• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제44회 KOSCO SYMPOSIUM 초록집
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• pp.29-31
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• 2012

The effects of combustion parameters on the characteristics of a steam-methane reformer. The reformer system was numerically simulated using a simplified two-dimensional axisymmetric model domain with an appropriate user-defined function. The fuel ratio, defined as the ratio of methane flow rate in the combustor to that in the reactor, was varied from 20 to 80%. The equivalence ratio was changed from 0.5 to 1.0. The results indicated that as the fuel ratio increased, the production rates of hydrogen and carbon monoxide increased, although their rates of increase diminished. In fact, at the highest heat supply rates, hydrogen production was actually slightly decreased. Simulations showed that equivalence ratio of 0.7 yielded the highest steam-methane mixture temperature despite a 43% higher air flow rate than the stoichiometric flow rate. This means that the production of hydrogen and carbon monoxide can be increased by adjusting the equivalence ratio, especially when the heat supply is insufficient.

• 한국전기전자재료학회논문지
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• 제18권7호
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• pp.662-666
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• 2005

Silicon nitride $(SiN_x)$ film is a promising material for anti-reflection coating and passivation of multicrystalline silicon (me-Si) solar cells. In this work, a plasma-enhanced chemical vapor deposition (PECVD) system with batch-type reactor tube was used to prepare highly robust $SiN_x$ films for screen-printed mc-Si solar cells. The Gas flow ratio, $R=[SiH_4]/[NH_3]$, in a mixture of silane and ammonia was varied in the range of 0.0910.235 while maintaining the total flow rate of the process gases to 4,200 sccm. The refractive index of the $SiN_x$ film deposited with a gas flow ratio of 0.091 was measured to be 2.03 and increased to 2.37 as the gas flow ratio increased to 0.235. The highest efficiency of the cell was $14.99\%$ when the flow rate of $SiH_4$ was 350 sccm (R=0.091). Generally, we observed that the efficiency of the mc-Si solar cell decreased with increasing R. From the analysis of the reflectance and the quantum efficiency of the cell, the decrease in the efficiency was shown to originate mainly from an increase in the surface reflectance for a high flow rate of $SiH_4$ during the deposition of $SiN_x$ films.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.9-12
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• 2010

본 논문은 연료 과농 연소 환경 하의 이중 와류 동축형 분사기의 유량 통과 특성 파악을 위해 수행한 실험결과를 수록하였다. 액체산소와 케로신(Jet A-1)을 사용하여 연소시험을 수행하고 유량 통과 특성을 유량계수로 표현하였다. 유량계수 산출을 위해 유량, 압력, 온도를 계측하였다. 연료 분사기의 경우, 산화제 측 분사기 형상, 연소압, 혼합비에 관계없이 일정한 유량 계수 값을 보였다. 이에 반해 산화제 분사기는 연소압과 혼합비 변화에 영향을 받는 것으로 나타났다. 화염 형성 변화가 유량계수 변화에 특히 산화제 측에 영향을 주고 있음을 밝혔다.

• 한국표면공학회지
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• 제25권5호
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• pp.271-281
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• 1992

Amorphous hydrogenated silicon carbide(a-Si1-xCx : H) films have been prepared by the rf sputtering using a silicon target in a gas mixture of Argon and methane with varying methane gas flow rate(fCH) in the range of 1.5 to 3.5 sccm at constant Argon flow rate of 30sccm and rf power in the range of 3 to 6 W/$\textrm{cm}^2$. The effects of methane flow rate and rf power on the structure and optical properties of a-Si1-xCx : H films have been analysed by measuring both the IR absorption spectrum and the UV transmittance for the films. With increasing the methane flow rate, the optical band gap(Eg) of a-Si1-xCx : H films increases gradually from 1.6eV to the maximum value of 2.42eV at rf power of 4 W/$\textrm{cm}^2$, which is due to an increases in C/Si ratio in the films by an significant increase in the number of C-Hn bonds. As the rf power increases, the number of Si-C and Si-Hn bonds increases rapidly with simultaneous reduction in the number of C-Hn bonds, which is associated with an increase in both degree of methane decomposition and sputtering of silicon. The effects of rf power on the Eg of films are considerably influenced by the methane flow rate. At low methane flow rate, the Eg of films decreased from 2.3eV to 1.8eV with the rf power. On the other hand, at high methane flow rate, that of films increased slowly to 2.4eV.

• 소성∙가공
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• 제14권1호
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• pp.65-70
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• 2005

A phase mixture model was employed to simulate the deformation behaviour of metallic materials covering a wide grain size range from micrometer to nanometer scale. In this model a polycrystalline material is treated as a mixture of two phases: grain interior phase whose plastic deformation is governed by dislocation and diffusion mechanisms and grain boundary 'phase' whose plastic flow is controlled by a boundary diffusion mechanism. The main target of this study was the effect of grain size on stress and its strain rate sensitivity as well as on the strain hardening. Conventional Hall-Petch behaviour in coarse grained materials at high strain rates governed by the dislocation glide mechanism was shown to be replaced with inverse Hall-Petch behaviour in ultrafine grained materials at low strain rates, when both phases deform predominantly by diffusion controlled mechanisms. The model predictions are illustrated by examples from literature.

• The Journal of Asian Finance, Economics and Business
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• 제7권11호
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• pp.45-53
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• 2020

Past literatures have not studied the impact of real-world events or information on the return and volatility of virtual currencies, particularly on the COVID-19 event, day-of-the-week effect, daily high-low price spreads and information flow rate. The study uses the ARMA-GARCH model to capture Bitcoin's return and conditional volatility, and explores the impact of information flow rate on conditional volatility in the Bitcoin market based on the Mixture Distribution Hypothesis (Clark, 1973). There were 3,064 samples collected during the period from 1^st of January 2012 to 20^th April, 2020. Empirical results show that in the Bitcoin market, a daily high-low price spread has a significant inverse relationship for daily return, and information flow rate has a significant positive relationship for condition volatility. The study supports a significant negative relationship between information asymmetry and daily return, and there is a significant positive relationship between daily trading volume and condition volatility. When Bitcoin trades on Saturday & Sunday, there is a significant reverse relationship for conditional volatility and there exists a day-of-the-week volatility effect. Under the impact of COVID-19 event, Bitcoin's condition volatility has increased significantly, indicating the risk of price changes. Finally, the Bitcoin's return has no impact on COVID-19 events and holidays (Saturday & Sunday).

• 한국산업정보학회논문지
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• 제5권4호
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• pp.67-72
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• 2000

본 논문에서는 산업폐기물인 폐아스콘을 산업자원으로 재활용하기 위해 플랜트 설비면에서는 2중 드라이어 구조를 개발하였고 이 설비를 바탕으로 폐아스콘의 혼합비율에 따른 안전도 및 경제성분석을 실시하였다. 다양한 혼합비율에 따른 연구분석 결과, 폐아스콘 용량이 35%에서 흐름값, 안정도, 공극률, 밀도 및 수분 취약성이 충분한 안전도를 가지는 것으로 나타났다. 다만 간접인장강도가 다소 기준치에 못미치거나 근소한 차이이기 때문에 문제가 되지 않는다고 판단된다. 이 기준에 적합하게 사용될 때 설비투자에 대한 경제성도 있는 것으로 판명되었다.

• 한국산업정보학회:학술대회논문집
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• 한국산업정보학회 2000년도 추계공동학술대회논문집
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• pp.471-482
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• 2000

본 논문에서는 산업폐기물인 페아스콘을 산업자원으로 재활용하기 위해 플랜트 설비면에서는 2중 드라이어 구조를 개발하였고 이 설비를 바탕으로 폐아스콘의 혼합비율에 따른 안전도 및 경제성분석을 실시하였다. 다양한 혼합비율에 따른 연구분석 결과, 폐아스콘 사용량이 35%에서 흐름 값, 안정도, 공극률, 밀도 및. 수분 취약성이 충분한 안전도를 가지는 것으로 나타났다. 다만 간접인장강도가 다소 기준치에 못 미치나 근소한 차이이기 때문에 문제가 되지 않는다고 판단된다. 이 기준에 적합하게 사용될 때 설비투자에 대한 경제성도 있는 것으로 판명되었다.

• Advances in environmental research
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• 제3권3호
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• pp.231-251
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• 2014

The present study examines the phosphate adsorption potential and behavior of mixture of Ground Burnt Patties (GBP), a solid waste generated from cooking fuel used in earthen stoves and Red Soil (RS), a natural substance in fixed bed column mode operation. The characterization of adsorbent was done by Proton Induced X-ray Emission (PIXE), and Proton Induced ${\gamma}$-ray Emission (PIGE) methods. The FTIR spectroscopy of spent adsorbent reveals the presence of absorbance peak at $1127cm^{-1}$ which appears due to P = O stretching, thus confirming phosphate adsorption. The effects of bed height (10, 15 and 20 cm), flow rate (2.5, 5 and 7.5 mL/min) and initial phosphate concentration (5 and 15 mg/L) on breakthrough curves were explored. Both the breakthrough and exhaustion time increased with increase in bed depth, decrease in flow rate and influent concentration. Thomas model, Yoon-Nelson model and Modified Dose Response model were used to fit the column adsorption data using nonlinear regression analysis while Bed Depth Service Time model followed linear regression analysis under different experimental condition to evaluate model parameters that are useful in scale up of the process. The values of correlation coefficient ($R^2$) and the Sum of Square Error (SSE) revealed the Modified Dose Response model as the best fitted model to the experimental data. The adsorbent mixture responded effectively to the desorption and reusability experiment. The results of this finding advocated that mixture of GBP and RS can be used as a low cost, highly efficient adsorbent for phosphate removal from aqueous solution.

• 멤브레인
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• 제4권4호
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• pp.197-204
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• 1994

본 연구에서는 hollow fiber 막모듈을 통한 순수 $CH_4,\;CO_2$기체와 $CH_4/CO_2$ 혼합기체의 투과 특성을 살펴 보고, 이를 모사값과 비교하여 보았다. 순수 기체의 투고율은 온도에 따라 Arrhenius type으로 증가하였으며, 활성화에너지는 $CO_2$는 6.61kJ/mol, $CH_4$는 25.26kJ/mol로 나타났다. 혼합기체의 투과에 있어서 투과부의 유량과 $CO_2$ 조성, 그리고 배제부의 $CH_4$조성은 cut의 증가에 따라 증가하였다. 분리인자는 5~20atm의 압력과 cut이 20으로 고정된 상태에서 20~40의 범위에 있었으며, 압력이 증가하고 온도가 감소할수록 증가하는 경향을 나타내었다. 실험결과와 모사결과는 투과부 유량과 $CO_2$조성의 경우 8% 이내에서, 배제부의 $CH_4$조성의 경우 15% 이내에서 일치하였다.