• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.7
• /
• pp.1-8
• /
• 2003

Numerical characteristics of air chemistry associated with hypersonic flows are described and are compared with those of hydrogen oxygen combustion, applying the partially implicit time integration method to air chemistry. This paper reveals that the time integration of air chemistry needs a chemical Jacobian for stable calculations. However the positive real eigenvalues in air chemistry are relatively smaller than those of hydrogen combustion, and the numerical integration is less sensitive than that with combustion. lt is also found that the application of the partia1ly irnplicit method reduces the computing time without numerical instabilities.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.05a
• /
• pp.88.2-88.2
• /
• 2011

본 연구는 아연/공기전지 설계기술 개발을 위한 기초 연구로서 전산해석을 이용하여 전해질 유동에 따른 아연/공기전지의 성능 예측에 관한 것이다. 전산해석모델은 전기화학 방정식과 유체유동 방정식으로 구성하였으며, 화학종 반응에 관한 지배방정식으로는 Nernst-Planck식을 이용하였고 전극표면의 전기화학반응은 Butler-Volmer식을 이용하였다. 또한 유체유동 방정식은 Navier-Stoke식을 적용하여 전해질 유동에 따른 전기화학적 성능 변화를 모사하였다. 아연/공기전지 성능 평가 실험으로부터 얻은 I-V 곡선과 전산해석결과와의 비교/분석을 통하여 전기화학모델의 타당성을 검증하였으며, 유체 유동 방정식과의 연동해석을 적용하여 전해질 유입 위치 및 유입 속도에 따른 아연/공기전지의 성능 변화를 조사하였다. 아연/공기전지의 성능은 전해질 유입 위치가 아연극에 가까울수록, 유입 속도가 빠를수록 향상되는 것을 확인할 수 있었다.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2001.11a
• /
• pp.83-84
• /
• 2001

액적화학은 SO4$^{-2}$ 생성에 중요한 역할을 할 뿐만 아니라 OH와 HO$_2$ 라디칼 생성에도 영향을 미친다. 따라서 기존 기상 광화학반응에 액적화학을 추가하여 산성비 모사를 하여왔다. 그러나 액적화학을 추가하기 위해서는 기액간의 물질전달을 포함하여야 하고 액적화학반응속도와 기상화학반응속도가 크게 다름으로써 수치적 풀이의 어려움이 가중되는 문제가 있다. 따라서 기존 연구에서는 기액간의 평형 및 시간 분리 등의 가정을 사용하여 액적화학 반응 추가에 따른 문제를 해결하여 왔다. 본 논문은 이러한 수치단순화의 정확도를 평가하려 한다. (중략)

• Fire Science and Engineering
• /
• v.22 no.3
• /
• pp.234-238
• /
• 2008

Autoignition suppression of hydrogen/air premixed mixtures by $CF_3CHFCF_3(HFP)$ was investigated computationally. Numerical simulation was performed in isobaric and homogeneous system to evaluate the induction times. The detailed chemistry of 93 species and 817 reaction mechanism was introduced for hydrogen/air/HFP mixtures. The result of pure hydrogen/air mixture show that the resulting value of induction time depends relatively weakly on the definition used event though there are various criteria for defining the induction time such as the inflection of temperature, OH and $O_2$ concentrations generally. Also, the autoignition temperature of $H_2/air$ mixture is estimated to about 850K, which is corresponds to the literature value. In the case of HFP addition in $H_2/air$ mixture, the results shows that there are several inflection points of radical concentration, and hence it might be to use the temperature for defining ignition delay. When HFP is added to stoichiometric $H_2/air$ mixture, the effect of ignition delay is outstanding above 10% HFP concentration. As HFP concentration increases, both dilution and chemical effects contribute to delay the ignition. Also, the chemical effect on the ignition delay is more considerable with the higher HFP concentration.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.6
• /
• pp.647-653
• /
• 2012

A short reaction mechanism for premixed $CH_4$-air flames at high pressure was developed using a reduction method based on the combined application of the simulation error minimization connectivity method and the iterative species-removal sensitivity method. It consisted of 43 species and 554 elementary reactions under the condition that it produces less than 5% of the maximum error. The flame structures obtained using a detailed reaction mechanism and the short reaction mechanism were compared for $CH_4$-air flames with various initial temperatures and equivalence ratios at high pressure, and the results were in good agreement. Therefore, the short reaction mechanism developed could reproduce the flame speeds, temperatures, and concentrations of major and minor species at high pressure.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.2
• /
• pp.197-204
• /
• 2012

We explore the evolution of metal plasma generated by high laser irradiances and its effect on the surrounding air by using shadowgraph images after laser pulse termination and X-ray diffraction (XRD) of aluminum plasma ablated by a high-power laser pulse (>1000 mJ/pulse) and oxygen from air. Hence, the formation of laser-supported detonation and combustion processes has been investigated. The essence of this paper is in observing the initiation of chemical reaction between the ablated aluminum plasma and oxygen from air by the high-power laser pulse (>1000 mJ/pulse) and in conducting a quantitative comparison of the chemically reactive laser-initiated waves with the classical detonation of an exploding aluminum (dust) cloud in air. The findings in this work may lead to a new method of initiating detonation from a metal sample in its bulk form without any need to mix nanoparticles with oxygen for initiation.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.6
• /
• pp.485-496
• /
• 2015

The present study presents experimental results on the characteristics of emission spectra of kerosene/air swirl flames. The aviation fuel Jet A-1, which is used for the liquid rocket engines of the Korea Space Launch Vehicle, is used with three different swirlers to investigate the swirl strength effects. The emission spectra from the flames are measured with a spectrometer as the swirl strength and combustion air temperature are varied. Chemiluminescence intensities of $OH^*$, $CH^*$ and $C_2{^*}$ are identified from the spectra. The chemiluminescence intensities from the kerosene flames show sensitivity to the swirl strength and are affected by changes in the combustion air temperature. Among the three radicals of interest, $C_2{^*}$ show the most significant changes in chemiluminescence intensity with the swirl strength and equivalence ratio. The intensity ratios $I_{OH^*}/I_{CH^*}$ and $I_{C_2{^*}}/I_{CH^*}$ are adequate for indicating changes in the equivalence ratio with the air and fuel mass flow rates, respectively.

• Korean Chemical Engineering Research
• /
• v.61 no.3
• /
• pp.446-455
• /
• 2023

A mathematical model for predicting the liquid circulation velocity in an airlift reactor was developed based on the mechanical energy balance of the fluid circulation loop. The model considered the energy loss due to a 90° turn, the energy loss due to friction, and the energy loss due to the change in cross-sectional area at each part of the reactor. The model that separately considered the loss coefficients related to friction, direction change, and cross-sectional area change was able to predict the liquid circulation velocity better than the previous model using lumped parameters. The liquid circulation velocity was measured by the tracer pulse method. Most of our experimental results obtained in external-loop airlift reactors, which had the top and bottom connecting pipes, as well as other investigators' results obtained in various types of airlift reactors, were well predicted by the developed model with an error within 20%. Useful empirical equations for the loss coefficient related to the 90° turn of the circulating fluid were obtained in external and internal-loop airlift reactors and used to predict the liquid circulation velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.4
• /
• pp.365-373
• /
• 2010

A chemical reactor model (CRM) was developed for a jet stirred reactor (JSR) to predict the emission of exhaust such as NOx. In this study, a two-PSR model was chosen as the chemical reactor model for the JSR. The predictions of NO formation in lean premixed methane-air combustion in the JSR were carried out by using CHEMKIN and GRI 3.0 methane-air combustion mechanism which include the four NO formation mechanisms. The calculated results were compared with Rutar's experimental data for the validation of the model. The effects of important parameters on NO formation and the contributions of the four NO pathways were investigated. In the flame region, the major pathway is the prompt mechanism, and in the post flame region, the major pathway is the Zelodovich mechanism. Under the lean premixed condition, the N2O mechanism is the important pathway in both flame and postflame regions.

• Proceedings of the Korean Institute of Industrial Safety Conference
• /
• 1997.05a
• /
• pp.55-58
• /
• 1997

대기오염의 주요원인은 소각로 연소가스와 자동차의 배기가스로 이들 이동 오염원에서 배출되는 오염가스는 일산화탄소, 탄화수소, 질소 및 황산화물 둥이고 이들은 공기중의 산소와 반응하여 광화학반응을하여 오존을 생성하며 기타 미세먼지, 수분과 반응하여 스모그를 생성하여 인체의 호흡기 계통 질병을 유발케한다. (중략)