• Tunnel and Underground Space
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• v.9 no.1
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• pp.27-35
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• 1999

The characteristics of heat conduction for the heat source boundary like an arch shape cavern are different from those for the semi-infinite or circular boundary which can be driven theoretically. A new form of transient heat conduction equation in rock mass around the arch shape cavern is evaluated with analyzing the pattern of the rock temperature distribution measured at the cold storage pilot plant. The new equation, which is driven by adopting a shape function, $SF=\sqrt{logx_0/log(x_0+x)}$ to the solution for a semi-infinite boundary, has the semi-radial form of temperature variation with distance. And, thermal properties of rock mass are estimated by comparing the rock temperature distributions by this equation with those by measurement. Thermal conductivity and specific heat of rock mass are estimated as giving the difference of 20~25% compared to those of laboratory scale. This difference seems to be caused by discontinuity like joint and water content in rock mass.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.4-4
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• 1998

고체 추진제의 비정상적인 연소 현상을 해석하여 연소 불안정을 예측하는 것은 추진시스템의 설계 시 매우 중요하다. 로켓의 비정상 연소 현상을 해석하기 위하여 많은 이론적 연구가 진행되어 왔다. 이론적인 해는 주로 선형 해석의 결과들로 정상 상태에서 발생하는 불안정 현상을 예측하는 데에는 적합하지만 비정상 현상을 설명하기에는 부족하다. 따라서 수치 기법을 이용한 비선형 해석이 수행되어 졌다. 기존의 비정상 연소에 관한 연구들은 일정한 물성치를 사용하고 추진제 내에서의 화학 반응과 복사 열전달 등을 무시하여 추진제의 특성을 단순화 시켜 비정상 해석을 수행하였다. 본 연구에서는 비정상 연소 현상에 대한 비선형 수치 해석을 하려한다. 실험에서 밝혀진 것과 같이 추진제의 물성치를 온도의 함수로 사용하고 응축영역으로의 복사 열전달을 고려하였다.

• Korean Chemical Engineering Research
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• v.47 no.5
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• pp.587-592
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• 2009

Heat transfer model and energy dissipation rate were investigated to examine the heat transfer mechanism in bubble columns with continuous operation. The energy dissipation rate($E_D$) obtained from the unsteady state heat transfer model based on the surface renewal theory was significantly small, comparing with the hydrodynamic energy dissipation rate($P_v$) calculated from the overall hydrodynamic energy balance based on the behaviors and holdups of gas and liquid phases in the column. It was found from these results that the energy dissipation rate based on the surface renewal theory is independent of the hydrodynamic energy dissipation rate obtained from the overall hydrodynamic energy balance in the bubble column, in considering their mechanism. The different two energy dissipation rates were correlated in terms of operating variables within this experimental conditions, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.408-418
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• 1986

본 연구에서는 표면은 단단하고 내면은 강인한 조직을 얻기위하여 대형 성형 탄 로울에 대하여 노에서의 급속가열 및 대기 상태에서의 자연냉각의 열처리가 수행 되어진다. 급속가열 및 냉각시 성형탄 로울 내부의 온도 분포 예측을 위하여 대류 및 복사 열전달 경계조건을 가지는 1차원 비정상 열전도 방정식이 유한 차분법을 사 용하여 해석되어졌다. 여기서 급속가열시 연소가스로 부터 기체복사에 의하여 성 형탄 로울의 바깥표면을 통하여 흡수되는 열량은

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.101-113
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• 2015

This paper introduces a numerical analysis method for reinforced-concrete(RC) members exposed to fire and proposes considerations in designing RC structures on the basis of the comparison between numerical results and design codes. The proposed analysis method consists of two procedures of the transient heat transfer analysis and the non-linear structural analysis. To exactly evaluate the structural behavior under fire, two material models are considered in this paper. One is "Under-Fire" condition for the material properties at the high temperature and the other one is "After-Cooling" condition for the material properties after cooling down to air temperature. The proposed method is validated through the correlation study between experimental data and numerical results. In advance, the obtained results show that the material properties which are fittable to the corresponding temperature must be taken into account for an accurate prediction of the ultimate resisting capacity of RC members. Finally, comparison of the numerical results with the design code of EN1992-1-2 also shows that the design code needs to be revised to reserve the safety of the fire-damaged structural member.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.352-357
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• 1995

원자력발전소 화학 및 체적제어계통의 일부인 밀봉수주입계통은 원자로 냉각재펌프 밀봉장치로 일정한 온도 범위의 밀봉수를 공급하여 밀봉장치의 건전성 및 원자로 냉각재 계통의 압력경계를 유지한다. 그러나 발전소 과도상태시 밀봉수 주입온도가 허용범위를 벗어나게 되면 온도조절기 폐쇄신호에 의해 밀봉장치로의 밀봉수 주입이 차단될 수 있다. 본 연구에서는 발전소 과도시에도 밀봉수 주입이 지속적으로 가능한 설계개선 방안으로 밀봉수주입 열교환기 주위에 우회라인을 설치하는 방안을 제시하고 밀봉수주입 열교환기 내에서의 비정상 열전달 현상을 수치해석을 이용하여 분석하였다. 계산은 속도장을 정상 상태인 power-law분포로 가정하고 시간 t=0에서 입구온도가 급격히 변하는 과도시 우회 유량 및 시간 변화에 대한 온도분포, 국부 Nusselt 수, 평균온도 등을 구하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.65-71
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• 2003

In this research, we make the thin wall chamber to the measurement of heat flux of using a Kerosene/LOx liquid rocket engine's thrust chamber. The wall thickness is one millimeter. We measured outside wall temperature of thrust chamber by nine thermocouple. We suppose the system to the one-dimension unsteady state, and so the heat flux and heat transfer coefficient of thurst chamber are calculated using one-dimensional the transient energy equation by outside wall temperature. In this case, O/F ratio is 2.0, experimental variation is chamber pressure and we got the heat transfer coefficient of the proportion relation of 0.88 times for the chamber pressure.

• Journal of Welding and Joining
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• v.8 no.2
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• pp.53-57
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• 1990

Analytic solutions of heat conduction during welding which were first found by Resenthal have some restrictions. One of these is that models to which analytic solutions can be applied must have simple geometric shape, and another is that quasi-stationary state must be created. On the other hand, computational methods developed recently with the aid of the computer can overcome these shortcomings, but the methods raise problems from economic point of view when they are applied to 3 dimensional problems. Taking account of these problems, a new method combinig the analytic method with the computational one is proposed. This method can be ued in weldments with complicated geometric shape in non-stationary state, but with the aid of the analytic method can reduce the computing time.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.123.1-123.1
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• 2010

수평형 지중열교환기의 최적설계를 위해서는 되메움재의 광물특성 및 입자크기, 열전도도(thermal conductivity), 열용량(heat capacity)등과 같은 열적 특성을 파악 하는 것은 중요하다. 수평형 지중 열교환기용 되메움재의 열전도도를 파악하기 위해 비정상 열선법을 적용한 QTM-500을 사용하여 포화도에 따른 천연규사-물-공기 혼합물의 열전도도를 측정하였다. 측정된 열전도도를 개별요소법(Discrete Element Mothod)에 근거한 2차원 수치해석 프로그램인 PFC2D(Particle Flow Code in 2 Dimension)를 이용하여 비교 분석하였다. 수치해석에서는 혼합물의 건조밀도를 일정하게 유지한 상태에서 포화도에 따라 가상의 물 입자 개수를 변화시켰다. 개별요소법을 이용한 열전달 수치해석에서는 입자의 접촉을 통해 발생한 thermal pipe에 의해 열전달이 이루어진다. 이러한 thermal pipe의 열전도도는 접촉된 두 입자의 열전도도와 접촉면의 평균 열전도도를 고려하여 적용하였다.

• Journal of Energy Engineering
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• v.21 no.2
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• pp.138-143
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• 2012

The present study has been carried out to elucidate the unsteady temperature characteristics of a refrigerator near gasket region by measuring time dependent temperature measurements. From the measured values of the time dependent temperature inside and outside region of a refrigerator, one could see that the temperature varies periodically with time from the effect of refrigerator operation. The measured mean temperatures at the wall had great different value from the previous other research results conducted by numeric ofheat transfer using improperfheat transfer boundary condition. The present study could give the experiment ofdata for the properfnumeric ofheat transfer an oysis and suggest more accuratefheat transfer boundary conditions for the inside and outside of a refrigerator.