• Journal of the korean Society of Automotive Engineers
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• v.11 no.2
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• pp.41-54
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• 1989

In this study, steady state heat conduction problems of the cylinder block of turbocharged gasoline engine were solved by the boundary element method. Surface of the cylinder block was divided by the triangular cells with constant potential. Temperature distribution, effective heat transfer coefficient of the cylinder block were investigated with variation of equivalence ratio, engine speed and boost pressure. The results show that maximum temperature of cylinder block increase rapidly with increasing engine speed and boost pressure. The monolithic structure of cylinder block results in sever inhomogeneity of inner wall temperature at the high engine speed and boost pressure.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1372-1377
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• 2008

Since metallic foam will increase the performance of heat exchanger, it have caused many researcher's attention recently. Our research base on the model that metallic foams applied to heat exchanger. In this case, there is three kind of heat transfer mechanisms, heat conduction in fibers, heat transfer by conduction in fluid phase, and internal heat change between solid and fluid phases. In this paper, we first discuss the acceptance of applying thermal equilibrium among the two phases. then to calculate the dimensionless temperature profile along 7 metallic foams. The 7 samples have different characteristics, such as area ratio, effective conductivity, porosity, etc.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.290-290
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• 2011

In this study Diamond-like carbon (DLC) films were deposited on p-type Si substrates using a Radio-Frequency magnetron Sputtering system. The DLC film was deposited by bombarding graphite target with a N2/Ar plasma mixture with various conditions: substrate, pressure, deposition time, temperature of substrate, power and ratio of gas mixture. The effect on the conduction and hardness of DLC thin films were investigated. The conduction of DLC films were measured by I-V measurement. In addition, Raman analysis was performed to study the chemical bonding structure. The hardness was measured by Nano indentation. Atomic Force Microscopy was used for determined surface morphology of DLC film.

• Structural Engineering and Mechanics
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• v.11 no.4
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• pp.373-392
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• 2001

The main idea behind the paper is to present two alternative methods of homogenization of the heat conduction problem in composite materials, where the heat conductivity coefficients are assumed to be random variables. These two methods are the Monte-Carlo simulation (MCS) technique and the second order perturbation second probabilistic moment method, with its computational implementation known as the Stochastic Finite Element Method (SFEM). From the mathematical point of view, the deterministic homogenization method, being extended to probabilistic spaces, is based on the effective modules approach. Numerical results obtained in the paper allow to compare MCS against the SFEM and, on the other hand, to verify the sensitivity of effective heat conductivity probabilistic moments to the reinforcement ratio. These computational studies are provided in the range of up to fourth order probabilistic moments of effective conductivity coefficient and compared with probabilistic characteristics of the Voigt-Reuss bounds.

• Journal of information and communication convergence engineering
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• v.1 no.1
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• pp.23-26
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• 2003

A photodiode capable of obtaining a sufficient photo/dark current ratio at both a forward bias state and a reverse bias state is proposed. The photodiode includes a glass substrate, an aluminum film formed as a lower electrode over the glass substrate, an alumina film formed as a schottky barrier over the aluminum film, a hydrogenated amorphous silicon film formed as a photo conduction layer over a portion of the alumina film, and a transparent conduction film formed as an upper electrode over the hydro-generated amorphous silicon film. Growth of high quality alumina($Al_{2}O_{3}$) film using anodizing technology is proposed and analyzed by experiment. We have obtained the film with a superior characteristics

• Journal of Power Electronics
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• v.12 no.5
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• pp.708-714
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• 2012

This paper presents a new interleaved pulse-width modulation (PWM) boost-flyback converter to achieve power factor correction (PFC) and regulate DC bus voltage. The adopted boost-flyback converter has a high voltage conversion ratio to overcome the limit of conventional boost or buck-boost converter with narrow turn-off period. The proposed converter has wide turn-off period compared with a conventional boost converter. Thus, the higher output voltage can be achieved in the proposed converter. The interleaved PWM can further reduce the input and output ripple currents such that the sizes of inductor and capacitor are reduced. Since boundary conduction mode (BCM) is adopted to achieve power factor correction, power switches are turned on at zero current switching (ZCS) and switching losses are reduced. The circuit configuration, principle operation, system analysis, and design consideration of the proposed converter are presented in detail. Finally, experiments conducted on a laboratory prototype rated at 500W were presented to verify the effectiveness of the converter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.156-165
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• 1994

Unsteady heat conduction in stacked disks in a furnace has been numerically solved The effects of relevant parameters such as disk spacing, aspect ratio, environmental temperature, Biot nember, etc. have been investigated. The highest temperature appears at the disk edge and the lowest at the center. Penetration of heat form the surface to the center requires some time. Heating should be slow for uniform temperature rise. Geometric parameters complicates the radiative and conductive heat transfer. Though the resulting dependence of temperature nonuniformity on various parameters is complicated, high uniformity of temperature is in general available by low Biot number and/or low environmental temperature.

• Journal of IKEEE
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• v.23 no.1
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• pp.273-279
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• 2019

A high boost dc-dc converter based on the switched-inductor cell (SL-cell) is suggested in this paper. The suggested converter can provide a high voltage gain that is more than 6. Moreover, the voltage gain can be easily increased by extending a SL cell or a modular voltage boost stage. This paper shows the key waveforms, the operating principles at the continuous conduction mode (CCM), and a comparison between the suggested converter and the other non-isolated converters. In addition, the extension of the suggested converter is presented. The simulation results were shown to reconfirm the theoretical analysis.

• Korean Journal of Materials Research
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• v.13 no.8
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• pp.519-523
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• 2003

We report the synthesis of cubic spinel $ZnCo_2$$O_4$thin films and the tunability of the conduction type by control of the oxygen partial pressure ratio. Zinc cobalt oxide films were grown on$ SiO_2$(200 nm)/Si substrates by reactive magnetron sputtering method using Zn and Co metal targets in a mixed Ar/$O_2$atmosphere. We found from X-ray diffraction measurements that the crystal structure of the zinc cobalt oxide films grown under an oxygen-rich condition (the $O_2$/Ar partial pressure ratio of 9/1) changes from wurtzite-type $Zn_{1-x}$ $Co_{X}$O to spinel-type $ZnCo_2$$O_4$with the increase of the Co/Zn sputtering ratio,$ D_{co}$ $D_{zn}$ . We noted that the above structural change accompanied by the variation of the majority electrical conduction type from n-type (electrons) to p-type (holes). For a fixed $D_{co}$ $D_{zn}$ / of 2.0 yielding homogeneous spinel-type $_2$O$ZnCo_4$films, the type of the majority carriers also varied, depending on the$ O_2$/Ar partial pressure ratio: p-type for an $O_2$-rich and n-type for an Ar-rich atmosphere. The maximum electron and hole concentrations for the Zn $Co_2$ $O_4$films were found to be 1.37${\times}$10$^{20}$ c $m^{-3}$ and 2.41${\times}$10$^{20}$ c $m^{-3}$ , respectively, with a mobility of about 0.2 $\textrm{cm}^2$/Vs and a high conductivity of about 1.8 Ω/$cm^{-1}$ /.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.5
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• pp.434-441
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• 2016

This paper deals with transformer turns ratio design with the consideration of loss minimization in isolated bidirectional DC-DC converter. Generally, the rms value of current, magnitude of current at switching instance, and duty ratio of a converter vary according to the turns ratio of an isolation transformer in the converter under the same voltages and output power level. Therefore, the transformer turns ratio has an effect on the total loss in a converter. The switching and conduction losses of IGBTs and MOSFETs consisting of dual-active bridge converter are analyzed, and iron and copper losses in an isolation transformer and inductor are calculated. Total losses are calculated and measured in cases of four different transformer turns ratios through simulation and experiment with 3-kW converter, and an optimum turns ratio that provides minimum losses is found. The usefulness of the proposed transformer turns ratio design approach is verified through simulation and experimental results.