• Tribology and Lubricants
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• 제14권1호
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• pp.28-36
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• 1998

This paper presents the thermal behaviours of a solid type disk brake for a high-speed train. The thermal behaviours of a brake disk with 50mm thickness shows good performance compared with 45mm thickness of a disk because of a high specific heat capacity. The FEM results show that the thickness of the disk with a same weight of the brake disk should be increased for a good flexibility of the contact thermal problems. Therefore, the ratio between the pad and disk in diameter may be reduced and the thickness of a disk increased.

• 분석과학
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• 제9권3호
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• pp.302-309
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• 1996

Fe-5.7%Al-1.1%Cr-0.5%Si 및 여기에 0.12wt.%C가 함유된 합금의 최종 열처리를 $800^{\circ}C$에서 가열 후 수냉 또는 노냉함으로써 냉각방법에 의한 제진특성의 변화를 조사한 결과, 수냉은 이 합금의 제진특성을 현저히 악화시켰다. 그 원인을 미세조직 및 우선방위 특성과 관련시켜 조사하여 다음과 같은 결과를 얻었다. 열처리 후의 냉각방법에 의해 결정립 크기 및 잔류응력은 거의 무시할 정도로 변화가 없었으며, 이로부터 이들은 제진특성과 직접적인 상관이 없다고 판단되었다. 그러나 이 합금의 집합조직 형성은 수냉의 경우(200) 및 노냉의 경우(110)가 우세하게 형성되어, 이 현상을 이 합금의 자화용이축 <100>과 관련시켜 수냉시의 제진특성 악화를 해석할 수가 있었다. 즉 수냉에 의해 $180^{\circ}$ 자구벽이 $90^{\circ}$ 자구벽에 비해 많이 형성되어 제진에 결정적 역할을 하는 $90^{\circ}$ 자구벽이 적어져 그 제진특성이 악화된 것이다.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2552-2559
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• 2000

Most of ferrous b.c.c weld materials have martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is necessary to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions, i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. In this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis. In addition to, since the transformation temperature changes by the kind and control of alloying elements, the steel with many kinds of transformation temperature were selected and the effect of transformation on stress releasement was investigated by the numerical procedures considering phase transformation.

• 열처리공학회지
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• 제18권2호
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• pp.99-104
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• 2005

In this study, the effects of C and Si on damping capacity and mechanical properties of as-cast and as-rolled Fe-17%Mn alloys were investigated as a basic study for the purpose of the commercialization of the alloy. The $M_s$ temperature of ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation in Fe-17%Mn alloy was decreased with increasing C and Si contents, resulting in the less volume fraction of ${\varepsilon}$ martensite. The damping capacity was also decreased with increasing alloying content because of less ${\varepsilon}$ amount and the reduction in mobility of the damping sources such as the stacking fault boundaries and ${\gamma}/{\varepsilon}$ interfaces due to the pinning effect by alloying elements. The mechanical properties of as-rolled alloys were superior to those of as-cast alloys probably because of finer ${\gamma}$ grains, larger amount of ${\varepsilon}$ martensite, and chemical homogeneity.

• 한국대기환경학회지
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• 제26권3호
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• pp.286-297
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• 2010

This study deals with the effect of pretreatment on the $CO_2$ adsorption capacity of zeolitic adsorbents including a commercial A-type zeolite and cation exchanged adsorbents. The pre-heating could change the intrinsic properties such as specific surface area and adsorption capacity of the adsorbent. As a result of the experiment, the moisture previously filled inside might affect the potential adsorption capacity of the adsorbent, and could be disappeared throughout the heat treatment. An optimum pretreatment temperature for the test adsorbent was found to be $400^{\circ}C$, at which temperature enabled more than 90% refreshment. Precise examination through the TPD test showed that the TSA (Temperature Swing Adsorption) process would be desirable in dry adsorption of $CO_2$.

• 설비공학논문집
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• 제5권2호
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• pp.141-155
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• 1993

Thermodynamic properties of R-32 are calculated and its refrigeration performance is evaluated for the purpose the feasibility study of replacing R-22 with R-32. (1) Refrigeration effect of R-32 is superior to that of R-22 because heat of evaporation of R 32 is about 50% higher than that of R-22. However, COP of R-32 system is 10-30% lower than that of R-22 system. It is mainly attributed to the vapor pressore of R-32 being about 62% higher than R-22. (2) Since the pressure ratio and the specific heat ratio of R-32 system is higher than those of R -22, compressor discharging temperature rises as high as to $130-150^{\circ}C$. It may cause mechanical failure of compressor due to the breakdown of lubricant. Compressor should be improved to lower the temperature if R-32 is to replace R-22. (3) Averaged two-phase heat transfer coefficient of R-32 is about 10-20% higher than that of R-22. It may assume better heat exchanger effectiveness but not guarantee the better COP of R-32 system than R-22. (4) The high vapor pressure is the first reason to drop R-32 out of the line of R-22 alternative refrigerant. So, refrigerant mixtures based on R-32 are recommended to adjust the vapor pressure first and keep superior volumetric capacity of R-32.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1603-1605
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• 1997

$LiNiO_2$ is prepared by heating LiOH $H_2O$ and $Ni(OH)_2$ (mole ratio 1:1). In this study, we investigated X-ray diffraction, and charge/discharge property heat treatment condition and conductive agent sort and volume of $LiNiO_2$ prepared at various temperature and time. All $LiNiO_2$ prepared at this study showed hexagonal structure. In charge/discharge capacities, heated at $O_2$ than air and $750^{\circ}C$ than $700^{\circ}C$, specific capacity is higher. Therefore, when preliminary heat at $650^{\circ}C$ $O_2$ and heat at $750^{\circ}C$ carried out, charge/discharge property is best.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2073-2078
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• 2007

This study was performed to develop a dryer for home clothes using thermoelectric module. The thermoelectric module was used as a heat source and a dehumidification device because it has heating part and cooling part at once. To design for maximizing the energy efficiency and the rate of dehumidification, the parameters of the dryer using thermoelectric module are heat capacity and air flow rate. This study showed that the thermoelectric module can be used in the clothes dryer and energy efficiency of clothes dryer be better than that of electric heating dryer.

• Nuclear Engineering and Technology
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• 제46권6호
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• pp.863-868
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• 2014

The evaluation of thermal properties of actinide oxide fuels is a problem of high importance for the development of new generation reactors. In the present study, an expression obtained for n-dimensional Debye functions is used to derive a simple analytical expression for the specific heat capacity of nuclear fuels. To test the validity and reliability of this expression, the analytical expression is applied to $UO_2$, $NpO_2$, $ThO_2$, and $PuO_2$. It is seen that the formula was in agreement with the experimental and theoretical results reported in the literature.

• 한국세라믹학회지
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• 제36권5호
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• pp.497-503
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• 1999

Recently regenerative burner system was developed and begins to be gradually used for better energy savings. Compared to conventional burner system the regenrative one has the several merits such as higher fuel efficiency light weigh of apparatus low harmful toxic gas and homogeneous heating zone etc. The regenerative material a very important component of the new regenerative burner system should possess the properties of low specific density higher surface area and high specific heat capacity. Ceramics is the best regenerative material because of stable mechanical properties even at high temperature and better thermal properties and excellent chemical stability. In this study alumina ball alumina tube 3-D ceramic foam and hoeycomb as regenerative materials were tested and evaluated. The computer silumation was conducted and compared to the result of field test. This paper is aimed to introduce a new application of ceramics at high temperature.