• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3207-3216
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• 2021

Three-dimensional structures of a vortical flow field and heat transfer characteristics in a partially blocked 7-pin fuel assembly mock-up of sodium-cooled fast reactor have been investigated through a numerical analysis using a commercial computational fluid dynamics code, ANSYS CFX. The simulation with the SST turbulence model agrees well with the experimental data of outlet and cladding wall temperatures. From the analysis on the limiting streamline at the wall, multi-scale vortexes developed in axial direction were found around the blockage. The vortex core has a high cladding wall temperature, and the attachment line has a low cladding wall temperature. The small-scale vortex structures significantly enhance the convective heat transfer because it increases the turbulent mixing and the turbulence kinetic energy. The large-scale vortex structures supply thermal energy near the heated cladding wall surface. It is expected that control of the vortex structures in the fuel assembly plays a significant role in the convective heat transfer enhancement. Furthermore, the blockage plate and grid spacer increase the pressure drop to about 36% compared to the bare case.

• Journal of Hydrogen and New Energy
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• v.33 no.4
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• pp.451-461
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• 2022

CFD analysis including optimization process was conducted to design shell and tube CO₂ methanation reactor cooling system. The high-pressure saturated water flowed into the cooling system and was evaporated by heat flux from reacting tubes. The optimization process decided the gap between tubes and reactor diameter to satisfy objective functions related to temperature. The results showed that the gap and diameter reduced about 30% and 3.6% respectively. Averaged surface temperature satisfied the target value and the min-max deviation was minimized.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4215-4219
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• 2022

The Cd_0.95Mn_0.05Te_0.98Se_0.02 (CMTS) ingot was grown by the vertical Bridgman technique at low pressure. All wafers showed high resistivity, which suggests potential as a room-temperature semiconductor detector. The resistivity of the CMTS planar detector was 1.47 × 10¹⁰ Ω·cm and mobility lifetime product of electrons was 1.29 × 10^-3 cm²/V. The spectroscopic property with Am-241 and Co-57 was evaluated. The energy resolution about 59.5 keV gamma-ray of Am-241 was 11% and the photo-peak of 122 keV gamma-ray from Co-57 was clearly distinguished. The result shows the first detector-grade CMTS in the world and proves CMTS's potential as a radiation detector operating at room temperature.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.1-4
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• 2023

Recently, a claim of material, named LK-99 (a lead apatite-based compound), exhibiting a superconducting transition temperature of over 400 K under standard atmospheric pressure, was reported [1, 2]. This claim has generated considerable attention from scientists worldwide. Here, we synthesized five LK-99 samples following the method detailed in the original papers [1, 2], and measured structural and resistivity data for each of these samples. The structure of the synthesized samples (P6₃/m, a=9.82 Å , c=7.34 Å ) was very close to the reported one. Contrary to the report, however, no hint of room-temperature superconductivity was noted from any of the samples. The results of Energy-dispersive X-ray spectroscopy (EDXS) measurements demonstrate that the atomic distribution in the sample was inhomogenous, and unreacted precursors were included in the samples. To investigate the intrinsic superconducting properties of LK-99, we propose to synthesize samples having high structural purity and chemical uniformity.

• Journal of Aerospace System Engineering
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• v.17 no.5
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• pp.11-18
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• 2023

The architecture of the Fuel Thermal Management System (FTMS) in a commercial aircraft engine was built to model and simulate the fuel system. The study shows the thermal interactions between the fuel and engine lubrication oil through the mission profile of a high bypass ratio, two-spool turbofan engine. Fuel temperature was monitored as it flowed through each sub-component of the fuel system during the mission. The heat load in the fuel system strongly depended on the fuel flow rate, and was significantly increased for the periods of cruise and descent with decrease of fuel flow rate, rather than for the periods of take-off. Due to the thermal interaction in the pump housing, the fuel temperature at the outlet of the low-pressure pump was increased (4.0, 9.2, and 30.0) % over the case without thermal interaction for take-off, cruise, and descent, respectively.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3961-3968
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• 2024

The Korea Atomic Energy Research Institute (KAERI) is developing a novel Two-Region Arc Plasma Ion Source (TRAP) as a negative hydrogen (deuterium) ion source for a Neutral Beam Injection (NBI) system in a fusion tokamak. The TRAP ion source is based on a two-region configuration, comprising a high energy electron region that creates highly vibrationally excited molecules and a low electron temperature region that generates negative ions by attaching electrons to molecules. This configuration can be achieved by optimizing the filament position and magnetic cusp field. In order to optimize the TRAP configuration, the plasma parameters are investigated under various operating conditions, such as filament position, gas pressure, and arc power. Electron density and temperature are determined using Langmuir probe measurements. In this paper, the detailed experimental results are described and discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.451-464
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• 2014

This study used numerical methods to investigates investigate the exhaust gas recirculation (EGR) effect under the condition of boost pressure condition on a homogeneous charge compression ignition (HCCI) combustion engine using numerical methods. The detailed chemical-kinetic mechanisms and thermodynamic parameters for n-heptane, iso-octane, and PRF50 from the Lawrence Livermore National Laboratory (LLNL) are were used for this study. The combustion phase affects the efficiency and power. To exclude these effects, this study decided to maintain a 50 burn point (CA50) at 5 CA after top dead center aTDC. The results showed that the EGR increased, but the low temperature heat release (LTHR), negative temperature coefficient (NTC), and high temperature heat release (HTHR) were weakened due by theto effect of the O2 reduction. The combined EGR and boost pressure enhanced the autoignition reactivity, Hhence, the LTHR, NTC, and HTHR were enhanced, and the heat-release rate was increased. also In addition, EGR decraeased the indicated mean effective pressure (IMEP), but the combined EGR and boost pressure increased the IMEP. As a results, combining the ed EGR and boost pressure was effective to at increase increasing the IMEP and maintaining the a low PRR.

• Membrane Journal
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• v.13 no.4
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• pp.246-256
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• 2003

For the olefin recovery from polyolefin off-gas, the permeation behaviors of olefins and nitrogen were investigated through three kinds of PDMS membranes - cross-linked PDMS membranes, a polysiloxaneimide membrane, and oligo-PDMS modified PDMS membranes. Their pure gas permeabilities were measured as a function of operation temperature(-20 to $50^{\circ}C$) and pressure(1 to 25 atm) with ethylene($C_2\;H_4$), propylene($C_3\;H_6$), butylene($C_4\;H_8$), and nitrogen($N_2$) gases. The permeabilities of olefins and nitrogen highly depended upon the nature of PDMS membranes. Among these membranes, cross-linked PDMS membranes showed stable and high olefin/nitrogen selectivities over a wide operation pressure range and further study in various test conditions. Their permeability of olefin and nitrogen were governed by the condensation temperature(solubility selectivity) and plasticization, not the order of the size(diffusivity selectivity) of gases, which matched well with the general permeation behavior of rubbery polymeric membranes for condensable and non-condensable gases. With increasing feed pressure or decreasing feed temperature, the permeabilities of more condensible olefins increase highly, presumably due to high solubility and plasticization, but that of non-condensible nitrogen decreases slightly and thus, the selectivities of olefin/nitrogen increase highly.

• Journal of the Korean earth science society
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• v.34 no.1
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• pp.28-40
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• 2013

This study examined the geochemical characteristics, equilibrium temperature and pressure conditions, and oxygen isotopic ratios of mantle xenoliths from the various geological sites of the Korean peninsula. The results are as follows: (1) The ultramafic xenoliths from the Korean peninsula mainly consist of typical high magnesium olivine (MgO : 49.12-50.95 wt.%, Mg value: 90.1-92.2), corresponding to worldwide Cenozoic ultramafic xenoliths in chemical compositions. (2) The pressure-temperature conditions of ultramafic xenoliths in the Korean peninsula are from 854 to $1016^{\circ}C$ and 4.6 to 24.4 kbar. (3) The oxygen isotopic ratios (${\delta}^{18}O$) for olivines in ultramafic xenoliths range from 5.06‰ to 5.51‰, which are relatively uniform oxygen isotopic values and overlapped by the values of N-MORB and upper mantle peridotite (${\delta}^{18}O$: $5.2{\pm}0.2$‰). However, olivines of the ultramafic xenoliths from the Baegdusan and Chejudo have a relatively wide ${\delta}^{18}O$ values ranging from 5.07 to 5.51‰ and 5.07 to 5.45‰, respectively. Based on the results, this study suggests that the high ${\delta}^{18}O$ signature of the Baegdusan xenoliths give a hint that ~5% of the oxygen in typical EM2 sources originally derived from recycled sediments.

• Korean journal of food and cookery science
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• v.23 no.5
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• pp.635-643
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• 2007

This study was carried out to investigate the quality of cooked rice prepared by-an electric pressure cooker (EPC) and an electric cooker (EC) during storage at different temperatures. Four rice cultivars were used (Ilpoom, Saechucheong, Sindongjin, and Sura). The cooked rice samples were stored at room and warm temperatures for 48 hr, and at refrigerator temperatures for 10 days. Immediately after cooking, the moisture content of the EPC rice was lower than that of the EC rice; yet pH was higher for the EPC rice. The L-value of the EPC rice was reduced due to an increasing b-value. The overall acceptability of the EPC rice was high; in particular, it scored high for a roasted nutty flavor and texture. During storage, moisture content and pH decreased regardless of the cooking method. L-, a- and b-values were similar at room and refrigerator temperatures over the entire period, whereas the a-value (greenness) of the EC rice stored at warm temperature slightly decreased and the b-value (yellowness) increased after 24 hr, resulting in a decreasing L- value. Also, sensory characteristics were not significantly different for the samples stored at room temperature for 48 hr; however, at warm and refrigerator temperatures, the sensory characteristics were significantly different after 24 hr and 3 days, respectively. In conclusion, the quality of the cooked rice was effectively preserved during storage at room temperature, and qualify deterioration oaf dependent on using warming equipment as well as the rice cultivar.