• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.3
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• pp.297-307
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• 2020

In the study, energy flow analysis is performed to predict the performance of silencers. To date, deterministic approaches such as finite element method have been widely used for silencer analysis. However, they have limitations in analyzing large structures and mid-high frequency ranges due to unreasonable computational costs and errors. However, silencers used for ships and off-shore plants are much larger than those used in other engineering fields. Hence, energy governing equation, which is significantly efficient for systems with high modal density, is solved for silencers in ships and off-shore plants. The silencer is divided into two different acoustic media, air and absorption materials. The discontinuity of energy density at interfaces is solved via hypersingular integrals for the 3-D modified Helmholtz equation to analyze multi-domain problems with the energy flow boundary element method. The method is verified by comparing the measurements and analysis results for ship silencers over mid-high frequency ranges. The comparisons confirm good agreement between the measurement and analysis results. We confirm that the applied analysis method is useful for large silencers in mid-high frequency ranges. With the proven procedures, energy flow analysis can be performed for various types of silencer used in ships and off-shore plants in the first stage of the design.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.378-378
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• 2009

The ionic liquid-based sulfonated hydrocarbon composite membranes was prepared for use in anhydrous high temperature-polymer electrolyte fuel cells (HT-PEFCs). Ionic liquid behaves like water in the composite membranes under anhydrous condition. However the composite membranes show a low conductivity and high gas permeability as the content of ionic liquid increases due to its high viscosity and content of ionic liquid, respectively. Hence, in order to enhance the proton conductivity and to reduce the gas permeability of the composite membranes with low content of ionic liquids, the acid containing a common ion of ionic liquid was added to the composite membranes. The characterization of composite membranes was carried out using small-angle X-ray scattering (SAXS), thermogravimetric analyzer (TGA) and impedance spectroscopy. As a result, the composite membranes containing acid showed higher proton conductivity than those with no acid under the un-humidified condition due to a decrease in viscosity. In addition, the proton conductivity of composite membranes increased with increasing mole concentration of acid.

• Korean Journal of Materials Research
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• v.30 no.9
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• pp.458-464
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• 2020

Zinc-ion hybrid supercapacitors (ZICs) have recently been spotlighted as energy storage devices due to their high energy and high power densities. However, despite these merits, ZICs face many challenges related to their cathode materials, activated carbon (AC). AC as a cathode material has restrictive electrical conductivity, which leads to low capacity and lifetime at high current densities. To overcome this demerit, a novel boron (B) doped AC is suggested herein with improved electrical conductivity thanks to B-doping effect. Especially, in order to optimize B-doped AC, amounts of precursors are regulated. The optimized B-doped AC electrode shows a good charge-transfer process and superior electrochemical performance, including high specific capacity of 157.4 mAh g^-1 at current density of 0.5 A g^-1, high-rate performance with 66.6 mAh g^-1 at a current density of 10 A g^-1, and remarkable, ultrafast cycling stability (90.7 % after 10,000 cycles at a current density of 5 A g^-1). The superior energy storage performance is attributed to the B-doping effect, which leads to an excellent charge-transfer process of the AC cathode. Thus, our strategy can provide a rational design for ultrafast cycling stability of next-generation supercapacitors in the near future.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.467-472
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• 2020

The superconducting synchronous generator is one of the breakthrough elements for direct-drive wind turbines because it is light and small. Normally the superconducting one has copper armature windings in the stator and superconducting field windings on the rotor. The high resistance of the armature can make large copper losses, comparing with the conventional generators with a gear box. One of the solutions for the large copper losses could be a fully superconducting generator. But the high magnetic fields from the superconducting field windings on the rotor also make high perpendicular magnetic fields on the superconducting tapes in the armature windings. We have proposed a fully superconducting synchronous generator with dual field windings. It could immensely decrease the circumferential component of the magnetic field from the field windings at the armature windings. In this paper, we conceptually designed 3 types of superconducting synchronous generators. The first one is the fully superconducting one with conventional structure, which has superconducting armature windings in the stator and superconducting field windings on the rotor. The second one is the one with dual superconducting field windings and superconducting armature windings between them. The last one is the same as the third one except the structure of the armature. If the concentrated armature windings are superconducting ones with cryostats, then they cannot be installed within the span of 2 poles. So, we adopted 3 phases windings within 4 poles system. It makes more AC losses but can be manufactured really.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.2
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• pp.155-161
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• 2023

Recently, a study on alternative and renewable energy is being conducted due to energy depletion and environmental problems. In particular, a hydrogen has the advantage of converting and storing the remaining energy into water-electrolyzed hydrogen through renewable energy generation. In general, due to reasons such as insulation problems, a study on high-pressure hydrogen storage tanks and related parts has recently been conducted. However, in the case of liquid hydrogen, the volume can be reduced by about 800 times or more compared to high-pressure hydrogen gas, so the study on this is needed as a technology that can increase energy density. In this study, the evaporation characteristics were analyzed under fixed heat flux conditions for liquid hydrogen storage tanks and the change in thermal stratification according to sloshing was analyzed. The heat flux condition was fixed at 250 W/m² and the horizontal resonance frequency of the primary mode was applied to the storage tank. As a result, it was confirmed that the thermal stratification phenomenon decreased compared to the case where the slashing was not present due to forced convection when the slashing was present.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.812-818
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• 2024

The volume and toxicity of radioactive waste can be decreased by separating the components of high-level liquid waste according to their properties. An impregnated silica-based adsorbent was prepared in this study by combining N,N,N',N',N",N"-hexa-n-octylnitrilotriacetamide (HONTA) extractant, N',N'-di-n-hexyl-thiodiglycolamide (Crea) extractant, and macroporous silica polymer composite particles (SiO₂-P). The performance of platinum-group metals adsorption and separation on prepared (HONTA + Crea)/SiO₂-P adsorbent was then assessed together with that of co-existing metal ions by batch-adsorption and chromatographic separation studies. From the batch-adsorption experiment results, (HONTA + Crea)/SiO₂-P adsorbent showed high adsorption performance of Pd(II) owing to an affinity between Pd(II) and Crea extractant based on the Hard and Soft Acids and Bases theory. Additionally, significant adsorption performance was observed toward Zr(IV) and Mo(VI). Compared with studies using the Crea extractant, the high adsorption performance of Zr(IV) and Mo(VI) is attributed to the HONTA extractant. As revealed from the chromatographic experiment results, most of Pd(II) was recovered from the feed solution using 0.2 M thiourea in 0.1 M HNO₃. Additionally, the possibility of recovery of Zr(IV), Mo(VI), and Re(VII) was observed using the (HONTA + Crea)/SiO₂-P adsorbent.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.200-205
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• 2012

In the high oil price age, intensification of energy efficiency promotion in the building sector is required. Windows are dominating in large percent of whole building loads, and are regarding as the primary target of energy efficiency. In this study, in order to reduce heat loss of buildings, we investigate the thermal performance properties of Temperable Low-e glazing coated Ag membrane that has high electrical conductivity. The Temperable Low-e glazing windows has high insulation and shading properties, and it has strength that can supply various product which consumers want. In order to evaluate thermal performance of temperable windows, we install single low-e windows and double low-e windows in the experimental chamber and analysis the comparison heating energy consumption between single and double Low-e glazing windows. performance evaluation was conducted.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.99-106
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• 2009

The contents of transuranic elements ($^{237}Np$, $^{238}Pu$, $^{239}Pu$, $^{240}Pu$, $^{241}Am$, $^{244}Cm$, and $^{242}Cm$) in high-burnup spent fuel samples ($35.6{\sim}53.9\;GWd/MtU$) were determined by alpha spectrometry. Anion exchange chromatography and diethylhexyl phosphoric acid extraction chromatography were applied for the separation of these elements from the uranium matrix. The measured values of the nuclides were compared with ORIGEN-2 calculations. For plutonium, the measurements were higher than the calculations by about $2.6{\sim}32.7%$ on average according to each isotope, and those for americium and curium were also higher by about $35.9{\sim}63.1%$. However, for $^{237}Np$, the measurements were lower by about 52% on average for the samples.

• Nuclear Engineering and Technology
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• v.45 no.6
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• pp.821-826
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• 2013

In the present study, the effects of various heat treatments on the microstructure and mechanical properties of dual phase ODS steels were investigated to enhance the high strength at elevated temperature. Dual phase ODS steels have been designed by the control of ferrite and austenite formers, i.e., Cr, W and Ni, C in Fe-based alloys. The ODS steels were fabricated by mechanical alloying and a hot isostatic pressing process. Heat treatments, including hot rolling-tempering and normalizing-tempering with air- and furnace-cooling, were carefully carried out. It was revealed that the grain size and oxide distributions of the ODS steels can be changed by heat treatment, which significantly affected the strengths at elevated temperature. Therefore, the high temperature strength of dual phase ODS steel can be enhanced by a proper heat treatment process with a good combination of ferrite grains, nano-oxide particles, and grain boundary sliding.

• Laser Solutions
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• v.11 no.3
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• pp.5-9
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• 2008

The effect of a laser peening on the surface residual stress of SUS 304 was investigated using a second harmonic Nd:YAG laser beam. The energy density and the diameter of the laser beam were $400mJ/mm^2$ and about 1mm, respectively. According to the test results, the effect of a laser peening for improving the surface residual stress was not big enough to induce a high compressive stress on the SUS 304 surface. This is thought to be attributed to the small radius of the laser beam used in this study, even though its energy density is big enough. From this study, it can be concluded that to induce a recognizably high compressive stress on a metal surface, the energy density as well as the size (diameter) of the laser beam should be large enough to generate surface plasma with a high energy to have a big impact to a metal surface.