• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.35-42
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• 2023

This study analyzed the current and temperature characteristics of major components of an induction motor during normal and abnormal operations as functions of the difference in the rated capacities of medium and large-sized motors widely used in industrial settings. The temperature rise equation of the induction motor winding was derived through locked-rotor operation experiments and linear regression analysis. When the ambient temperature is 40 ℃, the time to reach 155 ℃, the temperature limit of the insulation class (F class) of the winding of the induction motor, was confirmed to be 48 seconds for the 2.2 kW induction motor and 39 seconds for the 3.7 kW induction motor. This means that when the rated capacity is large or the installation environment is high temperature, the time to reach the temperature limit of the insulation class during locked-rotor operation is short, and the risk of insulation deterioration and fire is high. In addition, even if the EOCR (Electronic Over Current Relay) is installed, if the setting time is excessively set, the EOCR does not operate even if the normal and locked-rotor operation of the induction motor is repeated, and the temperature limit of the insulation grade of the winding of the induction motor is exceeded. The results of this study can be used for preventive measures such as the promotion of electrical and mechanical measures for the failure of induction motors and fire prevention in industrial sites, or the installation of fire alarm systems.

• Membrane Journal
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• v.33 no.6
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• pp.279-304
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• 2023

Polybenzimidazole (PBI) based membranes have evolved in literature as a popular membrane material for various applications in the past two decades because of their high temperature thermal durability, strong mechanical and tensile properties, high glass transition temperature (T_g), ion conduction ability at elevated temperature (up to 200℃), oxidative or chemical durability along with robust network like structural rigidity, which make PBI membranes suitable for various potential applications in chemically challenging environments. Ion conducting PBI based membranes have been extensively utilized in high temperature proton exchange membrane fuel cells (HT-PEMFC). In addition, PBI based membranes have been vastly utilized for the development of gas separation membranes and organic solvent nanofiltration (OSN) membranes for their unique characteristics. This review will cover the recent progress and application of various types of flat sheet PBI based membranes for HT-PEMFC, gas separation and OSN application.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.495-507
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• 2023

The roughness of discontinuity significantly influences the mechanical characteristics of rock masses and extensively affects thermal and hydraulic behaviors. In this study, we utilized photogrammetry to generate 3D point cloud data for discontinuity and applied this data to characterize the roughness of discontinuity. The discontinuity profiles, reconstructed from the 3D point cloud data, were compared with those manually measured using a profile gauge. This comparison served to validate the accuracy and reliability of the acquired point cloud data in replicating the actual configurations of rock surfaces. Subsequent to this validation, influence of the number of profiles for representative JRC assessment was further investigated followed by suggestion of roughness anisotropy evaluation method with application of it to actual rock discontinuity surfaces.

• Journal of the Korean GEO-environmental Society
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• v.25 no.7
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• pp.29-34
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• 2024

Frost heave is one of the significant engineering characteristics of frozen ground and causes severe damages on geo-structures. Although thermo-hydro coupled analyses have been developed to predict frost heave behavior, these analyses involve excessive input parameters and have primarily been validated for frost heave in clayey soils. Frost heave mainly occurs in silty soils, which have relatively higher permeability compared to clayey soils, necessitating careful attention. This study introduces empirical models and verifies their reliability for silty soils. By using the validated model, the correlation of key input parameters is derived, which is expected to enhance the applicability of thermal-mechanical analysis for geo-structures on frozen ground in the future.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.166-172
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• 2016

This paper deals with the seismic qualification of the reflective metal insulation for thermal shielding that is installed on the outer surfaces of the main equipment of the primary coolant system of a nuclear power plant. A small-scale model of the reactor pressure vessel, which has equivalent dynamic characteristics, was designed to be tested in domestic seismic testing facilities in the future. In this study, seismic analysis of the small-scale model installed with metal insulation was performed using equivalent static analysis and response spectrum analysis. The required Response Spectrum for main equipment of the primary coolant system of APR-1400 plant were considered to establish the enveloping response spectrum, which was applied to the seismic analysis model. The results from two seismic analysis methods were compared to show the structural adequacy of the metal insulator design against a safe shutdown earthquake. This study will form the basis for the seismic testing to support the seismic qualification of the reflective metal insulator.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.642-642
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• 2013

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as high electron mobility, high thermal conductivity and optical transparency. Especially, chemical vapor deposition (CVD) grown graphene has been used as a promising material for high quality and large-scale graphene film. Unfortunately, although CVD-grown graphene has strong advantages, application of the CVD-grown graphene is limited due to ineffective transfer process that delivers the graphene onto a desired substrate by using polymer support layer such as PMMA(polymethyl methacrylate). The transferred CVD-grown graphene has serious drawback due to remaining polymeric residues generated during transfer process, which induces the poor physical and electrical characteristics by a p-doping effect and impurity scattering. To solve such issue incurred during polymer transfer process of CVD-grown graphene, various approaches including thermal annealing, chemical cleaning, mechanical cleaning have been tried but were not successful in getting rid of polymeric residues. On the other hand, lithographical patterning of graphene is an essential step in any form of microelectronic processing and most of conventional lithographic techniques employ photoresist for the definition of graphene patterns on substrates. But, application of photoresist is undesirable because of the presence of residual polymers that contaminate the graphene surface consistent with the effects generated during transfer process. Therefore, in order to fully utilize the excellent properties of CVD-grown graphene, new approach of transfer and patterning techniques which can avoid polymeric residue problem needs to be developed. In this work, we carried out transfer and patterning process simultaneously with no polymeric residue by using a metal etch mask. The patterned thin gold layer was deposited on CVD-grown graphene instead of photoresists in order to make much cleaner and smoother surface and then transferred onto a desired substrate with PMMA, which does not directly contact with graphene surface. We compare the surface properties and patterning morphology of graphene by scanning electron microscopy (SEM), atomic force microscopy(AFM) and Raman spectroscopy. Comparison with the effect of residual polymer and metal on performance of graphene FET will be discussed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.569-575
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• 2020

In this study, a fuel cell system model for ship power was developed and verified by comparing the experimental results obtained by supplying pure oxygen. To verify the proposed model, the fuel cell output characteristics when oxygen was supplied were compared with those when air was supplied using an air compressor. In addition, the effect of the change in the thermal properties of the fuel cell system on the output of the stack was examined. Within the experimental range of this study, when pure oxygen was supplied as the cathode supply gas, the calculated and experimental voltages and outputs obtained through modeling were almost the same over the entire load range. When air was supplied instead of oxygen for the cathode supply at a constant load of 560 A, each stack voltage was approximately 14 V, the stack output was approximately 8 kW, and the stack efficiency was approximately 3 %. It was confirmed that the overall system efficiency was reduced by approximately 8 %. Among the thermal properties examined in this study, the heat transfer coefficient of the coolant to the stack was found to have the greatest effect on the output of the stack.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.155-164
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• 2005

The characteristics of sintering for Mullite-Cordierite (MC) composites and the effect of $TiO_2$ addition were studied. The MC composites were manufactured by a solution-polymerization method using PVA as a polymer carrier, and $TiO_2$ was used as a sintering agent. They were calcined at $1300^{\circ}C$, planetary milled for 4 h and sintered at $1450^{\circ}C$. As cordierite content increased, relative density of materials was increased up to $98\%$ and sinterability was improved. In case of $50\;wt\%$ mullite/$5\;wt\%$ cordierite composition sintered for 16 h, the flexural strength and thermal expansion coefficient were 190 MPa and $3.07{\times}0^{-6}/^{\circ}C$, respectively. However, mechanical properties were decreased with the cordierite contents higher than $50\;wt\%$ because of the excess liquid-phase amount. As the addition of $TiO_2$ is increased, columnar crystal of mullite and liquid-phase contents were increased. In particular, the flexural strength and thermal expansion coefficient decreased in case of $5\;wt\%\;TiO_2$ addition.

• Polymer(Korea)
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• v.28 no.2
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• pp.143-148
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• 2004

${\alpha}$,$\omega$-Hydrogen polyorganosiloxane(HPMDMS) prepolymer was prepared from equilibrium polymerization ofoctamethylcyclotetrasiloxane, 1,3,5-trimethylcyclotrisiloxane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethyl-cyclotetrasiloxane, and 1,1,3,3-tetramethyl disiloxane as an end-blocker in the presence of tetramethylammonium siloxanolate as a catalyst. Polyorganosiloxane modified with dimethylacrylamide(APMDMS) was prepared by hydrosilylation of HPMDMS with dimethylacrylamide in the presence of Pt catalyst, and followed by coordination of metal oxide (APMDMS-MO), such as NiO and FeO, to the amide moieties of the resulting polymer. The chemical structures of HPMDMS and APMDMS were confirmed by FT-IR and $^1$H-NMR analysis. Liquid silicone rubber containing metal oxide composite (LSRMO) was prepared by compounding APMDMS-MO, ${\alpha}$,$\omega$-vinylpolydimethylsiloxane, and a catalyst in a high speed dissolver. The thermal conductivity of LSRMO composite was determined to be 0.29 W/mK, and the volume resistivity exhibited a lower value than that of LSR composite. The mechanical and thermal properties of LSRMO and LSR composite were measured by UTM and TGA.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.474-481
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• 2018

The policy-making and technological development of eco-friendly automobiles designed to increase their supply is ongoing, but the internal combustion engine still accounts for approximately 95% of automobiles in use. To meet the stricter emission regulations of internal combustion engines based on fossil fuels, the proportion of after-treatments for vehicles and (ocean going) vessels is increasing continuously. As diesel engines have high power and good fuel economy in addition to less CO2 emissions, their market share is increasing not only in commercial vehicles, but also in passenger cars. Because of the characteristics of the diesel combustion, however, NOx is generated in localized high-temperature combustion regions, and particulates are formed in the zones of diffusion combustion. LNT and urea-SCR catalysts have been developed for the after-treatment of exhaust gas to reduce NOx in diesel vehicles. This study examined the effect of a containing promoter on SCR catalysts to cope with the severe exhaust gas regulation. The de-NOx performance of the Mn-SCR catalyst was the best, and the de-NOx performance was improved as the ion exchange rate between Mn ion and Zeolyst was good and the activation energy was low. The de-NOx performance of the 7Cu-15Ba/78Zeoyst catalyst was 32% at $200^{\circ}C$ and 30% at $500^{\circ}C$, and showed the highest performance. The NOx storage material of BaO loaded as a promoter was well dispersed in the Cu-SCR catalyst and the additional de-NOx performance of BaO was affected by the reduction reaction of the Cu-SCR catalyst. Among the three catalysts, the 7Cu-15Ba/Zeolyst SCR catalyst was resistant to thermal degradation. The same type of CuO due to thermal degradation migrates and agglomerates because BaO reduces the agglomeration of the main catalyst CuO particles.