• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.4
• /
• pp.371-381
• /
• 2004

Numerical simulation of $CO_2$ addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H$_2$-O$_2$ diffusion flames of a counterflow configuration. An artificial species, which displaces added $CO_2$ in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added $CO_2$, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added $CO_2$ causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of $CO_2$ addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, $CO_2$＋H=CO＋OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added $CO_2$ mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.6
• /
• pp.1045-1049
• /
• 2001

Wireless LANs in the 2.4 ㎓ ISM- band create a new Electromagnetic Compatibility (EMC) problem. We investigated the interference characteristics between such wireless LANs in the case of identical systems, systems with different technical parameters for modulation and demodulation, and using a Gaussian noise source as a disturbance source. Experimental results show that higher throughput is obtained when adjacent wireless LANs use different systems, and that interference characteristics can be evaluated experimentally using a Gaussian noise source. Calculated BER characteristics for the interference agree with experimental measurements, indicating that this calculation method can be used for the design of the wireless LAN network to avoid interference. It is possible to construct an efficient wireless LAN network by combining different wireless LAN systems.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.1
• /
• pp.9-14
• /
• 2004

The fluorescent lamp has been successfully modeled by employing the radial variation of particle density and considering driving circuit effects on the characteristics of discharge process. The electron energy distribution is assumed to have a Maxwellian. The electron mobility and the ambipolar diffusion coefficients are considered to vary with an electron energy rather than a simple uniform value. Energy states of mercury atom in the discharge process are regarded as six levels rather than simple 4 or 5 levels. These discharge processes have been accurately solved by numerically employing mixed the FDM and the 2nd Runge-Kutta method. This model was applied to analyzing real circuit. Simulation and experimental results were presented to verify the feasibility of the modeling. Simulation and experimental results were presented to verify the feasibility of the modeling.

• Journal of Advanced Marine Engineering and Technology
• /
• v.35 no.1
• /
• pp.82-88
• /
• 2011

The objective of this study is to investigate the validity of the dynamic sub-grid G-equation model to a complex turbulent premixed combustion such as bluff body stabilized turbulent premixed flames for the considering of the realistic engineering application. In this study, a new turbulent flame speed model, introduced by the sub-grid turbulent diffusivity and the flame thickness, is also proposed and is compared with an usual model using sub-grid turbulent intensity and with the experimental data. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.4
• /
• pp.264-271
• /
• 2009

Characteristics of a counter flowing diffusion flame, which is formulated by an oppositely-injected methane-jet flow in a narrow channel of a uniform air flow. The location of the flame fronts and the flame lengths were compared by changing the flow rates of fuel. To distinguish the effects of the narrow channel on the diffusion flame, a numerical simulation for an ideal two-dimensional flame was conducted. Overall trends of the flame behavior were similar in both numerical and experimental results. With the increase of the ratio of jet velocity to air velocity flame front moved farther upstream. It is thought that the flow re-direction in the channel suppresses fuel momentum more significantly due to the higher temperature and increased viscosity of burned gas. Actual flames in a narrow channel suffer heat loss to the ambient and it has finite length of diffusion flame in contrast to the numerical results of infinite flame length. Thus a convective heat loss was additionally employed in numerical simulation and closer results were obtained. These results can be used as basic data in development of a small combustor of a nonpremixed flame.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.5 no.4
• /
• pp.357-368
• /
• 1993

With the assumption of the diffusion dominated flow, a numerical model has been developed for undertow and turbulence structure under the breaking wave by using the $textsc{k}$-$\varepsilon$ turbulence model. Undertow is a strong mean current which moves seqwards below the level of wave trough in the surf zone. The turbulence, generated by wave breaking in the roller, spreads and dissipates downwards. The governing equations are composed of the equation of motion with the period-averaged shear stress due to waves; $textsc{k}$- and $\varepsilon$-equations with the turbulence energy Production due to wave breaking. They are discretised by the three-level fully implicit scheme, which can be solved by using Thomas algorithm. The model gives good agreements with measurements except for the station that is closest to the breaking point.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.10 no.2
• /
• pp.45-53
• /
• 1996

평균조도 계산법 중에서 국내에서 주로 사용되는 3배광법과 ZCM의 정확도를 비교하고, 그 적용한계를 파악하였다. 비교방법은 전반확산형 조명기구와 직접식 조명기구에 대하여 3배광법과 ZCM에 의한 조명률을 계산하고, 이 값들을 이용하여 여러 상황하에서의 평균조도를 계산하였다. 몬테카를로 시뮬레이션으로 동일상황에서의 조도값을 구하고, 이 값과 3배광법과 ZCM의 조도값을 각각 비교하였다. MCS법의 정확도는 Moon위 해석적인 방법과 비교하여 입증하였다. 연구결과는 다음과 같다. 1. 방의 크기에 따른 평균조도 비교에서 전반확　형 조명기구와 직접식 조명기구의 경우 3배광법 보다 ZCM이 평균조도 오차가 적었다. 2. 광원의 수 변화에 따른 평균조도 비교에서 직접식 조명기구의 경우 3배광법은 광원의 수가 증가할수록 평균조도 오차가 감소하다가 다시 증가하였고 ZCM 은 점차적으로 감소하였다. 3. 실내면 반사율 변화에 따른 비교에서 직접식 조명기구의 경우 오차 범의가 3배광법에서 크고 ZCM에서 적게 나타냈다. 4. 방의 형태 변화에 따른 평균조도 비교에서 직접식 조명기구의 경우 방의 폭이 좁고 길이가 긴 공간에서 3배광법과 ZCM모두 오차가 크게 낱났다. 또 정방형에서 가까울수록 오차는 작아지면서 3배광법 보다 ZCM의 오차가 적었다. 그러므로 우리나라에서 혼용되고 있는 3배광법과 ZCM중에서 정확도가 높은 ZCM선택이 바람직하다.

• Journal of the Korean Applied Science and Technology
• /
• v.34 no.3
• /
• pp.694-703
• /
• 2017

Many residents living near the cement factories are facing unpleasant odors. Thus, various efforts have been attempted to reduce the emission of odorous compounds from the cement manufacturing processes. This study focused on analysis of Acetaldehyde and their dispersion in vicinity of the residential area using theoretical calculation such as numerical simulation and dispersion model. The most significant odor species was acetaldehyde indicating 2 ppb at the test point, and the estimated concentration was similar to the value by Calpuff calculation. The modelling work revealed the emission source of the factory to influence the test site.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.8 no.2
• /
• pp.95-101
• /
• 2004

An experimental investigation was conducted to investigate the effects of the equivalence ratio and air mass flux on the combustion efficiency in a solid fuel ramjet used fuel grains which were highly loaded with boron carbide. Combustion efficiency increased with increasing equivalence ratio (grain length), and decreasing air mass flux. Higher inlet air temperature produced higher combustion efficiencies, apparently the result of enhanced combustion of the larger boron particles those burn in a diffusion controlled regime. Short grains which considered primarily of the recirculation region produced larger particles and lower combustion efficiencies. The result of the normalized combustion efficiency increased with inlet air temperatures coincident with the result of the Brayton cycle thermal and the total efficiency relating to the heat input.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.4
• /
• pp.1-9
• /
• 2007

Many processing companies are facing environmental regulations such as decreasing NOx emissions when they by to increase thermal efficiencies of combustor. We study a potential new method that may achieve both increase of thermal efficiency and decrease of NOx emissions. This new concept of burner, the precessing jet burner, is known to significantly reduce pollutants such as NOx emissions and simultaneously increase radial heat transfer. This precessing jet nozzle may increase the combustion efficiency of gas turbine engine. A basic research on characteristics of precessing jet nozzle has been conducted using FLUENT and laser visualization technique. Velocities at He nozzle cross-section are compared with the published experimental results. Precessing jet nozzle with centerbody results in better precessing phenomena.