• 한국환경과학회지
• /
• 제13권2호
• /
• pp.175-180
• /
• 2004

A prompt gamma-ray neutron activation (PGNA) system was simulated by the Monte Carlo N-Particle transport code (MCNP-4A) to estimate the level at which the scattered photon fluence rate, the absolute efficiency of the HPGe-detector, the volume of the concrete sample and the $^{35}$ /Cl(n, ${\gamma}$) reaction rate in this sample contribute to the count rate in the NaCl concentration measurement. The n- ${\gamma}$ fluence rates at the ST-2 beam tube exit of the HANARO reactor were used as input data, and the GAMMA-X type HPGe detector was modeled to tally 1.1649 MeV ${\gamma}$ -rays emitted from the $^{35}$ Cl(n, ${\gamma}$) reaction in the concrete sample. For three cylindrical concrete samples of 13.8, 46.8 and 157.1 ㎤ volumes, respectively, the relations between the NaCl weight fractions of 0.1, 1, 2 and 5 % in each of the concrete samples and the 1.1 649 MeV pulses created in the HPGe detector model were studied. As a result, it was found that the count rate at the same NaCl concentration nearly depends on the volume of the samples in a simulated condition of the same NaCl concentration samples, and that the linearities of the NaCl concentration calibration curves were reasonable in the narrow range of the NaCl weight fraction.

• 한국수소및신에너지학회논문집
• /
• 제22권3호
• /
• pp.386-401
• /
• 2011

Mathematical models for various steps in coal gasification reactions were developed and applied to investigate the effects of operation parameters on dynamic behavior of gasification process. Chemical reactions considered in these models were pyrolysis, volatile combustion, water shift reaction, steam-methane reformation, and char gasification. Kinetics of heterogeneous reactions between char and gaseous agents was based on Random pore model. Momentum balance and Stokes' law were used to estimate the residence time of solid particles (char) in an up-flow reactor. The effects of operation parameters on syngas composition, reaction temperature, carbon conversion were verified. Parameters considered here for this purpose were $O_2$-to-coal mass ratio, pressure of reactor, composition of coal, diameter of char particle. On the basis of these parametric studies some quantitative parameter-response relationships were established from both dynamic and steady-state point of view. Without depending on steady state approximation, the present model can describe both transient and long-time limit behavior of the gasification system and accordingly serve as a proto-type dynamic simulator of coal gasification process. Incorporation of heat transfer through heterogenous boundaries, slag formation and steam generation is under progress and additional refinement of mathematical models to reflect the actual design of commercial gasifiers will be made in the near futureK.

• 대한환경공학회지
• /
• 제22권5호
• /
• pp.907-918
• /
• 2000

본 연구에서는 도시고형폐기물을 구성하는 주요한 성분중의 하나인 셀룰로오스와 플라스틱의 열분해 특성을 열중량시스템에서 조사하였다. 실험은 온도범위 400~900K에서 제 실험변수에 따라 질소분위기에서 수행하였으며, 압축한 도시고형폐기물에 적용하기 위한 수정 Arrhenius 열분해 모델을 제안하였다. 승온속도를 20, 30, 40K/min로 변화시키면서 수행한 실험에서, 도시고형폐기물을 구성하는 순수물질의 활성화에너지는 셀룰로오스계열의 경우 117~166kJ/mol, 플라스틱계열은 187~239kJ/mol이며, 반응차수는 1.1~1.9의 범위에 있었다. 압축한 도시고형폐기물은 승온속도, 압축비, 입경의 증가에 따라 char의 수율이 증가하였다. 또한 압축도시고형폐기물의 열분해 과정을 Arrhemius식과 열전달이론을 이용하여 수정 제안한 모델의 적용 결과 기존의 모델보다 실험결과와 더 잘 일치하였다.

• 전기학회논문지
• /
• 제62권4호
• /
• pp.554-561
• /
• 2013

In this paper, we introduce a modeling and a process simulator developed with the aid of pRBFNNs for activated sludge process in the sewage treatment system. Activated sludge process(ASP) of sewage treatment system facilities is a process that handles biological treatment reaction and is a very complex system with non-linear characteristics. In this paper, we carry out modeling by using essential ASP factors such as water effluent quality, the manipulated value of various pumps, and water inflow quality, and so on. Intelligent algorithms used for constructing process simulator are developed by considering multi-output polynomial radial basis function Neural Networks(pRBFNNs) as well as Fuzzy C-Means clustering and Particle Swarm Optimization. Here, the apexes of the antecedent gaussian functions of fuzzy rules are decided by C-means clustering algorithm and the apexes of the consequent part of fuzzy rules are learned by using back-propagation based on gradient decent method. Also, the parameters related to the fuzzy model are optimized by means of particle swarm optimization. The coefficients of the consequent polynomial of fuzzy rules and performance index are considered by the Least Square Estimation and Mean Squared Error. The descriptions of developed process simulator architecture and ensuing operation method are handled.

• 한국입자에어로졸학회지
• /
• 제8권4호
• /
• pp.173-180
• /
• 2012

SiC particles, 8.3 ${\mu}m$ in volume average diameter, were chlorinated in an alumina tubular reactor, 2.4 cm in diameter and 32 cm in length, with reactor temperature varied from 100 to $1200^{\circ}C$. The flow rate of the gas admitted to the reactor was held constant at 300 cc/min, the mole fraction of chlorine in the gas at 0.1 and the reaction time at 4 h. The chlorination was negligibly small up to the temperature of $500^{\circ}C$. Thereafter, the degree of chlorination increased remarkably with increasing temperature until $900^{\circ}C$. As the temperature was increased further from 900 to $1200^{\circ}C$, the increments in chlorination degree were rather small. At $1200^{\circ}C$, the chlorination has nearly been completed. The surface area of the residual carbon varied with chlorination temperature in a manner similar to that with the variation of chlorination degree with temperature. The surface area at $1200^{\circ}C$ was 912 $m^{2}/g$. A simple model was developed to predict the conversion of a SiC under various conditions. A Langmuir-Hinshelwood type rate law with two rate constants was employed in the model. Assuming that the two rate constants, $k_{1}$ and $k_{2}$, can be expressed as $A_{1e}^{-E_{1}/RT}$ and $A_{2e}^{-E_{2}/RT}$, the four parameters, $A_{1}$, $E_{1}$, $A_{2}$, and $E_{2}$ were determined to be 32.0 m/min, 103,071 J/mol, 2.24 $m^{3}/mol$ and 39,526 J/mol, respectively, through regression to best fit experimental data.

• International Journal of Aeronautical and Space Sciences
• /
• 제16권4호
• /
• pp.548-559
• /
• 2015

We performed a numerical simulation based on the two-dimensional (2-D) unsteady Euler's equation with a single-step Arrhenius reaction model in order to investigate the detonation wave front propagation of an Argon (Ar) diluted oxy-hydrogen mixture ($2H_2+O_2+12Ar$). This simulation operates in the detonation frame of reference. We examine the effect of grid size and the performance impact of integrated quantities such as mass flow. For a given set of baseline conditions, the minimal and maximum grid resolutions required to simulate the respective detonation waves and the detonation cell structures are determined. Tertiary shock wave behavior for various grids and pre-exponential factors are analyzed. We found that particle fluctuation can be weakened by controlling the mass flow going through the oblique shock waves.

• 한국군사과학기술학회지
• /
• 제14권5호
• /
• pp.932-940
• /
• 2011

This study describes computational simulation results in 2-dimensional and 3-dimensional space concerning large scale gap test(LSGT) by using commercial hydrocode such as AUTODYN and LS-DYNA to analyze the detonation phenomenons of high explosives. To consider the possibilities of LSGT simulation, we used Lee - Tarver reaction rate model of PBX-9404 and Comp-B which were implemented AUTODYN's material library. Also we have tried the diverse numerical schemes such as Lagrangian, Eulerian and ALE(Arbitary Lagrangian Eulerian), SPH(Smoothed Particle Hydrodynamics) in LSGT simulations. After LSGT simulations, we compared the simulation results with published results to verify the LSGT simulations. According to the LSGT simulations, we have concluded as follows. In 2-dimensional and 3-dimensional space, Lagrangian solver provided the most reliable results based on analysis time and accuracy. When using two hydrocodes in 2-dimensional space, the simulation results are almost same except one explosive model. We have verified the modeling method and simulation results of the LSGT by using the commenrcial hydrocode in this study.

• 한국분말재료학회지
• /
• 제24권1호
• /
• pp.6-10
• /
• 2017

This study investigates the main growth mechanism of InP during InP/ZnS reaction of quantum dots (QDs). The size of the InP core, considering a synthesis time of 1-30 min, increased from the initial 2.56 nm to 3.97 nm. As a result of applying the proposed particle growth model, the migration mechanism, with time index 7, was found to be the main reaction. In addition, after the removal of unreacted In and P precursors from bath, further InP growth (of up to 4.19 nm (5%)), was observed when ZnS was added. The full width at half maximum (FWHM) of the synthesized InP/ZnS quantum dots was found to be relatively uniform, measuring about 59 nm. However, kinetic growth mechanism provides limited information for InP / ZnS core shell QDs, because the surface state of InP changes with reaction time. Further study is necessary, in order to clearly determine the kinetic growth mechanism of InP / ZnS core shell QDs.

• Elastomers and Composites
• /
• 제49권3호
• /
• pp.239-244
• /
• 2014

용매를 사용하지 않고 실리카와 실란커플링제의 반응을 투과 방식 휴리에 변환 적외선 분광법(FTIR)과 열중량 분석법(TGA)을 이용하여 조사하였다. 실란커플링제로 bis[3-(triethoxysilylpropyl) tetrasulfide] (TESPT)를 사용하였다. 미반응 TESPT를 제거한 후, FTIR로 화학 결합 형성을 분석하였고 TGA로 반응한 TESPT 함량을 결정하였다. 커플링제의 함량이 증가할수록 실리카에 결합한 커플링제의 양이 증가하였으나, 커플링제를 과량으로 첨가하면 커플링제 간의 축합반응에 의해 올리고머를 형성하였다. 실리카와 커플링제 그리고 고무의 결합을 확인하기 위하여 개질 실리카와 저분자량 액상 BR을 반응시켜 실리카-커플링제-BR 모델 복합체를 제조하여 화학 결합 형성을 조사하였다. 미반응 고무는 용매를 사용하여 제거하였고 FTIR과 TGA로 분석하였다. BR은 개질 실리카의 커플링제와 반응하여 화학 결합을 형성하였다. 실리카-커플링제-BR의 화학 결합 형성으로 인해 실리카 표면의 극성은 크게 낮아졌고 실리카 입자 크기는 커지는 효과를 보였다.

• 자원리싸이클링
• /
• 제25권3호
• /
• pp.74-81
• /
• 2016

고정층 반응기에서 PVC를 염화제로 사용하여 일메나이트 광석 중 철을 선택적으로 제거하기 위한 염화반응에 대하여 조사하였다. 철의 제거율에 미치는 PVC첨가량과 반응온도의 영향에 대하여 조사하였다. 철의 제거율은 PVC 첨가량과 온도가 증가할수록 상승하였다. PVC에서 생성된 HCl가스와 반응한 후의 시편 표면에는 많은 기공이 관찰되었다. 이러한 기공에 의해서 일메나이트 입자의 중앙부분에 있는 철과 반응할 수 있었던 것으로 생각된다. 선택적 염화반응을 속도론적 모델에 의해 조사한 결과 입자 계면에서의 화학반응에 의해서 율속되는 것으로 생각된다. PVC를 사용한 일메나이트의 선택적 염화반응에서 활성화 에너지는 20.47 kJ/mol로 계산되었다.