• Nuclear Engineering and Technology
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• 제50권1호
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• pp.145-150
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• 2018

A new methodology, the crack-spallation model, has been developed to analyze gas-solid reactions dominated by crack growth inside of the solid reactant and spallation phenomena. The new model physically represents three processes of the reaction progress: (1) diffusion of gas reactant through pores; (2) growth of product particle in pores; and (3) crack and spallation of solid reactant. The validation of this method has been conducted by comparison of results obtained in an experiment for oxidation of $UO_2$ and the shrinking core model. The reaction progress evaluated by the crack-spallation model shows better agreement with the experimental data than that evaluated by the shrinking core model. To understand the trigger point during the reaction progress, a detailed analysis has been conducted. A parametric study also has been performed to determine mass diffusivities of the gas reactant and volume increase constants of the product particles. This method can be appropriately applied to the gas-solid reaction based on the crack and spallation phenomena such as the voloxidation process.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.79-82
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• 2012

The gas-solid reactor, such as rotary kiln, sintering bed, incinerator and CFB boiler, is the one of most widely used industrial reactors for contacting gases and solids. the gas-solid reactor are mainly used for drying, calcining and reducing solid materials. In the gas-solid reactor, heat is supplied to the outside of the wall or inside of the reactor. The heat transfer in gas-solid reactor encompasses all the modes of transport mechanisms, that is, conduction, convection and radiation. The chemical reactions occurring in the bed are driven by energy supplied by the heat transfer. This paper deal with the effect of heat transfer and chemical reaction in the gas-solid reactor.

• Bulletin of the Korean Chemical Society
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• 제20권10호
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• pp.1136-1144
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• 1999

The collision-induced reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon (001)-(2×1) surface is studied by use of the classical trajectory approach. The model is based on reaction zone atoms interacting with a finite number of primary system silicon atoms, which then are coupled to the heat bath, i.e., the bulk solid phase. The potential energy of the Hads‥Hgas interaction is the primary driver of the reaction, and in all reactive collisions, there is an efficient flow of energy from this interaction to the Hads-Si bond. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability shows the maximum near 700K as the gas temperature increases, but it is nearly independent of the surface temperature up to 700 K. Over the surface temperature range of 0-700 K and gas temperature range of 300 to 2500 K, the reaction probability lies at about 0.1. The reaction energy available for the product states is small, and most of this energy is carried away by the desorbing H2 in its translational and vibrational motions. The Langevin equation is used to consider energy exchange between the reaction zone and the bulk solid phase.

• 대한기계학회논문집
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• 제19권9호
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• pp.2353-2364
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• 1995

The ignition phenomena of a solid fuel plate of polymethyl-methacrylate(PMMA), which is vertically positioned and exposed to a thermal radiation source, is numerically studied here. A two-dimensional transient model includes such various aspects as thermal decomposition of PMMA, gas phase radiation absorption, gas phase chemical reaction and air entrainment by natural convection. Whereas the previous studies considers the problem approximately in a one-dimensional form by neglecting the natural convection, the present model takes account of the two-dimensional effect of radiation and air entrainment. The inert heating of the solid fuel is also taken into consideration. Radiative heat transfer is incorporated by th Discrete Ordinates Method(DOM) with the absorption coefficient evaluated using gas species concentration. The thermal history of the solid fuel plate shows a good agreement compared with experimental results. Despite of induced natural convective flow that induces heat loss from the fuel surface, the locally absorbed radiant energy, which is converted to the internal energy, is found to play an important role in the onset of gas phase ignition. The ignition is considered to occur when the rate of variation of gas phase reaction rate reaches its maximum value. Once the ignition takes place, the flame propagates downward.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.746-754
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• 2015

본 연구는 이온교환법을 통해 Ni촉매를 담지한 저등급 석탄(인도네시아 Eco탄)과 바이오매스(대한민국 상록수)의 혼합물로부터 제조된 촤(char)를 $700{\sim}900^{\circ}C$ 등온조건에서 온도가 반응속도에 미치는 영향에 대해 알아보았다. $Char-CO_2$ 가스화 반응은 700, 750, 800, 850, $900^{\circ}C$의 온도에서 진행하였으며, 기-고체 반응의 가스화 거동특성을 알아보기 위하여 각각 다른 가정을 갖고 있는 shrinking core model(SCM), volumetric reaction model(VRM), random pore model(RPM), modified volumetric reaction model(MVRM)을 실험결과에 적용하여 비교하였다. Arrhenius equation를 이용하여 Ni-coal/biomass와 Non-catalyst coal/biomass의 활성화에너지를 구하였고 이를 비교하였다.

• 자원리싸이클링
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• 제24권6호
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• pp.3-8
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• 2015

일정 온도에서 중량 변화를 통하여 가스화 반응 특성을 살펴볼 수 있는 열중량 분석기(thermobalance)를 이용하여 하수슬러지의 수증기 가스화 특성 및 발생 가스의 농도 분석을 실시하였다. 반응 온도 및 수증기의 분압이 증가할수록 가스화 반응이 촉진되어 반응 속도가 증가하는 것으로 나타났다. 반응 kinetics 해석은 기체-고체 화학반응의 세 가지 모델이 이용되었다. 이 중 하수슬러지 촤의 수증기 가스화는 modified volumetric reaction model이 반응 kinetics를 가장 잘 나타내었으며, 이 때 activation energy와 빈도 인자는 각각 155.5 kJ/mol, $14,087s^{-1}atm^{-1}$로 분석되었다. 또한, 수증기의 분압에 따른 반응 차수는 0.68이었다. 합성가스의 발생 특성을 살펴보고자 $900^{\circ}C$에서 생성 합성가스를 분석한 결과 수소의 농도가 가장 높았으며 수증기 분압이 증가할수록 생성기체의 농도 특히 수소 농도가 급격히 증가하였다. 가스화와 동시에 수성가스화 변환반응이 진행되어 생성기체의 수소 생성 농도가 일산화탄소에 비하여 2-4배 높은 값을 나타내었다.

• 전기화학회지
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• 제8권2호
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• pp.106-114
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• 2005

This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.165-166
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• 2014

The application of particle reaction model in the packed bed process modeling is discussed for iron ore pellet induration process. Combustion of coke breeze in the pellet is estimated by using shrinking unreacted-core model and grain model in which the progress of chemical reaction is described in different concepts. Under the identical inlet gas and solid conditions, the calculation using shrinking core model showed deviated results in terms of temperature profile and conversion fraction, which may imply the significance of selecting proper particle reaction model in consideration of particle characteristics and process operation conditions.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.233-239
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• 2003

본 연구는 고체 추진제 로켓 엔진의 연소과정을 수치적으로 해석하였다. 고체 추진제로는 double-base propellant를 이용하였으며 고체상에서는 2개의 포괄적인 반응식을 기체상에서는 5개의 포괄적인 반응식을 이용하였고 난류와 화학반응의 상호작용 PaSR(Partially Stirred Reactor)모델을 사용하였다. 고체 연료 벽면에서의 분출 효과로 야기되는 대류열전달의 불확실성을 줄이기 위하여 낮은 레이놀즈 수 k-$\varepsilon$난류모델을 적용하였다. 계산된 수치결과를 토대로 고체 추진제 로켓 엔진의 난류연소 과정 및 온도장과 압력장의 비정상 특성에 대하여 상세히 기술하였다.

• 한국세라믹학회지
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• 제53권5호
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• pp.511-520
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• 2016

Electrolyte-supported symmetric Ni-YSZ cermet electrodes of ca. $23{\mu}m$ were prepared by screenprinting and the impedance was measured as a function of humidity from 2% to 90% balanced in $H_2$ at a total flow rate of 50 sccm. The Ni felt current collector of 1 mm thickness exhibited a Gerischer-like gas concentration impedance in the low frequency range, which was similarly observed in the cermet-supported solid oxide cells, while the Pt paste collector exhibited only electrochemical polarization. The electrochemical polarization of both samples was modeled by a non-ideal diffusion-reaction transmission line model including CPEs with ${\alpha}$= 0.5. In the case of the Pt paste collector, all the Bisquert parameters exhibited humidity dependence to the -1/2 power, supporting a non-faradaic chemical reaction mechanism at three phase boundaries. Consequently, the surface diffusivity and reaction rate increased linearly with humidity. Less pronounced humidity dependence and somewhat lower utilization length with an Ni felt collector can be attributed to the diffusion-limited gas flow through the collector.