• 한국연소학회지
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• 제20권3호
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• pp.35-42
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• 2015

Investigating coal combustion in a large-scale boiler using computational fluid dynamics (CFD) requires a combination of flow and reaction models. These models include a number of rate constants which are often difficult to determine or validate for particular coals or furnaces. Nonetheless, CFD plays an important role in developing new combustion technologies and improving the operation. In this study, the model selection and rate constants for coal devolatilization, char conversion, and turbulent reaction were evaluated for a commercial wall-firing boiler. The influence of devolatilization and char reaction models was found not significant on the overall temperature distribution and heat transfer rate. However, the difference in the flame shapes near the burners were noticeable. Compared to the coal conversion models, the rate constant used for the eddy dissipation rate of gaseous reactions had a larger influence on the temperature and heat transfer rate. Based on the operation data, a value for the rate constant was recommended.

• 대한화학회지
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• 제30권1호
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• pp.3-8
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• 1986

물-글리세롤, 물-에틸렌 글리콜, 물-이소프로필 알코올 및 물-t-부틸 알코올의 2성분 혼합용매 중에서 cis-$[Co(en)_2ClNO_2]^+$착이온의 가용매 분해반응을 분광광도법으로 연구하였다. 용매의 극성이 커짐에 따라 반응속도도 커지는 경향이 있었으며 반응속도의 대수값과 $\frac{D-1}{2D+1}$값을 도시한 결과 비직선적인 관계를 나타내는 것으로 보아서 용매의 수소결합이나 분산력등의 비정전기적인 상호작용이 지배적으로 작용함을 알 수 있었다. log k와 Grundwald-Winstein의 Y값을 도시한 직선의 기울기와 Kivinen식에서 구한 전이상태에 관여하는 물분자의 수 n값으로부터 실험에 사용한 착물의 가용매 분해반응은 Id메카니즘으로 진행됨을 알았다. 한편 자유에너지 사이클의 결과는 초기상태에서 보다 전이상태에서 용매구조의 효과가 더 큼을 알 수 있었다.

• 대한화학회지
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• 제52권3호
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• pp.217-222
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• 2008

본 논문에서는 반응 매질의 부피가 촉매 반응 속도에 미치는 영향을 조사하였다. 단순하지만 정확한 모델에 대한 연구로부터 촉매 반응의 반응 속도 계수는 매질의 부피가 줄어들 수록 증가함을 알게 되었다. 평균 반응속도 상수(average reaction rate constant)는 Collins-Kimball 속도 상수의 일반화 된 형태로 얻어졌는데, 속도 상수는 부피의 효과를 보정해주는 인자를 포함하고 있다. 조사한 모델의 반응물 농도는 전통적 화학 반응론에서 예측되는 지수함수적 감소와는 상당한 차이를 보이는데 이는 기존 화학 반응속도론에서는 무시되는 반응분자 공간 분포의 비평형 확산운동(non-equilibrium diffusive dynamics)의 효과 때문이다. 반응 매질의 부피 가 유한한 점을 고려하면, 반응 시간이 충분히 오래 지났을 때, 기존의 확산지배 반응에서는 예측 되는 않는 지수 함수적 농도 감소가 얻어지는데, 그 속도 상수 역시 반응매질 크기에 의존한다.

• 한국재료학회지
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• 제14권3호
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• pp.163-167
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• 2004

TiAl(La)N thin films were oxidized in vacuum of about 7 Pa to reduce the oxidation of WC-Co as a substrate. The oxidation rate constants of the thin films were quantified by an assumption of parabolic oxidation. Increasing AI content significantly decreased the parabolic oxidation rate constant. A simultaneous addition of AI and La was more effective to reduce the oxidation rate. The parabolic oxidation rate constant of $Ti_{0.66}$ $Al_{0.32}$ $La_{ 0.02}$N thin film at 1273 K showed about ten times lower than that of TiN. The addition of a small amount of La with Al induced the preferential formation of dense $\alpha$ $-Al_2$$O_3$ film in oxide film, leading to the abrupt reduction of oxidation rate.

• 한국재료학회지
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• 제26권11호
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• pp.662-669
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• 2016

In order to identify changes in the nature of the particles due to changes in the inflow rate of the raw material solution, the present study was intended to prepare nano-sized cobalt oxide ($Co_3O_4$) powder with an average particle size of 50 nm or less by spray pyrolysis reaction using raw cobalt chloride solution. As the inflow rate of the raw material solution increased, droplets formed by the pyrolysis reaction showed more divided form and the particle size distribution was more uneven. As the inflow rate of the solution increased from 2 to 10 ml/min, the average particle size of the formed particles increased from about 25 nm to 40 nm, while the average particle size did not show significant changes when the inflow rate increased from 10 to 50 ml/min. XRD analysis showed that the intensity of the XRD peaks increased remarkably when the inflow rate of the solution increased from 2 to 10 ml/min. On the other hand, the peak intensity stayed almost constant when the inflow rate increased from 10 to 50 ml/min. With the increase in the inflow rate from 2 to 10 ml/min, the specific surface area of the particles decreased by approximately 20 %. On the contrary, the specific surface area stayed constant when the inflow rate increased from 10 to 50 ml/min.

• International Journal of Automotive Technology
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• 제2권3호
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• pp.109-115
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• 2001

A study has been conducted to clarify the effect of watery vapor concentration in hot ambient on droplet evaporation. Droplets of water, ethanol, n-hexadecaneand n-heptane were used in this experimental study. Ambient conditions are fixed at 470 K in temperature, 0.1 MPa in pressure and 2 m/s in velocity of ambient air. Watery vapor concentration was changed 0%～40% by 10% by add water to air. To obtain the time histories of droplet diameter after exposed in ambient, a suspended droplet in hot and humid ambient stream was synchronized with a back flash light, and enlarged droplet images were taken by a CCD camera. The evaporation rate constant of water droplet decreases slightly with the vapor concentration because diffusion velocity reduction of droplet vapor occurs on the surface. The values of ethanol and n-heptane droplet actively increase by effect that water from condensation of vapor flows into the droplet. The evaporation rate constant of n-hexadecane which has higher boiling point than water increases within around 30% of the concentration.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.173-180
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• 2004

In this study, a consolidometer for radially inward drainage under constant rate of strain (CRS) loading was developed. Theoretical solutions for determining the effective vertical stress and the coefficient of consolidation from the test result were also proposed. Reconstituted kaolinite samples which were consolidated up to 130 kPa were used to verify the developed consolidometer and the theory. Comparative experiments with CRS loading and incremental loading (IL) were carried out in radially in ward drainage as well as vertical and radially outward drainage. The results obtained from the developed CRS loading test agreed consistently with those of the conventional incremental loading test according to drainage directions. And the effect of drainage direction and drain diameter to consolidation characteristics was also evaluated. From the test results the applicability and the reliability of the suggested method were verified.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.221-228
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• 2003

The stress corrosion index of Kumamoto andesite are evaluated by two types of testing method. One is the uniaxial compression test under various water vapor pressures, and the other is the double torsion (DT) test under a constant water vapor pressure. For the uniaxial compression tests, the uniaxial compressive strength increases linearly with decreasing water vapor pressure on the double logarithmic coordinates. As the results, the stress corrosion index obtained is estimated 44. On the other hand, in the DT test, the relaxation (RLX) test and the constant displacement rate (CDR) test were conducted. For the CDR test, as the displacement rate of loading point increases, the crack velocity increases. However, the fracture toughness is constant regardless of the change in displacement rate and the average fracture toughness is evaluated $2.07MN/m^{3/2}$. For the RLX test, the crack velocity-stress intensity factor curves are smooth and linear. The stress corrosion index estimated from the curves is 37. Comparing stress corrosion indexes in the uniaxial compression test and the DT test, there is no significant difference in these values, and they are considered to be in coincident each other regardless of testing methods. Therefore, it is concluded that stress corrosion is one of material constants of rock.

• 대한화학회지
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• 제19권6호
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• pp.403-407
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• 1975

히드라진과 브롬의 반응속도를 직접 혼합법 및 일정전류 전해법에 의한 브롬화 이온의 전이시간을 측정하는 방법으로 측정하여, 황산 및 브롬화칼륨의 농도가 작을 때에 2차 반응속도 상수는 각각 $10^5\;및\;10^3mole^{-1}sec^{-1}$로 얻어졌다. 이는 $N_2H_4+Br_2{\rightarrow}N_2H_2,k_1=10^5$ 및 $N_2H_2+Br_2{\rightarrow}X,k_2=10^3$인 것으로 간주된다. 황산과 브롬화 이온의 농도가 클때에는 속도상수가 크게 감소하나 그 원인은 해명하지 못하였다.

• Journal of Pharmaceutical Investigation
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• 제20권2호
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• pp.89-95
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• 1990

Ethylcellulose-PEG 4000 film coated on core tablets was investigated as a potential drug delivery system for the controlled release of chlorpheniramine maleate (CPM). The kinetic analysis of the release data indicated that CPM release followed a diffusion-controlled model, where the quantity released per unit area is proportional to the square root of time. The effect of the film composition, CPM concentration, plasticizer concentration and CPM solubility on the release characteristics were examined. The release rate constant increased as CPM concentration increased. It also increased as the PEG 4000 content in the film increased above 10%(w/w), however, it decreased as the PEG 4000 content increased in the concentration range below 10%(w/w). The release rate constant was not affected by the coated weight on the core tablet. The film-coated tablets which contain CPM only in the coated film layer seemed to be a potential oral drug delivery system for the controlled release of CPM.