• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.856-866
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• 1987

In the present paper a statistical method using probability density function has been applied to investigate experimentally the flow patterns and fluctuations of time-averaged local void fraction in air-water two-phase mixtures which flow vertically upwards in concentric annuli. This study was carried out using three vertical concentric annuli. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel inner rod. The rod diameter is either 12mm, 16mm or 20mm. The two-phase flow patterns observed in the experiment were bubbly, slug, annular and each transition patterns. It was first demonstrated that the variance, coefficients of skewness and kurtosis calculated from probability density function on time-averaged local void fraction can be used to identify the flow patterns in the annular passage, and the fluctuation of time-averaged local void fraction varies with the radial position in annular gap and the flow pattern.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.2005-2006
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• 2011

Due to the advantages of small sizes, more I/O ports, etc., Ball Grid Array (BGA) has been used in the production of printed circuit board (PCB). However, BGA voids can degrade the performance of the board and cause failure. To automatically detect the voids in X-ray image, a novel blob filter that makes use of the local image gradient magnitude is proposed in this paper. The utilization of the local image gradient magnitude makes the proposed filter invariant to the image brightness, void shape, void position, and component interference. Furthermore, different sizes of box filters are employed to analyze the image in multi-scale, and as a result, the proposed blob filter is robust to void size. Experimental results show that the proposed method can obtain void detection accuracy up to 96.104% while keep low false ratio.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.1
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• pp.28-33
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• 2015

The needle electrode is inserted into the cross-linked polyethylene(XLPE) which is the ultra high voltage cable for electric power. By changing the tilt of the needle electrode, we investigated how the void and the thickness of the insulating layer influence the partial discharge(PD) characteristics and the insulating breakdown. In order to investigate the PD characteristics, The XLPE cable was used to the specimens and the tungsten electrode was used with the needle electrode. And the inner semi-conductive layer material of XLPE cable was used with the negative electrode by bonding with the use of conduction tape. The size of the specimens was manufactured to be $16{\times}40{\times}30[mm^3]$. We confirmed the effect on changing the PD characteristics according to the changing voltage and the tilt of the electrode after applying the voltage on the electrode from 1[kV] to 40[kV] at room temperature. In the PD characteristics, it was confirmed that the PD current of air void specimens with tilt was unstable more than that of no void specimens with tilt. It was also confirmed that the breakdown voltage was decreased because the effect of air void is more active than the change of the needle electrode tilt in the specimen with air void inside the insulation.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.51-61
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• 2013

This paper presents results from a study undertaken to quantitatively evaluate the geotextile pore sizes using optical image analysis. The evaluation was conducted by observing surfaces of coupons cut from resin-impregnated specimens of geotextile-geomembrane layered under various load conditions. Stereological concepts were applied to collect representative specimens from a series of laboratory tests. The sizes of voids enclosed by filaments were expressed in terms of the largest inscribing opening size (LIOS) distribution. The opening diameter corresponding to the 50% cumulative frequency decreased by about 45mm as the load increased from 10 to 300kPa and recovered to about 90% of its initial state on unloading back to 10kPa. The average void size was reduced by 32 and 16.5% as the geotextile was sheared against a textured geomembrane under normal stresses of 100 and 300kPa, respectively. The results showed how the LIOS distribution varied as a function of normal stress and interface shear displacement against a smooth and a textured geomembrane surfaces.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3E
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• pp.69-76
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• 2008

Measurements of bubble size and distribution in the surface layer of the sea, wind speed, and variation of ocean environments were made continually over a four-day period in an experiment conducted in the South Sea of Korea during 17-20 September 2007. Theoretical background of bubble population model indicates that bubble population is a function of the depth, range and wind speed and bubble effects on sound speed shows that sound speed varies with frequency. Observational evidence exhibited that the middle size bubble population fit the model very well, however, smaller ones can not follow the model probably due to their short lifetime. Meanwhile, there is also a hysteresis effect of void fraction. Observational evidence also indicates that strong changes in sound speed are produced by the presence of swarms of micro bubbles especially from 7 kHz to 50 kHz, and calculation results are consistent with the measured data in the high frequency band, but inconsistent in the low frequency band. Based on the measurements of the sound speed and high frequency transmission configuration in the bubble layer, we present an estimation of underwater acoustic channel capacity in the bubble layer.

• Journal of the Korean Ceramic Society
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• v.55 no.4
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• pp.352-357
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• 2018

The slip casting process is widely used to make green bodies from ceramic slips into dense compacts with homogeneous microstructure. However, stress may be generated inside the green body during drying, and can lead to cracking and bending during sintering. When starting from the spherical powders with mono-size distribution to make the close packed body, interstitial voids on octahedral and tetrahedral sites are formed. In this research, experiments were carried out with powders of three size types (host powder (H), octahedral void filling powder (O) and tetrahedral void filling powder (T)) controlled for average particle size by milling from two commercial alumina powders. Slips were prepared using three different powder batches from H only, H+O or H+O+T mixed powders. After manufacturing green compacts by solid-casting, compacts were dried at constant temperature and humidity and sintered at $1650^{\circ}C$. Alumina samples fabricated from the multi-sized powder mixture had improved compacted and sintered densities.

• Korean Journal of Agricultural Science
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• v.33 no.2
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• pp.167-177
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• 2006

This study was performed to evaluate void ratio, compressive and flexural strength, and pH properties according to the admixture ratio of rice husk ash, aggregate size, and neutral treatment time of porous concrete with an admixture of rice husk ash produced as an agricultural by-product. The SEM results for cement mortar with a 5% rice husk ash admixture for the weight of cement formed more C-S-H hydrates due to the $SiO_2$ present in the applied rice husk ash. According to the results of the SEM test, the $SiO_2$ that was a major chemical element of rice husk ash generated a large amount of calcium hydroxide in the early stage of the hydration process of cement leading to the formation of ettringite. The void ratio of porous concrete with an admixture of rice husk ash decreased with increasing admixture ratio of rice husk ash. In addition, the void ratio of porous concrete with an admixture of rice husk ash decreased compared to porous concrete with no admixture of rice husk ash. The compressive and flexural strength of porous concrete with a 5% and 10% admixture ratio of rice husk ash slightly increased compared to concrete with no admixture of rice husk ash. The pH value of porous concrete rapidly decreased immediately after neutral treatment. Then, it gradually increased and decreased again after 14 days. Also, for neutral treatment, the pH value of porous concrete showed appropriate pH levels(less than 9.5) in all mixtures for planting at 28 curing days.

• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.3
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• pp.81-89
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• 1984

To examine the moisture adsorption and permeability characteristics, weathered granite soils of different degrees of weathering, cultivated upland soils and sands of Han-river were sampled. The results are as follows: 1. In case that the mother rock was same, the pF values under same moisture content decreased according as the grain size of soil became finer by the weathering process. 2. In case that the mother rock was different, the pF value varied by the behavior of clay minerals, and the cultivated upland soils showed more sensitive reaction than sands and fresh granite soils. 3. The pF value changed by the difference of primary moisture content and also influenced by soil structure, testing method and etc. 4. The pF value and compaction curve had close relation, however under same moisture content, the pF value decreased by the increment of density. 5. The permeability depend on the available void ratio between the soil particles according to the degree of weathering, and the pF value of available void water between the soil particles which related directly to permeability was about 3.3 except the void water holded in the soil particles. 6. As the above, the pF value and permeability were differentiated by degree of weathering, primary moisture content, density and etc. Therefore it is considered unreasonable to define uniformly by soil texture.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1131-1136
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• 2020

Xenon behaves differently in molten salt reactors (MSRs) compared to solid fuel reactors. This behavior needs exploring due to the large reactivity effect of the ¹³⁵Xe isotope, given the current interest in MSR power plant development for commercial deployment. This paper focuses on select topics in xenon transport, reviews relevant past works, and proposes specific research questions to advance the state of the art in each of the focus areas. Specifically, the paper discusses the issue of xenon solubility in MSRs, the behavior of particulates circulating in MSR fuel salt and its influence on the xenon transport, the possibility of ionization of xenon atoms which changes its effective size and thus affects its mass transport, and finally the issue of circulating void fraction and how it is measured. This work presents specific recommendations for MSR designers to research the limits of Henry's law validity, circulating particulate scrubbers, validity of mass transport coefficients in high radiation fields, and the effects of pump speed on circulating void fraction.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.4
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• pp.484-492
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• 2015

The purpose of this study is to compare the ichthyofauna between the eelgrass bed waters located in the open sea and the nearby sea free of eelgrass, and this study collected a total of 26 species. Comparing the fish collected on the eelgrass bed (St.2) of Geomun-do coast with the fish collected on the coastal waters (St.1) void of the nearby eelgrass bed, the fish collected from the eelgrass bed included 19 species, 413 individual with 16,110.6g in weight while the fish collected from the coastal waters void of the eelgrass bed included 19 species, 290 individuals with 12,961.5g in weight. Accordingly, it was found that the population size and biomass of the fish collected from the eelgrass bed were higher than the coastal waters void of the eelgrass. This study could identify that diversity, richness, evenness index except dominance were also much higher even in the result of cluster analysis.