• 한국태양에너지학회 논문집
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• 제34권5호
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• pp.73-80
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• 2014

This study introduces and analyzes the geothermal energy availability in Non-active volcanic region. Jeju island in Korea is situated in non-active volcanic region. The island is composed of rock with high pore and clinker, scoria geological layer formed by volcanic activity about two million ago. Volcanic geological layers with porous characteristics have air, vapor, water and a underground structure through which air or water can move easily. For this reason, it is probable that the mechanism of energy acquisition is by convective heat transfer. For this presumption, the availability of underground air as energy source has been studied here through theoretical analysis and experimental data. The energy output of our system ranged from 2,485,076 kJ/day to 4,060,978 kJ/day monitored using variable velocity air flow controller. Our system has capability to be a reliable energy source irrespective of environmental changes. Consequently, underground air can be utilized for energy source and provide the optimal design of heating/cooling system.

• Steel and Composite Structures
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• 제1권4호
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• pp.427-440
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• 2001

The growing use of unprotected or partially protected steelwork in buildings has caused a lively debate regarding the safety of this form of construction. A good deal of recent research has indicated that steel members have a substantial inherent ability to resist fire so that additional fire protection can be either reduced or eliminated completely. A performance based philosophy also extends the study into the effect of structural continuity and the performance of the whole structural totality. As part of the structural system, thermal expansion during the heating phase or contraction during the cooling phase in most beams is likely to be restrained by adjacent parts of the whole system or sub-frame assembly due to compartmentation. This has not been properly addressed before. This paper describes an experimental programme in which unprotected steel beams were tested under load while it is restrained between two columns and additional horizontal restraints with particular concern on the effect of catenary action in the beams when subjected to large deflection at very high temperature. This paper also presents a three-dimensional mathematical modelling, based on the finite element method, of the series of fire tests on the part-frame. The complete analysis starts with an evaluation of temperature distribution in the structure at various time levels. It is followed by a detail 3-D finite element analysis on its structural response as a result of the changing temperature distribution. The principal part of the analysis makes use of an existing finite element package FEAST. The effect of columns being fire-protected and the beam being axially restrained has been modelled adequately in terms of their thermal and structural responses. The consequence of the beam being restrained is that the axial force in the restrained beam starts as a compression, which increases gradually up to a point when the material has deteriorated to such a level that the beam deflects excessively. The axial compression force drops rapidly and changes into a tension force leading to a catenary action, which slows down the beam deflection from running away. Design engineers will be benefited with the consideration of the catenary action.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.713-721
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• 2004

Variable air intake and variable exhaust nozzle of hypersonic engines are designed and tested in this study. Dimensions for variable geometry air intake, ram combustor and variable geometry exhaust nozzle are defined based on the requirements of a pre-cooled turbojet engine. Hypersonic Ramjet Engine is designed as a scaled test bed for each component. Actuation forces of moving parts for variable intake and variable nozzle are reduced by balancing the other force in the opposite direction. A demonstrator engine which includes variable intake and variable nozzle is designed and the components are fabricated. Composite material with silicone carbide is applied for high temperature parts under oxidation environment such as leading edge of the variable intake and combustor liner. Internal cooling structure is adopted for both moving and static parts of the variable nozzle. Pressure recovery and mass capture ratio of the variable intake at Mach 5 is obtained by a hypersonic wind tunnel test. Flow characteristics of the variable nozzle are obtained by a low temperature flow test. Wall temperature and heat flux of the nozzle at Mach 3 is obtained by a firing test. As results, the intake and the nozzle are proved to be used at designed pressure and temperature environment.

• 한국재료학회지
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• 제8권8호
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• pp.678-684
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• 1998

정압분자동역학 시뮬레이션에 의하여 주기경계조건을 지닌 L-J 입자들로 구성된 계의 액체-유리-결정 전이를 연구하였다. 원자체적과 엔탈피는 가열 및 냉각과정에서 온도의 함수로 계산되었다. 반경분포함수로부터 유도된 Wendt-Abraham비와 단거리규칙도를 나타내는 각도분포함수를 분석하여 액체, 유리 및 결정상태를 구분하였다. 초기 fcc 결정을 가열하여 얻은 액체상은 급냉시에 비정질화하나 서냉시엔 결정화하였다. 급냉으로 생긴 유리는 다시 서서히 가열하면 fcc로 결정화하였다. 자유표면을 지닌결정은 표면에서부터 용해가 시작되어 벌크에 비하여 낮은 온도에서 녹고 냉각시에는 빠른 냉각속도에서도 결정화가 쉽게 일어나는 경향을 보였다.

• 대한기계학회논문집A
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• 제41권4호
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• pp.333-336
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• 2017

스피커 진동판은 고유 특성에 의해 분할진동을 발생 시킨다. 이 분할진동은 진동판의 형상 변화를 가져올 정도로 뚜렷한 영향을 주는데, 본 논문에서는 IT 분야의 첨병인 스마트 폰을 포함한 초박형 멀티미디어 기기에서 많이 사용되는 마이크로 스피커를 그 대상으로 삼는다. 마이크로 스피커는 일반적인 스피커와 다른 평판형의 구조적인 형태와 공간적인 제약이 존재한다. 특히 구동 공간이 밀폐형으로 설계되어 무빙 코일에서 발생하는 열의 냉각이 열악하고 보조적인 서스펜션 구조를 갖추기 어렵다. 본 연구에서는 진동판의 열전달과 분할진동 모드의 연관성을 연구한다. 이를 위해 진동판의 레이저 스캔을 통한 분할진동 측정과 열화상 카메라 촬영을 통한 열변화 측정의 두 단계로 나누어 실험을 진행한다. 이를 통해 특정 주파수 범위에서 분할진동 모드와 열전달 형태를 비교함으로써, 열화상 카메라를 통한 촬영 결과로 진동판 분할진동 모드의 경향성을 빠르게 예상할 수 있어, 마이크로 스피커의 최적 설계에 도움이 되는 지표를 제공할 수 있을 것으로 기대한다.

• 한국가스학회지
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• 제24권4호
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• pp.56-61
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• 2020

수소의 액화에는 예냉 에너지, 상변화 에너지, 수소 변환열 제거 등 다량의 에너지가 요구되어진다. 본 논문의 목적은 예냉공정에 필요한 에너지로 LNG냉열로 액체질소를 제조하여 사용하는 LNG냉열 간접 이용 방식과, Cold box의 단열에 냉공기를 이용하는 새로운 에너지절약 공정을 제안하여 수소액화 수율을 향상시키고자 하였다. 분석 결과를 보면, LNG냉열 간접이용 방식은 에너지 절약과 함께 액체수소 플랜트의 안전성을 제공하는 장점을 갖는다. 새로운 Cold box 단열 방식은 외벽 철판 3mm/우레탄폼 20cm/공기 5cm/우레탄폼 20cm/설비의 구조일 때 현재 펄라이트 단열에 비교하여 열유입량이 약 35%~50%가 감소하게 된다. 또한 냉공기 보다 온도가 높은 설비는 냉각의 효과를 얻게 된다. 수소액화 플랜트의 공정에 본 결과를 적용한다면 액체 수율이 50% 내외로 크게 향상되는 효과를 제공하게 된다.

• Advances in materials Research
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• 제8권2호
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• pp.117-135
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• 2019

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

• 대한건축학회논문집:구조계
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• 제36권5호
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• pp.177-185
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• 2020

The building energy performance indicator, called Energy Performance Index (EPI), has been used for the past decades in South Korea. It has a list of design variables assigned with weighting factors (a, b). Unfortunately, the current EPI method is not performance-based but very close to a prescriptive rating. With this in mind, this study aims to propose a new performance-based EPI method. For this purpose, a global sensitivity analysis method, Sobol, is employed. The Sobol method is suitable for complex nonlinear models and can decompose all the output variance due to every input. The Sobol sensitivity index of each variable is defined as 0 to 1 (0 to 100%), and the sum of all sensitivity indices is equal to 1 (100%). In this study, an office building was modeled using EnergyPlus and then the Latin Hypercube Sampling (LHS) was conducted to generate a surrogate model to EnergyPlus. The sensitivity index was suggested to replace weight (a) in the existing EPI. In addition, the discrete weight (b) in the existing EPI was replaced by a set of continuous regression functions. Due to the introduction of the sensitivity index and the continuous regression functions, the new proposed approach can provide far more accurate outcome than the existing EPI (R²: 0.83 vs. R²: 0.01 for cooling, R²: 0.66 vs. R²: 0.01 for total energy). The new proposed approach proves to be more rational, objective and performance-based than the existing EPI method.

• 에너지공학
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• 제7권2호
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• pp.194-201
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• 1998

전기 철도 차량의 A.C 모터 속도제어에는 여러 개의 GTO thyristor와 다이오드가 필요하다. 그런데 이러한 반도체 소자들은 약 1~2 kW의 열을 발생하기 때문에 냉각장치가 필요하며 이러한 반도체의 냉각에는 Perfluorocarbon(PFC)을 작동유체로 하는 히트파이프를 많이 사용하고 있다. 본 연구에서는 PFC 히트파이프의 증발 및 응축 열전달 계수에 미치는 관련변수로 주입율, 관의 내부 표면상태, 경사각, 증기압, 열유속 등의 영향을 파악하고, 열전달 계수를 예측할 수 있는 상관식을 제시하고자 하였다. 이를 위해 내부 표면에 그루브가 설치된 동관과 표면이 매끈한 외경 15.88mm인 동관을 이용하여 주입율이 다른 총 길이 520mm의 PFC 히트파이프와 열사이폰을 제작하고 실험을 수행하였다. 증발 열전달 계수는 열유속 15~45 kW/$m^2$의 범위일 때 2 kW/$m^2$K~5.5 kW/$m^2$K 사이의 분포를 보였다. 실험결과는 수정계수 CR=1.3을 적용할 때 Rohsenow의 핵비등 상관식과 실험치가 매우 접근된 결과를 보였으며 이러한 결과는 내부 벽면 그루브의 열전달 촉진효과이다. 응축 열전달 계수의 측정치는 1.5kW/$m^2$K~3.5kW/$m^2$K 사이의 분포를 보였으며 Nusselt 막응축 모델에 수정계수 CN=4를 도입함으로써 매우 접근된 예측이 가능하였다. 증발부 체적에 대한 작동유체 주입율은 40~100%의 범위가 적절하였다. 그리고 30$^{\circ}$이상의 경사각에서는 경사각의 영향이 미소하였다.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2204-2220
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• 2020

An open-pool type research reactor is designed and operated considering the accessibility around the pool top area to enhance the reactor utilization. The reactor structure assembly is placed at the bottom of the pool and filled with water as a primary coolant for the core cooling and radiation shielding. Most radioactive materials are generated from the fuel assemblies in the reactor core and circulated with the primary coolant. If the primary coolant goes up to the pool surface, the radiation level increases around the working area near the top of the pool. Hence, the hot water layer is designed and formed at the upper part of the pool to suppress the rising of the primary coolant to the pool surface. The temperature gradient is established from the hot water layer to the primary coolant. As this temperature gradient suppresses the circulation of the primary coolant at the upper region of the pool, the radioactive primary coolant rising up directly to the pool surface is minimized. Water mixing between these layers is reduced because the hot water layer is formed above the primary coolant with a higher temperature. The radiation level above the pool surface area is maintained as low as reasonably achievable since the radioactive materials in the primary coolant are trapped under the hot water layer. The key to maintaining the stable hot water layer and keeping the radiation level low on the pool surface is to have a stable flow of the primary coolant. In the research reactor with a downward core flow, the primary coolant is dumped into the reactor pool and goes to the reactor core through the flow guide structure. Flow fields of the primary coolant at the lower region of the reactor pool are largely affected by the dumped primary coolant. Simple, circular, and duct type discharge headers are designed to control the flow fields and make the primary coolant flow stable in the reactor pool. In this research, flow fields of the primary coolant and hot water layer are numerically simulated in the reactor pool. The heat transfer rate, temperature, and velocity fields are taken into consideration to determine the formation of the stable hot water layer and primary coolant flow. The bulk Richardson number is used to evaluate the stability of the flow field. A duct type discharge header is finally chosen to dump the primary coolant into the reactor pool. The bulk Richardson number should be higher than 2.7 and the temperature of the hot water layer should be 1 ℃ higher than the temperature of the primary coolant to maintain the stability of the stratified thermal layer.