• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.723-729
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• 2019

Turbochargers are an effective device to reduce the fuel consumption. In this study, the mass flow rate of pulsating flow in the twin-scroll turbocharger for the gasoline engine of passenger vehicles was measured. Pulsating flow was achieved using a pulse generator and the mass flow rate of the unsteady pulsating flow was analyzed by comparing it with those of the steady flow. The pulse generator consisted of a rotating upper plate and a fixed lower plate. To measure the mass flow rate of unsteady flow, the orifice flow meter equipped with the difference pressure transducer was used. To analyze the low speed performance of the turbocharger, the measurement was carried out in the speed of turbocharger from 60,000rpm to 100,000rpm. The mass flow parameters of the unsteady pulsating flow showed a large difference compared to those of the steady flow. Those of the unsteady flow showed the hysteresis loop surrounding the mass flow parameters of the steady flow and the maximum variation of the mass flow parameters were 5.0 times those of the steady flow. This phenomenon is the result of the filling and emptying the turbine volute space due to pulsating flow.

• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.

• Journal of Biosystems Engineering
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• v.26 no.3
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• pp.263-270
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• 2001

This study was conducted in order to develop wind-water heating system where frictional heat is creased between the rotor and working fluid when they are rotating in the cylindrical heat generator. The wind-water heating system is composed of rotor, stator, working fluid, motor, inverter and heat generation tank. Instead of wind turbine, we have used an electrical motor of 30㎾ to rotate the rotor in this system. Two working fluids and six levels of rotor rpm were tested to quantify heat amounts generated by the system. Generally, as motor rpm goes up heat amount increases that we have expected. At the same rpm, viscous fluid showed up better performance than the water, generating more heat by 10$\^{C}$ difference. The greatest heat amount of 31,500kJ/h was obtained when the system constantly drained out the hot water of at the flow rate of 500ℓ/h. Power consumption rate of the motor was measured by thee phase electric power meter where the largest power consumption rate was 14㎾ when motor rpm was 600 and gained heat was 31,500kJ/h, that indicated total thermal efficiency of the wind power water heating system was 62%.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.2
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• pp.182-190
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• 2011

This paper proposes a LVRT (Low Voltage Ride Through) control strategy which should be satisfied by grid-connected wind power system when grid faults occur. The LVRT regulation indicates rules or actions which have to be executed according to the voltage dip ratio and the fault duration. Especially the wind power system has to support the grid with specified reactive current to secure the grid stability when voltage reduction ratio is over 10%. The LVRT regulation in this paper is based on the German Grid Code and full-scale variable speed wind power conversion system is considered for LVRT control strategy. The proposed LVRT control strategy satisfies not only LVRT regulation but also makes power balance between wind turbine and power system through additional DC link voltage regulation algorithms. Because it is impossible to control grid side power when the 3-phase to ground fault occurs, the DC link voltage is controlled by a generator side inverter using the DC link voltage control strategy. Through the simulation and experiment result, the proposed LVRT control strategy is evaluated and its effectiveness is verified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.175-181
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• 2018

Electric pump system is new technology for next generation propulsion unit. The system has simple structure which dose not need gas generator, injector and turbine and might better pump for low cost and low payload rocket. Therefore, this paper suggests conceptual design of electric-pump Permanent-Magnet Synchronous Motor (PMSM) which has 50 kW & 50,000 RPM for rocket. To satisfy the system's requirement, electromagnetic analysis is conducted for suitable inner and outer diameter of stator and rotor which uses 4000 Gauss cylinder magnet and Inconel 718 can to fix whole rotor. Futhermore, to confirm rotational vibration, rotordynamics analysis is conducted. By this analysis, Campbell diagram is printed. From the diagram, natural frequency could be determined for the only motor and dynamo meter test bench.

• Journal of computational fluids engineering
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• v.9 no.3
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• pp.49-56
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• 2004

A heated and expanded helium is used to pressurize liquid propellants in propellant tanks of propulsion system of liquid propellant launch vehicles. To produce a heated and expanded helium, an hot-gas heat exchanger is used by utilizing heat source from an exhausted gas, which was generated in a gas generator to operate turbine of turbo-pump and dumped out through an exhaust duct of engine. Both experimental and numerical approaches of hot-gas heat exchanger design were conducted in the present study. Experimentally, siliconites - electrical resistance types - were used to simulate the full heat condition instead of an exhausted gas. Cryogenic heat exchangers, which were immersed in a liquid nitrogen pool, were used to feed cryogenic gaseous helium in a hot-gas heat exchanger. Numerical simulation was made using commercially utilized solver - Fluent V.6.0 - to validate experimental results. Helically coiled stainless steel pipe and stainless steel exhausted duct were consisted of tetrahedron unstructured mesh. Helium was a working fluid Inside helical heat coil and regarded as an ideal gas. Realizable k-』 turbulent modeling was adopted to take turbulent mixing effects in consideration. Comparisons between experimental results and numerical solutions are Presented. It is observed that a resulted hot-gas heat exchanger design is reliable based on the comparison of both results.

• Environmental and Resource Economics Review
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• v.23 no.4
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• pp.617-641
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• 2014

Korean electricity market is a Cost-Based Pool (CBP) designed to minimize electricity production cost through cost by providing cost reduction incentives to generators. Generation companies have shown diverse efforts to reduce costs in CBP market such as procuring low-price fuels, installing high efficiency gas turbine and constructing power plants near the heavy-load site. Recently, as a way to improve CBP market, a proposal to exclude no-load cost from System Marginal Price (SMP) and to compensate generators ex post was suggested to Korea Power Exchange. This study analyzes the impact of excluding no-load cost from SMP on the cost reduction incentive of generators. We found that excluding no-load cost from SMP enhances the likelihood of decreasing the cost reduction incentives of LNG combined-cycle generators lying on the price-setting range.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.23-30
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• 2016

Wake effects cause wind turbine generators (WTGs) within a wind power plant (WPP) to produce different levels of active power and subsequent reactive power capabilities. Further, the impedance between a WTG and the point of interconnection (POI)-which depends on the distance between them-impacts the WPP's reactive power injection capability at the POI. This paper proposes a voltage control scheme for a WPP based on the available reactive current of the doubly-fed induction generators (DFIGs) and its impacts on the POI to improve the reactive power injection capability of the WPP. In this paper, a design strategy for modifying the gain of DFIG controller is suggested and the comprehensive properties of these control gains are investigated. In the proposed scheme, the WPP controller, which operates in a voltage control mode, sends the command signal to the DFIGs based on the voltage difference at the POI. The DFIG controllers, which operate in a voltage control mode, employ a proportional controller with a limiter. The gain of the proportional controller is adjusted depending on the available reactive current of the DFIG and the series impedance between the DFIG and the POI. The performance of the proposed scheme is validated for various disturbances such as a reactive load connection and grid fault using an EMTP-RV simulator. Simulation results demonstrate that the proposed scheme promptly recovers the POI voltage by injecting more reactive power after a disturbance than the conventional scheme.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.157-164
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• 2017

A parallel slide gate valve (PSGV) is located between the heat recovery steam generator (HRSG) and the steam turbine in a combined cycle power plant (CCPP). It is used to control the flow of steam and runs with repetitive operations such as startups, load changes, and shutdowns during its operation period. Therefore, it is necessary to evaluate the fatigue damage and the structural integrity under a large compressive thermal stress due to the temperature difference through the valve wall thickness during the startup operations. In this paper, the thermal-structural analysis and the fatigue life evaluation of a 16-inch PSGV, which is installed on the HP steam line, is performed according to the fatigue life assessment method described in the ASME B&PVC VIII-2; the method uses the equivalent stress from the elastic stress analysis.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.126-133
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• 2007

An experimental apparatus has been designed and prepared in order to measure a pressure loss coefficient of hydropneumatic components, which is an important parameter in a hydropneumatic system Blow-down system has been adopted for the experimental apparatu to meet the high flow energy requirement as well as the apparatus safety. Especially, pressure loss coefficient measurements of pyrostarter filters have been performed and the pressure loss coefficient, K of CQSF has been experimentally acquired. Then it is shown that the turbine inlet pressure $p_2$, which is predicted from the measured K, is in accord with the results of combustion tests. Moreover, the relation between K and combustion pressure $p_0$ has been presented and it is disclosed that the relation accords well with the results of combustion tests. It is anticipated that K of a filter could play a role in PS size reduction by rising up the combustion pressure resulting in increasing the burning rate of solid propellant.