• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.5
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• pp.384-393
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• 1998

A mixed powder of electrolyte and matrix support materials with a proper proportion was used for the fabrication of an electrolyte matrix sheet. The purpose of this study is to reduce the large change in MCFC cell thickness occurring in the initial start-up period when separate sheets of electrolyte and support are used. A focus was put on how small the carbonate particles could be made. The particle size of the carbonate powder was controlled by ball milling and the distribution was measured using a particle size analyser. The thickness change was reduced to 20% by this approach, which could be compared to 27% observed in a conventional cell. The thickness changes of electrolyte matrix have linear relation sizes of carbonate powders.

• Elastomers and Composites
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• v.56 no.1
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• pp.12-19
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• 2021

The abrasion behaviors of NR/BR blend vulcanizates were investigated using NR/BR = 100/0, 80/20, and 60/40 compounds. The abrasion test was performed using a laboratory abrasion tester (LAT) at slip angles of 1° and 7°. The size distributions of the wear particles and the abrasion rates were examined according to the rubber compositions and slip angles. The most abundant wear particles at the slip angle of 1° were sizes above 1,000 ㎛, irrespective of the rubber composition. The most abundant wear particles at 7° slip angle had sizes in the range of 212-500 ㎛, except for the NR = 100 sample. The wear particle size distribution shifted to a smaller size as the slip angle and BR content increased. The abrasion rate at 7° was much larger than that at 1° slip angle. Furthermore, the abrasion rate was notably increased by adding BR to NR.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.717-721
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• 2005

Silica powders were synthesized using emulsion solution containing water, nonionic surfactant of Triton N-57, and cyclohexane. Silica powders were prepared at low cost using inexpensive starting material of sodium silicate and ammonium sulfate. Morphology, size and size distribution were observed and determined using SEM. The powder was identified as silica by FT-IR and XRD analysis. Particle size and size distributions were affected by concentration of reactants, reaction time, and concentration of surfactant. Particle size were increased with increasing concentration of reactants and particles became dense with increasing reaction time. As R value increased, tile particle size was increased, reached a certain value and then decreased again. The silica powders synthesized under optimum condition were spherical in shape, $0.8{\mu}m$ in average particle size, narrow in particles size distribution, and well dispersed.

• Nuclear Engineering and Technology
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• v.31 no.1
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• pp.29-48
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• 1999

Local two-phase flow parameters of subcooled flow boiling in inclined annulus were measured to investigate the effect of inclination on the internal flow structure. Two-conductivity probe technique was applied to measure local gas phasic parameters, including void fraction, vapor bubble frequency, chord length, vapor bubble velocity and interfacial area concentration. Local liquid velocity was measured by Pilot tube. Experiments were conducted for three angles of inclination; 0$^{\circ}$(vertical), 30$^{\circ}$, 60$^{\circ}$. The system pressure was maintained at atmospheric pressure. The range of average void fraction was up to 10% and the average liquid superficial velocities were less than 1.3 m/sec. The results of experiments showed that the distributions of two-phase How parameters were influenced by the angle of channel inclination. Especially, the void fraction and chord length distributions were strongly affected by the increase of inclination angle, and flow pattern transition to slug flow was observed depending on the How conditions. The profiles of vapor velocity, liquid velocity and interfacial area concentration were found to be affected by the non-symmetric bubble size distribution in inclined channel. Using the measured distributions of local phasic parameters, an analysis for predicting average void fraction was performed based on the drift flux model and flowing volumetric concentration. And it was demonstrated that the average void fraction can be more appropriately presented in terms of flowing volumetric concentration.

• Bulletin of the Society of Naval Architects of Korea
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• v.9 no.2
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• pp.21-32
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• 1972

The problems of thermal stress and residual stress in resistance spot welding are studied from two standpoint namely, effect of temperature distributions and effect of the radius of free boundary. The radius of the region where the temperature distributions are occured is taken as a function of time after welding and as a finite size, 6 times of heated zone. The region of the radial stress distribution is treated as a function of time under Saint-Venant's principle and 6 or 12 times of originally heated zone. Thermal stresses and strains are obtained by analytic solution under constant mechanical properties and by the finite difference method for varing properties under temperature variation. From the computed results following conclusions are derived (1) For the engineering purpose, the region of temperature distribution and stress distribution can be treated as a finite region, $R=r_o=6r_e$ (2) If the maximum temperature of the aluminum alloy plate is less than $500^{\circ}F$, thermal stresses and strains can be obtained with constant mechanical properties. (3) The residual stresses and strains will be remained in welds and its vicinity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.5
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• pp.418-423
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• 2003

AC loss is an important issue in the design of high-T$\sub$c/ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. So special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The critical current and AC loss characteristics in the conductor have experimentally investigated. The results show that for uniform current distributions the conductor's critical current is proportional to the critical current of the Bi-2223 tape to which a voltage lead is attached. However it depends on the current non-uniformity parameter in the conductor rather than the tape's critical currents for nonuniform current distributions. The loss tests indicate that the AC loss is dependent on arrangements of voltage leads but not on their contact positions. The measured losses in the conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.18-22
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• 2004

The Fire Dynamics Simulator (FDS) was applied to a center fire in a room, of which dimensions were 1.8m${\times}$1.38m with an opening of 0.45m${\times}$1.2m doorway, to evaluate the numerical method. The time-variation of temperature at a top point of thedoorway centerline and distributions of evaluate the numerical method. The time-variation of temperature at a top point of the doorway centerline and distributions of average temperature along the doorway centerline and corner stack were compared with measurements for three different fire sizes, 7.65, 21.25 and 51.71kW. The results showed FDS predicted a very rapid fire growth compared with the experiment for all the three fire sizes, that is an importand shortcoming of FDS in compartment fire simulations. The average temperature distributions, and heights of hot gas layers and neutral planes in steady state were in reasonable agreement with the measurements.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.7 no.2
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• pp.196-208
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• 1997

This study was performed to estimate quartz contents in the both bulk and airborne dust samples and to determine particle size distribution of airborne dust from the selected foundry operations. Total dust samples were collected by a 37mm cassette and respirable by a 10 mm nylon cyclone. Particle size distributions were determined by a Marple's 8-stage cascade impactor at the melting, molding, shakeout and finishing operations. The presence of elements in the dust samples were confirmed by the scanning electron microscopy equipped with the energy dispersive x-ray spectrometry. The quartz contents were estimated using the intensity of the absorption peak of quartz at 799 cm-l by the Fourie Transformed Infrared Spectroscopy (FTIR). The results were as follows: 1. The analysis of data from cascade Impactor showed bimodal distributions of particle size at the melting, molding and shakeout operations. Mass median aerodynamic diameters for the distributions determined by histogram were $0.48-1.65{\mu}m$ for small and $13.43-19.58{\mu}m$ for large modes. In the dust samples collected at the finishing operations, however, only a large mode of $18.89{\mu}m$ was found. 2. The percentages of total to respirable dust concentration calculated from the impactor data ranged from 42 % to 66 %. The average concentrations of respirable dust by cyclone were $0.85-1.28mg/m^3$ collected from the workers, and were $0.23-0.56mg/m^3$ from the areas surveyed. Dust concentrations of personal samples were statistically significantly higher than those of area samples. The highest dust concentration was obtained from the personal samples of the finishing operation. 3. The mean percentages of silicon and oxygen estimated by SEM-EDXA in the bulk samples ranged from 35.83 % to 36.02 % and from 39.93 %-41.64 %, respectively. 4. The average quartz contents estimated by FTIR in the respirable dust from personal samples ranged from 4.32 % to 5.36 % and 4.54 % to 4.70 % in the bulk samples. No statistical difference of quartz content was found between foundry operations. In this study, quartz content was quantified by FTIR. Although no statistically significant difference in quartz content between airborne and bulk, samples and between different foundry operations was found, it is recommended that quartz content in the individual sample of respirable dust be analyzed and the results be used either to select an applicable quartz limits or to calculate the exposure limit. Further studies, however, are needed to compare the results by FTIR and XRD since it is reported that the quartz content determined by FTIR is different from that by XRD.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.380-391
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• 1997

A numerical study has been done on the evolution of particle size distribution in particle laden high temperature jet flows undergoing convection, diffusion, thermophoresis and coagulation. The dynamic behavior of these particles have been modelled by approximating the particle size distribution by a lognormal function throughout the process and the moments of the particle size distribution have been used to solve the general dynamic equation. The size distributions of spherical particles in the radial and axial direction have been obtained including the effect of buoyancy. Of particular interests are the variations of geometric mean diameter, number concentration and polydispersity. Results show that buoyancy significantly alters the size distribution in both axial and radial direction. One dimensional analysis for non-spherical particles has also been done and the results have been compared with the existing experimental data.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.360-365
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• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.