• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.14 no.6
• /
• pp.45-51
• /
• 2005

Braking performance of a vehicle can be significantly affected by the temperature increment in the brake system. Therefore, the important problem in brake system is to reduce the thermal effect by friction heat. Recently, many studies have been performed and good results have been reported on the prediction of the brake disk temperature. However, the study on the pad, piston and brake fluid temperature is rarely found despite of its importance. In this study, the temperature distribution of the disc brake system is studied according to the material properties of brake piston. Vehicle deceleration, weight distribution by deceleration, disc-pad heat division and the cooling of brake components are considered in the analysis of heat transfer. Unsteady state temperature distributions are analyzed by using the finite element method and the numerical results are compared with the experimental data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.709-712
• /
• 2017

Liquid nitrogen jet has been imaged by using backlight method. In addition to the images, simultaneously measured temperature by thermocouples has been used to investigate the role of 'Pseudo-flash-boiling' in breakup of the supercritical jet. The backlight image can provide qualitative appearance of the jet, but not the density profile for the high density of injected fluid.

• 전기의세계
• /
• v.38 no.3
• /
• pp.26-35
• /
• 1989

발전플랜트의 입지조건과 경제성을 고려하여 원자력 및 화력발전소의 단위 설비용량이 커지면서 개개 발전소가 전력계통에 미치는 영향이 지대해지고 있다. 따라서 발전제어의 신뢰성 확보, 운전조작의 간편화와 송전의 장거리화로 전력계통의 안정성 향상 및 전압과 주파수의 일정한 유지가 중요한 문제로 대두되고 있다. 이러한 문제를 해결하기 위해서는 터빈제어, 보일러 제어 및 발전기제어 등으로 분리 제어되어 온 발전제어 계통을 통합하고 Digital화하여 발전계통과 송.배전계통을 연계, 제어해야 전기의 품질을 향상시킬 수 있을 것이다. 따라서 현재 전력계통에 보급되고 있는 원방집중 제어방식에 의한 전력계통의 조류 및 전압의 감시, 각 발전소의 운전상황, 송.배전선로의 상태등 모든 변수들은 취합, 전력계통의 상황에 따라 각 발전기의 출력 및 무효전력의 적장분배, 전압과 주파수 조정, 및 조상설비등 제어하는 전력계통 통합시스템이 적용되어야 할 것으로 본다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.66-66
• /
• 2010

알루미나는 높은 온도에서 열적으로 안정되고 경도가 높으며 내화학, 내마모 특성이 우수하며 또한 강도대비 비중이 낮아 무게를 줄일 수 있다는 장점을 가지고 있다. 이러한 특성으로 인하여 우주항공, 국방, 원자력등 극한의 온도를 견뎌야 하는 고도의 신뢰성이 요구되는 고온구 조물로서 응용이 되고 있다. 특히 알루미나를 휘스커 형태로 만들어 세라믹 복합체에 결합 할 경우 복합체의 기지 내에서 강화재의 역할을 함으로써 취성 파괴를 억제하고 열 전도율 저하등의 이점을 가져올 수 있다. 그리하여 본 연구에서는 알루미나 휘스커를 성장을 위하여 Al-triisoproxide계를 이용하여 화학기상증착법으로 가장 안정된 열적 특성을 가지고 온도의 변화에 따라 상 변화가 일어 나지 않는 알파 알루미나 상을 가지는 알루미나 휘스커를 성장시키기 위한 연구를 하였다. 또한 증착 온도, 압력, 입력기체비등 증착 조건을 변화시켜가면서 알파 알루미나 휘스커의 성장 거동을 살펴 보았다. 증착 조건 변화에 따라 알파 알루미나는 막이 증착되는 부분과 휘스커가 성장되는 부분이 있으며 휘스커의 밀집도와 길이방향, 직경방향 성장등 여러 가지 성장 특성을 달리하였다. 이러한 결과를 바탕으로 증착조건에 따른 알파 알루미나 휘스커 성장영역을 도식화하였다.

• Polymer(Korea)
• /
• v.29 no.6
• /
• pp.549-556
• /
• 2005

Effects of the dimensionless variables on the heat transport phenomena in the extrusion process of a single screw extruder have been studied numerically. Based on the understanding of the solids conveying related to the geometrical structure and characteristics of the screw, the heat balance equation for the solids conveying zone was established and normalized. The finite volume method and power-law scheme were applied to derive a discretized equation and the equation was solved using the alternating direction iterative method with relaxation. Effects of the dimensionless parameters, Biot and Peclet numbers, that define the heat transfer characteristics of the solids conveying zone have been investigated with respect to the temperature of the feeding zone and the length of the solids conveying zone. As the Biot number is increased, the heat loss by cooling dominates to decrease the temperature of the barrel but it has little effects on the temperature of the solids bed and the length of the solids conveying zone. On the other hand, if the Peclet number is increased, the convection term dominates to decrease the temperature of the solids bed and it results in an increase in the length of the solids conveying zone.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.11
• /
• pp.1437-1446
• /
• 2000

A numerical analysis on the freeze coating process of a non-isothermal finite dimensional plate with a binary alloy is performed to investigate the growth and decay behavior of the solid and the mushy layer of the freeze coat and a complete procedure to calculate the process is obtained in this study. The continuously varying solid and mushy layers are immobilized by a coordinate transform and the resulting governing differential equations are solved by a finite difference technique. To account for the latent heat release and property change during solidification, proper phase change models are adopted. And the convection in the liquid melt is modeled as an appropriate heat transfer boundary condition at the liquid/mushy interface. The present results are compared with analytic solutions derived for the freeze coating of infinite dimensional plates and the discrepancy is found to be less than 0.5 percent in relative magnitude for all simulation cases. In addition the conservation of thermal energy is checked. The results show that the freeze coat grows proportional to the 1.2 square of axial position as predicted by analytic solutions ar first. But after the short period of initial growth, the growth rate of the freeze coat gradually decreases and finally the freeze coat starts to decay. The effects of various non-dimensional processing parameters on the behavior of freeze coat are also investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.177-180
• /
• 2009

This study was investigated to know the thermal decomposition for the propellant ingredients and 2 kinds of HTPE propellants. The thermal analysis of the propellant ingredients used in this study showed that the thermal stability of these materials decreases in the following order : AP > HTPE > AN > BuNENA. In addition, propellant HTPE 002 containing AN showed that an endothermic process at around $125^{\circ}C$ corresponding to the solid-solid phase change($II{\rightarrow}I$) of AN was followed by the exothermic process due to decomposition of BuNENA/AN until $200^{\circ}C$. The critical temperature, $T_c$, of thermal explosion for the propellants HTPE 001 and HTPE 002, were obtained from the non-isothermal curves at various heating rates, by using Semenov's thermal explosion theory. Kissinger's method was employed to obtain the activation energy of the thermal decomposition, and it was used to calculate the $T_c$.

• Korean Journal of Food Science and Technology
• /
• v.25 no.6
• /
• pp.643-648
• /
• 1993

A simple approximate model using equivalent time at a reference temperature ($t_{eq}$) was derived to predict quality changes caused by temperature fluctuations. The validity and effectiveness of this model have been assessed with experimental data of sucrose hydrolysis. Kinetic parameters of sucrose hydrolysis were estimated by one step method using equivalent time at a reference temperature with linearly increasing temperature profile. Sucrose hydrolysis was a first order reaction, and the activation energy was 25.84 kcal/mol. The extent of sucrose hydrolysis of liquid model system under accelerated test with sinusoidal temperature fluctuations were determined. The proposed model yielded accurate prediction with the correlation coefficient in the range of $0.92{\sim}0.99$.

• Applied Chemistry for Engineering
• /
• v.10 no.4
• /
• pp.548-556
• /
• 1999

The thermal degradation of polyethylene has been studied using a nonisothermal thermogravimetric technique under a nitrogen atmosphere condition at several heating rates from 10 to $50^{\circ}C/min$. To obtain information on the kinetic parameters, the dynamic thermogravimetric analysis curve and its derivative have been analyzed by a variety of analytical methods such as Kissinger, Freeman-Carroll, Flynn-Wall, Coats-Redfern, Chatterjee-Conrad, Friedman, Horowitz-Metzger, Ozawa and Denq methods. The comparative works for the kinetic results obtained from various methods should be performed to determine the kinetic parameters, because three are tremendous differences in the calculated kinetic parameters depending upon the mathematical method taken in the analysis. From this work, it was found that the apparent activation energy of HDPE was larger than those of LDPE and LLDPE.

• Proceedings of the Korean Society for Rock Mechanics Conference
• /
• 2000.09a
• /
• pp.105-115
• /
• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.