• Journal of Power Electronics
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• v.11 no.4
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• pp.408-417
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• 2011

The plug-in hybrid electric vehicles (PHEVs) are specialized hybrid electric vehicles that have the potential to obtain enough energy for average daily commuting from batteries. The PHEV battery would be recharged from the power grid at home or at work and would thus allow for a reduction in the overall fuel consumption. This paper proposes an integrated power electronics interface for PHEVs, which consists of a novel Eight-Switch Inverter (ESI) and an interleaved DC/DC converter, in order to reduce the cost, the mass and the size of the power electronics unit (PEU) with high performance at any operating mode. In the proposed configuration, a novel Eight-Switch Inverter (ESI) is able to function as a bidirectional single-phase AC/DC battery charger/ vehicle to grid (V2G) and to transfer electrical energy between the DC-link (connected to the battery) and the electric traction system as DC/AC inverter. In addition, a bidirectional-interleaved DC/DC converter with dual-loop controller is proposed for interfacing the ESI to a low-voltage battery pack in order to minimize the ripple of the battery current and to improve the efficiency of the DC system with lower inductor size. To validate the performance of the proposed configuration, the indirect field-oriented control (IFOC) based on particle swarm optimization (PSO) is proposed to optimize the efficiency of the AC drive system in PHEVs. The maximum efficiency of the motor is obtained by the evaluation of optimal rotor flux at any operating point, where the PSO is applied to evaluate the optimal flux. Moreover, an improved AC/DC controller based Proportional-Resonant Control (PRC) is proposed in order to reduce the THD of the input current in charger/V2G modes. The proposed configuration is analyzed and its performance is validated using simulated results obtained in MATLAB/ SIMULINK. Furthermore, it is experimentally validated with results obtained from the prototypes that have been developed and built in the laboratory based on TMS320F2808 DSP.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1383-1389
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• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.61.1-61.1
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• 2011

We have performed simultaneous observations at 22GHz and 43GHz on AGNs hosted by elliptical galaxies using KVN radio telescope. We have constructed the sample, based on two major surveys in radio and optical band, i.e. Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) and Sloan Digital Sky Survey (SDSS) DR7, respectively. We restricted the redshift range 0.01 < z < 0.06 and the absolute magnitude Mr < -19.4 in order to satisfy volume limited sample. We also checked clear detection of four distinctive emission lines ([NII], [OIII], $H{\alpha}$, $H{\beta}$) so as to utilize on BPT diagram, distinguishing AGNs from star-forming galaxies. Elliptical galaxies have been selected by visual inspection making use of SDSS optical images. Then, we cross-matched the elliptical galaxies with FIRST detections. About 35% of the galaxies have been detected throughout KVN observations. We derive spectral index, applying the flux of different radio frequencies from FIRST (1.4GHz) and KVN (22GHz) and classify into steep, flat or inverted spectrum. We have found that most of the detected galaxies have flat spectrum while the rest of them have steep spectrum. This implies that a number of detected galaxies might have compact structure associated with the central region of the galaxies. The relation between black hole mass and radio luminosity has shown relatively tighter correlation in high frequency than in low frequency, which confirms that high frequency in radio band is appropriate to study the center of the galaxies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.699-708
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• 2000

To make compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled small diameter tube were taken in this research. The experiments were performed with HCFC-22 in the helically coiled small diameter tube; inner diameter=1.0(mm), tube length=2.0(m), and curvature diameter=31, 34, 46.2(mm). The experiments were also carried out with the following test conditions; saturation pressure=0.588(MPa), mass velocity=$150{\sim}500(kg/m^2s)$, and heat flux=$1{\sim}5(kW/m^2)$. The experiment results are that the empirical correlation to predict heat transfer coefficient for single phase flow in helically coiled small diameter tube was obtained. It was found that dry-out is occurred at low-quality region for evaporation heat transfer because of breaking of annular liquid film. The friction factor of single phase flow of helically coiled tube was agreed with Prandtl's correlation. Finally, It was proposed for correlation that can precisely predict the friction factor of two phase flow of helically coiled tube.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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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.

• Journal of Conservation Science
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• v.6 no.1 s.7
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• pp.3-14
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• 1997

Twelve Punchong sherds collected in Hakbongni, Kongju where the well known iron-painted on white slip were manufactured from late 15C to early 16C were analyzed for their composition and microstructure. The composition of the body was analyzed by X-ray fluorescence and that of glaze by electron probe micro-analyzer. Microstructure was observed by optical microscope, polarizing microscope, EPMA, and X-ray diffractometer. The results of composition of body and glaze of Hakbongni were compared with those of Punchong from Yongsuri, Boryong which was close to Hakbongni. The composition of body and glaze of these two areas were compared by principal component analysis using SPSS program. Hakbongni bodies have higher silica and flux materials but lower alumina and their glaze have higher silica, soda, iron oxide but lower alumina, calcia. Hakbongni punchong itself is divided into two groups. Their glaze is lime type. There are many remnant minerals, such as quartz, large feldspar mass with partially melted surrounding area, albite, biotite, and iron-oxide. From such a microstructure we can assume that preparation of raw material was rather crude and firing temperature quite low. Iron-painted material is identified as Mg/Fe/Al spinel by composition analysis and XRD pattern.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.1066-1080
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• 2024

SMART100 has a containment pressure and radioactivity suppression system (CPRSS) for passive containment cooling system (PCCS). This prevents overheating and over-pressurization of a containment through direct contact condensation in an in-containment refueling water storage tank (IRWST) and wall condensation in a CPRSS heat exchanger (CHX) in an emergency cool-down tank (ECT). The Korea Atomic Energy Research Institute (KAERI) constructed scaled-down test facilities, SISTA1 and SISTA2, for the thermal-hydraulic validation of the SMART100 CPRSS. Three separate effect tests were performed using SISTA1 to confirm the heat removal characteristics of SMART100 CPRSS. When the low mass flux steam with or without non-condensable gas is released into an IRWST, the conditions for mitigation of the chugging phenomenon were identified, and the physical variables were quantified by the 3D reconstruction method. The local behavior of the non-condensable gas was measured after condensation inside heat exchanger using a traverse system. Stratification of non-condensable gas occurred in large tank of the natural circulation loop. SISTA2 was used to simulate a small break loss-of-coolant accident (SBLCOA) transient. Since the test apparatus was a metal tank, compensations of initial heat transfer to the material and effect of heat loss during long-term operation were important for simulating cooling performance of SMART100 CPRSS. The pressure of SMART100 CPRSS was maintained below the design limit for 3 days even under sufficiently conservative conditions of an SBLOCA transient.

• Membrane Journal
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• v.22 no.4
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• pp.235-242
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• 2012

Ammonium perchlorate (AP) is primarily derived from the process of liquid incineration treatment when dismantling a solid rocket propellant. A series of batch dead-end nanofiltration (NF) and reverse osmosis (RO) membrane experiments were conducted to explore the retention mechanisms of AP under various hydrodynamic and solution conditions. Low levels of silicate type of siloxane had been detected through the GC/MS and FTIR analysis of liquid solutions extracted from solid ammonium perchlorate composite propellant (APCP). It is indicated that NF/RO membranes fouling in the presence of APCP was mainly attributed to the AP interactions because the concentration of silicate type of siloxane was negligible compared to that of AP. The osmotic pressure of AP was presumably resulted in the flux declines ranging from 13 to 17% in the case of the application of low-pressure (551 and 896 kPa for NF and RO) compared to those in application of high-pressure. The retention of AP by NF/RO membranes significantly varied from approximately 10 to 70% for NF and 26 to 87% for RO, depending on the operating and solution water chemistry conditions. The results suggested that retention efficiency of AP was fairly increased by reducing concentration polarization (i.e. application of low-pressure and stirring speed of 600 rpm) and increasing the pH of a solution. The result of this study was also consistent with the previous modeling of 'solute mass transfer of NF/RO membranes' and demonstrated that hydrodynamic and solution water chemistry conditions are to be a key factor in the retention of AP by NF/RO membranes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.9-18
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• 2013

Two-phase vapor-liquid flows exist in many shell and tube heat exchangers such as condensers, evaporators, and nuclear steam generators. To understand the fluid dynamic forces acting on a structure subjected to a two-phase flow, it is essential to obtain detailed information about the characteristics of a two-phase flow. The characteristics of a two-phase flow and the flow parameters were introduced, and then, an experiment was performed to evaluate the pressure loss in the tube bundles and the fluid-dynamic force acting on the cylinder owing to the pressure distribution. A two-phase flow was pre-mixed at the entrance of the test section, and the experiments were undertaken using a normal triangular array of cylinders subjected to a two-phase cross-flow. The pressure loss along the flow direction in the tube bundles was measured to calculate the two-phase friction multiplier, and the multiplier was compared with the analytical value. Furthermore, the circular distributions of the pressure on the cylinders were measured. Based on the distribution and the fundamental theory of two-phase flow, the effects of the void fraction and mass flux per unit area on the pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure on the tube by a numerical method. It was found that for low mass fluxes, the measured two-phase friction multipliers agree well with the analytical results, and good agreement for the effect of the void fraction on the drag coefficients, as calculated by the measured pressure distributions, is shown qualitatively, as compared to the existing experimental results.

• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.167-178
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• 2014

We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4 113 local type 2 AGNs at 0.02 < z < 0.05 selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the $H{\alpha}$ line with a Full-Width at Half-Maximum (FWHM) ranging from 1 700 to $19090km\;s^{-1}$ for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is ~3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad $H{\alpha}$ luminosity, log $L_{H\alpha}=40.50{\pm}0.35\;erg\;s^{-1}$, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log $M_{BH}=6.94{\pm}0.51\;M_{\odot}$. The mean Eddington ratio of the sample is log $L_{bol}/L_{Edd}=-2.00{\pm}0.40$, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the O III lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the $H{\alpha}$ line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.