• 한국분말재료학회지
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• 제23권2호
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• pp.136-142
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• 2016

As precursors of cathode materials for lithium ion batteries, $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of $NH_4OH$ in air or nitrogen ambient. Calcination of the precursors with $Li_2CO_3$ for 8 h at $1,000^{\circ}C$ in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$. Regardless of the atmosphere, the final powders exhibit the XRD patterns of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

• 한국수소및신에너지학회논문집
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• 제21권3호
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• pp.227-240
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• 2010

Coal gasification is heading for a great future as one of the cleanest energy sources, which can produce not only electricity and heat, but also gaseous and liquid fuels from the synthesis. The work focuses on 300MW shell type one-stage entrained flow coal gasifier which is used in the Integrated coal Gasification Combined Cycle(IGCC) plant as a reactor. As constructing an IGCC plant is considerably complicated and expensive compared with a pulverized-coal power plant, it is important to determine optimum design factors and operating conditions using a computational fluid dynamics (CFD) model. In this study, the results of numerical calculations show that $O_2$/Coal ratio, 0.83, Steam/Coal ratio, 0.05, coal particle diameter, $100{\mu}m$, injection angle, $4^{\circ}$ (clockwise) are the most optimum in this research.

• 청정기술
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• 제20권4호
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• pp.359-366
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• 2014

연소전 $CO_2$ 흡수제인 PKM1-SU와 원유의 접촉분해 촉매인 FCC (fluid catalytic cracking)입자의 고온, 고압 조건 마모 실험을 수행하였다. 지름 15.1 cm, 높이 120 cm에 스파저 튜브(sparger tube, 1 mm 오리피스)를 장착한 원통형 기포유동층반응기를 이용하여, 다양한 온도조건($0{\sim}400^{\circ}C$), 압력조건(0~20 bar)에서 입자마모 실험을 수행하였다. BET, 광학현미경, 입도분석기 등을 이용하여 실험 전, 후 입자를 분석 하였다. 또한 기존의 마모도 측정 방법인 ASTM D5757-95방법을 이용하여 층물질의 높이(4.4~10.2 cm) 및 수분 주입이 입자 마모에 미치는 영향에 대하여 확인하였다.

• 상하수도학회지
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• 제34권6호
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• pp.463-471
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• 2020

A 1,000 ㎥/d DAF(dissolved air flotation) pilot plant was installed to evaluate the performance of the floating process using the Nakdong River. Efficiency of various DAF operations under different conditions, such as hydraulic loading rate, coagulant concentration was evaluated in the current research. The operation conditions were evaluated, based on the removal or turbidity, TOC(total organic carbon), THMFP(trihalomethane formation potential), Mn(manganese), and Al(aluminum). Also, particle size analysis of treated water by DAF was performed to examine the characteristics of particles existing in the treated water. The turbidity removal was higher than 90%, and it could be operated at 0.5 NTU or less, which is suitable for the drinking water quality standard. Turbidity, TOC, and THMFP resulted in stable water quality when replacing the coagulant from alum to PAC(poly aluminum chloride). A 100% removal of Chl-a was recorded during the summer period of the DAF operations. Mn removal was not as effective as where the removal did not satisfy the water quality standards for the majority of the operation period. Hydraulic loading of 10 m/h, and coagulant concentrations of 40 mg/L was determined to be the optimal operating conditions for turbidity and TOC removal. When the coagulant concentration increases, the Al concentration of the DAF treated water also increases, so coagulant injection control is required according to the raw water quality. Particle size distribution results indicated that particles larger than 25 ㎛ showed higher removal rates than smaller particles. The total particel count in the treated water was 2,214.7 counts/ml under the operation conditions of 10 m/h of hydraulic loading rate and coagulant concentrations of 60 mg/L.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.449-456
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• 2003

In this study, numerical and experimental analysis on the spray atomization characteristics of a GDI injector is performed. For numerical approach, four hybrid models that are composed of primary and secondary breakup model are considered. Concerning the primary breakup, a conical sheet disintegration model and LISA model are used. The secondary breakup models are made based on the DDB model and RT model. The global spray behavior is also visualized by the shadowgraph technique and local Sauter mean diameter and axial mean velocity are measured by using phase Doppler particle analyzer Based on the comparison of numerical and experimental results, it is shown that good agreement is obtained in terms of spray developing process and spray tip penetration at the all hybrid models. However, the hybrid breakup models show different prediction of accuracy in the cases of local SMD and the spatial distribution of breakup.

• 한국주조공학회지
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• 제22권5호
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• pp.245-251
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• 2002

Cast AZ91 and extruded AM50 alloys were isothermally heated as solid/liquid coexistent temperatures, and semi-solid formed into sheets. Mold filling ability of semi-solid slurry with different liquid fractions was investigated in relation to process variables such as injection speed and mold temperature. Relatively uniform distribution of solid particle size and liquid fraction were observed throughout the semi-solid formed sheet. AZ91 alloy sheets were also manufactured by conventional die casting and compared with the semi-solid formed. It was found that the surface was more smooth and the dimensional accuracy was higher in case of the semi-solid formed.

• Composites Research
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• 제26권4호
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• pp.213-217
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• 2013

The focus in the present work is to study the agro-waste corn husk bio-filler as reinforcement for polypropylene. These materials have been created by extrusion and injection molding. The effect of filler content by 10, 20, 30 and 40 wt. % and mesh sizes of 50~100, 100 and 300 on the mechanical properties was studied. For the un-notched specimens, the results of flexural strength showed a declining trend with increase the filler loading and the results of impact strength showed an increasing trend with increase the mesh size. In contrast, enhanced flexural modulus was observed with increasing filler loading and size.

• 한국분무공학회지
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• 제13권3호
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• pp.149-155
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• 2008

An experimental study was performed to understand spray characteristics of the rotary atomizer for the slinger combustor. In this fuel injection system, fuel is injected and atomized in the combustor by centrifugal forces to engine shaft. The experimental apparatus consists of a high speed rotational spindle, rotary atomizer, pressure tank and acrylic case. The droplet size and velocity were measured by PDPA (phase Doppler particle analyzer), and spray was visualized by using high speed camera and Nd:Yag laser-based flash photography. From the test results, the droplet size (SMD) is largely affected by rotational speed, mass flow rate and the number of orifice. As the experimental results, we could understand the spray characteristics of the rotary atomizer for the slinger combustor and obtain the optimum shape of the rotary atomizer which is suitable for the small gas turbine engine.

• 한국분무공학회지
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• 제4권1호
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• pp.13-18
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• 1999

It has been known that spray characteristics have an important effect on the mixture formation and directly influence the engine performances and the emissions. Up to now, the measurement of droplet size is well developed such as PDPA and PMAS though the behavior of small droplets during secondary atomization is not clear. Particle image velocimetry(PIV), a planar measuring technique, is a very efficient tool for studying complicated behavior and a fast and reliable method to track numerous droplets during injection. In this study, two-color scanning PIV is designed to obtain quasi-instantaneous two dimensional velocity data by using he-ion laser, rotating mirror and beam splitter. This PIV method which has high temporal and spatial resolution provides the information about the small complex droplet behavior.

• 한국가시화정보학회지
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• 제1권1호
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• pp.75-81
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• 2003

A custom micro-PIV optics assembly has been used to measure the flow fold inside a T-junction of a microchannel. The micro-PIV system consists of microscope objectives of various magnifications, a dichroic cube, and an 8-bit CCD camera. Fluorescent particles of diameters 620 nm have been used with a Nd:YAG laser and color filters. A programmable syringe pump with Teflon tubings were used to inject particle-seeded distilled water into the channel at flow rates of 2.0, 4.0, 6.0 mL/hr. The micro-channels are fabricated with PDMS with a silicon mold, then O$_{2}$ -ion bonded onto a slide glass. Results show differences in flow characteristics and resolution according to fluid injection rates, and magnifications, respectively. The results include PIV data with vector-to-vector distances of 2 $\mu$m with 32 pixel-square interrogation windows at 50$\%$ overlap.