• 한국산업융합학회 논문집
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• 제7권1호
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• pp.25-31
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• 2004

The heat transfer characteristics of a plasma display panel has been investigated for cooling an electronic module. Hence, a two dimensional $\kappa-{\varepsilon}$ turbulent model was developed to predict the temperatures of the panel and module. The heat conduction was solve for the material region. To consider the mixed convection at the solid-fluid interfaces between the air and the panel and module, the energy equation was solved simultaneously. When the electronic module stands face to face with the panel, the temperatures of panel and module are lower than other arrangement due to the chimney effect. However the gap between the panel and module does not affect significantly the maximum temperature when the aspect ratio is less than 0.1. To maintain the maximum temperature of the module under a certain limit, the passage of air should be well designed by the optimal layout of electronic modules which have different heat emission.

• 한국전기전자재료학회논문지
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• 제22권9호
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• pp.728-731
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• 2009

We report numerical simulations to investigate of the dependendce of the on/off current ratio and channel charge distributions in silicon nanowire (SiNW) field-effect transistors (FETs) on the channel width and thicknesses. In order to investigate the transport behavior in devices with different channel geometries, we have performed detailed two-dimensional simulations of SiNWFETs and control FETs with a fixed channel length L of $10\;{\mu}m$, but varying the channel width W from 5 nm to $5\;{\mu}m$, and thickness t from 10 nm to 30 nm. We have show that $Q_{ON}/Q_{OFF}$ drastically decreases (from $^{\sim}2.9{\times}10^4$ to $^{\sim}9.8{\times}10^3$) as the channel thickness increases (from 10 nm to 30 nm). As a result of the simulation using a quantum model, even higher charge density in the bottom of SiNW channel was observed then in the bottom of control channel.

• 전력전자학회논문지
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• 제25권5호
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• pp.412-419
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• 2020

In this study, a 70 W buck converter using GaN metal-oxide-semiconductor field-effect transistor (MOSFET) is developed. This converter exhibits over 97 % efficiency, high power density, and 48 V-to-12 V/1.2 V/1 V (triple output). Three gate drivers and six GaN MOSFETs are placed in a 1 ㎠ area to enhance power density and heat dissipation capacity. The theoretical switching and conduction losses of the GaN MOSFETs are calculated. Inductances, capacitances, and resistances for the output filters of the three buck converters are determined to achieve the desired current, voltage ripples, and efficiency. An equivalent circuit model for the thermal analysis of the proposed triple-output buck converter is presented. The junction temperatures of the GaN MOSFETs are estimated using the thermal model. Circuit operation and temperature analysis are evaluated using a circuit simulation tool and the finite element analysis results. An experimental test bed is built to evaluate the proposed design. The estimated switch and heat sink temperatures coincide well with the measured results. The designed buck converter has 130 W/in³ power density and 97.6 % efficiency.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.369-374
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• 2010

본 연구에서는 가스 연료와 공기 혼합물 내 압력파에 의해 유도되는 화염 가속과 연소폭발천이 현상을 수치적 계산을 통하여 살펴본다. 실험에 기반을 둔 초기 조건 하에서 점성력, 열전단, 몰질량 확산, 그리고 화학 반응을 고려한 reactive compressible Navier-Stokes 방정식을 사용하여 계산을 수행하였다. 반복되는 압력파와 화염의 상호 작용에 의해 발생되는 화염의 Richtmyer-Meshkov (RM) 불안정성에 의해 증가된 화염면을 통하여 생기는 hot spot들에 의한 폭굉의 발생을 모델링하였다. 또한 압력파의 강도 변화에 따른 연소폭발천이 현상의 변화를 살펴보았다.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.815-829
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• 2012

This paper proposes a nonlinear computational modeling approach for the behaviors of structural systems subjected to fire. The proposed modeling approach consists of fire dynamics analysis, nonlinear transient-heat transfer analysis for predicting thermal distributions, and thermomechanical analysis for structural behaviors. For concretes, transient heat formulations are written considering temperature dependent heat conduction and specific heat capacity and included within the thermomechanical analyses. Also, temperature dependent stress-strain behaviors including compression hardening and tension softening effects are implemented within the analyses. The proposed modeling technique for transient heat and thermomechanical analyses is first validated with experimental data of reinforced concrete (RC) beams subjected to high temperatures, and then applied to a bridge model. The bridge model is generated to simulate the fire incident occurred by a gas truck on April 29, 2007 in Oakland California, USA. From the simulation, not only temperature distributions and deformations of the bridge can be found, but critical locations and time frame where collapse occurs can be predicted. The analytical results from the simulation are qualitatively compared with the real incident and show good agreements.

• Journal of Magnetics
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• 제21권2호
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• pp.239-243
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• 2016

High temperature superconductor (HTS) magnet systems usually employ metal current leads which bridge between the cryogenic environment and room temperature. Such current leads are the dominant heat load for these magnet systems due to a combination of electrical resistance and heat conduction. HTS flux pumps enable large currents to be injected into a HTS magnet circuit without this heat load. We present results from an axial-type HTS mechanically rotating flux pump which employs a ferromagnetic circuit and a Cu-stabilized coated conductor (CC) HTS stator. We show the device can be described by a simple circuit model which was previously used to describe barrel-type flux pumps, where the model comprises an internal resistance due to dynamic resistance and a DC voltage source. Unlike previously reported devices, we show the internal resistance and DC voltage in the flux pump are not exactly proportional to frequency, and we ascribe this to the presence of eddy currents. We also show that this axial-type flux pump has superior current injection capability over barrel-type flux pumps which do not incorporate a magnetic circuit.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.540-548
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• 2019

This study was conducted to develop insulation for solid oxide fuel cell (SOFC). The developed insulation is based on the lamination technology and the radiation shielding technology of the satellite insulation. The insulation material is consisting of insulation material for conduction resistance, spacer, and radiation shielding material. The experimental apparatus consisting vacuum bell jar, pump, heater and temperature recording device has developed to verify the performance of the insulation. The experimental values were used as reference data for the modeling development. In this paper, heat transfer is assumed to be one- dimensional phenomena for the prediction of insulation performance and internal temperature distribution in high temperature region of SOFC. The developed model was used to compare the performance difference of insulation types according to composition materials. The analysis result shows that the insulation including spacer and radiation shielding has better heat insulation performance than other cases. In this study, the thickness reduction effect of about 20% was shown compared to the insulation including only conductive material. It is noted that the radiant shielding material should be carefully selected for durability, because SOFC insulation should be used for a long time at high temperature.

• 한국안전학회지
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• 제8권4호
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• pp.207-212
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• 1993

상변화 에너지 저장장치는 변동하는 액체-고체 상접합면과 자연대류의 존재에 기인한 비선형성 때문에 해석적으로 분석하기가 어렵다. 핀(fin) 형태의 상변화 에너지 저장장치를 준선형화 시켜 열전달을 수치적으로 해석하여 실험 데이타와 비교 검증하였다. 대칭형 수평 핀에 대하여 준선형, 비정상의 얇은 2차원적 모델을 세우고 유한체적방법(FVM)에 의해 시간의 함수로 융해된 상변화물질의 비율과 액체-고체 상접합면의 형상을 예측하였다. 유한체적방법(FVM)에 의한 결과는 실험결과와 비교적 잘 일치하였다. 벽과 융해점 사이의 온도차가 클수록 융해된 상변화물질의 비율은 증가하였으며 대류항을 포함하는 경우가 없는 경우보다 실험결과에 더 가까운 해를 얻을 수 있었다.

• 한국조명전기설비학회지:조명전기설비
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• 제7권1호
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• pp.30-36
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• 1993

본 연구는 정류기의 입력전류에 포함되어 있는 고조파성분을 제거하고 입력역률을 개선하기 위해 무손실 저항(Loss Free Resistor) 개념에 기본을 둔, PC, 가전기기 및 형광등용 전자안정기등과 같은 저전력 전원설비에 적합한 불연속 도통모드(DCM) 플라이백 방식의 능동역률 보정기의 등가회로모델 및 설계법을 제시하였다. 이 개념에 의하여 능동역률 보정기의 등가입력저항, 출력전력원 특성을 정확하게 나타낼 수 있었으며 또 설계방정식을 유도하여 능동역률 보정기를 설계 시험한 결과, 적은 부품으로 정류기의 입력교류 전류에 포함되어 있는 고주파를 제거하였고 따라서 0.98의 고입력역률의 정류를 할 수 있었다.

• Journal of Power Electronics
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• 제11권5호
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• pp.639-654
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• 2011

This paper presents a Current Distribution Control design for Paralleled Positive Output Elementary Super Lift Luo Converters (PPOESLLCs) operated in Continuous Conduction Mode using a Sliding Mode Controller (SMC). Manipulating the higher current requirement of the load through the paralleling of POESLLCs, results in a current inequality. This is mainly due to dissimilarities in the power semiconductor switches and circuit components used in POESLLCs, which may lead to converter failures. In order to balance the proper load current sharing and the load voltage regulation of PPOESLLCs, a SMC is developed. The SMC is designed for the inherently variable-structured of POESLLCs by using the state-space average based model. The static and dynamic performance of the developed controller with PPOESLLCs is validated for its robustness to perform over a wide range of operating conditions through both a laboratory prototype and MatLab/Simulink models, which are compared with a Proportional-Integral (PI) controller. Theoretical analysis, simulation and experimental results are presented to demonstrate the feasibility of the developed SMC along with the complete design procedure.