• 터널과지하공간
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• 제19권6호
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• pp.507-516
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• 2009

고준위 방사성 폐기물 처분장의 경우 폐기물의 방사성 붕괴에 의해 발열 현상이 나타나게 되며, 암반을 통한 열전달에 의해 처분장 주변 환경이 변화됨으로써 처분장의 안전성에 영향을 미칠 수 있다. 그러므로 처분장의 안전성 확보를 위해선 적절한 처분장 내 환기장치가 필요하다. 적절한 환기시스템의 구축을 위해서는 암반 열물성치와 처분장 내 열전달계수의 산정을 통한 컴퓨터 시뮬레이션 연구가 핵심이라고 할 수 있다. 이에 본 연구에서는 KAERI Underground Research Tunnel(이하 KURT) 내부 환경 인자(건습구온도, 암반표면온도, 대기압)들의 측정을 통해 열전달계수를 산정하는 것에 초점을 맞추었다. KURT 내부 우측 연구모듈의 막장 벽면에 길이 2 m, 용량 5 kw의 히터가 $90^{\circ}C$로 암반 내부를 가열하고 있는 히터구간의 열전달계수 산정 결과, 태양의 위치에 따른 처분장 외부 대기의 온도변화에 의해 열전달계수의 수치 변화가 최대 7.9% 발생하였으며, 평균 열전달계수 h는 약 4.533 W/$m^2{\cdot}K$의 수치를 나타내었다.

• 터널과지하공간
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• 제2권1호
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• pp.116-122
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• 1992

A comprehensive, nonsteady state, computer simulation program for the environmental conditions in advancing tunnels (the HEADSIM simulation program) is constructed and successfully validated with heat balance amongst all heat sources, and with mass conservation amongst various airflows including the leakage air from ducts, under timedependent variations of inlet air conditions. which include sudden, diurnal and seasonal changes. Heat conduction in the wall strata and face strata is simulated with most complicated boundary conditions using the finite difference method, and the climatic conditions in roadway sections which contain air ducts, booster fan, spray cooler, compressed air pipes, cold water pipes, return water pipes, machinery and broken rock are simulated taking into account the variations of face operation and the heat storage mechanism in the strata. The limitations of simulation time steps and roadway section lengths are defined according to the stability criteria satisfying the principles of thermodynamics. Variations of heat transfer coefficients, which are newly set, and those of wetness factors are taken into account according to the variations of other parameters and the stepwise advance of the face. Newly-derived formulae are used for computing the air duct leakage and the pressure inside of the duct. A new concept of an 'imaginary duct' is introduced to simulate the climatic conditions in tunnels during holiday periods, which directly affect conditions on subsequent working days under the consideration of natural convection. A subsidiary program (the WALLSIM simulation program) is made to compute the dimensionless tunnel surface temperatures and to compare the results with those from analytical approaches, and to demonstrate the stability, convergence and accuracy of the strata heat conduction simulation, adopting the finite difference method. The WALLSIM also has wide applications, including those for the computation of age coefficients.

• 한국전산유체공학회지
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• 제21권2호
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• pp.54-61
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• 2016

When spent fuel assemblies from the reactor of nuclear power plants(NPPs) are transported, the assemblies are exposed to short-term operations that can affect the peak cladding temperature of spent fuel assemblies. Therefore, it needs to perform the analysis of heat transfer on spent fuel dry cask during the operation. For 3 dimensional computational fluid dynamnics(CFD) simulation, it is proposed that the short-term operation is divided into three processes: Wet, dry, and vacuum drying condition. The three processes have different heat transfer mode and medium. Metal transportation cask, which is Korea Radioactive Waste Agency(KORAD)'s developing cask, is evaluated by the methods proposed in this work. During working hours, the boiling at wet process does not occur in the cask and the peak cladding temperatures of all processes remain below $400^{\circ}C$. The maximum peak cladding temperature is $173.8^{\circ}C$ at vacuum drying process and the temperature rise of dry, and vacuum drying process occurs steeply.

• Journal of Advanced Marine Engineering and Technology
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• 제41권1호
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• pp.1-7
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• 2017

두 판을 맞대기 용접할 경우 용접부 시종단부 측면에 열전도도가 큰 금속(예를 들어 구리)으로 만든 엔드 탭을 장착하고 용접을 진행하면 용접부 끝부분의 비드흘러내림과 결함을 방지할 수 있다. 본 논문에서는 엔드 탭의 방열 성능을 강화시키기 위하여 자연 대류에 의한 방열 특성이 뛰어난 것으로 알려진 평판 휜 모양을 적용하였고, 실험 및 수치해석을 통하여 엔드 탭에 평판 휜 모양의 구멍이 있는 형상이 구멍이 없는 형상보다 방열 성능이 더 뛰어남을 확인하였다. 그리고 열, 유동해석을 통하여 엔드 탭의 휜 형상에 대한 냉각 속도를 평가하여, 방열 성능 측면으로 도움이 될 형상 인자적인 특성을 파악하였다. 그 결과, 엔드 탭에 수직 휜이 있으며 휜 간 간격에 최적 휜 간 간격 식을 적용한 구조가 우수한 형상으로 판단되었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.427-432
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• 2005

This study treats the advantage of in situ line source method measuring the heat transfer capacity of a borehole, using mobile equipment, to determine the thermal properties of the entire borehole system such as thermal conductivity, diffusiveity. volumetric heat capacity, and borehole thermal resistance. The results from the response test include not only the thermal properties of the ground and the borehole, but also conditions that are difficult to estimate, e,g. natural convection in the boreholes, asymmetry in the construction, etc. In this study, 1) theoretical in situ methods for assessing working fluid temperature variation in V-type PE tube have been introduced, and 2) TRTE(Thermal Response Test Equipment) has been built based on these kinds of theoretical in situ methods. Basically TRTE consists of a pump, a heater and temperature sensors for measuring the inlet and outlet temperatures of the borehole. In order to make equipment easily transportable it is set up on a small trailer. Since the response test takes above two days to execute, the test was fully automatic in recording measured data using Labview DAS(Data acquisition system) program. The test was demonstrated in the course of intensive research in this field through the one site at Ulsan city in Korea. From this kind of thermal properties test of borehole systems in situ, the design of the borehole system can be optimized regarding the total geological, hydro-geological and technical conditions at the location.

• 한국자동차공학회논문집
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• 제20권4호
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• pp.125-132
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• 2012

Urea-SCR system, which converts nitrogen oxides to nitrogen and water in the presence of a reducing agent, usually AdBlue urea solution, is known as one of the powerful NOx reduction systems for mobile as well as stationary applications. For its consistent and reliable operation in mobile applications, such various problems as transient injection, ammonia slip, and freezing in cold weather have to be resolved. In this work, therefore, numerical study on three-dimensional unsteady heating problems were analyzed to understand the melting and heat transfer characteristics such as urea liquid volume fraction, temperature profiles and generated natural convection behavior in urea solution by using the commercial software Fluent 6.3. After validating by comparing numerical and experimental data with pure gallium melting phenomena, numerical experiment for urea melting is conducted with three different coolant heating models named CH1, 2, and 3, respectively. Finally, it can be found that the CH3 model, in which more coolant is concentrated on the lower part of the urea tank, has relatively better melting capability than others in terms of urea quantity of $1{\ell}$ for start-up schedule.

• KIEAE Journal
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• 제3권2호
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• pp.37-44
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• 2003

The aim of this study was to analyze the thermal performance through Test-Cell of TI-wall in domestic climate. This study was carried out as follows: 1) The TI-wall was studied for ability to reduce heat loss through the building envelope and analyzed to TIM properties. 2) Test models of TI-wall were designed through the investigation of previous paper and work, measured for winter and spring, and the thermal effects were analyzed. The type of the TIM used in test model is small-celled(diameter 4mm and thickness 50mm) capillary and cement brick(density $1500kg/m^3$) was used by thermal mass. 3) Test-cell of TI-wall was calibrated from measured data and the dynamic simulation program ESP-r 9.0. In these simulations, the measured climate conditions of TaeJon were used as outdoor conditions, and the simulation model of Test-cell was developed. 4) The sensitivity analysis is executed in various aspects with standard weather files and ESP-r 9.0, and then most suitable system of TI-wall are predicted. Finally, The suitable system of TI-wall was analysed according to sizes of air gap, kinds, thickness, and the surface absorption of therm wall. The result is following. In TI-wall, Concrete is better than cement brick, at that time the surface absorption is 95%, and the most efficient thickness is 250mm. As smaller of a air gap, as reducer of convection heat loss, it is efficient for heating energy. However, ensuring of a air gap at least more than 50mm is desirable for natural ventilation in Summer.

• 대한기계학회논문집B
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• 제23권1호
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• pp.140-148
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• 1999

Experiments on flame spread in an one-dimensional droplet array up to supercritical pressures of fuel droplet have been conducted In normal gravity and microgravity. Evaporating process around unburnt droplet is observed through high-speed Schlieren and direct visualizations in detail, and flame spread rate is measured using high speed chemiluminescence images of OH radical. Flame spread behaviors are categorized into three: flame spread is continuous at low pressures and is regularly intermittent up to the critical pressure of fuel. flame spread is irregularly intermittent and zig-zag at supercritical pressures of fuel. At atmospheric pressure, the limit droplet spacing and the droplet spacing of maximum flame spread rate in microgravity are larger than those in normal gravity. In microgravity, the flame spread rate with the increase of ambient pressure decreases initially, takes a minimum, and then decreases after taking maximum. This is so because the flame spread time is determined by competing effects between the increased transfer time of thermal boundary layer due to reduced flame diameter and the reduced ignition delay time in terms of the increase of ambient pressure. Consequently, it is found that flame spread behaviors in microgravity are considerably different from those in normal gravity due to the absence of natural convection.

• 한국수소및신에너지학회논문집
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• 제7권2호
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• pp.121-128
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• 1996

수소액화를 위한 직접냉각장치를 개발하고, 이의 성능특성을 시험하였다. 직접냉각장치는 액화용기, 복사쉴드, 저온조와 GM냉동기 등으로 구성하였다. 개발된 액화장치의 cool-down 및 warm-up특성이 상세하게 규명되었다. 본 냉각장치에서 냉각이 시작된지 약 45분 후, 액화용기내의 수소가 액화되기 시작함을 확인하였다. 또한 동일한 실험을 기체헬륨에 대하여 수행하였으며, 기체헬륨은 주어진 작동조건에서 액화되지 않으므로 수소의 경우와는 다른 cool-down 및 warm-up 특성을 보였다. 충전된 기체의 자연대류현상의 영향을 고찰하기 위하여 액화용기내에 진공상태를 유지하면서 시험하였다. 이때 진공상태에서의 액화용기의 냉각시간은 현저히 증가함을 보였다.

• 한국수소및신에너지학회논문집
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• 제24권2호
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• pp.128-135
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• 2013

The nuclear fuel cycle plant is composed of various subsystems such as a fuel storage and delivery system (SDS), a tokamak exhaust processing system, a hydrogen isotope separation system, and a tritium plant analytical system. Korea is sharing in the construction of the International Thermonuclear Experimental Reactor (ITER) fuel cycle plant with the EU, Japan, and the US, and is responsible for the development and supply of the SDS. Hydrogen isotopes are the main fuel for nuclear fusion reactors. Metal hydrides offer a safe and convenient method for hydrogen isotope storage. The storage of hydrogen isotopes is carried out by absorption and desorption in a metal hydride bed. These reactions require heat removal and supply respectively. Accordingly, the rapid storage and delivery of hydrogen isotopes are enabled by a rapid cooling and heating of the metal hydride bed. In this study, we designed and manufactured a vertical-type hydrogen isotope storage bed, which is used to enhance the cooling performance. We present the experimental details of the cooling performances of the bed using various cooling parameters. We also present the modeling results to estimate the heat transport phenomena. We compared the cooling performance of the bed by testing different cooling modes, such as an isolation mode, a natural convection mode, and an outer jacket helium circulation mode. We found that helium circulation mode is the most effective which was confirmed in our model calculations. Thus we can expect a more efficient bed design by employing a forced helium circulation method for new beds.