• Korean Chemical Engineering Research
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• 제59권1호
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• pp.138-151
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• 2021

The effect of a reactant ratio on the growth of a buoyancy-driven instability in an irreversible A+B→C reaction system is analyzed theoretically and numerically. Taking a non-stoichiometric reactant ratio into account, new linear stability equations are derived without the quasi-steady state assumption (QSSA) and solved analytically. It is found that the main parameters to explain the present system are the Damköhler number, the dimensionless density difference of chemical species and the ratio of reactants. The present initial grow rate analysis without QSSA shows that the system is initially unconditionally stable regardless of the parameter values; however, the previous initial growth rate analysis based on the QSSA predicted the system is unstable if the system is physically unstable. For time evolving cases, the present growth rates obtained from the spectral analysis and pseudo-spectral method support each other, but quite differently from that obtained under the conventional QSSA. Adopting the result of the linear stability analysis as an initial condition, fully nonlinear direct numerical simulations are conducted. Both the linear analysis and the nonlinear simulation show that the reactant ratio plays an important role in the onset and the growth of the instability motion.

• 한국대기환경학회지
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• 제25권5호
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• pp.402-409
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• 2009

Sodium bicarbonate ($NaHCO_3$) was used as a reactant for the removal of acid gases from a waste incinerator. The removal efficiencies of HCl and $SO_x$ were tested with a reactant mixing apparatus and a distributor installed at the bag filter inlet. It was shown that the stoichiometric ratio of $NaHCO_3$ to the acid gases which allows a removal of over 90% for both HCl and $SO_2$ was about 1.2. When a reactant mixing apparatus was installed on the duct, the removal efficiencies of HCl and $SO_2$ at the end of the duct were increased by approximately 1.5 and 3 times respectively, compared to when the apparatus was not installed. At the end of the bag filter, the removal efficiencies of the both were as high as 98% with a stoichiometric ratio of 1.35. Installing a reactant mixing apparatus on the duct and a distributor at the entrance of the bag filter and using $NaHCO_3$ as a reactant helped overcome the problem of low removal efficiencies of acid gases by dry scrubbing.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.359-360
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• 2013

The effect of electrode and deposition methods on non-linear interfacial resistive switching in HfO2 based $250{\times}250$ nm2 cross-point device was studied. HfO2 based device has the interfacial resistive switching properties of non-linearity and self-compliance current switching. The operating current in HfO2 based device was increased with negatively increasing the heat of formation energy in top electrode. Also, it was investigated that the operating current in HfO2 based device was changed with deposition methods of O3 reactant ALD, H2O reactant ALD and dc reactive sputtering, resulting the magnitude of the operating current and on/off ratio in order of HfO2 films deposited by dc reactive sputtering, H2O reactant ALD, and O3 reactant ALD. To investigate the effect of electrode and deposition methods on operating current of non-linear interfacial resistive switching in the cross-point device, X-ray photoelectron spectroscopy was measured. Through the analysis of O 1s spectra, non-lattice oxygen concentration, which is closely related to oxygen vacancies, was increased in order of Pt, TiN, and Ti top electrodes and in order of O3 reactant ALD, H2O reactant ALD, and O3 reactant ALD, and dc reactive sputtering deposition method. From all results, non-lattice oxygen concentration in ultra-thin HfO2 films play a crucial role in the operating current and memory states (LRS & HRS) in the non-linear interfacial resistive switching.

• 한국표면공학회지
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• 제44권2호
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• pp.60-67
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• 2011

Ternary B-C-N coatings were deposited on Si(100) wafer substrate from $B_4C$ target by RF magnetron sputtering technique in $Ar+N_2+CH_4$ gas mixture. In this work, the effect of reactant gas ratio, $CH_4/(N_2+CH_4)$ on the composition, kinds and amounts of bonding states comprising B-C-N coatings were investigated using two different bias power sources of continuous and unipolar DCs. In addition, the tribological properties of coatings were studied with the composition and bonding state of coating. It was found that the substrate bias power had an effect on chemical composition, and all of the obtained coatings were nearly amorphous. Main bonding states of coatings were revealed from FTIR analyses to be h-BN, C-C, C-N, and B-C. The amount of C-C bonging mainly increased with increase of the reactant gas ratio. From our studies, both C-C and h-BN bonding states improved the tribological properties but B-C one was found to be harmful on those. The best coating from tribological points of view was found to be $BC_{1.9}N_{2.3}$ composition.

• 수산해양기술연구
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• 제33권3호
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• pp.218-225
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• 1997

The formerly proposed spectral model of turbulent burning velocity is refined for nonstoichiometric hydrocarbon mixtures. Refinements are made in regard to the following two points : (1) an effect of the diffusivity of deficient reactant on the turbulent burning velocity and (2) consideration of increasing laminar name thickness with a decrease in the laminar burning velocity A comparison between the predicted turbulent velocities and the measured ones is made. The predictions by the refined spectral model agree quantatively well with the experimental results in the regime of practical equivalence ratio, but not in the high and low equivalence ratio regime.

• 전자공학회논문지A
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• 제30A권12호
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• pp.69-76
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• 1993

The statistical methodology using RSM (response surface method) was used too ptimize the deposition conditions of selective CVD tungsten process for improving the deposition rate and the adhesion property. Temperature, flow rate of SiH$_4$ and WF$_6$ and H$_2$ and Ar carrier gases were chosen for the deposition variables and process characteristics due to carrier gas were intensively investigated. It was observed that temperature was the main factor influencingthe deposition rate in the case of H$_2$ carrier gas while the reactant ratio, $SiH_{4}/WF_{6}$, had the principal effect on the deposition rate in the case of Ar carrier gas. The increased deposition rate and the good adhesion to Si were obtained under Ar carrier gas compared to H$_2$ carrier gas. The optimum conditions for deposition rate and antipeeling property were found to be the temperature range of 300~32$0^{\circ}C$ and the reactant ratio, $SiH_{4}/WF_{6}$, of 0.5~0.6.

• 한국세라믹학회지
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• 제31권6호
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• pp.601-608
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• 1994

Aluminum oxide thin films were deposited on p-type(100) silicon substrates by electron cyclotron resonance plasma enhanced CVD(ECR-PECVD) using TMA[Al(CH3)3] and oxygen as reactant gases at 16$0^{\circ}C$ or lower temperatures. The aluminum oxide films deposited by ECR-PECVD have the amorphous structure with the refractive index of 1.62~1.64 and the O/Al ratio of 1.6~1.7. Oxygen flow rate necessary for the stable deposition of the aluminum oxide films increases as the deposition temperature increases. It was found from the OES analysis that the ECR plasma had les cooling effect by introducing the TMA reactant gas in comparison with the RF plasma. The properties of aluminum oxide films prepared by ECR-PECVD were compared with those prepared by RF-PECVD. The ECR-PECVD aluminum oxide films have the higher refractive indices, the lower contents of impurities (H and C) and the stronger wet etch resistance than those deposited by RF-PECVD.

• 멤브레인
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• 제13권4호
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• pp.268-282
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• 2003

불완전 분리의 실질적인 분리투과 특성을 근거로 하는 모사모델을 이용하여 투과증발 막촉진 에스터화 반응의 실질적인 거동을 연구하였다. 막의 분리효율, 막의 물제거 능력을 모델에 포함시킴으로써 반응모사를 통하여 이들이 막촉진반응에 어떻게 영향을 끼치는지를 체계적으로 관찰할 수 있었다. 막을 통한 비완전분리가 일어날 경우에 초기 반응물 몰비율이 1이 아닐 때 반응 혼합물중 소량으로 존재하는 반응성분이 투과되거나, 혹은 초기 반응물 몰비율이 1인 반응 혼합물중 어느 반응성분이 투과되든지 반응이 완결될 수 없었다. 생성물인 에스터가 물과 함께 일부 투과될 경우 정방향 반응속도를 증가시켜 시간에 따른 반응 전환률을 증가시킨다. 막을 통한 불완전 분리시 막을 통한 투과로 인하여 발생하는 반응혼합물의 부피감소로 인하여 반응성분 뿐 아니라 생성성분의 농도가 증가되는데 이들 농도증가가 반응속도에 상반된 영향을 끼친다; 반응물 농축은 반응속도를 증가시키나 생성물 농축은 역방향의 반응을 촉진시킴으로서 반응속도를 감소시킨다. 반응초기에는 반응물 농축효과가 우세하나 반응이 진행됨에 따라 생성물 농축효과가 우세하여 반응속도를 저하시킴이 모사결과 관찰되었다.

• Korean Chemical Engineering Research
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• 제45권5호
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• pp.448-454
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• 2007

미세 $BaTiO_3$ 분말의 합성을 위해 함수 티타니아와 수산화바륨을 원료로 수열합성 실험을 수행하여, 반응시간, 온도, 농도 변화에 따른 전화율, 결정구조 및 생성 분말의 물성을 조사하였다. 전화율에 미치는 영향은 시간 < 온도 < 농도 순이었으며, 2.0 M의 원료를 $180^{\circ}C$에서 2 h 수열합성 시킬 때 최대 전화율을 99.5%를 얻을 수 있었다. 낮은 농도(0.25 M)에서는 고온에서도 미반응 $BaCO_3$와 미반응 $TiO_2$ 생성을 피할 수 없었으며, 이 미반응 물질들은 고온에서 $BaTi_2O_5$를 생성시켜 불순물로 존재하였다. 농도를 높일수록 합성 $BaTiO_3$ 분말의 크기는 작아졌으며, 분말의 Ba/Ti 비도 1에 접근하였다. 2.0M 이상의 농도에서는 $180^{\circ}C$, 2 h 반응에서 Ba/Ti 비는 $1{\pm}0.005$ 이였다.

• 한국수소및신에너지학회논문집
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• 제26권1호
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• pp.1-7
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• 2015

In this study, characteristics of reforming process of automotive liquefied petroleum gas (LPG) fuel using plasma reactor are investigated. Because plasma reformer technology has advantages of a fast start-up and wide fuel/oxidizer ratio of operation, and reactor size is smaller and more simple compared to typical combustor and catalytic reactor, plasma reforming is suitable to the on-board vehicle reformer. To evaluate the characteristics of the reforming process, parametric effect of $O_2/C$ ratios, reactant flow rate and metal form on the process were investigated. In the test of varying $O_2/C$ ratio from partial oxidation to stoichiometry combustion, conversion of LPG was increased but selectivity of $H_2$ decreased. The optimum condition of $O_2/C$ ratio for the highest $H_2$ yield was determined to be around 1.0 for 20~50 lpm, and 1.35 for 100 lpm. Specific energy density (SED) was major factor in reforming process and higher SED leads to higher $H_2$ yield. And metal form in the reformer increased $H_2$ yield of about 34 % as compared to the case of no metal form. The result can be a guide to map optimal condition of reforming process.