• Journal of the Korean Solar Energy Society
• /
• v.25 no.4
• /
• pp.85-92
• /
• 2005

One of the most effective methods for utilizing solar energy is to combine thermal solar and optical energy simultaneously using a hybrid panel. Many systems using various kinds of photovoltaic panels have already been constructed. But utilizing solar energy by means of a hybrid panel with concentrator has not been to be attempted yet. Normally if sunlight is directed on the solar cell, and there is no increase in temperature, the absorption energy of each cell will increase per unit area. In a silicon solar cell. however, cell conversion efficiency decreases according to the increasing temperature. Therefore, to maintain cell conversion efficiency under normal condition, it is necessary to keep the cell at operating temperature. we design and make new hybrid panel with cooling system to prevent increasing of temperature on cell, collect effectively thermal energy. We compared performance of new hybrid panel with PV module and thermal panel. We also evaluated conversion efficiency, electric power and thermal capacity and confirmed cooling effect from thermal absorption efficiency.

• Journal of Power Electronics
• /
• v.10 no.5
• /
• pp.538-547
• /
• 2010

This paper deals with a stand-alone wind energy conversion system (WECS) with an isolated asynchronous generator (IAG) and voltage and frequency (VF) control feeding three-phase four-wire loads. The reference generator currents are estimated using the instantaneous symmetrical component theory to control the voltage and frequency of an IAG system. A three-leg voltage source converter (VSC) with an isolated star/delta transformer is used as an integrated VSC. An integrated VSC with a battery energy storage system (BESS) is used to control the active and reactive powers of the WECS. The WECS is modeled and simulated in MATLAB using the Simulink and the Sim Power System (SPS) toolboxes. The proposed VF controller functions as a voltage and frequency regulator, a load leveler, a load balancer and a harmonic eliminator in the WECS. A comparison is made on the rating of the VSC with and without ac capacitors connected at the terminals of an IAG. Simulation and test results are presented to verify the control algorithm.

• Korean Chemical Engineering Research
• /
• v.52 no.1
• /
• pp.133-140
• /
• 2014

The experiment was designed to compare the char combustion kinetics of pulverized Indonesia coals commonly utilized in Korea power plants. The reaction rate of coal char has been formulated using the external and internal effectiveness factors to describe the diffusion effect quantitatively. The Random Pore Model (RPM) was used for applying internal specific surface area as a function of carbon conversion ratio. Reaction rate was obtained from reaction time using the Wire Heating Reactor (WHR) which can heat and measure the char particle temperature at the same time. BET and TGA were used to obtain physical properties such as internal specific surface area and structural parameter. Three kinds of Indonesia Sub-bituminous coals "BARAMULTI, ENERGYMAN, AGM" were used in order to derive the activation energy and pre-exponential factor. The results of this study showed that the effect of internal diffusion than that of external diffusion is the dominant as comparison of kinetics was reflected in external and internal effectiveness factors. For three kinds of coal char, finally, activation energy of intrinsic kinetics indicates 110~118 kJ/mol.

• Journal of Ocean Engineering and Technology
• /
• v.23 no.5
• /
• pp.15-24
• /
• 2009

The results of a simulation study of variable liquid column oscillations in U-tanks with a novel control scheme are presented. The configuration under investigation is analogous to that of the tuned liquid-column damper used to suppress oscillatory motion in large structures like tall buildings and cargo ships. However, by virtue of an adequate controller, the response of amplitude of the U-tanks becomes larger in a desired frequency range. The motion of wave energy conversion system equipped with a variable liquid column oscillator is described by a series of nonlinear differential equations. The equations describe the motion of body under ocean wave excitation, and the motion of liquid with an air-spring effect caused by the compression and expansion of air in vertical liquid columns and air chambers. It is shown that the effect of the air-spring has a vital role to maintain the natural frequency of oscillation in the system to synchronize with the frequency of the ocean wave, thus the system provides the most effective mode for energy extraction from the ocean.

• Journal of the Korean Solar Energy Society
• /
• v.35 no.1
• /
• pp.21-28
• /
• 2015

A small washer powered directly and solely by thermal radiation was constructed and tested to explore the feasibility of using solar energy or other types of thermal radiation for washing and cleaning. In principle, TA (ThermoAcoustic) washers have the benefits of simpler design and operation and fewer energy conversion processes, thus should be more energy efficient and cost less than electric washing/cleaning systems. The prototype TA converter we constructed could sustain itself with consistent fluid oscillations for more than 20 minutes when powered by either concentrated solar radiation or an IR (infrared) heater. The frequencies of water oscillations in the wash chamber ranged from 2.6 to 3.6 Hz. The overall conversion efficiency was lower than the typical efficiencies of TA engines. Change in water temperature had little effect on the oscillatory flow in the TA washer due to its low efficiency. On the other hand higher water temperatures enhanced grease removal considerably in our tests. Methods for measuring the overall conversion efficiency, frictional loss, and grease removal of the TA washing system we designed were developed and discussed.

• Nuclear Engineering and Technology
• /
• v.41 no.8
• /
• pp.1025-1044
• /
• 2009

Systematic research has been conducted by KAERI to develop a supercritical carbon dioxide Brayton cycle energy conversion system coupled with a sodium cooled fast reactor. For the development of the supercritical $CO_2$ Brayton cycle ECS, KAERI researched four major fields, separately. For the system development, computer codes were developed to design and analyze the supercritical $CO_2$ Brayton cycle ECS coupled with the KALIMER-600. Computer codes were developed to design and analyze the performance of the major components such as the turbomachinery and the high compactness PCHE heat exchanger. Three dimensional flow analysis was conducted to evaluate their performance. A new configuration for a PCHE heat exchanger was developed by using flow analysis, which showed a very small pressure loss compared with a previous PCHE while maintaining its heat transfer rate. Transient characteristics for the supercritical $CO_2$ Brayton cycle coupled with KALIMER-600 were also analyzed using the developed computer codes. A Na-$CO_2$ pressure boundary failure accident was analyzed with a computer code that included a developed model for the Na-$CO_2$ chemical reaction phenomena. The MMS-LMR code was developed to analyze the system transient and control logic. On the basis of the code, the system behavior was analyzed when a turbine load was changed. This paper contains the current research overview of the supercritical $CO_2$ Brayton cycle coupled to the KALIMER-600 as an alternative energy conversion system.

• Solar Energy
• /
• v.2 no.1
• /
• pp.33-48
• /
• 1982

A planetary boundary layer model has been modified to study the feasibility of siting the wind energy conversion systems over Jejudo island. Our objective is to demonstrate a numerical model that is simple enough to be economical in terms of computational cost and contains most of the mesoscale processes occurring in the planetary boundary layer at the same time. Simulated fields of atmospheric parameters are compared favorably with available climatological data and interpreted in terms of physical phenomena occurring.

• Proceedings of the KIEE Conference
• /
• 2002.11d
• /
• pp.320-322
• /
• 2002

The paper presents an electrical model of a grid-connected wind energy conversion system (WECS) with a variable speed drive, a fixed pitch angle, a synchronous generator as a wind generator and AC-DC-AC conversion scheme for simulating dynamic behaviors and performance responding to varying wind speed input. The electric output of the WECS is controlled by the AC-DC-AC conversion scheme, the objective of which is to capture the maximum active power under varying wind conditions and to keep the voltage of WECS terminal bus at a specific level. Aerodynamic models are used to incorporate the power characteristics to wind speed. The modeling and simulation of the WECS are realized on PSCAD/EMTDC environment.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.3
• /
• pp.15-26
• /
• 1997

In this study, the theoretical investigation of the electrically heated catalyst(EHC) for vehicle application has been carried out using the thermal equivalence of EHC system and the data of vehicle tests to meet ultra low emission vehicle(ULEV) standard. To improve the efficiency of EHC system, it is necessary to understand relation between the power, the operating time and the conversion efficiency of EHC system. The relation was found with thermal equivalence of EHC system which considers the power supply to EHC, heat loss, chemical exothermic energy generated by oxidation reaction and net energy coming in via the exhaust gas. From this relation, the limits of needful power and operating time to meet the ULEV standard can be suggested, when the conversion efficiency of catalyst was known.

• Journal of Navigation and Port Research
• /
• v.38 no.1
• /
• pp.39-44
• /
• 2014

Due to the oil price is increasing continuously, active researches on sources of renewable energy has been invigorated. Above all, ocean energy has high-usability because of ocean current has high density and large quantity compared to the wind energy. In this paper, efficiency enhancement of the wave power generation was described through horizontal plate installation at the break water wave power generation system that converts the ocean energy into electricity. The power-conversion efficiency can be improved by horizontal plate installation at existing system, but there has been insufficient studies domestically. The purpose of this paper is to analyze about the effects of the horizontal plate installation on the breakwater wave power generation system by wave basin experiment and to propose a position of horizontal plate installation.