• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.3
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• pp.85-90
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• 2006

The purpose of this research is to design an imitation boiler similar to the waste heat boiler installed on a plasma melting furnace in order to acquire a capability of a thermal design as to the circulation of heat and the discharge of noxious gas inside a boiler and to improve the efficiency of a waste heat boiler using the CFD (Computation Fluid Dynamics) program. The position of corrosion and the generation of a clinker inside a boiler due to temperature changes, combustion gas flows, and corrosive gases inside a boiler are examined to design the structure of an efficient boiler and recycle energy. As a result of this research, the boiler installed on a plasma melting furnace met the conditions of design by cooling the combustion gases discharged after the second combustion from an exhaust port, originally at 1,200 degrees Celsius, down to around 450 degrees Celsius. On the other hand, the circulation of corrosive gases (SOx and HCL) may lead to the generation of corrosion or a clinker in the upper and lower parts of an exhaust port more easily than any other parts of a boiler. Accordingly, the corrosion on the inside and outside walls of a boiler may result in a shortened lifespan of a boiler and an inability to recycle waste heat in an efficient manner. A prevention against corrosion at high and low temperatures needs to be considered in detail.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.742-754
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• 2020

Zircaloy cladding oxidation is an important phenomenon for both design basis accident and severe accidents, because it results in cladding embrittlement and rapid fuel temperature escalation. For this reason during the last decade, many experts have been conducting experiments to identify the oxidation phenomena that occur under design basis accidents and to develop mathematical analysis models. However, since the study of design extension conditions (DEC) is relatively insufficient, it is essential to develop and validate a physical and mathematical model simulating the oxidation of the cladding material at high temperatures. In this study, the QUENCH-05 and -06 experiments were utilized to develop the best-fitted oxidation model and to validate the SPACE code modified with it under the design extension condition. It is found out that the cladding temperature and oxidation thickness predicted by the Cathcart-Pawel oxidation model at low temperature (T < 1853 K) and Urbanic-Heidrick at high temperature (T > 1853 K) were in excellent agreement with the data of the QUENCH experiments. For 'LOCA without SI' (Safety Injection) accidents, which should be considered in design extension conditions, it has been performed the evaluation of the operator action time to prevent core melting for the APR1400 plant using the modified SPACE. For the 'LBLOCA without SI' and 'SBLOCA without SI' accidents, it has been performed that sensitivity analysis for the operator action time in terms of the number of SIT (Safety Injection Tank), the recovery number of the SIP (Safety Injection Pump), and the break sizes for the SBLOCA. Also, with the extended acceptance criteria, it has been evaluated the available operator action time margin and the power margin. It is confirmed that the power can be enabled to uprate about 12% through best-estimate calculations.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1769-1785
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• 2021

The Integral Pressurized Water Reactors (IPWRs) as the innovative advanced and generation-III + reactors are under study and developments in a lot of countries. This paper is aimed at the thermal hydraulic study of the hot and average fuel sub-channel in a Generation III + IPWR by loose external coupling to the neutronic simulation. The power produced in fuel pins is calculated by the neutronic simulation via MCNPX2.6 then fuel and coolant temperature changes along fuel sub-channels evaluated by computational fluid dynamic thermal hydraulic calculation through an iterative coupling. The relative power densities along the fuel pin in hot and average fuel sub-channel are calculated in sixteen equal divisions. The highest centerline temperature of the hottest and the average fuel pin are calculated as 633 K (359.85 ℃) and 596 K (322.85 ℃), respectively. The coolant enters the sub-channel with a temperature of 557.15 K (284 ℃) and leaves the hot sub-channel and the average sub-channel with a temperature of 596 K (322.85 ℃) and 579 K (305.85 ℃), respectively. It is shown that the spacer grids result in the enhancement of turbulence kinetic energy, convection heat transfer coefficient along the fuel sub-channels so that there is an increase in heat transfer coefficient about 40%. The local fuel pin temperature reduction in the place and downstream the space grids due to heat transfer coefficient enhancement is depicted via a graph through six iterations of neutronic and thermal hydraulic coupling calculations. Working in a low fuel temperature and keeping a significant gap below the melting point of fuel, make the IPWR as a safe type of generation -III + nuclear reactor.

• Journal of the Korean Society of Food Science and Nutrition
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• v.31 no.5
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• pp.749-753
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• 2002

The effects of green tea powder (GTP) on the rheological properties of dough and gelatinization characteristics were evaluated by farinograph, extensograph, amylograph and DSC. The flours used were high strength flour (HF: 12.5% protein) and blend of 50% high strength flour and 50% low strength flour (HLF: 10.5% protein). As the amount of GTP increased, water absorption, development time and weakness of the dough decreased for both flours, but dough stability increased only for HLF; the extension of the dough decreased but the resistance to extension increased. The pasting temperature increased and maximum viscosity decreased. On the other hand, with the addition of green tea extract to the wheat starch, transition onset temperature, transition peak temper-ature and enthalpy decreased, demonstrating that catechins in green tea facilitate the starch crystal melting.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.811-818
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• 2020

Y-containing CLAM steels were melted via vacuum induction melting and electroslag remelting. In this study, the evolution, microstructure, and mechanical properties of the alloy inclusions (ESR-1 (0 wt.% Y), ESR-2 (0.016 wt.% Y) and ESR-3 (0.042 wt.% Y)) were investigated. Further, the number of inclusions in ESRed steel was observed to obviously decrease, and the distributions were more uniform. The fine Y-Al-O inclusions (1-2 ㎛) were the main inclusions in ESR-2. The addition of Y affected the prior austenite grain size (PAGZ), increasing the tensile strength at test temperature. Low ductile-brittle transition temperature (DBTT) was obtained because of the fine PAGZ and dispersive inclusions. For the ESRed CLAM steel with 0.016 wt.% Y, the yield strengths were 621 MPa at 20 ℃ and 354 MPa at 600 ℃ in air. Further, the uniform elongation and elongation of the ESR-2 alloy were 5.5% and 20.1% at 20 ℃, respectively. Meanwhile, the DBTT tested using full-size Charpy impact specimen (55 cm × 10 cm × 10 cm) was reduced to -83 ℃.

• Journal of Magnetics
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• v.20 no.4
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• Journal of Magnetics
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• v.19 no.3
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• pp.205-209
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• 2014

$MnBi_{1-x}Ti_x$ (x = 0, 0.4, 0.7, 1) alloys were prepared by arc-melting, followed by heat treatment. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to measure and investigate the phase structure and magnetic properties. The temperature dependent magnetization curves indicate that the phase transitions between LTP and HTP MnBi occur with heating or cooling in $MnBi_{1-x}Ti_x$ ($x{\leq}0.7$) samples. However, MnTi samples are in $Mn_2Ti$ single-phase, with very low magnetic properties. Furthermore, the coercivity exhibits a positive temperature coefficient. The results show that the optimal content of Ti for the coercivity of $MnBi_{1-x}Ti_x$ alloy is x = 0.4. For MnBi sample, the coercivity reaches a maximum value of 1.13 T at 550 K. However, the remanence and energy product show apparent decrease with the addition of Ti in $MnBi_{1-x}Ti_x$ alloys.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.45-50
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• 2000

We have investigated the influence of columnar defects (CD) on the vortex dynamics in pristine and iodine-intercalated Bi$_2$Sr$_2$CaCu$_2$O$_{8+{\delta}} single crystals from do SQUID magnetization measurements. Especially, the temperature dependence of the irreversibility fields, H$_{irr}$(T), were studied. Anisotropy ratio ${\gamma}$, estimated from the fitting to the 2-dimensional melting model (A. Schilling et al., Phys. Rev. Lett. 71 1899 (1993)) in higher fields than the matching field B$_{\phi}$ at low temperature region, turns out to be decreased by the iodine-intercalation and additionally by the heavy-ion irradiation.

• Journal of the Korean Chemical Society
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• v.15 no.5
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• pp.256-265
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• 1971

An ESR study has been made on free radicals produced in frozen aqueous solutions (ices) of glycine, DL-${\alpha}$-alanine, DL-serine, L-cysteine, DL-leucine and DL-isoleucine by gamma-irradiation at dry ice temperature. All free radicals induced were decayed concomitant to the successive annealing but the radical species which is believed to be dominant seems to be stable even near the melting point of the ice. These dominant species were found to be identical to those resulted from direct action of radiation in the solid at room temperature. Small but significant changes in the spectra of glycine and DL-${\alpha}$-alanine were observed by varying the microwave power. These results seem to support the view that the spectra obtained were composite consisting of more than two different resonances having different power saturation characteristics. The relative contribution of unidentified resonances to the composite spectra was greater for solutions of low concentration. These resonances are assumed to be induced by indirect effects, mainly hydrogen abstraction by radiation produced hydroxyl radicals and also C-N bond cleavage by hydrated electrons.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.90-96
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• 2014

The conventional SnPb solders were widely used for several decades in the electronic packing system due to the superior mechanical properties such as low melting point, better wettavility and good mechanical fatigue. However, in recent years, owing to adverse effect on the human health and environment, conventional SnPb solders have been replaced by Lead-free solders. In this research, the shear punch(SP) test of Sn-4Ag-(Cu)/Ni pad was performed. Pb-free solder alloys which are the environmentally friendly of the electronic components were performed at $150^{\circ}C$ for 100hr~1000hr to artificial aging processing. In order to evaluate the mechanical properties of solder joints, the SP test was conducted at $30^{\circ}C$ and $50^{\circ}C$. As a result, the maximum shear strength of almost the whole specimens was decreased with the increase in aging time and temperature of SP test. The mechanical properties of Sn-4Ag-0.5Cu solder were most excellent in all Pb-free solder which were produced by the SP test at $30^{\circ}C$.