• Elastomers and Composites
• /
• 제50권2호
• /
• pp.92-97
• /
• 2015

A study on reaction kinetics for a PTMG/TDI prepolymer with 2,2'-dichloro-4,4'-methylenedianiline (MOCA), of which formulations may be generally used for fabricating high performance polyurethane elastomers, was peformed using non-isothermal differential scanning calorimetry (DSC). A number of thermograms were obtained at several constant heating rates, and analysed using Flynn-Wall-Ozawa (FWO) isoconversional method for activation energy, $E_a$ and extended-Avrami equation for reaction order, n. Urea formation reaction of the present system was observed to occur through the simple exothermic reaction process in the temperature range of $100{\sim}130^{\circ}C$ for the heating rate of $3{\sim}7^{\circ}C/min$. and could be well-fitted with generalized sigmoid function. Though activation energy was nearly constant as $53.0{\pm}0.5kJ/mol$, it tended to increase a little at initial stage, but it decreases at later stage by the transformation into diffusion-controlled reaction due to the increased viscosity. Reaction order was evaluated as about 2.8, which was somewhat higher than the generally well-known $2^{nd}$ order values for the various urea reactions. Both the reaction order and reaction rate explicitly increased with temperature, which was considered as the indication of occurring the side reactions such as allophanate or biuret formation.

• Korean Chemical Engineering Research
• /
• 제46권1호
• /
• pp.200-204
• /
• 2008

비대칭성 고리형 지방족 아민 경화제를 이용한 diglycidyl ether of bisphenol F(DGEBF) 계열의 에폭시의 경화 반응을 등온 및 동적 경화 실험을 통하여 분석하였다. 등온 부분경화 실험 및 동적 경화반응을 통하여 아민 경화제의 비대칭성으로 인해 경화 반응이 저온부 및 고온부분의 두 가지 반응으로 구성되어 있다는 것을 확인하였고, 따라서 경화도가 0.6 이상인 영역에서는 등온경화반응 모델식을 이용하여 실험값을 예측하기는 어렵다는 것을 확인하였다. 승온 속도를 여러 가지로 변화시키며 동적 경화반응을 분석하여 저온부 및 고온부 각각의 반응에 대한 활성화에너지 및 속도상수를 알아보았고, 경화 초기에는 저온부의 반응이 주가 되는 것을 확인하였다.

• 한국표면공학회지
• /
• 제43권6호
• /
• pp.309-314
• /
• 2010

The numerical study for the effect of various factors that affect the temperature distribution of the process glass installed above the large rectangular heater plate was carried out. For the calculation, heat flux, distance between heat source and process glass plate, effect of vacuum condition and convection in a chamber were considered as important factors. The results showed that the temperature gradient on the glass was increased at the natural convection because of the buoyancy force increases due to the heated air. Also, the more heat flux and distance between the heater plate and glass increases, the more increasing the temperature gradient was. In the case of isothermal heating wall, the temperature variation was smaller than the uniform heat flux condition.

• Metals and materials international
• /
• 제24권6호
• /
• pp.1293-1302
• /
• 2018

Nanocrystalline (NC) Ni electrodeposits (EDs) with a mean grain size of $34{\pm}12nm$ has been investigated, from room temperature to $800^{\circ}C$ under a purge gas of argon, by both non-isothermal and isothermal differential scanning calorimetry measurements, in combination with characterization of temperature-dependent microstructural evolution. A significant exothermic peak resulting from superimposition of recrystallization and surface oxidation occurs between 340 and $745^{\circ}C$ at a heating rate of $10^{\circ}C/min$ for the NC Ni EDs. The temperatures for recrystallization and oxidation increase with increasing the heating rate. In addition, recrystallization leads to a profound brittle-ductile transition of the Ni EDs in a narrow range around the peak temperature for the recrystallization.

• Coupled systems mechanics
• /
• 제8권2호
• /
• pp.147-168
• /
• 2019

This work aims to simulate three-dimensional heavy oil flow in a reservoir with heater-wells. Mass, momentum and energy balances, as well as correlations for rock and fluid properties, are used to obtain non-linear partial differential equations for the fluid pressure and temperature, and for the rock temperature. Heat transfer is simulated using a two-equation model that is more appropriate when fluid and rock have very different thermal properties, and we also perform comparisons between one- and two-equation models. The governing equations are discretized using the Finite Volume Method. For the numerical solution, we apply a linearization and an operator splitting. As a consequence, three algebraic subsystems of linearized equations are solved using the Conjugate Gradient Method. The results obtained show the suitability of the numerical method and the technical feasibility of heating the reservoir with static equipment.

• 대한기계학회논문집B
• /
• 제24권3호
• /
• pp.450-458
• /
• 2000

This study deals with the unsteady close-contact melting of solid blocks on a flat surface subject to convective heating. Normalizing the model equations in reference to the steady solution successfully leads them to cover constant heat flux and isothermal limits at small and large extremes of the Biot number, respectively. The resulting equations admit a compactly expressed analytical solution, which includes the previous solutions as a subset. Based on the steady solution, the characteristics of close-contact melting can be categorized into constant heat flux, transition, and isothermal regimes, the boundaries of which appear to be nearly independent of the contact force. The unsteady solutions corresponding to Biot numbers in the transition regime show intermediate behaviors between those of the two limits. With a proper approximation, the present solution procedure can cope with the case of variable fluid temperature and heat transfer coefficient. Regardless of imposed conditions, the mean normalized Nusselt number during the unsteady process asymptotically approaches to a constant value as the Biot number comes close to each limit.

• 대한기계학회논문집
• /
• 제13권4호
• /
• pp.680-688
• /
• 1989

본 연구의 목적은 2차원 유한요소법을 이용하여 변형과 열전달의 복합된 열소성 문제를 해석하여 재료의 성형성에 대한 가공열의 영향을 연구하는 것이다. 2차원 해석은 종래 단순 인장시험의 해석에 사용되던 1차원 해석에 비해 보다 정확한 해를 가지며 특히 넥킹의 발생 이후의 해석에 유용하다.

• 한국응용과학기술학회지
• /
• 제24권3호
• /
• pp.278-286
• /
• 2007

As a part of enhancing the performance of wood-plastic composites (WPC), polypropylene (PP)/ nanoclay (NC)/ wood flour (WF) nanocomposites were prepared using melt blending and injection molding process to evaluate their thermal stability. Thermogravimetric analysis (TGA) was employed to investigate thermal degradation kinetics of the nanocomposites both dynamic and isothermal conditions. Dynamic scans of the TGA showed an increased thermal stability of the nanocomposites at moderate wood flour concentrations (up to 20 phr, percentage based on hundred percent resin) while it decreased with the addition of 30 phr wood flour. The activation energy $(E_a)$ of thermal degradation of nanocomposites increased when nanoclay was added and the concentration of wood flour increased. Different equations were used to evaluate isothermal degradation kinetics using the rate of thermal degradation of the composites, expressed as weight loss (%) from their isothermal TGA curves. Degradation occurred at faster rate in the initial stages of about 60 min., and then proceeded in a gradual manner. However, nanocomposites with wood flour of 30 phr heated at $300^{\circ}C$ showed a drastic difference in their degradation behavior, and reached almost a complete decomposition after 40 min. of the isothermal heating. The degree of decomposition was greater at higher temperatures, and the residual weight of isothermal degradation of nanocomposites greatly varied from about 10 to 90%, depending on isothermal temperatures. The isothermal degradation of nanocomposites also increased their thermal stability with the addition of 1 phr nanoclay and of wood flour up to 20 phr. But, the degradation of PP100/NC1/MAPP3/WF30 nanocomposites with 30 phr wood flour occurs at a faster rate compared to those of the others, indicating a decrease in their thermal stability.

• 생명과학회지
• /
• 제24권4호
• /
• pp.428-436
• /
• 2014

Loop-mediated isothermal amplification (LAMP)법은 등온에서 DNA 주형을 변성시키지 않고 실시하기 때문에, autocycling 가닥 변위 DNA 합성에 의존한다. 그래서 고가의 PCR 장비를 필요로 하지 않고 등온 유지가 가능한 저가의 장비인 항온 수조, 오븐, 온장고 등에서 증폭이 가능하다. 본 연구진은 Streptococcus parauberis의 random primer중에서 5개를 선정하여, 신장도가 높은 2개의 primer를 이용하여 최적 반응온도 및 최적 반응시간, 최적 반응 조건들을 확립하였다. 그리고 기존의 PCR과 LAMP의 민감도의 비교 분석을 측정한 결과, LAMP의 높은 검출 한계를 확인할 수 있었다. 본 논문에서는 non-target DNA의 영향을 받지 않고 등온 조건 하에서 DNA를 증폭시킬 수 있는 LAMP법과 SYBR-green I를 이용하여 시각화시켰으며, 기존의 PCR과 비교 분석함으로써, S. parauberis에 대한 신속하고 정확한 진단법을 확립하였다.

• 설비공학논문집
• /
• 제5권2호
• /
• pp.102-110
• /
• 1993

An isothermal analysis was conducted to develop the design tool of an aquifer thermal energy storage system. Taejeon aquifer was chosen for the analysis, and the variation of FRE(Fluid Recovery Efficiency) with respect to the aquifer natural velocity and thermal load were investigated. The analysis results were compared with those of ATESSS(Aquifer Thermal Energy Storage System Simulator) and agreed within 2% of discrepancy. It is recommended, based on the result of this study, that the system may be suitable for a large volume of hot or chill thermal energy storage system, such as for district heating or cooling.