• 한국초전도ㆍ저온공학회논문지
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• 제19권3호
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• pp.8-12
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• 2017

If the part of the HTS magnet is exposed to the outside of the cryogenic coolant due to the fluctuation of the height of the cooling liquid or the vapor generation, the uncooled part becomes very unstable. In this paper, the unstable equilibrium temperature distribution of the uncooled part of a superconductor is obtained, and the maximum temperature and energy are calculated as a function of the uncooled length. Similar to the superconductor stability problem, the current sharing model was applied to derive the theoretical formula and calculated by numerical integration. We also applied a jump model, which assumes that joule heat is generated in all of the uncooled segment, and compares it with the current sharing model results. As a result of the analysis, the stable equilibrium state and the critical uncooled length in the jump model are not shown in the current sharing model. The stability of the conductors to external disturbances was discussed based on the obtained temperature distribution, maximum temperature, and energy.

• 한국진공학회지
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• 제9권1호
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• pp.48-59
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• 2000

Electrochromic NiO films were prepared by using an electron-beam deposition method. The influence of the preparation conditions, especially the substrate temperature, on the electrochemical stability of film was investigated. The optical properties and stability of as-deposited films strongly depended on the substrate temperature during deposition. The NiO film prepared at a substrate temperature of 150~$200^{\circ}C$ was found to be the stabel when subjected to 5000cycles in a 0.5M solution of KOH between -6.0 and +0.8V. The best electrochromic parameters after 5000cycles were obtained for samples with substrate temperature of $150^{\circ}C$. The obtained electrochromic parameters are CE=-0.049($\lambda$=550nm), $\Delta$OD=0.88($\lambda$=550nm)$\textrm{cm}^2$/mC, Qin=-18.11mC/$\textrm{cm}^2$ and Qleft= 14.8mC/$\textrm{cm}^2$.

• 한국세라믹학회지
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• 제56권1호
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• pp.84-90
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• 2019

The varistor properties and stability against dc-accelerated stress of $V_2O_5-Mn_3O_4-Co_3O_4-Dy_2O_3-Nb_2O_5-Bi_2O_3$ (VMCDNB)-doped zinc oxide ceramics sintered at $850-925^{\circ}C$ were investigated. Increasing the sintering temperature increased the average grain size from 4.6 to 8.7 mm and decreased the density of the sintered pellet density from 5.54 to $5.42g/cm^3$. The breakdown field decreased from 5919 to 1465 V/cm because of the increase in the average grain size. Zinc oxide ceramics sintered at $875^{\circ}C$ showed the highest nonlinear coefficient (43.6) and the highest potential barrier height (0.96 eV). Zinc oxide ceramics sintered at $850^{\circ}C$ showed the highest stability: the variation rate of the breakdown field was -2.0% and the variation rate of the nonlinear coefficient was -23.3%, after application of the specified stress (applied voltage/temperature/time).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.215-218
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• 1998

The thermal stability of polyaniline-camphorsulfonic acid(PANI-CSA) film was studied as a function of temperature and time. A decrease in electrical conductivity of PANI-CSA film occurred when PANI-CSA film is subjected to temperature above 60$^{\circ}C$. From the result of thermogravimetry (TG), it was thought that the deterioration in electrical conductivity of PANI-CSA film was due to evaporation of water and residual solvent.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.351-354
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• 2002

The new enhanced method of temperature control need not any reference temperature, the system itself can find the melting temperature of gallium as a reference point by dithering input heat flux. If gallium is in melting state, the latent heat of fusion works, so gallium temperature does not change on dithering input heat flux. Also, the control method can determine the state of gallium; solid, liquid, or melting state by investigating the temperature in gallium. We apply this new temperature stabilization method to stabilize a Fabry-Perot cavity, which serves as a ultimate length measurement technique. We achieved 1 mK-temperature stability and 1.5426 nm/ 95 mm-length stability over 10 hours.

• Composites Research
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• 제28권6호
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• pp.395-401
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• 2015

본 연구에서는 자가손상보수에 적용되는 Grubbs' catalyst의 열안정성과 자가치료제와의 반응성을 조사하였다. 이를 위해 제조사에서 공급된 4종류를 고려하였으며 제조사에서 공급받은 상태와 기계적으로 분쇄시킨 상태로 시험하였다. 자가치료제는 Dicyclopentadiene (DCPD)과 5-ethylidene-2-norbonene (ENB)을 적절한 비율로 혼합한 4종류를 고려하였다. 촉매의 열안정성을 조사하기 위해 시차주사 열량측정장치를 통해 온도에 따른 열흐름 변화를 측정하였다. 자가치료제와의 반응성을 평가하기 위해 촉매와 혼합된 자가치료제의 반응열을 측정하였다. 이때 촉매는 자가치료제와 반응할 때의 최대온도와 최대온도 도달시간을 고려하여 Fluka Chemika Grubbs' catalyst를 적용하였다. 연구결과에 따르면 촉매는 제조사에 따라 다른 형상을 나타내며 입자의 크기가 작은 촉매가 자가치료제와 높은 반응성을 나타내었다. ENB의 혼합비가 높은 자가치료제가 촉매와 혼합되면 최대온도는 증가하고 최대온도 도달시간은 빨라졌다. 또한 촉매의 양이 많을수록 최대온도는 높아지고 최대온도 도달시간은 빨라졌다. 촉매의 열안정성과 자가치료제와의 반응성을 고려할 때 0.5 wt% 촉매와 D3E1 자가치료제가 자가손상보수를 위한 최적 조건임을 알 수 있었다. 마지막으로 노출된 분위기 온도에 따라 촉매에 열분해가 발생할 수 있기 때문에 촉매가 열안정성을 갖는 온도보다 높은 온도에 노출되지 않도록 하여야 한다.

• 산업식품공학
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• 제23권2호
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• pp.87-93
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• 2019

공기 주입식 스팀-에어 레토르트 내에서 스팀온도, 내부가압, CUT 등의 공정변수가 레토르트 내부의 온도 균일성에 미치는 영향을 평가하였다. 고온살균(121℃)이 저온살균(82℃) 보다 공정구간동안 온도분포가 더 균일하고 안정적이었다. 내부 가압이 클수록 저온살균조건의 공정에서는 온도분포가 안정적이었고, 이와 반대로 고온살균조건의 공정에서 온도분포가 더 불균일한 것으로 나타났다. 승온구간을 조절한 경우에는 레토르트 내의 온도분포에는 유의적인 차이를 나타내지 않았다. 공정구간동안 레토르트 내부에서 냉점은 수직방향 1층의 위로 확인되었고, 수평방향에서는 맨 뒤쪽 중앙 부분이 가장 높은 온도를 유지하여 공정 동안 이 위치들을 주의를 할 필요가 있었다. 또한 레토르트 내부의 양 옆 위치가 다른 위치에 비해 특히 온도분포가 불안정한 것으로 확인되었으므로 레토르트 가공 공정에서 주의해야 할 것으로 판단되었다.

• 한국전기전자재료학회논문지
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• 제19권12호
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• pp.1085-1091
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• 2006

The microstructure, electrical properties, and its stability of (Pr, Co, Cr, La)-doped ZnO varistors were investigated at different sintering temperatures in the range of $1230{\sim}1300^{\circ}C$. As the sintering temperature increased, the sintered density increased from 5.50 to $5.77g/cm^3$, the varistor voltage decreased from 777.9 to 108.0 V/mm, the nonlinear coefficient decreased from 77.0 to 7.1, and the leakage current increased from $0.4{\mu}A\;to\;50.6{\mu}A$. On the other hand, the donor concentration increased from $0.90{\times}10^{18}\;to\;2.59{\times}10^{18}/cm^3$ and the barrier height decreased from 1.89 to 0.69 eV with increasing temperature. The stability of nonlinear electrical properties was obtained from sintering temperature of $1260^{\circ}C$. The varistors sintered at $1260^{\circ}C$ marked the high electrical stability, with $%{\Delta}V_{1mA}=+1.9%,\;%{\Delta}a=10.6%,\;and\;%{\Delta}I_L=+20%$ for DC accelerated aging stress state of $0.95V_{1mA}/150^{\circ}C/24h$.

• Geomechanics and Engineering
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• 제16권3호
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• pp.331-339
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• 2018

Worldwide growth in hydrocarbon and energy demand is driving the oil and gas companies to drill more wells in complex situations such as areas with high-pressure, high-temperature conditions. As a result, in recent years the number of wells in these conditions have been increased significantly. Wellbore instability is one of the main issues during the drilling operation especially for directional and horizontal wells. Many researchers have studied the wellbore stability in complex situations and developed mathematical models to mitigate the instability problems before drilling operation. In this work, a fully coupled thermoporoelastic model is developed to study the well stability in high-pressure, high-temperature conditions. The results show that the performance of the model is highly dependent on the truly evaluated rock mechanical properties. It is noted that the rock mechanical properties should be evaluated at elevated pressures and temperatures. However, in many works, this is skipped and the mechanical properties, which are evaluated at room conditions, are entered into the model. Therefore, an accurate stability analysis of high-pressure, high-temperature wells is achieved by measuring the rock mechanical properties at elevated pressures and temperatures, as the difference between the model outputs is significant.

• Interaction and multiscale mechanics
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• 제5권1호
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• pp.1-12
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• 2012

Considerable longitudinal rail forces and displacements may develop in continuous welded rail (CWR) track on long-span bridges due to temperature variations. The track stability may be disturbed due to excessive relative displacements between the sleepers and ballast bed and the accompanied reduction in frictional resistance. For high-speed tracks, however, solving these problems by installing rail expansion devices in the track is not an attractive solution as these devices may cause a local disturbance of the vertical track stiffness and track geometry which will require intensive maintenance. With reference to temperature, two actions are considered by the bridge loading standards, the uniform variation in the rail and deck temperature and the temperature gradient in deck. Generally, the effect of temperature gradient has been disregarded in the interaction analysis. This paper mainly deals with the effect of temperature gradient on the track-bridge interaction with respect to the support reaction, rail stresses and stability. The study presented in this paper was not mentioned in the related codes so far.