• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.639-639
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• 2013

In this research we report the significant contribution of the as-spun multi-walled carbon nanotube (MWCNT) on the x-ray images formation using a low tube voltage x-ray source. The MWCNT, which was used for the fabrication of the spun CNT, was grown using a microwave plasma-enhanced chemical vapor deposition machine. Electrical-optics simulation software was utilized to determine the electron field emission trajectory of the triode-structure-as-spun CNT-based x-ray source. It was shown that a significant amount of converging electrons hit the target anode producing a clear x-ray image. These x-ray images where produced at a small amount of anode current of 0.67 mA at a tube voltage of 5 kV with the gate voltage of 0 V. Also, comparisons of the radiographs at various exposure times of the sample where analyzed with and without an x-ray dose filter. Results showed that spatially-resolved images were formed using the as-spun CNT at a low tube voltage with a $54-{\mu}m$ Al x-ray filter. This study can be used for low-voltage medical applications.

• Steel and Composite Structures
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• 제19권4호
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• pp.877-895
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• 2015

Connections to circular hollow steel sections (CHS) are considered one of the most complex and time consuming connections in steel construction. Such connections are usually composed of gusset plates welded to the outside of the steel tube or penetrating the steel tube. Design guides, accounting for the effect of connection configuration on the strength of the connection, are not present. This study aims to investigate, through experimental testing and a parametric study, the influence of connection configuration on the strength of one sided branch plate-to-CHS members. A notable effect was observed on the behavior of the connections due to its detailing changes with respect to capacity, failure mode, ductility, and stress distribution. A parametric study is performed using the calibrated analytical model to include a wider range of parameters. The study involves 26 numerical analyses of finite element models including parameters of the diameter-to-thickness (D/t) ratio, length of gusset plate, and connection configuration. Accordingly, a modification to the formulas provided by the current design recommendations was suggested to include connection configuration effects for the one sided branch plate-to-CHS members.

• 조명전기설비학회논문지
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• 제26권9호
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• pp.73-79
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• 2012

In this paper, we study on how to determine the number of hidden layer neurons in neural network for predicting defect size of steam generator tube. It was reported in the literature that the number of hidden layer neurons can be efficiently determined with the help of cross-validation. Although the cross-validation provides decent estimation performance in most cases, the performance depends on the selection of validation set and rather poor performance may be led to in some cases. In order to avoid such a problem, we propose to use multifold cross-validation. Through the simulation study, it is shown that the estimation performance of defect width (defect depth, respectively) attains 94% (99.4%, respectively) of the best performance achievable among the considered neuron numbers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1319-1321
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• 2001

The purpose of this study is to manufacture and test a thermoelectric generator which converts unused energy from close-at-hand sources, such as garbage incineration heat and industrial exhaust, to electricity. A manufacturing process and the properties of a thermoelectric generator are discussed before simulation the thermal stress and thermal properties of a thermoelectric module located between an aluminum tube and alumina plate. We can design the thermoelectric modules having the good properties of thermoelectric generation. Resistivity of thermoelectric module for thermoelectric generation consisting of 62 cells was $0.15{\sim}0.4{\Omega}$. The maximum power of thermoelectric generator using thermoelectric generation modules can be defined as temperature function, and in this case. It can be analogized the lineal relation between current and voltage characteristics as function of temperature. The thermoelectric generator using 32 thermoelectric modules was assembled with 32 directly connected modules that they constrained for two kinds of heat transfer tube with key joints.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.151-154
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• 2002

The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee's total variation diminishing (TVD) scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The Mach number $M_{s}$, of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two parallel tubes, the peak pressure produced by the twin-impulse waves and its location strongly depend upon the distance between two parallel tubes, L/d and the incident shock Mach number, $M_{s}$. The predicted Schlieren images represent the measured twin-impulse wave with a good accuracy.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.830-837
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• 2010

Since it started the researches on a maglev train on 1960, Germany and Japan arrived to putting to practical use level and accomplished most tests from their test-line. Korea is in progress the preparation for a practical use of low-speed maglev train in 110 [km/h] class and Korea Railroad Research Institute(KRRI) is in progress of a research about core technology of maglev system for high-speed tube train of 700 [km/h] class. In this paper, authors suggest an effective design method of Linear Synchronous Motor(LSM) for high-speed tube train of 700 [km/h] class which has a wound type electro-magnet. Then, authors calculate a variety of properties by changing speed of the LSM model which is designed by a method based on some theoretical equations. Then, authors verify the validity of the method based on some theoretical equations through a verification of property values by Finite Element Method(FEM) analysis method. Finally, in order to design a shape of pole-shoe part of LSM electro-magnet which is hard to design with a basic design method, authors analyze a transition of property values by changing a pole-shoe width and current of the electro-magnet through an analytical method by FEM.

• 대한기계학회논문집B
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• 제20권2호
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• pp.730-740
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• 1996

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW$^2$. Mass fluxes are set to 424 ~ 742kg/m$^{2}$s for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/m$^{2}$s for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1934-1941
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• 2006

As the operating time of heat exchangers progresses, fouling caused by water-borne deposits and the number of plugged tubes increase and thermal performance decreases. Both fouling and tube plugging are known to interfere with normal flow characteristics and to reduce thermal efficiencies of heat exchangers. The heat exchangers of Korean nuclear power plants have been analyzed in terms of heat transfer rate and overall heat transfer coefficient as a means of heat exchanger management. Except for fouling resulting from the operation of heat exchangers, all the tubes of heat exchangers have been replaced when the number of plugged tubes exceeded the plugging criteria based on design performance sheet. This paper describes a plugging margin evaluation method taking into account the fouling of shell-and-tube heat exchangers. The method can evaluate thermal performance, estimate future fouling variation, and consider current fouling level in the calculation of plugging margin. To identify the effectiveness of the developed method, fouling and plugging margin evaluations were performed at a component cooling heat exchanger in a Korean nuclear power plant.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.723-726
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• 2002

In this paper, a high efficiency leakage transformer for neon tube is developed to improve its power factor, to reduce its core loss and weight by using a technique of shape optimization and direction of grain-oriented silicon steel sheet. A protection circuit is designed for all types of neon transformer loaded with one or more neon lamps. Whenever the neon tube fails to be started up or comes to the life end, or encounters faults with open-circuits at the output terminals of the neon transformer, the protection circuit will be initiated to avoid more critical hazards. These neon transformers need a protection circuit to prevent from current stresses on circuit components by neon tube fail. The input of the transformer is automatically cut off when the abnormal condition occurs, preventing waste of no-load power. As the results of the study, the core weight is reduced by $11\%$, the power factor improved by $5\%$ and the efficiency increased by $6\%$ compared with the conventional type due to the employment of the grain-oriented steel sl)eel and the optimized core shape.

• 한국표면공학회지
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• 제41권4호
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• pp.134-141
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• 2008

We have developed a numerical model for a remote ICP(inductively coupled plasma) system in 2D and 3D with gas distribution configurations and confirmed it by plasma diagnostics. The ICP source has a Cu tube antenna wound along a quartz tube driven by a variable frequency rf power source($1.9{\sim}3.2$ MHz) for fast tuning without resort to motor driven variable capacitors. We investigated what conditions should be met to make the plasma remotely localized within the quartz tube region without charged particles' diffusing down to a substrate which is 300 mm below the source, using the numerical model. OES(optical emission spectroscopy), Langmuir probe measurements, and thermocouple measurement were used to verify it. To maintain ion current density at the substrate less than 0.1 $mA/cm^2$, two requirements were found to be necessary; higher gas pressure than 100 mTorr and smaller rf power than 1 kW for Ar.