• 한국신뢰성학회지:신뢰성응용연구
• /
• 제9권4호
• /
• pp.275-290
• /
• 2009

This paper considers accelerated thermal degradation tests which are performed for rubber seal materials used for undersea tunnels constructed by immersion method. Three types of rubber seals are tested; rubber expansion seal, omega seal, and shock absorber hose. Main ingredient of rubber expansion seal is EPDM(Ethylene Propylene Diene Monomer) and that of both omega seal and shock absorber hose is SBR(Styrene Butadiene Rubber). The accelerated stress is temperature and an Arrhenius model is introduced to describe the relationship between the lifetime and the stress. From the accelerated degradation tests, dominant failure mode of the rubber seals is found to be the loss of elongation. The lifetime distribution and the service life of the rubber seals at use condition are estimated from the test results. The acceleration factor for three types of rubber seals are also investigated.

• 한국포장학회지
• /
• 제24권1호
• /
• pp.13-16
• /
• 2018

Powdered infant formula is susceptible to oxidation in the presence of oxygen. Even though the product is usually packaged in nitrogen atmosphere, the oxygen ingress through the package layer may occur in case of flexible pouches and affects the oxidation of the product. $O_2$ barrier of the package is thus important variable to protect the product from oxidative deterioration. $O_2$ barrier property was investigated for aluminum-laminated small pillow packs of $3.5{\times}17.5cm$. Storage temperature and combination of primary and secondary packages were evaluated as variables affecting the barrier for conditions of empty pouch flushed with nitrogen. Apparent oxygen transmission rate of the primary package exposed to air was $2.32{\times}10^{-3}mL\;(STP)\;atm^{-1}\;d^{-1}$ at $30^{\circ}C$ and its temperature dependence could be explained by activation energy of $28.5kJ\;mol^{-1}$ in Arrhenius relationship. The additional secondary package of nylon/PE film containing 20 primary packages was ineffective in modulating package $O_2$ transmission and was only marginally helpful when combined with oxygen scavenger. The same was true in suppressing the product oxidation when the primary package was filled with 14 g of the formula.

• Preventive Nutrition and Food Science
• /
• 제13권3호
• /
• pp.225-230
• /
• 2008

Onion slices were dehydrated in a single layer at drying air temperatures ranging from $50{\sim}70^{\circ}C$ in a laboratory scale convective hot-air dryer at an air velocity of 0.66 m/s. The effect of drying air temperature on the drying kinetic characteristics were determined. It was found that onion slices would dry within $210{\sim}460\;min$ under these drying conditions. Moisture transfer during dehydration was described by applying the Fick's diffusion model and the effective diffusivity changed between $1.345{\times}10^{-8}$ and $2.658{\times}10^{-8}\;m^2/s$. A non-linear regression procedure was used to fit 9 thin layer drying models available in the literature to the experimental drying curves. The Logarithmic model provided a better fit to the experimental drying data as compared to other models. Temperature dependency of the effective diffusivity during the hot-air drying process obeyed the Arrhenius relationship with estimated activation energy being 31.36 kJ/mol. The effect of the drying air temperature on the drying model constants and coefficients were also determined.

• Nuclear Engineering and Technology
• /
• 제48권6호
• /
• pp.1387-1395
• /
• 2016

To investigate the dynamic strain aging (DSA) behavior of Alloy 617, high-temperature tensile tests were carried out with strain rates variations of $10^{-3}/s$, $10^{-4}/s$, and $10^{-5}/s$ from $24^{\circ}C$ to $950^{\circ}C$. Five flow relationships, Hollomon, Ludwik, Swift, Ludwigson, and Voce, were applied to describe the tensile true stress-strain curves, and the DSA region was defined. In describing the tensile curves, Ludwigson's equation was superior to the other equations, and the DSA region was adequately defined by this equation as plateaus at intermediate temperatures from $200^{\circ}C$ to $700^{\circ}C$. It was identified that Alloy 617 is dominated by three types of serrations, known as Types D, A+B, and C. The activation energy values for each serration type were obtained by the Arrhenius equation. By using the obtained activation energy values, the serrated yielding map and the DSA mechanism were drawn and manifested. In addition, the relationship between the tensile strength and strain rate at higher temperatures above $700^{\circ}C$ was found to be closely related to the amounts of slip lines. In the scanning electron microscope (SEM) fractographs, there was a significant difference at the low, intermediate, and high temperatures, but almost the same to the three strain rates.

• Food Science and Biotechnology
• /
• 제17권4호
• /
• pp.780-786
• /
• 2008

Effect of acetylated starches (acetylated rice starch and acetylated tapioca starch) on rheological properties of hot pepper-soybean paste (HPSP) at different mixing ratios of rice flour (RF) and acetylated starch (AS) (10/0, 9/1, 8/2, and 7/3) was evaluated in steady and dynamic shear. All HPSP samples at $25^{\circ}C$ exhibited shear-thinning (n=0.31-0.36) and thixotropic behavior with high yield stresses and their steady flow curves were well described by power law and Casson models. The presence of AS resulted in the decrease in consistency index (K), apparent viscosity (${\eta}_{a,100}$), and yield stress (${\sigma}_{oc}$), and their predominant decreases were noticed at higher ratio of RF to AS (7/3 ratio). Arrhenius temperature relationship represents variation with temperature in the range of $5-35^{\circ}C$ with the high determination coefficients ($R^2=0.97-0.99$). Dynamic moduli (G', G", and ${\eta}^*$) values of HPSP samples mixed with AS were lower than those of HPSP with no added AS within the experimental range of frequency (0.63-62.8 rad/sec). Steady and dynamic shear rheological properties of HPSP samples seem to be greatly influenced by the presence of acetylated starch.

• Bulletin of the Korean Chemical Society
• /
• 제5권3호
• /
• pp.104-108
• /
• 1984

The self-diffusion experiment of THO was performed across a series of copolymer hydrogel membranes at different temperatures. Copolymer hydrogel membranes were prepared by copolymerizing 2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate (AEMA) in the presence of the solvent and the crosslinker, ethylene glycol dimethacrylate (EGDMA). By changing the crosslinker content and the ratio of HEMA and AEMA monomer, two series of copolymer hydrogel membranes were synthesized. The tagging material was THO and efflux of THO was counted on a Liquid Sc-intillation Counter. The experimental data show that the permeability decreases as the amount of EGDMA and the mole fraction of HEMA increase, and the permeability is proportional to the temperature. The partition coefficient shows a parallel trend with permeability. Using the relationship between viscosity and diffusivity, the viscosity of water within the membrane was obtained. According to the result, the viscosity of watler within the membrane has the same value with those of supercooling water. And we obtained the activation energy of THO for transport in the membrane by using Arrhenius plotting.

• 한국표면공학회지
• /
• 제46권1호
• /
• pp.29-35
• /
• 2013

The effect of DC bias on the growth of nanocrystalline diamond films on silicon substrate by microwave plasma chemical vapor deposition has been studied varying the substrate temperature (400, 500, 600, and $700^{\circ}C$), deposition time (0.5, 1, and 2h), and bias voltage (-50, -100, -150, and -200 V) at the microwave power of 1.2 kW, working pressure of 110 torr, and gas ratio of Ar/1%$CH_4$. In the case of low negative bias voltages (-50 and -100 V), the diamond particles were observed to grow to thin film slower than the case without bias. Applying the moderate DC bias is believed to induce the bombardment of energetic carbon and argon ions on the substrate to result in etching the surfaces of growing diamond particles or film. In the case of higher negative voltages (-150 and -200 V), the growth rate of diamond film increased with the increasing DC bias. Applying the higher DC bias increased the number of nucleation sites, and, subsequently, enhanced the film growth rate. Under the -150 V bias, the height (h) of diamond films exhibited an $h=k{\sqrt{t}}$ relationship with deposition time (t), where the growth rate constant (k) showed an Arrhenius relationship with the activation energy of 7.19 kcal/mol. The rate determining step is believed to be the surface diffusion of activated carbon species, but the more subtle theoretical treatment is required for the more precise interpretation.

• 한국자기학회지
• /
• 제21권2호
• /
• pp.48-51
• /
• 2011

본 논문에서는 짧은 전류 펄스를 이용한 미소자기 소자에서의 전류 유도 자화 반전에 대한 매크로 스핀 시뮬레이션 연구를 수행하였다. 자화 반전 전류 분포에 있어서 에너지 장벽이 미치는 효과에 특별히 주목하였다. 자화 반전 전류의 크기 및 분포는 전류 펄스 폭의 감소에 따라 증가했다. 여기서 긴 전류 펄스 폭 영역에서는 에너지 장벽과 자화 반전 전류 분포 사이의 관계가 아레니우스-닐 법칙에 의해 서술된다. 하지만 짧은 전류 펄스 폭의 영역에서는 이 관계가 풀리지 않은 채로 남아있다. 이는 짧은 전류 펄스로 인한 자화 반전이 열적 활성화에 의해서가 아닌 세차 운동에 의해 좌우되기 때문이며, 이를 해결하는 데에 있어서 어려움이 발생한다. 그러므로 포커-플랑크 방정식을 풀어서 짧은 전류 펄스 영역에서의 자화 반전에 대한 정확한 공식을 얻어내는 것이 필요하며 이를 통해 짧은 전류 펄스 영역에서의 자화 반전 양상을 이해 할 수 있을 것으로 본다.

• Applied Biological Chemistry
• /
• 제40권5호
• /
• pp.409-415
• /
• 1997

식품 및 배합사료 첨가제로서 치아민 모노유도체인 치아민 모노로단염이외, 치아민 모노요오드염 치아민 모노브름염 등의 3종류의 용해도를 $40,{\;}50,{\;}60^{\circ}C$에서 구하였고 그 온도에서 4수준(0.5, 1.0, 2.5, 5.0 w/w%)의 물을 첨가한 다음 경시적으로 겉보기 착색속도정수(ka)를 산출하였다. 그리고 산제이외 제제에 대하여는 착색도 가능성을 검토할 목적으로 비교적 조성이 간단한 과립, 정제를 만들어 이것에 3수준(0.5, 1.0, 2.5 w/w%)의 물을 첨가한 후 산제와 동일한 온도에서 경시적으로 착색시험으로부터 ka를 산출하였고, 구배 ka인 직선에 대하여는 회귀분산을 이용하여 직선성의 검정을 행하였다. 실험 범위 내에서는 위험률 5%수준에서 모두 유의한 결과를 얻었다. 과립 및 정제의 착색변화로부터 얻은 ka와 1/T간에 직선적인 관계가 성립하여 Arrhenius식을 만족시켰다.

• Korean Chemical Engineering Research
• /
• 제51권6호
• /
• pp.692-699
• /
• 2013

본 연구에서는 국내 상용 순환유동층 보일러에서 아역청탄과 혼소용 연료로 사용예정인 폐플라스틱 고형연료(RPF)의 열분해 반응특성을 규명하기 위해 열천칭 반응기를 이용하여 등온(350, 375, 400, 425, 450, 500, $850^{\circ}C$) 열분해 실험을 수행하였다. 등온 열분해 결과, 반응온도 구간 $375{\sim}450^{\circ}C$에서의 반응모델 변화는 관찰되지 않았으며, 12개 반응모델 중 1차 화학반응(F1)이 가장 적합한 반응모델로 판명되었다. 이때 Arrhenius 식을 사용하여 계산한 활성화에너지는 39.44 kcal/mol이었으며, Iso-conversional 방법을 적용할 경우 활성화에너지 평균값($0.5{\leq}X{\leq}0.9$ 구간)은 36.96 kcal/mol로 반응모델 결정 여부와 관계없이 유사한 값을 보였다. 한편 순환유동층보일러의 운전온도인 $850^{\circ}C$에서 RPF 입도(d) 변화에 따른 탈휘발 시간은 $t_{dev}=10.38d^{2.88}$으로 표현할 수 있었으며, 보일러 내부에서 RPF가 균일하게 연소되기 위해서는 연료 입도와 평균 분산 거리(x)가 $x{\leq}1.58d^{1.44}$의 상관관계를 만족하여야 함을 확인할 수 있었다.