• 임산에너지
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• 제21권2호
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• pp.62-68
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• 2002

본 실험에서는 합판벽체내의 단열재 종류에 따른 단열성능을 비교 평가하였다. 열의 통과량을 비교해 보기 위하여 열관류 실험을 하였다. 열관류 실험결과 스티로폼과 유리섬유의 열관류율이 적게 나타났다. 용적비열은 황토보드와 집성목이 높은 결과를 나타내었다. 합판 벽체로 제작된 모형 주택을 이용한 실내외 온도변화를 비교해 본 결과 단열재료로스티로폼과 유리섬유를 사용한 벽체의 경우 외부 온도에 쉽게 영향을 받는 것을 알 수 있었으며 용적비열이 높은 황토보드, 황토ㆍ톱밥 혼합재, 집성목을 사용한 벽체의 경우는 외부온도의 변화에 비해 적은 온도변화를 보였다. 실험결과 열관류율은 스티로폼과 유리섬유가 작았지만 용적비열이 높은 황토보드와 황토ㆍ톱밥 혼합재, 집성목이 단열성능면에서 우수함을나타내었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.427-733
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• 2003

Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy. The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5T$\sub$m/. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.

• 대한기계학회논문집B
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• 제40권3호
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• pp.139-148
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• 2016

터빈과 압축기의 1차 근사 모델을 대상으로 열역학적 해석을 하여 단열 효율의 특성을 파악하였다. 비단열 터빈과 압축기에 대해서는 엔트로피 평균 온도와 생성 엔트로피, 열원 온도, 열전달량 등의 값에 따라 단열 효율이 1보다 커질 수 있다. 즉, 단열 효율을 비단열 검사체적에 적용하면 실제보다 성능을 높게 평가하는 오류가 생길 수 있다. 이 문제를 해결하는 대안으로 실제 과정과 동일한 열이 전달되는 가역 비단열 과정을 이상 과정으로 채택하여 정의하는 비단열 효율을 제안한다. 이 비단열 효율은 항상 0과 1 사이에 있으며, 대부분의 경우 엑서지 효율보다 작음을 입증하였다. 비단열 효율은 단열 효율을 포함하는 더 일반적인 효율의 정의식으로 사용할 수 있다.

• 한국기계가공학회지
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• 제21권8호
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• pp.93-98
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• 2022

Adiabatic blanking is a method to improve productivity through an autocatalytic cycle that occurs repeatedly through plastic deformation and thermal softening caused by impact energy. In this study, an axisymmetric analysis model comprising a punch, die, holder, and specimen was developed to confirm the temperature and deformation characteristics caused by an impact load. Through this, the impact energy, diameter of the punch, gap between the punch and die, and the effect of the fillet were analyzed. Because this process occurs in a very short time, adiabatic analysis can be performed using the explicit time-integration method. The analysis, confirmed that it is necessary to design a structure capable of increasing the local temperature and plastic deformation by controlling the impact energy, working area, gap, and the fillet.

• 대한기계학회논문집
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• 제11권1호
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• pp.177-188
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• 1987

본 논문에서는 연소기체의 열력학적 평형조성 계산을 위한 수식을 Gibbs의 자 유에너지 최소화법에 의하여 유도하고 이를 컴퓨터 프로그램화하여, Table 1의 특성을 지닌 연료에 대하여 ⅰ) 연소공기량에 따른 평형조성 및 단열불꽃온도, ⅱ) 연소온도 변화에 따른 평형조성의 변화를 계산함으로써 연소기체의 생성기구를 열력학적으로 해 석하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
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• pp.9-10
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• 2013

This study reports the results of an experimental investigation of emission and temperatures from the syngas-air premixed flame with a various mixture composition in the region of large equivalence ratios. The effects of hydrogen contents and equivalence ratios on the flame velocity, which reported before, and emission of syngas fuel are examined. In this study, representative syngas mixture compositions ($H_2:CO$) such as $H_2:CO=10:90$, 25:75, 50:50 and 75:25 and equivalence ratios from 0.5 to 5.0 have been conducted. The emissions of syngas fuel were measured by the high precision analyzer with enclosure configuration and the adiabatic temperatures are calculated by used Chemkin basis. The NOx emission level is coincided relatively well with the adiabatic temperature distributions in lean mixture conditions, but for rich mixture conditions NOx level was also increased again even though the adiabatic temperature decreases. Such an increasing characteristics in rich mixture conditions is coincided well with the tendency that rather the flue gas temperature increases.

• 한국재료학회지
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• 제11권3호
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• pp.164-170
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• 2001

자전고온합성반응법을 이용하여 이규화 몰리브덴-텅스텐($Mo_{1-z}$ , $W_{z}$)$Si_2$을 합성하였다. 조성 (z)을 변화시켜 성형한 원통형 시편에 합성반응 중 전달되는 온도변화를 예측하기 위하여 시편의 중앙에 열전대를 삽입하였다. 반응 선단면이 열전대를 통과할 때 가장 높은 반응온도를 보이고 이것을 단열반응 온도라 간주하였다. 따라서 본 연구에서는 이러한 온도변화를 예측하기 위하여 자전조온합성반응의 모델링을 계시하고자 하였으며, 실험을 통하여 측정한 반응온도 분포곡선의 거동을 비교하였다. 각각의 시료에 대한 실험결과 측정된 반응속도는 약 2.14~1.35mm/sec, 반응온도는 1883K~1507K의 간을 보였다. 두 항 모두 텅스텐의 함량이 증가함에 따라 감소하는 경향을 나타냈으며, 수치해석을 통하여 거의 유사한 반응온도를 얻었다. 시료의 초기온도를 증가시킬 경우 반응온도는 증가함이 예측되었고, z=0.5인 시료에 대하여 반응온도가 1900k 이상이 되기 위해서는 약 800K-900K의 예열이 필요하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.101-102
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• 2012

In this study, it was evaluated about hydration heat reduction under hot weather condition. Placement temperature set 25℃ and 35℃, For hydration heat reduction was applied such as FA and BFS. As a results, mixture of BFS70% is the most effective hydration temperature reduction.

• 콘크리트학회논문집
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• 제17권2호
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• pp.293-302
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• 2005

This study describes data from determination of the optimum mix proportion and site application of the mass concrete placed in bottom slab and side wall having a large depth and section as main structures of LNG in-ground tank. This concrete requires low heat hydration, excellent balance between workability and consistency because concreting work of LNG in-ground tank is usually classified by under-pumping, adaptation of longer vertical and horizontal pumping line than ordinary pumping condition. For this purpose, low heat Portland cement and lime stone powder as cementitious materials are selected and design factors including unit cement and water content, water-binder ratio, fine aggregate ratio and adiabatic temperature rising are tested in the laboratory and batch plant. As experimental results, the optimum unit cement and water content are selected under $270kg/m^3$ and $l55{\~}l60 kg/m^3$ separately to control adiabatic temperature rising below $30^{\circ}C$ and to improve properties of the fresh and hardened concrete. Also, considering test results of the confined water ratio($\beta$p) and deformable coefficient(Ep), $30\%$ of lime stone powder by cement weight is selected as the optimum replacement ratio. After mix proportions of 5cases are tested and compared the adiabatic temperature rising($Q^{\infty}$, r), tensile and compressive strength, modulus of elasticity, teases satisfied with the required performances are chosen as the optimum mix design proportions of the side wall and bottom slab concrete. $Q^{\infty}$ and r are proved smaller than those of another project. Before application in the site, properties of the fresh concrete and actual mixing time by its ampere load are checked in the batch plant. Based on the results of this study, the optimum mix proportions of the massive concrete are applied successfully to the bottom slab and side wall in LNG in-ground tank.

• 한국환경과학회지
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• 제11권9호
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• pp.857-863
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• 2002

The meteorological elements were measured to investigate cause of summertime ice formation at Unchiri, Gangwon Province. The cause of freezing at valley was conformed as adiabatic expansion theory, latent heat of evaporation, natural convective theory, cold air remain theory, and convective freezing theory according to former study. However nither theory produced a satisfactory explanation. This studying area is not valley but ridge, and underground water surface exists at below than freezing height. wintertime temperature drop and summertime cold air spouting were explain as natural convective theory, generation of water drop on the rock was explained as cooling theory by air expansion, and ice formation on the rock was explained as adiabatic expansion theory. In conclusion, formation of ice valley at Unchiri was formed by natural convective theory, adiabatic expansion theory, and latent heat of evaporation successively.