• Computers and Concrete
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• v.30 no.6
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• pp.421-432
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• 2022

Recently, the interminable ozone depletion and the global warming concerns has led to construction industries to seek for construction materials which are eco-friendly. Regarding this, Geopolymer Concrete (GPC) is getting great interest from researchers and scientists, since it can operate by-product waste to replace cement which can lead to the reduction of greenhouse gas emission through its production. Also, compared to ordinary concrete, geopolymer concrete belongs improved mechanical and durability properties. In spite of its positive properties, the practical use of geopolymer concrete is currently limited. This is primarily owing to the scarce structural, design and application knowledge. This study investigates the Mechanical and Durability of Geopolymer Concrete Containing Fibers and Recycled Aggregate. Mixtures of elastoplastic fiber reinforced geopolymer concrete with partial replacement of recycled coarse aggregate in different proportions of 10, 20, 30, and 40% with natural aggregate were fabricated. On the other hand, geopolymer concrete of 100% natural aggregate was prepared as a control specimen. To consider both strength and durability properties and to evaluate the combined effect of recycled coarse aggregate and elastoplastic fiber, an elastoplastic fiber with the ratio of 0.4% and 0.8% were incorporated. The highest compressive strength achieved was 35 MPa when the incorporation of recycled aggregates was 10% with the inclusion of 0.4% elastoplastic fiber. From the result, it was noticed that incorporation of 10% recycled aggregate with 0.8% of the elastoplastic fiber is the perfect combination that can give a GPC having enhanced tensile strength. When specimens exposed to freezing-thawing condition, the physical appearance, compressive strength, weight loss, and ultrasonic pulse velocity of the samples was investigated. In general, all specimens tested performed resistance to freezing thawing. the obtained results indicated that combination of recycled aggregate and elastoplastic fiber up to some extent could be achieved a geopolymer concrete that can replace conventional concrete.

• Membrane Journal
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• v.28 no.2
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• pp.136-141
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• 2018

Carbon dioxide ($CO_2$) exists not only as a component of natural gas, biogas, and landfill gas, but also as a major combustion product of fossil fuels which leads to a major contributor to greenhouse gases. Hence it is essential to reduce or eliminate carbon dioxide ($CO_2$) in order to obtain high fuel efficiency of internal combustion engine, to prevent corrosion of gas transportation system, and to cope with climate change preemptively. In recent years, there has been a growing interest in not only conventional membrane-based separation but also new adsorbent-based separation technology. Particularly, in the case of metal-organic frameworks (MOFs), it has been received tremendous attentions due to its unique properties (eg : flexibility, gate effect or strong binding site such as open metal sites) which are different from those of typical porous adsorbents. Therefore, in this study, stereotype of two MOFs have been selected as its flexible MOFs (MIL-53) representative and numerous open metal sites MOFs (MOF-74) representative, and compared each other for $CO_2/CH_4$ separation performance. Furthermore, varying and changeable separation performance conditions depending on the temperature, pressure or samples' unique properties are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.429-435
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• 2016

Cold stretching(CS) pressure vessels from ASS304 (austenitic stainless steel 304) are used for the transportation and storage of liquefied natural gas(LNG). CS pressure vessels are manufactured by pressurizing the finished vessels to a specific pressure to produce the required stress ${\sigma}_k$. After CS, there is some degree of plastic deformation. Therefore, CS vessels have a higher strength and lighter weight compared to conventional vessels. In this study, we investigate the tensile and fatigue behavior of ASS304 sampled by CS pressure vessels in accordance with the ASME code at cryogenic temperature. From the fatigue test results, we show S-N curves using a statistical method recommended by JSEM-S002. We carried out the fractography of fractured specimens using scanning electron microscopy (SEM).

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.332-340
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• 2015

Acoustic emission (AE) is an effective nondestructive test that uses transient elastic wave generated by the rapid release of energy within a material to detect any further growth or expansion of existing defects. Over the past decades, because of environmental issues, the use of compressed natural gas (CNG) as an alternative fuel for vehicles is increasing because of environmental issues. For this reason, the importance and necessity of detecting defects on a CNG fuel tank has also come to the fore. The conventional AE method used for source location is highly affected by the wave speed on the structure, and this creates problems in inspecting a composite CNG fuel tank. Because the speed and dispersion characteristics of the wave are different according to direction of structure and laminated layers. In this study, both the conventional AE method and the energy based contour map method were used for source location. This new method based on pre-acquired D/B was used for overcoming the limitation of damage localization in a composite CNG fuel tank specimen which consists of a steel liner cylinder overwrapped by GFRP. From the experimental results, it is observed that the damage localization is determined with a small error at all tested points by using the energy based contour map method, while there were a number of mis-locations or large errors at many tested points by using the conventional AE method. Therefore, the energy based contour map method used in this work is more suitable technology for inspecting composite structures.

• Analytical Science and Technology
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• v.24 no.5
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• pp.352-359
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• 2011

An analytical method for solvent-free determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using repetitive membrane extractions coupled to cryofocusing and GC-MS was derived. BTEX compounds that permeated through a nonporous silicone membrane from the aqueous phase and evaporated into the acceptor phase were purged into a cryofocusing trap ($-100^{\circ}C$) with helium gas. The BTEX compounds, thus enriched in the trap, were thermally desorbed into a capillary column GC and detected using an MS. The flow rate of the donor phase (30 mL water) was set at 10 mL/min, and membrane extractions, accomplished by returning the water drained from the extraction module to the sample container, were repeated three times at $20{\pm}2^{\circ}C$. Although recoveries (%) were variable, from the highest for benzene (approximately 80%) to the lowest for ethylbenzene and xylenes (3.5-10%), the method showed satisfactory precision (RSD 2.2-10%) with good-linearity calibration curves ($r^2$ 0.9976-0.9997 in 1-100 ${\mu}g$/L range) for all of the compounds. The method detection limits (MDLs) ranged from 0.16 to 1.8 ${\mu}g$/L. The results showed the method's advantages such as short analysis time and overall simplicity without solvent compared to the conventional techniques.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2961-2966
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• 2007

When the pressure at the weak spot established at a certain part of a high pressure vessel or piping system exceeds a design pressure, this weak spot is burst, and the pressurized gas emitted through the weak spot will cause a compression wave system. In this connection, in the present study, an experimental study by using a conventional shock tube facility is performed to estimate the effects of the material of diaphragm, curvature radius and thickness of materials on the valve opening time in diaphragm. Pressure sensor having 500kHz in natural frequency is installed at 35mm downstream of the rupture diaphragm to measure the static pressure history of propagating and being accumulated compression wave. 4 kinds of materials are used as diaphragm that is aluminium, copper, stainless steel and zinc. The diaphragm radii of curvature R are ${\infty}$, 120mm and 60, respectively. And the depth for $90^{\circ}$ groove is 0.04mm. It is found that the smaller the tensile strength and elongation of the rupture diaphragm is, the smaller the radius of curvature of the rupture diaphragm is, and for the same conditions the thinner the thickness of the rupture diaphragm is, the shorter the valve opening time becomes. Also, the tensile strength, elongation and the radius of curvature of the rupture diaphragm for the same conditions are smaller, the maximum pressure rise caused by the coalescences of the compression wave is smaller. Finally the pressure ratio is higher, the valve opening time is shortened and gradient of pressure increment is more steepen.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.215-220
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• 2002

The structures of 1-fluorosilatrane and the silatranyl cation were calculated by Hartree-Fock (HF), Mofller-Plesset second order (MP2), and various density functional theory (DFT) methods using many different basis sets, demonstrating that the Si-N bonds in two species are quite different. The N${\rightarrow}$Si bond distance of 1-fluorosilatrane from the hybrid DFT calculations $({\sim}2.32{\AA})$ using the Perdew-Wang correlation functional agrees with the gas phase experimental value $(2.324{\AA})$, while other functionals yield larger distances. The MP2 bond distance (2.287${\AA}$ with 6-311$G^{\ast}$) is shorter, and the HF one (2.544 ${\AA}$ with 6-311$G^{\ast}$) larger than those of DFT calculations. The MP2 bond distance is in good agreement with experiment indicating that the electron correlations are crucial for the correct description of the N${\rightarrow}$Si interaction. The silatranyl cation is a stable local minimum on the potential energy surface in all methods employed suggesting that the cation could be a reaction intermediate. The Si-N bond length for the cation is about 1.87 ${\AA}$ for all calculations tested implying that the Si-N bond is mainly conventional. Bonding characteristics of the Si-N bond in two species derived from the natural bond orbital analysis support the above argument based on calculated bond lengths.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.387-394
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• 2013

Hydrogen-compressed natural gas (HCNG) blend has attracted attention as a fuel that can reduce $CO_2$ emissions because it has low carbon content and burns efficiently. An increase in the compression ratio of HCNG engines was considered as one of the methods to improve their efficiency and reduce $CO_2$ emissions. However, a high combustion rate and flame temperature cause abnormal combustion such as pre-ignition or knocks, which in turn can cause damage to the engine components and decrease the engine power. In this study, the performance and knock characteristics with a change in the compression ratio of an HCNG engine were analyzed. The combustion characteristics of HCNG fuel were evaluated as a function of the excess air ratio using a conventional CNG engine. The effects of the compression ratio on the engine performance were evaluated through the same experimental procedures.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.279-286
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• 2018

The use of eco-friendly energy in the offshore plant system is expanding because conventional generators are operated by fossil fuel or natural gas. Eco-friendly energy, which replaces existing power generation methods, should be capable of generating the power for lighting protection equipment, airborne fault indication, parameter measurement, and others. Most of the eco-friendly energy used in offshore plant facilities is solar and wind power. In the case of using photovoltaic power, because the structure must be constructed based as flat solar panels, it can be damaged easily by the wind. Therefore, there is a need for a new generation system composed of a spherical structure that does not require a separate structure and is less influenced by the wind. Considering these characteristics, in this study we designed, fabricated, and tested a unit that could provide the most efficient spherical photovoltaic power generation considering wind direction and wind pressure. Our test results indicated that the proposed system reduced costs because it did not require any separate structure, used eco-friendly energy, reduced carbon dioxide emissions, and expanded the proportion of eco-friendly energy use by offshore plant facilities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.869-874
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• 2011

In a CNG/diesel dual-fuel engine, CNG is used as the main fuel and a small amount of diesel is injected into the cylinder to provide ignition priming. In this study, a remodeling of the existing diesel engine into a CNG/diesel dual-fuel engine is proposed. In this engine, diesel is injected at a high pressure by common rail direct injection (CRDI) and CNG is injected at the intake port for premixing. The CNG/diesel dual-fuel engine had an equally satisfactory coordinate torque and power as the conventional diesel engine. Moreover, the CNG alternation rate is over 89% throughout the operating range of the CNG/diesel dual-fuel engine. PM emission by the dual-fuel engine is 94% lower than that by the diesel engine; however, NOx emission by the dual-fuel engine is higher than that by the diesel engine.