• Journal of environmental and Sanitary engineering
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• v.11 no.3
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• pp.29-35
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• 1996

Numerical solutions were obtained to the model equations for various parameters characterizing the pore structure, effective internal diffusion and the chemical reaction constant. The conversion was decreased with the cause of pore closure at the surface of reacting particles, reduction of porosity, surface area of reaction and effective diffusion coefficient in the solid with the progress of reaction. Total conversion was strongly depend on the local conversion at surface. According to the decreasing of impregnated concentration of the copper oxide and the increase of the flue gases concentration, total conversion was increased. And the conversion were affected by gas flow rate and pore size distribution of the reacting solid.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.2
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• pp.159-169
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• 2004

Sedimentation and depositional pattern of the fine-grained sediments in the southeastern inner shelf of Korea were studied using a very high-resolution seismic profiles and sediment data. The recent mud deposits up to 45 m thick are distributed in the inner shelf forming a nearshore belt from the eastern part of Geoje Island to off the Pohang along the coast. The sediment in this area consists of homogeneous mud with mean grain size between $8.6\;to\;5.3\phi$ and does not show any distinct variability It gradually becomes finer and well sorted northeastward along the coast. Sediments normally appear as structureless massive mud but X-radiographs show that some bioturbation and faint lamination are present. The sediments accumulate at a rate of 0.18-0.44 cm/yr and the rate coincides well with the long-term (a 1000-year scale) accumulation based on very high-resolution seismic data. Distribution of wet bulk density and velocity shows a gradual increase from the southeastern part of Ulsan to off Pohang, whereas porosity shows a reverse pattern. Correlations between velocity and porosity/mean grain size are different from other regions compared, due to the difference of sediment texture and sedimentary environment. The recent shelf deposits are seismically characterized by three distinct facies: 1) well-stratified (near the river mouth), 2) semi-transparent (eastern part of Geoje Island), and 3) transparent (off Ulsan). The results suggest that fine-grained sediment derived from rivers, forming a nearshore mud belt, have been transported northeastward by the northeastward-flowing coastal current.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.457-469
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• 2016

During the late phase of severe accidents of light water reactors, a porous debris bed is expected to develop on the bottom of the flooded reactor cavity after breakup of the melt in water. The geometrical configuration, i.e., internal and external characteristics, of the debris bed is significant for the adequate assessment of the coolability of the relocated corium. The internal structure of a debris bed was investigated experimentally using the DAVINCI (Debris bed research Apparatus for Validation of the bubble-Induced Natural Convection effect Issue) test facility. Particle sedimentation under the influence of a two-phase natural convection flow due to the decay heat in the debris bed was simulated by dropping various sizes of particles into a water vessel with air bubble injection from the bottom. Settled particles were collected and sieved to obtain the particle mass, size distribution in the radial and axial positions, and the bed porosity and permeability. The experimental results showed that the center part of the particle bed tended to have larger particles than the peripheral area. For the axial distribution, the lower layer had a higher fraction of larger particles. As the sedimentation progressed, the size distribution in the upper layers can shift to larger sizes because of the higher vapor generation rate and stronger flow intensity.

• Ocean and Polar Research
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• v.32 no.2
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• pp.145-156
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• 2010

This study investigated organic carbon fluxes in Ulleung Basin sediments, East Sea based on a chamber experiment and geochemical analyses. At depths greater than 2,000 m, Ulleung Basin sediments have high organic carbon contents (over 2.0%). Apparent sedimentation rates (ASR) calculated from excess $^{210}Pb$ activity distribution, varied from 0.036 to $0.047\;cm\;yr^{-1}$. The mass accumulation rates (MAR) calculated from porosity, grain density (GD), and ASR, ranged from 131 to $184\;g\;m^{-2}\;yr^{-1}$. These results were in agreement with sediment trap results obtained at a water depth of 2100 m. Input fluxes of organic carbon varied from 7.89 to $11.08\;gC\;m^{-2}\;yr^{-1}$ at the basin sediments, with an average of $9.56\;gC\;m^{-2}\;yr^{-1}$. Below a sediment depth of 15cm, burial fluxes of organic carbon ranged from 2.02 to $3.10\;gC\;m^{-2}\;yr^{-1}$. Within the basin sediments, regenerated fluxes of organic carbon estimated with oxygen consumption rate, varied from 6.22 to $6.90\;gC\;m^{-2}\;yr^{-1}$. However, the regenerated fluxes of organic carbon calculated by subtracting burial flux from input flux, varied from 5.87 to $7.98\;gC\;m^{-2}\;yr^{-1}$. Respectively, the proportions of the input flux, regenerated flux, and burial flux to the primary production ($233.6\;gC\;m^{-2}\;yr^{-1}$) in the Ulleung Basin were about 4.1%, 3.0%, and 1.1%. These proportions were extraordinarily higher than the average of world open ocean. Based upon these results, the Ulleung Basin might play an integral role in the deposition and removal of organic carbon.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.82-86
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• 2011

Lightweight aggregate which is composed of sintered polycrystalline materials usually has a certain portion of pores inside of it. Because of such a structural characteristics, it tends to that movement of water in aggregate shows an abnormal behavior against the change of outside environment. In general, water movement behavior is controlled by porosity, distribution of pore size; however, dense surface layer will also affect water movement behavior in case of artificially sintered aggregates. Factors affecting water movement behavior in the aggregate are pore distribution, pore shape, pre-wetting method, etc. In this study, absorption characteristics of aggregate under the pressure and absorption rate according to water dipping time are analyzed for the basis of pressure pumping of lightweight concrete. Two kinds of aggregates were used for the test: one is made by 'L' company in Germany and the other is of our own made at the pilot plant in Kyonggi University. Absorption rate of aggregate is measured according to water dipping time, vacuum pressure, and quenching condition. Absorption rate of aggregate with $300^{\circ}C$ quenching is higher than that of aggregate with 24 hr water dipping. Generally the more vacuum the higher water absorption rate. Water absorption rate of 'L' aggregate under -300 mmHg is 54 % higher than that of aggregate with 24 hr water dipping; however, only 2 % increase in water absorption was measured for the K622 and K73 which were of our own.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.62-68
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• 2016

Laser welding has superior characteristic such as low distortion, high welding speed, easy automation and real time control. But it is easy to occur weld defects such as porosity, crater, humping bead in the area of welding start and end. These weld defects can be suppressed by applying the wave shape control. In this study CW fiber laser was used for welding of $0.5mm^t$ pure titanium. Penetration properties were evaluated with the time of slope up and down. After then the bead shape was observed, and the maximum depth and the area of crater were measured. The bead shape of welding start area changed to be sharp with increase of slope up time and non-weld area of welding start increased. The crater and humping bead were suppressed with slope down time. The cooling rate of crater area was understood through measure of the hardness. Also, The distribution tendency of alloying elements was observed by EPMA and EDS. When wave shape control didn't applied to weld, the hardness of end weld increased due to rapid cooling rate and the hardness of rear part in the crater was higher than that of fore part. On the other hand, when the wave shape control was used for end weld, the increase of hardness in the end weld couldn't be found due to gradual cooling rate.

• Journal of the Korean Society of Combustion
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• v.13 no.2
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• pp.33-41
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• 2008

The high permeability of the gas in the molten iron of the dripping zone of the blast furnace is a major factor in achieving the stable operation of a furnace with high productivity. Basic studies of the liquid flow behavior in a packed bed are necessary to grasp the effect of various operational changes on conditions in the dropping zone. Molten iron and slag together playa critical role in the lower zone, transporting mass and energy, while impairing and redistributing the gas flow. In turn, molten iron and slag undergo physical and chemical changes, and are redistributed radially as they descend to the hearth. In this research, mathematical formulations are derived for the gas and the liquid. The solid phase is fixed with constant porosity. The information for the molten iron and slag includes the hold-up, velocity, pressure, and information related to the areas of interaction between the gas and the liquid, and the solid and the liquid. Predictable results include the velocity, pressure and temperature distribution. Additional parameters include the packed particle size and the air blast rate.

• Membrane and Water Treatment
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• v.7 no.5
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• pp.377-401
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• 2016

To study the effect of titanium dioxide ($TiO_2$) nanoparticles on membrane performance and structure and to explore possible improvement of using mixed solvents in the casting solution, composite polyvinylidene fluoride (PVDF) ultrafiltration membranes were prepared via immersion precipitation method using a mixture of two solvents triethyl phosphate (TEP) and dimethylacetamide (DMAc) and addition of $TiO_2$ nanoparticles. Properties of the neat and composite membranes were characterized using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), Atomic force microscopy (AFM) and contact angle and membrane porosity measurements. The neat and composite membranes were further investigated in terms of BSA rejection and flux decline in cross flow filtration experiments. Following hydrophilicity improvement of the PVDF membrane by addition of 0.25 wt.% $TiO_2$, (from $70.53^{\circ}$ to $60.5^{\circ}$) degree of flux decline due to irreversible fouling resistance of the composite membrane reduced significantly and the flux recovery ratio (FRR) of 96.85% was obtained. The results showed that using mixed solvents (DMAc/TEP) with lower content of $TiO_2$ nanoparticles (0.25 wt.%) affected the sedimentation rate of nanoparticles and consequently the distribution of nanoparticles in the casting solution and membrane formation which influenced the properties of the ultimate composite membranes.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.34 no.3
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• pp.53-58
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• 2002

This paper was performed to investigate the effect of pore structure on ink residual behavior. To prepare different coating structures as substrates against inks, fine, medium and coarse calcium carbonate were used in the coating color. It is well known ink properties can affect to print qualities. After printing on the coated paper, ink layer can consider as third structure addition to paper and coating layer. To compare effect of ink properties on the surface structure and print qualities, several properties of ink were also adopted as raw material. Particle size of pigment effect on gloss evaluation of coated paper increased with calendering. It was shown that ink transfer rate increased as surface of the sample was smooth. The ink contained low viscosity resin evaluated more print gloss. Finer pigment particle size, smaller pore size and higher porosity. Pore volume of coated paper was slightly decreased with printing as the coating was prepared with the finest particle size. However, it founded that ink resin could not affect on pore volume and distribution of printed paper

• Carbon letters
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• v.4 no.4
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• pp.168-174
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• 2003

Silver nitrate ($AgNO_3$) powder was mixed into a reformed pitch precursor. Then, the silver-containing pitch was melt spun to form round and "C" shape fibers. A wire mesh was inserted prior to the nozzle to improve the spinnability of the silvercontaining precursor pitch. Silver particles in the carbon fibers (CFs) were detected by XRD and TEM. These tests showed that silver particles were uniformly distributed and the total amount of silver remained constant during stabilization and carbonization. Next, the silver-containing CFs were activated by steam diluted in nitrogen gas. Silver particles accelerated the activation rate, but the specific surface areas of the silver-containing ACFs were similar to those of non-silver containing ACFs at the same burn-off levels. The specific surface area of the C-shaped activated carbon fibers was larger than that of the round activated carbon fibers. The likely reason is that the surface area of a C-shaped CF is about two times larger than that of a round CF when equivalent cross-sectional areas are compared. A small amount of silver particles in the periphery of the CFs was removed during the activation, but the remainder of silver was stayed within the ACFs.