• 한국항공우주학회지
• /
• 제30권1호
• /
• pp.114-123
• /
• 2002

케로신/액체산소 추진기관을 갖는 초음속 로켓의 플룸 유동장을 9 화학종 14 반응 모델과 연계된 레이놀즈 평균 Navier-Stokes 방정식을 이용하여 해석하였다. 유한속도 화학반응이 플룸 유동장에 미치는 영향을 고찰하기 위하여 그 결과를 화학적 동결유동 해석 결과와 비교하였다. 계산은 상용 CFD 소프트웨어인 FLUENT 5를 이용하여 수행하였다. 반응 유동 해석 결과는 노즐 내부에서의 화학반응에 따른 연소가스의 온도 증가로 인해 전체적으로 동결유동에 비해 더 높은 온도장을 나타내었다. 플룸에서의 모든 화학반응은 전단류와 배럴 충격파 반사지점 후방의 고온 영역에 국한되어 일어났으며 본 해석의 경우 플룸내에서의 유한속도 화학반응이 유동에 미치는 영향은 미약한 것으로 나타났다. 그러나 본 연구에서 이루어진 유한속도 화학반응을 고려한 플룸 해석을 통하여 플룸에서의 주된 화학 반응 및 이들의 반응 메커니즘을 확인할 수 있었다.

• Journal of Electrochemical Science and Technology
• /
• 제6권4호
• /
• pp.146-151
• /
• 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.

• Bulletin of the Korean Chemical Society
• /
• 제12권6호
• /
• pp.692-698
• /
• 1991

The reaction path Smoluchowski equation approach developed in a recent work to calculate the rate constant for a diffusive multidimensional barrier crossing process is extended to incorporate the configuration-dependent diffusion matrix. The resulting formalism is then applied to the investigation of stilbene photoisomerization dynamics. Adapting a model two-dimensional potential and a model diffusion matrix proposed by Agmon and Kosloff [J. Phys. Chem.,91 (1987) 1988], we derive an eigenvalue equlation for the relaxation rate constant of the stilbene photoisomerization. This eigenvalue equation is solved numerically by using the finite element method. The advantages and limitations of the present method are discussed.

• 한국추진공학회지
• /
• 제6권1호
• /
• pp.12-20
• /
• 2002

케로신/액체산소 추진기관을 갖는 KSR-III 로켓의 플룸 유동장에 대하여 로켓 동체/플룸 유동장에 대한 통합적인 해석을 수행하였다. 기체 열-화학 모델이 유동장에 미치는 영향을 평가하여 로켓 유동장을 해석하는 목적에 가장 적합한 기체 모델을 제시하기 위하여 열량적 완전기체, 다윈 화학종 반응기체, 그리고 화학적 동결기체의 세 가지 기체 모델을 사용하여 유동장을 해석하고 그 차이를 검토하였다. 반응유동 해석 결과는 노즐 내부에서의 화학반응에 의한 연소가스의 온도 증가로 인해 다른 기체 열화학 모델에 비해 전체적으로 더 높은 온도 분포를 나타내었다. 플룸에서의 모든 화학반응은 전단류와 배럴 충격파 반사지점 후방의 고온 영역에 국한되어 일어났으며, 본 해석의 경우 플룸 내에서의 유한속도 화학반응이 유동에 미치는 영향은 미약한 것으로 나타났다. 그러나 본 연구에서 이루어진 유한속도 화학반응을 고려한 플룸 해석을 통하여 플룸에서의 주된 화학반응 및 반응 메커니즘을 확인할 수 있었다.

• 한국연소학회지
• /
• 제6권2호
• /
• pp.15-22
• /
• 2001

A pressure-based, unstructured finite volume method has been applied to couple the chemical kinetics and fluid dynamics and to capture effectively and accurately the steep gradient flame field. The pressure-velocity coupling is handled by two methodologies including the pressure-correction algorithm and the projection scheme. A stiff, operator-split projection scheme for the detailed nonequilibrium chemistry has been employed to treat the stiff reaction source terms. The conservative form of the governing equations are integrated over a cell-centered control volume with collocated storage for all transport variables. Computations using detailed chemistry and variable transport properties were performed for two laminar reacting flows: a counterflow hydrogen-air diffusion flame and a lifted methane-air triple flame. Numerical results favorably agree with measurements in terms of the detailed flame structure.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.1100-1103
• /
• 2003

One of the good ways to raise the rate of the electrochemical reaction is to broaden the effective surface area of the electrode by developing cylindrical nano-pores on the surfaces. The numerous pores of several nanometer in diameter can be used to enhance a specific faradaic reaction so that the nano-porous structure attract keen attention in terms of implication of new bio/chemical sensors, in which no chemical modification is involved. Amperometric glucose sensor is a representative example that needs the selective enhancement of glucose oxidation over the current due to physiological interferents such as ascorbic acid. The present paper reports how the ascorbic acid and glucose diffuse around the nano-porous surface by simulation study, for which 2D-FDM (Finite Difference Method) was adopted. The results of the simulation not only consist with those from electrochemical experiments but also reveal valuable potential for more advanced application of the nano-porous electrode.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1995년도 추계 학술대회논문집
• /
• pp.76-81
• /
• 1995

A numerical procedure for the analysis of transient behavior in a monolithic catalytic converter is presented. The thermal behavior of a monolithic catalytic converter is fully coupled with mass transfer and exothermic reaction between exhaust gases and the catalytic converter. In the present study, all these processes are solved simultaneously. The heat transfer process is approximated by combinging one dimensional convection and conduction and the chemical reaction is also simply modelled by using the concepts of reaction rate and reaction heat. All the partial diffenrential equations for the heat transfer, mass transfer and chemical reactions are appximated by using finite volume method. Resulting algebraic equations are solved using the Newton's method. To see the workability of present numerical method, two well known problems, say step increase and step decrease in the gas inlet temperature, have been calculated. Comparion of present solutions with previous solutions shows a good agreement.

• 한국정밀공학회지
• /
• 제19권8호
• /
• pp.92-99
• /
• 2002

This work investigated the optimal condition for an uniform deposition growth rate in the vertical cylindric CVD chamber. Heat transfer, surface chemical reaction and mass diffusion in the flow field of CVD chamber h,id been computed using Fluent v5.3 code. A SIMPLE based finite Volume Method (FVM) was adopted to solve the fully elliptic equations for momentum, temperature and concentration of a chemical species. The numerical analysis results show good agreements with the measurements obtained by N. Yoshikawa. The results obtained by the numerical analysis showed that the film growth rate in the center of a susceptor is increasing, as the inner flow approaches to the forced convection. To the contrast, as it approaches to the natural convection, that in the outside of a susceptor is increasing. As the Reynolds number increases, the uniformity may not hold due to the larger temperature gradient at a susceptor surface. Therefore, when the temperature gradient on the surface of a susceptor is zero, the film growth rate becomes uniform on most surface.

• 대한의용생체공학회:학술대회논문집
• /
• 대한의용생체공학회 1998년도 추계학술대회
• /
• pp.237-238
• /
• 1998

The kinetics of sulfite oxidation must be fast and the concentration of sulfite must be low to emulate oxygen uptake by blood. The kinetics were studied yielding a first order rate constant in sulfile, zero order in oxygen. Limitations of the technique were evaluated using the experimental rate constant and an adaptation of Lightfoot's approximation, while the reaction of hemoglobin is reversible and essentially instantaneous, that for sulfite is irreversible and finite. Thus if the approach to saturations not monotonic or if the mass transfer resistance is significantly lowered, e. g. when blood film thicknesses are thinner than a few hundred microns, deviations may occur.

• 전기화학회지
• /
• 제14권3호
• /
• pp.138-144
• /
• 2011

본 연구에서는 순환전위법으로 발생되는 전기화학적 신호를 모사하기 위한 전산프로그램을 구현하여, 전극주변에서 발생하는 전자 및 이온의 전달현상을 해석하였다. 물질확산이 지배적인 계에 대하여 반무한 확산모델과 전극반응만을 고려하여 지배방정식과 경계조건을 설정하였다. 순환전위법의 수치해를 구하기 위하여 양함수 유한차분법을 적용하였으며, MATLAB을 이용하여 프로그램을 작성하였다. 10 mM의 $K_3Fe(CN)_6$와 0.1 M KCl 전기화학계를 이용하여 ITO glass 전극에서 순환전위법을 실시하여 실험의 결과와 수치해를 비교하였다. 본 연구에서 구현된 프로그램은 실험 결과를 전반적으로 잘 예측하고 있으며, 특히 주사속도가 낮을수록 실험결과들이 수치해에 보다 근접하고 있었다. 주사속도에 부가하여 순환전위법에서 전극면적, 전극반응속도상수 그리고 전자이동수의 영향들을 정량적으로 고려할 수 있었다.