• Title/Summary/Keyword: Carbon density

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Measurements and CFD Analysis for Release Rate of CO2 and Characteristics of Natural Ventilation in Lecture Room (강의실 CO2 발생률과 자연환기 특성의 측정 및 CFD 분석)

  • Lee, Donghae;Choi, Youngbo
    • Journal of the Korean Society of Safety
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    • v.36 no.1
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    • pp.86-94
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    • 2021
  • Lecture rooms are crowded with many attendees. Moreover, they rely significantly on the natural ventilation through windows for removing and controlling indoor contaminants such as CO2. With the aim of broadening the understanding of the characteristics of natural ventilation phenomena in lecture rooms, the average individual CO2 release rates of attendees were measured during the course of a lecture and compared with previously reported CO2 release rates. In addition, the effects of natural ventilation through windows on the time-variant CO2 concentrations in the center of the lecture room were measured and analyzed. Moreover, details about the overall and regional CO2 concentrations, as well as the air flows in the lecture room, were simulated and analyzed with computational fluid dynamics software, Fluent 2020 R2. It was found that the average individual CO2 release rates were slightly slower than previously reported rates. The local CO2 concentrations in the lecture room for regions with a high density of attendees increased over a short period of time, although the natural ventilation was already started by opening the windows. The overall CO2 concentration in the lecture room rapidly decreased in the early stage of ventilation, but declined very slowly after a longer period of ventilation time. Therefore, in order to enhance the efficiency of a lecture room's natural ventilation, it is recommended to homogeneously distribute the attendees in the lecture room, and to frequently open the windows for short periods of time.

Removal of 2,4-D by an Fe(II)/persulfate/Electrochemical Oxidation Process (Fe(II)/과황산/전기화학적 산화 공정에 의한 2,4-D의 제거)

  • Hyun, Young Hwan;Choi, Jiyeon;Shin, Won Sik
    • Journal of Soil and Groundwater Environment
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    • v.26 no.1
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    • pp.45-53
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    • 2021
  • The removal of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution by coupled electro-oxidation and Fe(II) activated persulfate oxidation process was investigated. The electrochemical oxidation was performed using carbon sheet electrode and persulfate using Fe(II) ion as an activator. The oxidation efficiency was investigated by varying current density (2 - 10 mA/㎠), electrolyte (Na2SO4) concentration (10 - 100 mM), persulfate concentration (5 - 20 mM), and Fe(II) concentration (10 - 20 mM). The 2,4-D removal efficiency was in the order of Fe(II) activated persulfate-assisted electrochemical oxidation (Fe(II)/PS/ECO, 91%) > persulfate-electrochemical oxidation (PS/ECO, 51%) > electro-oxidation (EO, 36%). The persulfate can be activated by electron transfer in PS/ECO system, however, the addition of Fe(II) as an activator enhanced 2,4-D degradation in the Fe(II)/PS/ECO system. The 2,4-D removal efficiency was not affected by the initial pHs (3 - 9). The presence of anions (Cl- and HCO3-) inhibited the 2,4-D removal in Fe(II)/PS/ECO system due to scavenging of sulfate radical. Scavenger experiment using tert-butyl alcohol (TBA) and methanol (MeOH) confirmed that although both sulfate (SO4•-) and hydroxyl (•OH) radicals existed in Fe(II)/PS/ECO system, hydroxyl radical (SO4•-) was the predominant radical.

Characterization of LLDPE/CaCO3 Composite Drawn Film (연신된 LLDPE/CaCO3 composite film의 특성분석)

  • Lee, Jungeon;Park, Jae Min;Jung, Jae Hoon;Kim, Tae Young;Han, Myung Dong;Seo, Jang Min;Seo, Min Jeong;Yang, Seong Baek;Yeum, Jeong Hyun
    • Textile Coloration and Finishing
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    • v.34 no.1
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    • pp.68-75
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    • 2022
  • The breathable film refers to a high-functional film that allows gas and water vapor to pass through very fine and sophisticated pores but not liquid. In this research, the breathable film was prepared based on linear low-density polyethylene (LLDPE) and CaCO3 particles by extrude method. The LLDPE composite film containing CaCO3 particles had excellent mechanical properties and functionalties. The drawing is a technologically simple and excellent method for improving the mechanical properties of composite films. In this work, the effects of draw ratio on morphology, crystallinity, pore size distribution, mechanical properties, and water vapor permeability of the films were examined. The results revealed that both surface morphology and breathability were affected by the influence of chain orientation and crystal growth with increasing the draw ratio. The mechanical properties were improved with increasing the draw ratio.

Estimating TOC Concentrations Using an Optically-Active Water Quality Factors in Estuarine Reservoirs (광학특성을 가진 수질변수를 활용한 하구 담수호 내 TOC 농도 추정)

  • Kim, Jinuk;Jang, Wonjin;Shin, Jaeki;Kang, Euntae;Kim, Jinhwi;Park, Yongeun;Kim, Seongjoon
    • Journal of Korean Society on Water Environment
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    • v.37 no.6
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    • pp.531-538
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    • 2021
  • In this study, the TOC in six estuarine reservoirs in the West Sea (Ganwol, Namyang, Daeho, Bunam, Sapkyo, and Asan) was estimated using optically-active water quality factors by the water environment monitoring network. First, specification data and land use maps of each estuarine reservoir were collected. Subsequently, water quality data from 2013 to 2020 were collected. The data comprised of 11 parameters: pH, dissolved oxygen, BOD, COD, suspended solids (SS), total nitrogen, total phosphorus, water temperature, electrical conductivity, total coliforms, and chlorophyll-a (Chl-a). The TOC in the estuarine reservoirs was 4.9~7.0 mg/L, with the highest TOC of 7.0 mg/L observed at the Namyang reservoir, which has a low shape coefficient and high drainage density. The correlation of TOC with water quality factors was also analyzed, and the correlation coefficients of Chl-a and SS were 0.28 and 0.19, respectively, while the correlation coefficients of these factors in the Namyang reservoir were 0.42 and 0.27, respectively. To improve the estimation of TOC using Chl-a and SS, the TOC was averaged in 5 mg/L units, and Chl-a and SS were averaged. Correlation analysis was then performed and the R2 of Chl-a-TOC was 0.73. The R2 of SS-TOC was 0.73 with a non-linear relationship. TOC had a significant non-linear relationship with Chl-a and SS. However, the relationship should be assessed in terms of the spatial and temporal variations to construct a reliable remote sensing system.

Characteristics of nickel cobalt oxide (NiCo2O4) nanosheet electrodes prepared by hydrothermal synthesis and heat treatment (수열합성법으로 제조된 니켈코발트산화물(NiCo2O4) 나노시트 전극의 특성)

  • Lee, Seokhee;Cha, Hyunjin;Lee, Sangwoon;Kim, Juna;Park, Jeonghwan;Hwang, Donghyun;Son, Young Guk
    • Journal of Surface Science and Engineering
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    • v.55 no.1
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    • pp.32-37
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    • 2022
  • In a carbon-zero social atmospher, research is underway to reduce the use of fossil fuels. Interest in cleaner energy sources and their storage system is growing, and among them, research on effective energy storage is being actively conducted. Energy storage system(ESS) can be divided into secondary batteries, fuel cells, and capacitors, and the superiority of energy density of secondary batteries has a dominent influence on the ESS market. However, as problems with secondary batteries, charge/discharge speed, safety, and deterioration of electrodes are being highlighted. In this study, an electrode for supercapacitor with superior charge/discharge speed and specific capacitance is manufactured. The manufactured spinel nickel cobalt electrodes had specific capacitances of 1018.8 F/g, 690.8 F/g, and 475.1 F/g at 1 A/g in 1 M KOH electrolyte, and shows a performance retention rate of 77.48%, 63.30%, and 58.16% after 2000cycles at 7 A/g.

Effects of Long-Term Fertilizer Practices on Rhizosphere Soil Autotrophic CO2-Fixing Bacteria under Double Rice Ecosystem in Southern China

  • Tang, Haiming;Wen, Li;Shi, Lihong;Li, Chao;Cheng, Kaikai;Li, Weiyan;Xiao, Xiaoping
    • Journal of Microbiology and Biotechnology
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    • v.32 no.10
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    • pp.1292-1298
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    • 2022
  • Soil autotrophic bacterial communities play a significant role in the soil carbon (C) cycle in paddy fields, but little is known about how rhizosphere soil microorganisms respond to different long-term (35 years) fertilization practices under double rice cropping ecosystems in southern China. Here, we investigated the variation characteristics of rhizosphere soil RubisCO gene cbbL in the double rice ecosystems of in southern China where such fertilization practices are used. For this experiment we set up the following fertilizer regime: without any fertilizer input as a control (CK), inorganic fertilizer (MF), straw returning (RF), and organic and inorganic fertilizer (OM). We found that abundances of cbbL, 16S rRNA genes and RubisCO activity in rhizosphere soil with OM, RF and MF treatments were significantly higher than that of CK treatment. The abundances of cbbL and 16S rRNA genes in rhizosphere soil with OM treatment were 5.46 and 3.64 times higher than that of CK treatment, respectively. Rhizosphere soil RubisCO activity with OM and RF treatments increased by 50.56 and 45.22%, compared to CK treatment. Shannon and Chao1 indices for rhizosphere soil cbbL libraries with RF and OM treatments increased by 44.28, 28.56, 29.60, and 23.13% compared to CK treatment. Rhizosphere soil cbbL sequences with MF, RF and OM treatments mainly belonged to Variovorax paradoxus, uncultured proteobacterium, Ralstonia pickettii, Thermononospora curvata, and Azoarcus sp.KH33C. Meanwhile, cbbL-carrying bacterial composition was obviously influenced by soil bulk density, rhizosphere soil dissolved organic C, soil organic C, and microbial biomass C contents. Fertilizer practices were the principal factor influencing rhizosphere soil cbbL-carrying bacterial communities. These results showed that rhizosphere soil autotrophic bacterial communities were significantly changed under conditions of different long-term fertilization practices Therefore, increasing rhizosphere soil autotrophic bacteria community with crop residue and organic manure practices was found to be beneficial for management of double rice ecosystems in southern China.

Effect of Solution Temperature on the Cavitation Degradation Properties of Epoxy Coatings for Seawater Piping

  • Jeon, J.M.;Yoo, Y.R.;Jeong, M.J.;Kim, Y.C.;Kim, Y.S.
    • Corrosion Science and Technology
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    • v.20 no.6
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    • pp.335-346
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    • 2021
  • Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental aspects. As the solution temperature increased, even though with large fluctuation, the cavitation degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating.

Mo,Cu-doped CeO2 as Anode Material of Solid Oxide Fuel Cells (SOFCs) using Syngas as Fuel

  • Diaz-Aburto, Isaac;Hidalgo, Jacqueline;Fuentes-Mendoza, Eliana;Gonzalez-Poggini, Sergio;Estay, Humberto;Colet-Lagrille, Melanie
    • Journal of Electrochemical Science and Technology
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    • v.12 no.2
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    • pp.246-256
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    • 2021
  • Mo,Cu-doped CeO2 (CMCuO) nanopowders were synthesized by the nitrate-fuel combustion method aiming to improve the electrical and electrochemical properties of its Mo-doped CeO2 (CMO) parent by the addition of copper. An electrical conductivity of ca. 1.22·10-2 S cm-1 was measured in air at 800℃ for CMCuO, which is nearly 10 times higher than that reported for CMO. This increase was associated with the inclusion of copper into the crystal lattice of ceria and the presence of Cu and Cu2O as secondary phases in the CMCuO structure, which also could explain the increase in the charge transfer activities of the CMCuO based anode for the hydrogen and carbon monoxide electro-oxidation processes compared to the CMO based anode. A maximum power density of ca. 120 mW cm-2 was measured using a CMCuO based anode in a solid oxide fuel cell (SOFC) with YSZ electrolyte and LSM-YSZ cathode operating at 800℃ with humidified syngas as fuel, which is comparable to the power output reported for other SOFCs with anodes containing copper. An increase in the area specific resistance of the SOFC was observed after ca. 10 hours of operation under cycling open circuit voltage and polarization conditions, which was attributed to the anode delamination caused by the reduction of the Cu2O secondary phase contained in its microstructure. Therefore, the addition of a more electroactive phase for hydrogen oxidation is suggested to confer long-term stability to the CMCuO based anode.

Analysis of Electrochemical Performance of Reduced Graphene Oxide based Symmetric Supercapacitor with different Aqueous Electrolytes

  • Ravi, Sneha;Kosta, Shivangi;Rana, Kuldeep
    • Journal of the Korean Electrochemical Society
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    • v.25 no.1
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    • pp.22-31
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    • 2022
  • Carbon nanomaterials are considered to be the materials of choice for the fabrication of electrochemical energy storage devices due to their stability, cost-effectiveness, well-established processing techniques, and superior performance compared to other active materials. In the present work, reduced graphene oxide (rGO) has been synthesized and used for the fabrication of a symmetric supercapacitor. The electrochemical performance of the fabricated supercapacitors with three different aqueous electrolytes namely 0.5 M H2SO4, 0.5 M H3PO4, and 1.0M Na2SO4 have been compared and analyzed. Among the three electrolytes, the highest areal specific capacitance of 14 mF/cm2 was calculated at a scan rate of 5 mV/s observed with 0.5M H3PO4 electrolyte. The results were also confirmed from the charge/discharge results where the supercapacitor with 0.5M H3PO4 electrolyte delivered a specific capacitance of 11 mF/cm2 at a current density of 0.16 mA/cm2. In order to assess the stability of the supercapacitor with different electrolytes, the cells were subjected to continuous charge/discharge cycling and it was observed that acidic electrolytes showed excellent cyclic stability with no appreciable drop in specific capacitance as compared to the neutral electrolyte.

Preparation of rGO-S-CPEs Composite Cathode and Electrochemical Performance of All-Solid-State Lithium-Sulfur Battery

  • Chen, Fei;Zhang, Gang;Zhang, Yiluo;Cao, Shiyu;Li, Jun
    • Journal of Electrochemical Science and Technology
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    • v.13 no.3
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    • pp.362-368
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    • 2022
  • The application of polymer composite electrolyte in all-solid-state lithium-sulfur battery (ASSLSBs) can guarantee high energy density and improve the interface contact between electrolyte and electrode, which has a broader application prospect. However, the inherent insulation of the sulfur-cathode leads to a low electron/ion transfer rate. Carbon materials with high electronic conductivity and electrolyte materials with high ionic conductivity are usually selected to improve the electron/ion conduction of the composite cathode. In this work, PEO-LiTFSI-LLZO composite polymer electrolyte (CPE) with high ionic conductivity was prepared. The ionic conductivity was 1.16×10-4 and 7.26×10-4 S cm-1 at 20 and 60℃, respectively. Meanwhile, the composite sulfur cathode was prepared with Sulfur, reduced graphene oxide and composite polymer electrolyte slurry (S-rGO-CPEs). In addition to improving the ion conductivity in the cathode, CPEs also replaces the role of binder. The influence of different contents of CPEs in the cathode material on the performance of the constructed battery was investigated. The results show that the electrochemical performance of the all-solid-state lithium-sulfur battery is the best when the content of the composite electrolyte in the cathode is 40%. Under the condition of 0.2C and 45℃, the charging and discharging capacity of the first cycle is 923 mAh g-1, and the retention capacity is 653 mAh g-1 after 50 cycles.