• 제목/요약/키워드: Reaction rate

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수소 생산을 위한 동축원통형 수증기 개질기의 성능 및 열유속에 대한 수치해석 연구 (Numerical Study on the Performance and the Heat Flux of a Coaxial Cylindrical Steam Reformer for Hydrogen Production)

  • 박준근;이신구;배중면;김명준
    • 대한기계학회논문집B
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    • 제33권9호
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    • pp.709-717
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    • 2009
  • Heat transfer rate is a very important factor for the performance of a steam reformer because a steam reforming reaction is an endothermic reaction. Coaxial cylindrical reactor is the reactor design which can improve the heat transfer rate. Temperature, fuel conversion and heat flux in the coaxial cylindrical steam reformer are studied in this paper using numerical method under various operating conditions. Langmuir-Hinshelwood model and pseudo-homogeneous model are incorporated for the catalytic surface reaction. Dominant chemical reactions are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming (DSR) reaction. Although coaxial cylindrical steam reformer uses 33% less amount of catalyst than cylindrical steam reformer, its fuel conversion is increased 10 % more and its temperature is also high as about 30 degree. There is no heat transfer limitation near the inlet area at coaxial-type reactor. However, pressure drop of the coaxial cylindrical reactor is 10 times higher than that of cylindrical reactor. Operating parameters of coaxial cylindrical steam reformer are the wall temperature, the inlet temperature, and the Gas Hourly Space Velocity (GHSV). When the wall temperature is high, the temperature and the fuel conversion are increased due to the high heat transfer rate. The fuel conversion rate is increased with the high inlet temperature. However, temperature drop clearly occurs near the inlet area since an endothermic reaction is active due to the high inlet temperature. When GHSV is increased, the fuel conversion is decreased because of the heat transfer limitation and short residence time.

상용 미분탄 보일러 연소해석에서 석탄 탈휘발 모델 및 난류반응속도의 영향 평가 (Effects of coal devolatilization model and turbulent reaction rate in numerical simulations of a large-scale pulverized-coal-fired boiler)

  • 양주향;김정은;류창국
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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    • pp.59-62
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    • 2014
  • Predicting coal combustion by computational fluid dynamics (CFD) requires a combination of complicated flow and reaction models for turbulence, radiation, particle flows, heterogeneous combustion, and gaseous reactions. There are various levels of models available for each of the phenomena, but the use of advanced models are significantly restricted in a large-scale boiler due to the computational costs and the balance of accuracy between adopted models. In this study, the influence of coal devolatilization model and turbulent mixing rate was assessed in CFD for a commercial boiler at 500 MWe capacity. For coal devolatilization, two models were compared: i) a simple model assuming single volatile compound based on proximate analysis and ii) advanced model of FLASHCHAIN with multiple volatile species. It was found out that the influence of the model was observed near the flames but the overall gas temperature and heat transfer rate to the boiler were very similar. The devolatilization rate was found not significant since the difference in near-flame temperature became noticeable when it was multiplied by 10 or 0.1. In contrast, the influence of turbulent mixing rate (constant A in the Magnussen model) was found very large. Considering the heat transfer rate and flame temperature, a value of 1.0 was recommended for the rate constant.

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Methylthioisocyanate 합성반응 공정의 열적위험 특성 (Characteristics of Thermal Hazard in Methylthioisocyanate Synthesis Reaction Process)

  • 한인수;이근원;이주엽
    • 한국안전학회지
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    • 제27권5호
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    • pp.77-87
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    • 2012
  • Compared to a batch reactor, where all reactants are initially charged to the reactor, the semi-batch reactor presents serious advantages. The feed of at least one of the reactants provides an additional way of controlling the reaction course, which represents a safety factor and increases the constancy of the product quality. The aim of this study was to investigate the characteristics of thermal hazard such as a feed time, catalysis concentration and solvent concentration in methylthioisocyanate(MTI) synthesis reaction process. The experiments were carried out by the Multimax reactor system and Accelerating rate calorimeter(ARC). The MTI synthesis reaction process has many reaction factors and complicated reaction mechanism of multiphase reaction. Through this study, we can use as a tool for assessment of thermal hazard of other reaction processes by applying experiment method provided.

Effects of the Polarization Resistance on Cyclic Voltammograms for an Electrochemical-Chemical Reaction

  • Chang, Byoung-Yong
    • Journal of Electrochemical Science and Technology
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    • 제6권4호
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    • pp.146-151
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    • 2015
  • Here I report an electrochemical simulation work that compares voltammetric current and resistance of a complex electrochemical reaction over a potential scan. For this work, the finite element method is employed which are frequently used for voltammetry but rarely for impedance spectroscopy. Specifically, this method is used for simulation of a complex reaction where a heterogeneous faradaic reaction is followed by a homogeneous chemical reaction. By tracing the current and its polarization resistance, I learn that their relationship can be explained in terms of rate constants of charge transfer and chemical change. An unexpected observation is that even though the resistance is increased by the rate of the following chemical reaction, the current can be increased due to the potential shift of the resistance made by the proceeding faradaic reaction. This report envisions a possibility of the FEM-based resistance simulation to be applied to understand a complex electrochemical reaction. Until now, resistance simulations are mostly based on equivalent circuits or complete mathematical equations and have limitations to find proper models. However, this method is based on the first-principles, and is expected to be complementary to the other simulation methods.

평류안뜰자극이 자율신경성 반응에 미치는 영향 (The Effect of Galvanic Vestibular Stimulation on Autonomic Nervous System Response)

  • 문화영;강솔;김화성;허소영;손유리;이정우
    • 대한임상전기생리학회지
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    • 제8권2호
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    • pp.19-24
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    • 2010
  • Purpose : This study aims to examine the influences of galvanic vestibular stimulation on autonomic reaction of normal adults. Methods : Participants in this research totaled 28 (14 men and 14 women). Galvanic vestibular stimulation was conducted with a binaural electrode configuration for 60 sec. Galvanic vestibular stimulation measurements were conducted with the subjects in a prone position. Measured items included skin conductance, blood flow, pulse rate, and respiratory rate. Measurements were repeated for a total of five times, before application, during application, after application, 5 minutes after application and 10 minutes after application. Results : Skin conductance reaction showed statistically significant differences in changes depending on time after galvanic vestibular stimulation and there were statistically differences in changes of blood flow, pulse rate and respiratory rate after galvanic vestibular stimulation. Conclusion : Blood flow, pulse rate and respiratory rate of autonomic reactions were not influenced by galvanic vestibular stimulation, but skin conductance reaction was influenced by it and it was found that it was reduced during and after stimulation rather than before stimulation. Consequently, it was considered that galvanic vestibular stimulation affected the autonomic reaction.

Electrochemical Promotion of Pt Catalyst for The Oxidation of Carbon Monoxide

  • Shin, Seock-Jae;Kang, An-Soo
    • 대한안전경영과학회지
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    • 제2권4호
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    • pp.187-195
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    • 2000
  • Electrochemical promotion of the reaction rate was investigated for CO oxidation in a solid electrolyte catalytic reactor where a thin film of Pt was deposited on the yttria stabilized zirconia as an electrode as well as a catalyst. It was shown under open circuit condition that potential was a mixed potential of $O_2$exchange reaction and electrochemical reaction induced by CO. The effect of electrochemical modification on the CO oxidation rate was studied at various overpotentials and $P_{CO}$$P_{O2}$.

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Quantitative Evaluation on Photocatalytic Activity of Anatase TiO2 Nanocrystals in Aqueous Solution

  • Jeon, Byungwook;Kim, Yu Kwon
    • Applied Science and Convergence Technology
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    • 제24권4호
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    • pp.96-101
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    • 2015
  • Quantitative evaluation of photocatalytic activity of oxide nanoparticles in aqueous solution is quite challenging in that the kinetic reaction rate is determined by a complicated interplay among various limiting factors such as light scattering and absorption, diffusion and adsorption of reactants in condensed liquid phase, photoexcited charge separation and recombination rate, and the exact nature of active sites determined by detailed morphology and crystallinity of nanocrystals. Here, we present our simple experimental results showing that the kinetic regime of a typical photocatalytic degradation experiment over UV-irradiated $TiO_2$ nanoparticles in aqueous solution is in that dominated by the photoactivity of $TiO_2$ and its concentration. This result lays a firm ground of using the measured kinetic reaction rate in evaluating photocatalytic efficiency of oxide nanocrystals under evaluation.

패각 폐기물을 이용한 황화반응 모델에 관한 연구 (A Study on the Model of Sulfidation Kinetics Using Seashell Wastes)

  • 김영식
    • 한국환경보건학회지
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    • 제30권5호
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    • pp.395-401
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    • 2004
  • In this study, lots of methods have been studing to utilize energy and decrease contaminated effluents. There has been great progress on IGCC (Integrated gasification combined cycle) to reduce thermal energy losses. The following results have been conducted from desulfurization experiments using waste shell to remove $H_{2}S$. Unreacted core model ior desulfuriration rate prediction of sorbent was indicated. These were linear relationship between time and conversion. So co-current diffusion resistance was conducted reaction rate controlling step. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. Maximum desulfurization capacity was observed at 0.631 mm for lime, oyster and hard-shelled mussel. The kinetics of the sorption of $H_{2}S$ by CaO is sensitive to the reaction temperature and particle size at $800^{\circ}C$, and the reaction rate of oyster was faster than the calcined limestone at $700^{\circ}C$.

배치형 내부 사이클론식 순환유동층 연소로내 2차 공기 주입에 의한 슬러지 소각 유해 배가스 저감효과 (Effect of Secondary Air Injection on Emission from Sludge Incineration in a Batch-type Internally Cycloned Circulating Fluidized Bed Combustor)

  • 장석돈;신동훈;황정호
    • 한국연소학회지
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    • 제7권3호
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    • pp.16-22
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    • 2002
  • Combustion performance of an internally cycloned circulating fluidized bed for paper sludge was discussed through a series of batch type experiments. Operation parameters such as water content, feeding mass of sludge and secondary air injection rate were varied to find out the effect on the combustion performance, which was examined with carbon conversion rate and pollutant emission such as CO and NOx. A conventional solid fuel reaction was observed in the experiments of varying water content and feeding mass of the sludge, which is characterized with kinetic limited reaction zone, diffusion limited reaction zone and transition zone. Secondary air injection with swirl enhances the mixing of the gas phase as well as the solid phase, and improves combustion efficiency accompanied with higher carbon conversion rate and lower pollutant emission rate.

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${\beta}$-Nitrostyrene에 대한 Mercaptan의 親核性 添加反應에 關한 硏究 (I) (The Kinetics and Mechanism of Nucleophilic Addition of Mercaptan to a ${\beta}$-Nitrostyrene in Acidic Media (I))

  • 박옥현
    • 대한화학회지
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    • 제12권3호
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    • pp.106-113
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    • 1968
  • 여러 酸性溶媒 속에서 3,4-methylenedioxy-${\beta}$-nitrostyrene에 대한 n-butylmercaptan의 親核性 添加反應速度常數를 측정하여 넓은 pH범위에서 잘 맞는 反應速度式을 구하였다. 이 식에 의하면 pH3이하에서는 mercaptan분자가 첨가하며 pH6이상에서는 mercaptide ion이 첨가함을 알 수 있고 이 중간 pH범위에서 일어나는 복잡한 반응 메카니즘도 이 식에 의해 정량적으로 잘 설명할 수 있음을 알았다.

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