• 한국안전학회지
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• 제6권4호
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• pp.34-44
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• 1991

In this study, the general solution of heat balance equation including conductive heat loss were suggested and were determined the constants with the results of experiment in hot tunnel in order to derive the general equation for the response time and to investigate the response time index which represent the characteristics of response of sprinkler head in actual fires. Two types of test were considered, the plunge test, in which the air temperature is represented by a step function, and the ramp test, in which the air temperature increases at a constant rate. As a result, simple equations were derived, which can be predicted the response time for the ramp type fire with the rate of temperature rise and gas velocity, for the plunge type fire with temperature and gas velocity. Also other useful data, such as the effective temperature, time constant, response time index and conduction parameter were obtained.

• 폴리머
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• 제29권6호
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• pp.549-556
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• 2005

단축압출기의 압출공정에서 고체수송부의 열전달 현상에 미치는 무차원수의 효과를 수치 해석적인 방법으로 연구하였다. 스크루의 기하학적 구조 및 특성에 따른 압출기 내에서의 고체 흐름 상태에 대한 이해를 바탕으로 고체 수송부에 대하여 열 수지 방정식을 세우고 무차원화하였다. 이에 유한체적법과 멱법칙 도식을 적용하여 이산화 방정식을 유도한 다음 반복 대입법과 완화법으로 해를 구하였다. 고체수송부의 열전달 특성을 규정하는 무차원수인 Biot 수와 Peclet 수가 수지 공급부의 온도와 고체수송부의 길이에 끼치는 영향을 조사하였다. Biot 수가 증가하면 냉각에 의한 열 손실이 지배하여 배럴의 온도는 급격히 감소하지만 고체층의 온도와 고체수송부의 길이에 미치는 영향은 적으며, Peclet 수가 증가하면 대류 항이 지배하여 고체층의 온도가 감소하고 고체수송부의 길이가 증가한다.

• Nuclear Engineering and Technology
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• 제31권2호
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• pp.236-255
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• 1999

An improved mechanistic model was developed to predict a convective boiling critical heat flux (CHF) in the vertical round tubes with uniform heat fluxes. The CHF formula for subcooled and low quality boiling was derived from the local conservation equations of mass, energy and momentum, together with appropriate constitutive relations. The model is characterized by the momentum balance equation to determine the limiting transverse interchange of mass flux crossing the interface of wall bubbly layer and core by taking account of the convective shear effect due to the frictional drag on the wall-attached bubbles. Comparison between the present model predictions and experimental CHF data from several sources shows good agreement over a wide range of How conditions. The present model shows comparable prediction accuracy with the CHF look-up table of Groeneveld et al. Also the model correctly accounts for the effects of flow variables as well as geometry parameters.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.187-207
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• 1999

The thermal distributions near the growth interface of 150mm CZ crystals were measured by three thermocouples installed at the center, middle (half radius) and edge (10m from surface) of the crystals. The results show that larger growth rates produced smaller thermal gradients. This contradicts the widely used heat flux balance equation. Using this fact, it si confirmed in CZ crystals that the type of point defects created is determined by the value of the thermal gradient (G) near the interface during growth, as already reported for FZ crystals. Although depending on the growth systems the effective lengths of the thermal gradient for defect generation are varied, were defined the effective length as 10mm from the interface in this experiment. If the G is roughly smaller than 20C/cm, vacancy rich CZ crystals are produced. If G is larger than 25C/cm, the species of point defects changes dramatically from vacancies to interstitial. The experimental results which FZ and CZ crystals are detached from the melt show that growth interfaces are filled with vacancy. We propose that large G produces shrunk lattice spacing and in order to relax such lattice excess interstitial are necessary. Such interstitial recombine with vacancies which were generated at the growth interface, next occupy interstitial sites and residuals aggregate themselves to make stacking faults and dislocation loops during cooling. The shape of the growth interface is also determined by the distributions of G across the interface. That is, the small G and the large G in the center induce concave and convex interfaces to the melt, respectively.

• 대한공간정보학회지
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• 제19권4호
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• pp.145-151
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• 2011

증발산(Evapotranspiration)은 생태학 수문학적으로 지표 특성을 표현하는 변수로서 지구 물 순환과 에너지 수지에 중요한 역할을 한다. 본 연구에서는 높은 지표거칠기를 고려하여 에너지 수지식을 기반으로 실제 증발산량을 산출하였다. 2009년 한반도를 대상으로 다양한 위성 자료와 관측 자료를 이용하여 연구를 수행하였다. 실제 증발산량 산출에 있어 중요한 변수인 현열은 다양한 입력 변수가 사용되어 계산 과정이 복잡하므로 본 연구에서는 경험적 계수인 B를 사용하여 현열 산출을 단순화하였다. 또한 본 연구에서는 현열 산출 시 중요한 변수인 공기역학적 저항을 고려하여 높은 지표거칠기를 반영한 실제 증발산량 모델을 제시하였다. 산출된 실제 증발산량은 Priestley-Taylor 가능 증발산량을 통한 검증(RMSE 1.0179mm/day, BIAS 0.4516mm/day)을 수행하였으며 높은 지표거칠기를 고려한 실제 증발산량이전반적으로 잘 산출되었음을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2173-2187
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• 2022

A 3D thermo-elasto-hydrodynamic model is developed to analyze the sealing performance of a notched mechanical seal applied in the reactor coolant pump. In the model, the generalized Reynolds equation, the energy equation coupled with notch heat balance equation, the heat conduction equations, and the deformation equations of the sealing rings are iteratively solved by the finite element method. The film pressure and temperature distribution are obtained, and the deformation of the sealing rings is revealed to study the mechanism of the notched mechanical seals. A parameterized study is conducted to analyze the sealing performance under different operating conditions. As a comparison, the sealing performance of non-notched seals is also studied. The results show that the hydrostatic effect is dominant in the load-carrying capacity of the fluid film due to the radial mechanical and thermal deformations. The notch can cool the fluid film and influence the thermal deformation of seal rings. The sealing performance is sensitive to the pressure difference, ambient temperature, and rotational speed. It is suggested to set the notches on the softer sealing rings to acquire the greater hydrodynamic effect. Compared with the non-notched, the notched end face holds a better lubrication performance, especially under lower rotational speed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.104-107
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• 2000

Evaporative heat transfer characteristics of carbon dioxide has been investigated. Experiment has been carried out for seamless stainless steel tube with outer diameter of 9.55 mm and inner diameter of 7.75 mm. Direct heating method is used for supplying heat to the refrigerant was uniformly heated by electric current which was applied to the tube wall. The saturation temperature of refrigerant is calculated from the measured saturation pressure by using an equation of state. Inner wall temperature was calculated from measured outer wall temperature, accounting for heat generation in the tube and heat conduction through the tube wall. Mass Quality of refrigerant was calculated by considering energy balance in the preheater and the test section. Heat fluxes were set at 12, 16, 20, 23, and $27kW/m^2$, mass fluxes were controlled at 212, 318, 424, and $530 kg/m^2s$, and saturation temperature of refrigerant were adjusted at 0, 3.4, 6.7 and $10.5^{\circ}C$. From this study, heat transfer coefficients of carbon dioxide have been provided with respect to quality for several mass fluxes, heat fluxes. Finally, the experimental results in this study are compared with the correaltion by Gungor and Winterton(1987).

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.155-163
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• 1999

A numerical study for simulating a swirling pulverized coal combustion in axisymmetric geometry is done here by applying the weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard ${\kappa}-{\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase for soot. The eddydissipation model is employed for the reaction rate for gaseous mixture, and the single-step first-order reaction model for the devolatilization process for coal. By comparing the numerical results with experimental ones, the models used here are confirmed and found to be one of good alternatives for simulating the combustion as well as radiative characteristics.

• 한국산업융합학회 논문집
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• 제4권3호
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• pp.329-337
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• 2001

This simulator is developed for the analysis of a MOSFET based on Thermally Coupled Energy Transport Model(TCETM). The simulator has the ability to calculate not only stationary characteristics but also non - stationary characteristics of a MOSFET. It solves basic semiconductor devices equations including Possion equation, current continuity equations for electrons and holes, energy balance equation for electrons and heat flow equation, using finite difference method. The conventional semiconductor device simulation technique, based on the Drift-Diffusion Model (DDM), neglects the thermal and other energy-related properties of a miniaturized device. I, therefore, developed a simulator based on the Thermally Coupled Energy Transport Model (TCETM) which treats not only steady-state but also transient phenomena of such a small-size MOSFET. In particular, the present paper investigates the breakdown characteristics in transient conditions. As a result, we found that the breakdown voltage has been largely underestimated by the DDM in transient conditions.

• 소성∙가공
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• 제8권3호
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• pp.252-261
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• 1999

The 3-dimensional finite element program is developed to analyze the non-isothermal forming processes of aluminum-alloy sheet metals. Bishop's method is introduced to solve the heat balance and force equilibrium equations. Also, Barlat's non-quadratic anisotropic yield function depicts the planar anisotropy of the aluminum-alloy sheet. To find an appropriate constitutive equation, four different forms are reviewed. For the verification of the reliability of the developed program, the computational try-outs of the non-isothermal cylindrical cupping processes of AL5052-H32 and Al1050-H16 are carried out. As results, the constitutive equation relating to strain and strain-rate, in which the constants are represented by the 5th-degree polynomials of temperature, is in good agreement with measurement. The computational try-outs can predict optimal forming conditions in non-isothermal forming processes.