• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.112-116
• /
• 2011

In this paper, a preconverter of MCFC for an emergence electric power supplier is numerically simulated to increase the hydrogen production from natural gas (methane). Commercial code is used to simulated the porous catalyst with user subroutine to model three dominant chemical reactions which are Stream Reforming(SR), Water-Gas Shift(WGS), and Direct Stram Reforming(DSR). To get 10% fuel conversion rate in preconverter. the required external heat flux is supplied from outer wall of preconverter. The calculated results show that very nonuniform temperature distribution and chemical reaction happen near the wall of preconverter. These phenomena can be explained by the low heat conductivity of porous catalyst and the endothermic reforming reaction.

• 한국태양에너지학회 논문집
• /
• 제27권1호
• /
• pp.75-81
• /
• 2007

Steam reforming of methane using Xe-arc solar simulator was studied for the application of concentrated solar energy into chemical reaction. The reactor, a volumetric absorber, consisted of a porous ceramic foam disk coated with commercial reforming catalyst. Operating temperature was in the range of $450\;-\;550^{\circ}C$ and the excess steam ratio to methane was from 3.0 to 5.0. At the steady-state condition, the conversion of methane Increased with temperature in the range of 15 % - 30 % and the experimentally determined conversion was found to be close to theoretical equilibrium conversion. It was also found that the CO selectivity slightly decreased with excess steam ratio. Finally, the conversion of methane decreased significantly with space velocity of reactants.

• 한국태양에너지학회 논문집
• /
• 제21권3호
• /
• pp.1-8
• /
• 2001

고온의 태양열을 저장하기 위한 한 방편으로 화학반응을 이용한 태양에너지의 화학에너지로의 변환공정을 고려하였다. 태양에너지의 저장은 메탄의 수증기 개질반응으로 선정하였으며, 이 흡열반응에서 메탄의 전화율 특성을 살펴보았다. 반응기는 직경, 6.25 mm, 그리고 길이 30 cm 인 stainless steel을 코일형태로 제작하였다. 반응온도 범위내에서 메탄의 전화율은 반응온도에 따라서 선형적으로 증가하였으며 반응온도 $500^{\circ}C{\sim}900^{\circ}C$ 범위에서 메탄의 전화율은 약 $60%{\sim}90%$ 로 측정되었다. 이 실험을 통하여 태양열 저장을 위한 메탄의 수증기 개질반응의 타당성을 확인하였다.

• 한국세라믹학회지
• /
• 제51권6호
• /
• pp.533-538
• /
• 2014

Today, silicon and epoxy resin are used as materials of conversion lenses for white LEDs on the basis of their good bonding and transparency in LED packages. But these materials give rise to long-term performance problems such as reaction with water, yellowing transition, and shrinkage by heat. These problems are major factors underlying performance deterioration of LEDs. In this study, in order to address these problems, we fabricated a conversion lenses using glass, which has good chemical durability and is stable to heat. The fabricated conversion lenses were applied to a remote phosphor type. In this experiment, the conversion lens for white LED was coated on a glass substrate by a screen printing method using paste. The thickness of the coated conversion lens was controlled during 2 or 3 iterations of coating. The conversion lens fabricated under high heat treatment temperature and with a thin coating showed higher luminance efficiency and CCT closer to white light than fabricated lenses under low heat treatment temperature or a thick coating. The conversion lens with $32{\mu}m$ coating thickness showed the best optical properties: the measured values of the CCT, CRI, and luminance efficiency were 4468 K, 68, and 142.22 lm/w in 20 wt% glass frit, 80 wt% phosphor with sintering at $800^{\circ}C$.

• 한국태양에너지학회 논문집
• /
• 제21권4호
• /
• pp.29-35
• /
• 2001

고온의 태양열을 저장하기 위한 한 방편으로 화학반응을 이용한 태양에너지의 화학에너지로의 변환공정을 고려하였다. 태양에너지의 저장은 메탄의 수증기 개질반응으로 선정하였으며, 이 흡열반응에서 메탄의 전화율에 영향을 미치는 조업변수의 영향을 살펴보았다. 반응기는 직경 0.635 cm 그리고 길이 30 cm인 스테인레스 관을 코일형태로 제작하였다. 메탄의 수증기 개질반응에서 반응물의 공간속도, 그리고 스팀/메탄 비율에 따라서 메탄의 전화율과 CO의 선택도가 영향을 받음을 알 수 있었다. 이 실험을 통하여 최적의 수증기/메탄 비율을 확인하였다.

• 한국수소및신에너지학회논문집
• /
• 제24권2호
• /
• pp.113-120
• /
• 2013

A steam reformer is a chemical reactor to produce high purity hydrogen from fossil fuel. In the steam reformer, since endothermic steam reforming is heated by exothermic combustion of fossil fuel, the heat transfer between two reaction zones dominates conversion of fossil fuel to hydrogen. Steam Reforming is complex chemical reaction, mass and heat transfer due to the exothermic methane/air combustion reaction and the endothermic steam reforming reaction. Typically, a steam reformer employs burner to supply appropriate heat for endothermic steam reforming reaction which reduces system efficiency. In this study, the heat of steam reforming reaction is provided by anode-off gas combustion of stationary fuel cell. This paper presents a optimization of heat transfer effect and average temperature of cross-section using two-dimensional models of a coaxial cylindrical reactor, and analysis three-dimensional models of a coaxial cylindrical steam reformer with chemical reaction. Numerical analysis needs to dominant chemical reaction that are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming(DSR) reaction. The major parameters of analysis are temperature, fuel conversion and heat flux in the coaxial reactor.

• Bulletin of the Korean Chemical Society
• /
• 제17권8호
• /
• pp.696-699
• /
• 1996

Silicate and borosilicate gels were prepared by the sol-gel process and thermally treated in the 150-850 ℃ temperature range. Solid-state 1H MAS and 29Si CP/MAS NMR spectroscopy were used to investigate the effects of heat treatments on the silicate gel to glass conversion process. The 1H NMR isotropic chemical shifts and the relative intensities of hydrogen bonded and isolated silanol groups have been used to access the information concerning the dehydration process on the silicate gel surface. The 29Si NMR isotropic chemical shifts affected by the local silicon environment have been used to determine the degree of crosslinking, i.e. the number of siloxane bonds. These NMR results suggest that the silicate gel to glass conversion process is occurred by two stages which are dependent on the temperature; (1) the formation of particles up to 450 ℃ and (2) the formation of large particles by aggregation of each separated single particle above 450 ℃. In addition, the effects of B atom on the formation of borosiloxane bonds in borosilicates have been discussed.

• 대한기계학회논문집B
• /
• 제33권9호
• /
• pp.709-717
• /
• 2009

Heat transfer rate is a very important factor for the performance of a steam reformer because a steam reforming reaction is an endothermic reaction. Coaxial cylindrical reactor is the reactor design which can improve the heat transfer rate. Temperature, fuel conversion and heat flux in the coaxial cylindrical steam reformer are studied in this paper using numerical method under various operating conditions. Langmuir-Hinshelwood model and pseudo-homogeneous model are incorporated for the catalytic surface reaction. Dominant chemical reactions are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming (DSR) reaction. Although coaxial cylindrical steam reformer uses 33% less amount of catalyst than cylindrical steam reformer, its fuel conversion is increased 10 % more and its temperature is also high as about 30 degree. There is no heat transfer limitation near the inlet area at coaxial-type reactor. However, pressure drop of the coaxial cylindrical reactor is 10 times higher than that of cylindrical reactor. Operating parameters of coaxial cylindrical steam reformer are the wall temperature, the inlet temperature, and the Gas Hourly Space Velocity (GHSV). When the wall temperature is high, the temperature and the fuel conversion are increased due to the high heat transfer rate. The fuel conversion rate is increased with the high inlet temperature. However, temperature drop clearly occurs near the inlet area since an endothermic reaction is active due to the high inlet temperature. When GHSV is increased, the fuel conversion is decreased because of the heat transfer limitation and short residence time.

• Journal of Ginseng Research
• /
• 제42권4호
• /
• pp.532-539
• /
• 2018

Background: Heat treatments are applied to ginseng products in order to improve physiological activities through the conversion of ginsenosides, which are key bioactive components. During heat treatment, organic acids can affect ginsenoside conversion. Therefore, the influence of organic acids during heat treatment should be considered. Methods: Raw ginseng, crude saponin, and ginsenoside $Rb_1$ standard with different organic acids were treated at $130^{\circ}C$, and the chemical components, including ginsenosides and organic acids, were analyzed. Results: The organic acid content in raw ginseng was 5.55%. Organic acids were not detected in crude saponin that was not subjected to heat treatment, whereas organic acids were found in crude saponin subjected to heat treatment. Major ginsenosides ($Rb_1$, Re, and $Rg_1$) in ginseng and crude saponin were converted to minor ginsenosides at $130^{\circ}C$; the ginsenoside $Rb_1$ standard was very stable in the absence of organic acids and was converted into minor ginsenosides in the presence of organic acids at high temperatures. Conclusion: The major factor affecting ginsenoside conversion was organic acids in ginseng. Therefore, the organic acid content as well as ginsenoside content and processing conditions should be considered important factors affecting the quality of ginseng products.

• 대한기계학회논문집B
• /
• 제36권4호
• /
• pp.425-430
• /
• 2012

본 연구에서는 비상시 전기 공급용 MCFC 프리커버터의 천연가스(메탄)로부터 수소의 생산량을 증가시키는 경우를 수치적으로 해석하였다. 상용 코드를 사용하였으며 촉매는 다공성 매질로 시뮬레이션 하였다. 3가지 주요 화학반응인 수증기 개질반응(SR), 수성 가스 전환(WGS) 및 직접 수증기 개질 반응(DSR)은 사용자 부프로그램을 사용하여 해석하였다. 프리컨버터에서 10%의 연료전환율을 얻기 위해 요구되는 추가 열량을 벽면을 통해 공급하게 되면 프리컨버터의 벽면 부근에서만 매우 불균일한 온도 분포와 화학반응이 일어나는 것으로 분석되었다. 이와 같은 현상은 매우 작은 열전도율을 갖는 다공성 매질의 촉매와 흡열반응으로 설명되어질 수 있다. 해석결과 프리컨버터의 길이가 짧은 경우가 보다 균일한 연료전환율을 보여 주며, 촉매의 유지 보수 면에도 길이가 짧은 경우가 유리함을 보여 주었다.