegetation. The LID is believed to be the key to achieving the target requirements, specifically in development projects. This research was performed to evaluate the stormwater runoff and pollutant reduction performance of three different LID facilities (water circulation facilities) including an infiltration inlet, bioretention swale, and permeable pavement constructed in Seoul City. Results show that among the water circulation facilities, the permeable pavement achieved the highest runoff reduction as it was able to entirely capture and infiltrate the runoff to the ground. However, in order to attain a long-term performance it is necessary to manage the accumulated sediment and trapped pollutants in the landscape areas through other water circulation techniques such as through soil erosion control. In terms of pollutant reduction capability, the infiltration inlet performed well since it was applied in highly polluted areas. The bioretention facility integrating the physico-chemical and biological mechanisms of soil, microorganisms and plants were able to also achieve a high runoff and pollutant reduction. The water circulation facilities provided not only benefits for water circulation but also various other benefits such as pollutant reduction, ecological restoration, and aesthetic functions.

• Journal of Korean Society on Water Environment
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• v.35 no.1
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• pp.72-77
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• 2019

Soil type in LID infiltration practices plays a major role in runoff reduction efficacy. In this study, the effects of infiltration rate of foundation ground under bioretention on annual runoff reduction rate was evaluated using LIDMOD3 which is a simple excel based model for evaluating LID practices. A bioretention area of about 3.2 % was required to capture surface runoff from an impervious area for a 25.4 mm rainfall event. The relative error of runoff from bioretention using LIDMOD3 is 10 % less than that of SWMM5.1 for a total rainfall event of 257.1 mm during the period of Aug. 1 ~ 18, 2017, hence, the applicability of LIDMOD3 was confirmed. Annual runoff reduction rates for the period 2008 ~ 2017 were evaluated for various infiltration rates of foundation ground under the bioretention which ranged from 0.001 to 0.600 m/day and were converted to annual runoff reduction for hydrologic soil group. The runoff reduction rates within hydrologic soil group C and D were steeply increased through increased infiltration rate but not steep within hydrologic A and B with reduction rates ranging from 53 ~ 68 %. The estimated time required to completely empty a bioretention which has a storage depth of 0.632 m is 3.5 ~ 6.9 days and we could assume that the annual average of antecedent rainfall is longer than 3.5 ~ 6.9 days. Therefore, we recommended B type as the minimum hydrologic soil group installed LID infiltration practices for high runoff reduction rate.