• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.187-195
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• 2005

When a tunnel is excavated below groundwater table, the groundwater flow occurs towards the tunnel resulting in the seepage pressure. In this paper, the effect of groundwater flows on the behavior of shotcrete lining installed between ground-liner interfaces was studied considering permeability ratio between the ground and the shotcrete into account. Three-dimensional coupled finite element analysis was performed for this assessment. Seepage forces will seriously affect the shotcrete behavior since arching phenomena do not occur in seepage forces. A parametric study was conducted on the various tunnelling situations including interfacial properties between ground and shotcrete lining, the shape of tunnel cross-section and the thickness of liner, etc. Moreover, the convergence-confinement method (CCM) of a NATM tunnel considering seepage forces was proposed. The result showed that the more water tight is the shotcrete, the smaller is the convergence and the larger is the internal pressure. Therefore, the watertight fiber-reinforced shotcrete is found to be even more advantageous when used in under water tunnel.

• Solar Energy
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• v.15 no.2
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• pp.25-37
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• 1995

This paper presents an approximate analytical solution to one-dimensional model of the charging process for stratified thermal storage tanks, in which variation of the inlet temperature as well as the momemtum-induced mixing is taken into accout. The mixing is incorporated into the model as a constant-depth perfectly mixed layer above the plug flow region. Based on the superposition principle, the variable inlet temperature is approximated by a number of step functions. Temperature distributions for the thermocline corresponding to three types of interfacial condition arr successfully derived in terms of well-defined functions, so that a linear combination of them constitutes the final solution. Validity and utility of this work is examined through the comparison of the approximate solution with an exact solution available for the case of linearly increasing inlet temperature. With increasing the number of steps, the present solution asymptotically approaches to the exact one. Even with a limited number of steps, the present results favorably agree with those by the exact solution for a wide range of the mixing depth. Also, it is revealed that fewer steps are needed for meaningful predictions as the mixing. depth becomes larger.

• Transactions of Materials Processing
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• v.30 no.3
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• pp.142-148
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• 2021

In hot forging analysis, the interfacial heat transfer coefficient (IHTC) is a very important factor defining the heat flow between the die and the material. In particular, in the hot forging analysis of aluminum 6xxx series alloy, which are used in automobile parts, differences in load and microstructure occur due to changes in surface temperature according to the IHTC. This IHTC is not a constant value but changes depends on pressure. This study derived the IHTC under low load using aluminum 6082 alloy. An experiment was performed by fabricating a compression die, and a heat transfer analysis was performed based on the experimental data. The heat transfer analysis used DEFORM-2D, a commercial finite element analysis program. To derive the IHTC, heat transfer analysis was performed for the IHTC in the range of 10 to 50 kW/m²℃ at intervals of 10kW/m²℃. The heat transfer analysis results according to the IHTC and the actual experimental values were compared to derive the IHTC of the aluminum 6082 alloy under low load.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.671-678
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• 2001

All solid-state thin film micro supercapacitor, which consists of $RuO_2$/LiPON/$RuO_2$ multi layer structure, was fabricated on Pt/Ti/Si substrate using a $RuO_2$ electrode. Bottom $RuO_2$ electrode was grown by dc reactive sputtering system with increasing $O_2/[Ar+O_2]$ ratio at room temperature, and a LiPON electrolyte film was subsequently deposited on the bottom $RuO_2$ electrode at pure nitrogen ambient by rf reactive sputtering system. Room temperature charge-discharge measurements based on a symmetric $RuO_2$/LiPON/$RuO_2$ structure clearly demonstrates the cyclibility dependence on the microstructure of the $RuO_2$ electrode. Using both glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) analysis, it was found that the microstructure of the $RuO_2$ electrode was dependent on the oxygen flow ratio. In addition, x- ray photoelectron spectroscopy(XPS) examination shows that the Ru-O binding energy is affected by increasing oxygen flow ratio. Furthermore, TEM and AES depth profile analysis after cycling demonstrates that the interface layer formed by interfacial reaction between LiPON and $RuO_2$ act as a main factor in the degradation of the cyclibility of the thin film micro-supercapacitor.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.544-550
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• 2013

This work investigated the environmental application of an underwater dielectric barrier discharge plasma reactor consisting of a porous hydrophobic ceramic tube to the decolorization of an azo dyeing wastewater. The reactive species generated by the plasma are mostly short-lived, which also need to be transferred to the wastewater right after the formation. Moreover, the gas-liquid interfacial area should be as large as possible to increase the decolorization rate. The arrangement of the present wastewater treatment system capable of immediately dispersing the plasmatic gas as tiny bubbles makes it possible to effectively decolorize the dyeing wastewater alongside consuming less amount of electrical energy. The effect of discharge power, gas flow rate, dissolved anion and initial dye concentration on the decolorization was examined with dry air for the creation of plasma and amaranth as an azo dye. At a gas flow rate of $1.5Lmin^{-1}$, the good contact between the plasmatic gas and the wastewater was achieved, resulting in rapid decolorization. For an initial dye concentration of $40.2{\mu}molL^{-1}$ (volume : 0.8 L; discharge power : 3.37 W), it took about 25 min to attain a decolorization efficiency of above 99%. Besides, the decolorization rate increased with decreasing the initial dye concentration or increasing the discharge power. The presence of chlorine anion appeared to slightly enhance the decolorization rate, whereas the effect of dissolved nitrate anion was negligible.

• Restorative Dentistry and Endodontics
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• v.35 no.3
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• pp.173-179
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• 2010

The purpose of the present study was to compare the influence of post-surface treatment with silane, hydrogen peroxide, hydrofluoric acid or sandblasting and to investigate the effect of silane in combination of the other treatments on the microtensile bond strength between fiber posts and composite resins for core build-up. Thirty-two glass-fiber posts (FRC Postec Plus, Ivoclar Vivadent, Schaan, Liechtenstein) were divided into eight groups according to the different surface pretreatments performed: silane application (S); immersion in 28% hydrogen peroxide (HP); immersion in hydrogen peroxide followed by application of silane (HP-S); immersion in 4% hydrofluoric acid gel (HF); immersion in hydrofluoric acid gel followed by application of silane (HF-S); sandblasting with aluminum oxide particles (SB); sandblasting followed by application of silane (SB-S). In control group, no surface treatment was performed. The composite resin (Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein) was applied onto the posts to produce the composite cylinder specimen. It was sectioned into sticks to measure the microtensile bond strength. The data was analyzed with one-way ANOVA and LSD test for post hoc comparison (p < 0.05). Post pretreatment with sandblasting enhanced the interfacial strength between the fiber posts and core materials. Moreover, sandblasting followed by application of silane appears to be the most effective method that can improve the clinical performance of glass fiber posts.

• Economic and Environmental Geology
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• v.54 no.1
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• pp.105-115
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• 2021

The geological CO2 sequestration in underground geological formation such as deep saline aquifers and depleted hydrocarbon reservoirs is one of the most promising options for reducing the atmospheric CO2 emissions. The process in geological CO2 sequestration involves injection of supercritical CO2 (scCO2) into porous media saturated with pore water and initiates CO2 flooding with immiscible displacement. The CO2 migration and distribution, and, consequently, the displacement efficiency is governed by the interaction of fluids. Especially, the viscous force and capillary force are controlled by geological formation conditions and injection conditions. This study aimed to estimate the effects of surfactant on interfacial tension between the immiscible fluids, scCO2 and porewater, under high pressure and high temperature conditions by using a pair of proxy fluids under standard conditions through pendant drop method. It also aimed to observe migration and distribution patterns of the immiscible fluids and estimate the effects of surfactant concentrations on the displacement efficiency of scCO2. Micromodel experiments were conducted by applying n-hexane and deionized water as proxy fluids for scCO2 and porewater. In order to quantitatively analyze the immiscible displacement phenomena by n-hexane injection in pore network, the images of migration and distribution pattern of the two fluids are acquired through a imaging system. The experimental results revealed that the addition of surfactants sharply reduces the interfacial tension between hexane and deionized water at low concentrations and approaches a constant value as the concentration increases. Also it was found that, by directly affecting the flow path of the flooding fluid at the pore scale in the porous medium, the surfactant showed the identical effect on the displacement efficiency of n-hexane at equilibrium state. The experimental observation results could provide important fundamental information on immiscible displacement of fluids in porous media and suggest the potential to improve the displacement efficiency of scCO2 by using surfactants.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1292-1297
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• 2005

The use of ozone in water and wastewater treatment systems has been known to be a process that is limited by mass transfer. The most effective way to overcome this limitation is to increase the interfacial area available for mass transfer by decreasing the size of the ozone gas bubbles that are dispersed in solution. Electrostatic spraying(ES) of ozone into water was investigated in this work as a method of increasing the rate of mass transfer of ozone into a solution and thereby increasing the rate of phenol oxidation. Results were obtained for ES at input power levels ranging from 0 to 4 kV and compared with two different pore-size bubble diffusers($10{\sim}15{\mu}m$ and $40{\sim}60{\mu}m$). It was determined that the rate of mass transfer could be increased by as much as 40% when the applied voltage was increased from 0 to 4 kV as a result of the smaller bubbles generated by ES. In addition, ES was shown to be more effective than the medium-pore-size($10{\sim}15{\mu}m$) bubble diffuser and the best results were achieved at low gas flow rates.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.779-785
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• 2015

Cathodic protection is recognized as the most cost-effective and technically appropriate corrosion prevention method for the submerged zone of offshore structures, ships, and deep-sea facilities. When cathodic protection is applied, the cathodic currents cause dissolved oxygen reduction, generating hydroxyl ions near the polarized surface that increase the interfacial pH and result in enhanced carbonate ion concentration and precipitation of an inorganic layer whose principal component is calcium carbonate. Depending on the potential, magnesium hydroxide can also precipitate. This mixed deposit is generally called "calcareous deposit." This layer functions as a barrier against the corrosive environment, leading to a decrease in current demand. Hence, the importance of calcareous deposits for the effective, efficient operation of marine cathodic protection systems is recognized by engineers and scientists concerned with cathodic protection in submerged marine environments. Calcareous deposit formation on a marine structure depends on the potential, current, pH, temperature, pressure, sea-water chemistry, flow, and time; deposit quality is significantly influenced by these factors. This study determines how calcareous deposits form in sea water, and assesses the interrelationship of formation conditions (such as the sea water temperature and surface condition of steel), deposited structure, and properties and the effectiveness of the cathodic protection.

• Polymer(Korea)
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• v.33 no.4
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• pp.358-363
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• 2009

Maleic anhydride-grafted polypropylene has been widely used to improve the interfacial interaction between the components in PP/polar polymer blends and PP/filler composites and to maximize the physical properties and thermal properties. In this paper. the maleic anhydride (MAH)-grafted polypropylene (co-PP) was fabricated through reactive extrusion process with di-cumyl peroxide (DCP) as an initiator. The grafting degree of MAH depending on the contents of DCP and MAH was investigated by FT-IR spectra and chemical titration. The grafting degree increased with increasing MAH concentration and also showed maximum value at 0.06 wt% of DCP concentration. Melt flow index (MFI) of the grafted copolymer was increased with increasing the contents of MAH. The DSC and TGA analysis data indicate the melting temperature and thermal degradation of PP depending on the grafting degree of MAH.