• 한국수소및신에너지학회논문집
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• 제15권3호
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• pp.208-219
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• 2004

To find a suitable oxygen carrier particle for a 50kW chemical-looping combustor, which was designed and installed to demonstrate continuous oxidation and reduction, three oxygen carrier particles(NiO/bentonite, $NiO/NiAl_2O_4$, $CoO_x/CoAl_2O_4$) were prepared. The reactivity and the attrition resistance of particles were measured and investigated by a thermo-gravimetrical analyzer and an attrition test apparatus respectively. From the viewpoints of oxygen transfer capacity, optimum reaction temperature(operating temperature range), reaction rate, carbon deposition rate, and attrition resistance, NiO/bentonite particle showed better performance than the other particles, therefore we selected NiO/bentonite particle as an optimum oxygen carrier particle.

• 한국분말재료학회지
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• 제19권1호
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• pp.6-12
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• 2012

Electricity is generated by the combined reactions of hydrogen oxidation and oxygen reduction which occur on the Pt/C catalyst surface. There have been lots of researches to make high performance catalysts which can reduce Pt utilization. However, most of catalysts are synthesized by wet-processes and a significant amount of chemicals are emitted during Pt/C synthesis. In this study, Pt/C catalyst was produced by arc plasma deposition process in which Pt nano-particles are directly deposited on carbon black surfaces. During the process, islands of Pt nano-particles were produced and they were very fine and well-distributed on carbon black surface. Compared with a commercialized Pt/C catalyst (Johnson & Matthey), finer particle size, narrower size distribution, and uniform distribution of APD Pt/C resulted in higher electrochemical active surface area even at the less Pt content.

• 열처리공학회지
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• 제16권4호
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• pp.191-196
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• 2003

For improvement of the wear performance of Ti alloy, vacuum-carburizing technique was tried for the first time using propane atmosphere. During the low pressure carburizing carbide was formed at the surface and carbon transfer was occurred from the carbide to the matrix. It was found that: (i) surface hardness increased with the reduction of operating pressure and time; (ii) optimum hardness distribution could be obtained with the proper choice of temperature and carbon flux control; and, (iii) case depth was largely influenced not by time but by temperature. The two steps process was recommended for obtaining thick case depth and high surface hardness of Ti alloy. For the low oxygen partial pressure, it was necessary to introduce additional CO gas to the atmosphere.Grain boundary oxidation and non-uniformity could be prevented.

• Structural Engineering and Mechanics
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• 제91권1호
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• pp.49-61
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• 2024

In recent decades, the majority of studies have concentrated on the utilization of Steel Square Hollow Section (SHS) columns, with minimal attention given to reinforcing columns exhibiting inherent defects. This study addresses this gap by introducing initial vertical and horizontal defects at three distinct locations (top, middle, and bottom) and employing Carbon-FRP for reinforcement. The research investigates the dimensional and positional impacts of these defects on the axial behavior of SHS columns. A total of 29 samples, comprising 17 with defects, 11 strengthened, and 1 defect-free control, underwent examination. The study employed ABAQUS modeling and conducted experimental testing. Results revealed that defects located at different positions significantly diminished the load-bearing capacity and initial performance of the steel columns. Axial loading induced local buckling and lateral rupture, particularly at the defect side, in short columns. Notably, horizontal (across the column's width) and vertical (along the column's height) defects in the middle led to the most substantial reduction in strength and load-bearing capacity. The axial compressive failure increased with the length-to-width ratio of the defect. Moreover, the application of four carbon fiber layers to strengthen the steel columns resulted in increased Energy Dissipation and a delayed onset of local buckling in the face of axial ruptures.

• 한국건설순환자원학회논문집
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• 제11권4호
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• pp.416-424
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• 2023

콘크리트는 전 생애주기에서 막대한 양의 이산화탄소를 배출하며, 이산화탄소 감축을 위한 사회적인 요구에 따라 콘크리트에 이산화탄소를 광물형태로 저장하려는 연구가 지속되고 있다. 본 연구에서는 광합성을 통해 이산화탄소를 흡수하여 탄산칼슘으로 고정하는 남세균(Cyanobacteria)을 다공성 콘크리트 기질에 도포하였으며, 이의 특수 환경 양생에 따른 콘크리트 기질의 특성 변화를 분석하였다. 실험 결과 미생물에 의한 탄산칼슘 석출은 빛이 닿는 표면부에서 집중되어 있는 것을 확인하였으며, 대부분의 석출이 골재가 아닌 페이스트 부분에서 발생하였다. 이러한 미생물에 의한 탄산칼슘 석출은 페이스트의 역학성능을 강화하였으며, 양생 재령의 경과에 따라 전체 압축강도가 향상되는 효과를 보였다. 또한 미생물 막과 탄산칼슘의 증가로 공극구조가 개선되어 투수량 감소에도 영향을 끼쳤다.

• Advances in environmental research
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• 제5권4호
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• pp.251-262
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• 2016

The biodegradability and decomposition efficiencies increase with the pre-treatment of sludge in a digestion process. In this study, the feasibility of ultrasound coupled with potassium permanganate oxidation as a disintegration method and digestibility of aerobic reactor fed with disintegrated sludge with ultrasound coupled potassium permanganate were investigated. The first stage of the study focused on determining the optimum condition for ultrasonic pre-treatment for achieving better destruction efficiency of sludge. The second part of the study, the aerobic digestibility of sludge disintegrated with ultrasound and potassium permanganate oxidation alone and combined were examined comparatively. The results showed that when 20 min of ultrasonic pre-treatment applied, the specific energy output was 49384 kJ/kgTS with disintegration degree of 58.84%. During the operation of aerobic digester, VS/TS ratios of digesters fed with disintegrated sludge decreased indicating that disintegration methods could obviously enhance aerobic digestion performance. The highest reduction in volatile solids was 75% in the digester fed with ultrasound+potassium permanganate disintegrated sludge at the end of the operation compared to digester fed with raw sludge. Total Nitrogen (TN) and Total Phosphorus (TP) levels in sludge supernatant increased with this combined method significantly. Besides, it promoted the production of ${\bullet}OH$, thus enhancing the release of Carbon (C), Nitrogen (N) and Phosphorus (P) from the sludge. Disintegration with all methods used in this study could not improve Capillary Suction Time (CST) reduction in disintegrated digesters during the operation. The results demonstrated that the combined ultrasound treatment and potassium permanganate oxidation method improves the biodegradability compared to control reactor or their single application.

• Agricultural and Biosystems Engineering
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• 제3권2호
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• pp.59-64
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• 2002

Odor generated during composting of livestock manure is mainly due to ammonia emission. Biofiltration is a desirable method to control composting odor. This study was conducted to analyze the efficiency of using fresh compost as a biofilter. A mixture of cattle manure and recycled compost was composted in a bin equipped with a suction-type blower. The exhaust gas was filtered through the fresh compost. Residence time was controlled by the flow rate of exhaust gas and the depth of filtering materials. At the aeration rate of 30 L/min(experiment I), ammonia reduction rate varied from 100% to -15% for biofilter A(residence time 56.5 s) and almost 100% for biofilter B(residence time 113 s). At the aeration rate of 30 L/min, the cumulative ammonia reduction rate was 80.5% for biofilter A and 99.9% for biofilter B. At the aeration rate of 50 L/min(experiment II), the lowest reduction rate showed a negative value of -350% on the 8th and 9th day for biofilter A(residence time 33.9 5), and 50% on the loth day for biofilter B(residence time 67.8s). At the aeration rate of 50 L/min, the cumulative ammonia reduction rate was 82.5% fur biofilter A and 97.4% for biofilter B. Filtering efficiency was influenced by residence time. The moisture content(MC) and total nitrogen(T-N) of the filtering material were increased by absorbing moisture and ammonia included in the exhaust gas, while pH was decreased and total carbon(T-C) remained unchanged during the filtering operation.

• 한국수소및신에너지학회논문집
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• 제29권5호
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• pp.450-457
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• 2018

To design the practical core-shell electrocatalysts, combination of core and shell materials is important to meet catalytic activity and durability target. In general, Pd is considered as a good core material due to its best activity caused by strain/ligand effect. Preparing Pd nanoparticles can be a starting point in fabricating core-shell type electrocatalysts, much simplified Pd preparing process is suggested by using carbon monoxide (CO) as a reducing agent and/or capping agent. The solvent composition and reaction temperature can control to nanosheet, tetrahedron, and sphere without using additional stabilizer. Among them, Pd nanosheet which has mainly (111) plane showed about 3 times higher electrocatalytic activity for oxygen reduction reaction (ORR) to the spherical Pd nanoparticles. The enhanced ORR activity of Pd nanosheets can be attributed to the exposure of Pd (111) surface and the high electrochemical surface area. Therefore, we demonstrated that the shape of Pd nanomaterials is easily controlled via a facile reduction method using CO, and (111) plane-oriented Pd nanosheets can be a promising ORR catalysts and core material for polymer electrolyte fuel cells (PEFCs).

• Advances in aircraft and spacecraft science
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• 제10권2호
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• pp.107-125
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• 2023

Drag reduction is significant research in aircraft design due to its effect on the cost of operation and carbon footprint reduction. Aircraft currently use conventional solid winglets to reduce the induced drag, adding extra structural weight. Fluidic on-demand winglets can effectively reduce drag for low-speed flight regimes without adding any extra weight. These utilize the spanwise airflow from the wingtips using hydraulic actuators to create jets that negate tip vortices. This study develops a computational model to investigate fluidic on-demand winglets. The well-validated computational model is applied to investigate the effect of injection velocity and angle on the aerodynamic coefficients of a rectangular wing. Further, the turbulence parameters such as turbulent kinetic energy (TKE) and turbulent dissipation rate are studied in detail at various velocity injections and at an angle of 30°. The results show that the increase in injection velocity shifted the vortex core away from the wing tip and the increase in injection angle shifted the vortex core in the vertical direction. Further, it was found that a 30° injection is efficient among all injection velocities and highly efficient at a velocity ratio of 3. This technology can be adopted in any aircraft, effectively working at various angles of attack. The culmination of this study is that the implementation of fluidic winglets leads to a significant reduction in drag at low speeds for low aspect ratio wings.

• 청정기술
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• 제30권1호
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• pp.55-61
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• 2024

연료전지의 산소환원반응용 백금 촉매의 높은 비용을 극복하기 위하여 나노 구조 제어를 통한 고성능의 백금 합금 촉매 개발 연구가 활발히 수행되고 있다. 본 연구에서는 탄소에 담지된 니켈-니켈 질화물 복합체와 백금 이온 간의 갈바닉 치환 반응 시 용액의 pH 조절을 통한 촉매의 나노구조를 중공형이나 코어-쉘 구조로 제어하는 방법을 제시하였다. X선 회절 분석과 투과전자현미경, 유도결합 플라즈마를 이용한 분석을 통해 합성 조건에 따른 금속의 상태와 함량 및 합금 입자의 형상에 대한 물리적 특성 평가를 수행하였다. 제조된 촉매를 산소환원반응 촉매로 적용하였으며 상용 백금 촉매 대비 1.7배(중공형 촉매) 및 1.9배(코어-쉘 구조 촉매) 개선된 전기화학적 활성 면적 당 활성을 나타내었다.