• 한국산학기술학회논문지
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• 제11권2호
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• pp.449-454
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• 2010

본 논문은 균질유동모델을 적용하여 단열 모세관내 R600a의 유동 특성을 이론적으로 조사하였다. 이 모델은 시뮬레이션 해석에 필요한 기본적인 질량, 에너지, 운동량 방정식에 근거하고 있다. 또한 2개의 마찰인자와 점성계수모델을 이용하여 유동특성을 조사하였다. R600a의 열역학 및 전달 물성치는 EES 물성치 코드를 이용하여 계산하였다. 작동변수들에 대한 기초 설계자료를 제공하고자 단열 모세관내 R600a의 유동 특성을 분석하였다. 본 연구의 작동변수에는 응축온도, 증발온도, 과냉각도, 모세관의 직경이 있다. 주요 결과를 요약하면 다음과 같다. R600a용 단열 모세관내 응축온도, 증발온도, 과냉각도, 관직경은 모세관 전체길이에 영향을 준다. 즉 R600a용 모세관 전체길이는 식(15)와 같은 상관식으로 나타낸다.

• Computers and Concrete
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• 제17권2호
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• pp.271-280
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• 2016

This study examined the mechanical properties and adiabatic temperature rise of low-heat concrete developed based on ternary blended cement using ASTM type IV (LHC) cement, ground fly ash (GFA) and limestone powder (LSP). To enhance reactivity of fly ash, especially at an early age, the grassy membrane was scratched through the additional vibrator milling process. The targeted 28-day strength of concrete was selected to be 42 MPa for application to high-strength mass concrete including nuclear plant structures. The concrete mixes prepared were cured under the isothermal conditions of $5^{\circ}C$, $20^{\circ}C$, and $40^{\circ}C$. Most concrete specimens gained a relatively high strength exceeding 10 MPa at an early age, achieving the targeted 28-day strength. All concrete specimens had higher moduli of elasticity and rupture than the predictions using ACI 318-11 equations, regardless of the curing temperature. The peak temperature rise and the ascending rate of the adiabatic temperature curve measured from the prepared concrete mixes were lower by 12% and 32%, respectively, in average than those of the control specimen made using 80% ordinary Portland cement and 20% conventional fly ash.

• 한국건축시공학회지
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• 제21권6호
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• pp.563-571
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• 2021

최근 초고층 아파트 및 주상복합 건축물의 증가로 두께 3m이상의 메가급 매스콘크리트 부재의 설계가 다수 수행되고 있다. 초고층 주상복합 건축물은 기초부재 뿐만 아니라 특수한 구조형태로 전이 보 및 슬라브 등과 같은 매스콘크리트 시공이 증가하고 있어 매스콘크리트의 온도균열저감에 관한 연구가 수행되고 있다. 매스콘크리트의 온도균열을 검토하기 위해서는 콘크리트 열특성 검토가 중요하나 현장에서 단열온도상승 시험기를 활용하기는 어렵기 때문에 간이-단열온도상승시험을 주로 활용한다. 본 연구에서는 간이-단열온도상승시험에 의한 콘크리트 열특성 결과의 정밀도를 향상시키기 위해 열손실을 보정하기 위한 방안과 열손실 보정에 미치는 다양한 요인을 검토하여 제시하였다.

• 한국자동차공학회논문집
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• 제9권5호
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• pp.9-16
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• 2001

End-gas temperatures were measured using CARS technique in a conventional DOHC spark- ignition engine fueled with PRF80. The measured pressure data were analyzed using band pass filter method. The measured CARS temperatures were compared with adiabatic core temperatures calculated from measured pressures. Significant heating by pre-flame reaction in the end gas zone was observed in the late part of compression stroke under both knocking and non-knocking conditions. CARS temperatures measured at 10 crank angle degree before knock occurrence was higher than adiabatic core temperatures. These results indicate that there exist some exothermic reactions in low pressure and temperature region. CARS temperatures began to be higher than the adiabatic core temperature when the end-gas temperatures reached look. The temperature elevation due to the pre-flame reaction correlated better with CARS temperature than with cylinder pressure.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제20회 KOSCO SYMPOSIUM 논문집
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• pp.85-92
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• 2000

End-gas temperatures were measured using CARS technique in a conventional DOHC spark-ignition engine fueled with PRF80. The measured pressure data were analyzed using band pass filter method. The measured CARS temperatures were compared with adiabatic core temperatures calculated from measured pressure. Significant heating by pre-flame reaction in the end gas was observed in the late part of compression stroke under both knocking and non-knocking condition. CARS temperatures measured at 10 crank angle degree before knock occurrence was higher than adiabatic core temperatures. These results indicate that there exist some exothermic reactions in low pressure and temperature region. CARS temperatures began to be higher than the adiabatic core temperature when the end-gas temperatures reached 700 K. The temperature elevation due to the pre-flame reaction correlated better with CARS temperature than with cylinder pressure.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 추계 학술논문 발표대회
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• pp.56-57
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• 2013

In this study, in regard to concrete considering variety of admixture content rate, we evaluated property of adiabatic temperature rise. By setting up high temperature history, we evaluated effect to compression strength property of high strength concrete by early high temperature history. As a result, early high temperature history accelerated Hydration reaction of cement and contribute early strength development but it didn't accomplish performance objective in long-term aged.

• 한국건축시공학회지
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• 제16권2호
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• pp.185-192
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• 2016

The semi-adiabatic calorimetry technique is a robust and easy technique that can be used to measure the temperature rise of concrete. This method is often used for investigating the maturity of concrete, as well as to predict maximum temperature rise of mass concrete using various heat loss compensating models. Semi-adiabatic calorimetry can also be used for predicting setting time of concrete. However, it has seldom been used to investigate the hydration characteristics of various cement paste samples. In this research, semi-adiabatic calorimetry and X-ray diffraction methods were used to investigate the hydration characteristics of 3 different ASTM type I Portland cements. First derivative of temperature rise (dT/dt) curve was used to isolate individual peaks. Based on the results of the experiments, a combination of dT/dt curve with XRD could be used to successfully identify hydration at a specific time period, showing its potential to be used as an alternative tool for hydration studies of cement-based materials.

• 콘크리트학회지
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• 제7권6호
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• pp.186-196
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• 1995

본 연구에서는 국내에서 생산되는 시멘트의 발열상태에 대한 정량화를 목적으로 A시멘트사에서 생산되는 보통포틀란드시멘트를 그 대상으로 하여 단위시멘트량 및 타설온도를 주요변수로 한 단열온도 상승시험을 실시하여 각 변수가 콘크리트의 단열온도 상승량 및 발열속도에 미치는 영향을 검토하였고, 현재 시방서에 제시되어 있는 단열온도 상승시험 결과에 대하여 재검토를 하였다. 또한 이러한 시험결과가수치해석법에서 어떠한 영향을 미치는 가를 검토하였다. 검토결과 보통포틀란드시멘트에 대해서 시방서에 제시되어 잇는 단열온도상승량은 실제보다 과대평가하고 있으며, 시방서에 제시되어 있는 2-parameter 식 형태는 발열상태를 과대평가하고 있으며 이 식보다는 3- parameter식이 시멘트의 발열상태를 더 잘 근사하고 있음을 알았다. 또한 단열온도상승시험을 통해 얻어진 결과와 시방서에 제시된 값을 사용한 경우를 각각 수치해석법으로 해석한 결과, 온도는 큰 차이가 없었으나 온도응력은 외부구속이 강한 경우에는 약 20%정도가 큰 안전측의 해석결과를 나타내 시공계획 수립시에는 주의하지 않으면 안된다는 것을 알았다.

• 한국분말재료학회지
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• 제20권5호
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• pp.332-337
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• 2013

Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.934-939
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• 1998

This study discusses the results of adiabatic temperature rise tests which were performed considering various parameters, such as cement type, water-cement ratio, unit cement weigh, admixtures and placing temperature, which influence the temperature rise(K) and reaction velocity ($\alpha$). Theadiabatic temperature rise models obtained from this study are similar to those of Japan Concrete Institute. The models to calculate temperature rise and reaction velocity could be used the analysis f concrete thermal stress.