• Proceedings of the SAREK Conference
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• 2005.06a
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• pp.223-223
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• 2005

• Korean Journal of Metals and Materials
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• v.46 no.4
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• pp.241-248
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• 2008

Gas turbine blades serviced for a period are usually repaired for reuse via "rejuvenation processes" including fluoride ion cleaning, brazing or welding, and recoating. Among these processes, the welding process is applied to rebuilt damaged parts of the blade in which welding materials being mostly Ni base superalloy are supplied in the form of powder or wire. When powder is used in the welding process, the uniform supply of powder is a very important factor for the uniformity of welding. According to our experience, the uniformity was very poor with the powder supply system only utilizing pressurized air flow. A new powder supply system was developed in which powder is supplied via air flow and simultaneously mechanically. The welding uniformity was much improved with this new system. In this study, the microstructure and mechanical properties of welded parts obtained from several kinds of powder using the new powder supply system were characterized.

• Journal of IKEEE
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• v.25 no.2
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• pp.330-336
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• 2021

A typical way to reduce the number of hardware redundancy configurations is to implement them as analytical techniques for detecting, identifying and accepting failures with micro-controller. In this paper, one of the analytical techniques, the fault detection filter, is applied to aircraft turbofan engine system. The fault detection filter is a special type of observer that has the advantage of being able to determine the location of failures by maintaining a constant direction in the output space in the event of a particular failure. We present a single input/output dynamic system modeling of air turbine system in turbofan engine, a fault detection filter design, and simulation results applying it. Simulation results show that fault detection can be effectively applied as a sensitivity effect to the directionality of the detection filter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.11
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• pp.504-511
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• 2014

The objective of this study is to theoretically analyze the performance of an open wet air-cycle refrigeration system, which nowadays is increasingly generating environmental concern. The temperature and relative humidity of the outside air are selected as the most important parameters. As the temperature and relative humidity of the outside air increase, the pressure ratio of the ACM compressor is determined to be nearly constant, the air temperature at the exit of the system increases, and the amount of condensed water, the cooling capacity, the COP, and the total entropy production rate increase overall. The effects of the effectiveness of the heat exchanger and the efficiency of the turbine on the performance are greater than that of the efficiency of the ACM compressor. Also, the performance of the wet air-cycle refrigeration system with two heat exchangers is enhanced, with a high COP and low total entropy production rate, compared to the system with a single heat exchanger.

• Journal of IKEEE
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• v.19 no.2
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• pp.225-231
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• 2015

The parameter K which decides how much to convert wind energy to electric energy in MPPT(maximum power point tracking) control of wind turbine system using torque controller is changed because blade shape and air density change. If the parameter K is not optimal value, power lose occur. The changed parameter K is important issue in wind turbine system. In this paper, to solve this problem, considering wind turbine system using back-to-back converter control and torque control, we propose the adaptive MPPT algorithm which performs fast control by using initial K, estimates mechanical power using Kalman filter method, uses the estimated mechanical power as input for MPPT algorithm again, and consequently performs optimal MPPT control.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1397-1405
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• 2009

In recent decades, exergy analysis has been holding spotlight as a useful tool in the design, assessment, optimization, and improvement of energy system. This paper presents the results of the energy and exergy analysis of a steam turbine cogeneration system for industrial complex using two efficiency concepts of conventional one and exergetic one. In order to obtain the destroyed exergy of each component, mathematical analysis is conducted by using exergy balance and the second law of thermodynamics, according as the parameters are changed, such as the ratio of returned process steam, process steam supplied, temperature and pressure of boiler and power. The computer program developed in this study can determine the efficiencies and exergy destroyed at each component of cogeneration system. As a result of this study, a component having the largest destroyed exergy was boiler. And closed and opened feedwater heater had the lowest one. The affects to the cogeneration system due to the variation of process steam flow and return rate of condensed water is shown that the total electric power efficiency(${\eta}_E$) is decreased as increasing the return rate of condensed water under constant process steam flow. As the boiler pressure is increased for the more production of electricity, the efficiency of cogeneration system was decreased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.831-838
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• 2004

A fluid-solid conjugate solver has been newly developed and applied to an actual engine disk system. Most of the currently available conjugate solvers lack the special thermal modeling for turbomachinery disk system applications. In the present new code, these special models are implemented to expand the applicability of the conjugate method and to reduce the required computational resources. Most of the conjugate analysis work so far are limited to the axisymmetric framework. However, the actual disk system includes several non-axisymmetric components which inevitably affect the local heat transfer phenomena. Also the previous work devoted to this area usually concentrate their efforts on the steady-state thermal field, although the one in the transient condition is more critical to the engine components. This paper presents full 3D conjugate analysis of a single stage high pressure turbine rotor-stator disk system to assess the three-dimensional effects (Fig. 1). The analysis is carried out not only in the steady-state but also in the engine accelerating transient condition. The predicted temperatures shows good agreement with measured data.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.45-50
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• 2014

In this paper, the Ocean Thermal Energy Conversion(OTEC) with vapor-vapor ejector is proposed newly. At this OTEC system, a vapor-vapor ejector is installed at inlet of condenser. The vapor-vapor ejector plays a very important role in increasing of the production work of low-stage turbine throughout the decrement of outlet pressure of ejector. The performance analysis is conducted for optimizing the system with HYSYS program. The procedure of performance analysis consists of outlet pressure of high turbine, the mass ratio of working fluid at separator, total working fluid rate, and nozzle diameters of vapor-vapor ejector. The main results is summarized as follows. The nozzle diameter is most important thing in this study. When each nozzle diameter of vapor-vapor ejector is 10 mm, the efficiency of OTEC system with vapor-vapor ejector shows the highest value. So it is necessary to set the optimized nozzle diameters of vapor-vapor ejector for achieving the high efficiency OTEC power system.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.4
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• pp.36-45
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• 2014

Model based control methods are widely used to improve the control performance of diesel engine air systems because the control results of the air system significantly affect the emission level and drivability. However, the model based control algorithm requires a lot of unmeasurable states which are hard to be measured in a mass production engine. In this study, an air system model of the diesel engine is proposed to estimate 11 unmeasurable states using only sensors equipped in a mass production engine. In order to improve the estimation performance in the transient condition, dynamic characteristics of the air system are analyzed and implemented as discrete filters. Turbine and compressor efficiency models are also proposed to overcome a limitation of the constant or look-up table based efficiency values. The proposed air system model was validated in steady state and transient conditions by real-time engine experiments. The maximum error of the estimation for 11 physical states was 11.7%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.889-898
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• 2009

A mixed-type turbine was adopted and the rotor outer diameter was 108 mm. Turbine rotors were designed to the axial-type blade because the turbine operated at a low partial admission rate of 1.7-2.0% with two stages. Performance characteristics were studied when the spouting from the nozzle was toward radially inward or outward direction. Additionally, the effect at each stage of the rotor was measured. For comparing with each turbine performance, properties were measured based on various rotational speeds. Measured net specific torque was used to compare with the turbine system performance. On the mixed-type turbine, better performance was obtained when the operating air spouted toward radially inward direction. The specific torque was increased by 7.8% from using the second stage although its effect depended on the rotational speed.