• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.1043-1048
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• 2012

In this study, activated carbons (ACs) were modified as electrode materials for an electric double layer capacitor (EDLC) by controlling oxygen- and nitrogen-containing functional groups. The morphological and chemical properties of ACs were analyzed through scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectrometer, automatic elemental analyzer (EA) and Boehm titration. Also, charge/discharge tests were performed to investigate the EDLC performance. Oxygen- and nitrogen-containing functional groups were introduced on the surface of ACs through acid and urea treatments, respectively. ACs with nitrogen-containing functional groups showed 2 mA increase of gravimetric discharge capacity and quick achievement of maximum charge/discharge performance. However, ACs with oxygen-containing functional groups showed low discharge capacity and its gradual decrease during further cyclic test, since the functional groups interrupted adsorption/desorption of charges in the electrolyte on the surface of ACs.

• Progress in Superconductivity
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• v.11 no.1
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• pp.13-18
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• 2009

Partial discharge measurements in cryogenic dielectric materials of HTS transformer are very important because partial discharge was regarded as primary source for ageing and breakdown of cryogenic materials. But, partial discharge measurement techniques and its effects in low temperature high voltage environments were not suggested and there exist only a few reports on this research fields. Therefore, in order to implement reliable HTS transformers, partial discharge diagnosis techniques for cryogenic materials of HTS transformers were investigated using partial discharge (PD) pattern analysis methods. In this works, four different types of artificial defects including turn to turn insulation, free moving particle, void and protrusion, have been fabricated since it was commonly regarded that they might cause the sudden service failures of the power apparatus. For this purpose, these defects are installed into the dielectric materials in liquid nitrogen and experimental investigations have been carried out for the diagnosis of HTS transformer. And various PD patterns caused by the amount of quench of superconductors were analyzed. Throughout this works, the different PD patterns in cryogenic dielectric materials in liquid nitrogen, and PD measuring technique could be the fundamental steps to establish diagnosis technologies of HTS transformer for power applications.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.3
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• pp.270-276
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• 2014

Seasonal characteristics of water and sediment qualities and potential effects of the freshwater discharge from a small tide embankment interior in a coastal area in Goheung county were investigated from May to September in 2012. Chemical oxygen demand values (COD) were mostly higher than 2 mg/L in summer ebb tide, which exceed the standard value of water quality criteria II of acceptable level for aquaculture activities. Nitrogen and phosphorus were found as the limiting nutrients for algae growth in summer and fall and in spring, respectively. Nitrogen was the limiting nutrient for diatom growth in the whole studied period. The sudden high values of COD, ammonia, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) were found in water sample collected from station 5 which located in front of the tide embankment sluice gate during spring ebb tide. The freshwater discharge form the tide embankment interior maybe affected the survey areas during a short time interval. Mean values of eutrophication index of the surveyed coastal region in spring, summer and fall were all bigger than 1. Water quality was mostly considered at level II which acceptable for aquaculture activities. Sediment quality in this study was generally in the range of standard for fisheries environment.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1975-1977
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• 2000

In this study, a relationship between AC discharge progress and the radiated electromagnetic waves were investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The characteristics of frequency spectrum of the radiated electromagnetic waves was measured at the atmospheric pressure in liquid nitrogen($LN_2$) during partial discharges progress in nonuniform electric field depend on AC power supply. From this results, it was confirmed that when partial discharge was produced in liquid nitrogen, the signal of partial discharge was detected by frequency spectrum of the radiated electromagnetic waves. It is considered that these results obtained from this investigation may be used as fundamental data for diagnosis and prediction of insulation on superconducting and cryogenic power equipments.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.3
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• pp.49-55
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• 2003

This paper studied characteristics of surface discharge and tracking phenomena on the surface of solid insulators in Liquid Nitrogen(LN2) noticed as a cooling medium of high temperature superconductor. In order to investigate the bubble effect which have much influence on electric surface discharge in Liquid Nitrogen, knife type electrode and plane electrode were formed oppositely with A-mode, B-mode and C-mode configuration. It is considered that these result are fundamental data for electric insulation design of superconductor and cryogenic application machinery which will be studied and developed in the future.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.18-21
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• 2008

The study deals with the effects of parameters in the synthesis of carbon nanotubes in liquid nitrogen to find the most appropriate conditions such as electrical voltage and time that give carbon nanotubes with large volume and less proportion of impurity, which is a non-nanotubed carbon. The experiment employed the method of arc-discharge between graphite cathode and anode which are immersed in liquid nitrogen. The electrical DC current of 60A and 70A were applied with the time period ranging from 10 seconds to 25 seconds. It was found that the electrical current of 60A and 13 seconds arc-discharge time allowed the largest volume of carbon nanotubes generation. The longer time leads to more impurities around the carbon nanotubes. By the filtration of CNTs-suspended solution using 0.2 micrometers porous paper filter and the characterization using TEM, the carbon nanotubes synthesized in the study were approximately 25 layers multi-walled nanotubes with the average diameter of 18.2 nanometers.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.114-118
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• 2002

This paper were investigated discharge characteristics in the Liquid Nitrogen($LN_{2}$) noticed as a cooling medium of high temperature superconductor, and the characteristics of surface discharge and tracking phenomena on the solid insulators of cryocable. In order to investigate the bubbles which have much influence on electric surface discharge in Liquid Nitrogen, knife type electrode and plane electrode was formed oppositely with mode A and B, C configuration. It is considered that these result are fundamental data for electric insulation design of superconductivity and cryogenic application machinery which will be studied and developed in the future.

• Journal of Korean Society on Water Environment
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• v.31 no.4
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• pp.351-359
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• 2015

The study on the improvement of discharge water quality from domestic wastewater treatment plant (DWTP) was performed in a filter type bioelectrochemical system. The COD removal efficiency for a synthetic discharge water was about 88%, and the effluent COD was less than 5mg/L. The nitrification efficiency of the bioelectrochemical system was over 97%, but a considerable amount of the nitrogen was remained as nitrate form in the effluent. The total nitrogen removal efficiency was only around 30%. There are no significant differences in the removal of COD and nitrogen at 0.6 and 0.8V of the applied voltages between anode and cathode. The removal of COD and nitrogen in the system were quite stable when the HRT ranged from 60 to 15 minutes, and at 10 minutes of HRT, the nitrification efficiency was slightly decreased. The performance of the bioelectrochemical system has quickly recovered from the shocks in the influent due to high concentration of COD and nitrogen. For the effluent that discharged from the DWTP, the removal efficiencies of COD and total nitrogen from the bioelectrochemical system were 50 and 30%, respectively. Thus the bioelectrochemical system was a feasible process for further polishing the effluent quality from DWTP.

• Journal of Environmental Science International
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• v.27 no.3
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• pp.179-193
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• 2018

Nitrogen budgets in Sihwa-ho in 2010 were estimated using a mass balance approach. Major nitrogen fluxes sources can be divided into three sections: cities, agricultural area, and forest. Surplus nitrogen 2,030~2,214 ton/yr (2,123 ton/yr in average) was discharged to Sihwa Lake. 20% of the surplus nitrogen is removed from the wetland and 60% is removed tidal flats. Therefore net nitrogen discharge from Sihwa basin is estimated to be 650~708 ton/yr (679 ton/yr in average). Wet and dry nitrogen deposition and load from non-point sources ware estimated to be 97 ton/yr and 69 ton/yr, deposition is using CAMx model. So estimated total nitrogen discharge into Sihwa-ho was 817~875 ton/yr (846 ton/yr in average). The atmospheric load explains 11.1~11.9% (11.5% in average) of the total nitrogen load Sihwa-ho.

• Journal of Environmental Impact Assessment
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• v.12 no.5
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• pp.341-348
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• 2003

Seasonal characteristics of water quality and effect of the freshwater discharge during open the tide embankment in Haechang Bay were evaluated. In the freshwater, where interior of the tide embankment, COD and Chl-a exceeded about 4mg/L and $10mg/m^3$, respectively, independent of season, while in the seawater they showed high values in April and July in contrast to the other period due to input of freshwater and increase of phytoplankton, respectively. The content of seawater inorganic nitrogen maintained a relatively high level at inner part of the bay, whereas high values of inorganic phosphorus content was distributed at all over the bay. The limiting factor for algal growth was nitrogen with respect to the N/P ratio. The compass of influence by the freshwater discharge in April was quite different with water pollutants. As a result of the salinity variation with time, the freshwater extended strongly to offshore from the surface layer without mixing with depth when open the tide embankment, and reached within about one hour at a station which is 3.5km from the tide embankment. To effective water quality management of Haechang Bay, discharge rate and pollutant loads should be controlled.