• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.8
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• pp.8-14
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• 2020

In the air current pulverizing type grinding method, the blade wings fitted inside a casing are rotated at a high speed to generate a cornering air current, which facilitates the collision of materials with one another, leading to the pulverizing phenomenon. In contrast to mechanical grinding, grit pulverizing leads to fine grinding and less acid waste and degeneration of the material. Moreover, this approach prevents the loss of nutritional value, while allowing the milling grain to have an excellent texture. However, the existing air current pulverizing type machines consist of prefabricated blades, which cannot be rotated at a speed higher than 5,000 rpm. Consequently, the grinding process becomes time consuming with a low productivity. To overcome these problems, in this study, the shape and structure of the air current pulverizing type wings were optimized to allow rapid grinding at more than 8,000 rpm. Moreover, the optimal design for the ripening parts for the air current pulverizing type device was determined by performing a computational fluid dynamics analysis based on airflow analyses to produce machinery that can grinding materials to the order of micrometers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.120-129
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• 1994

A numerical investigation has been carried out for the electrochemical reaction, mass and heat transfer characteristics of the Molten Carbonate Fuel Cell(MCFC) stack. The effects of cooling air channel and water gas shift reaction were taken into account. The current density distribution of electrodes, the molecular fractions of reactant gasses and three dimensional temperature distribution can be calculated and shown by several lines of equivalent values. The results have been compared with the existing ones, and reasonable agreement has been obtained. To examine the influence of changing parameters, such as the composition of reactant gases, the target average current density, the utilization of reactant gases, the cooling air inlet temperature and flow rates, the computer simulation has been done. The analysis method and computer program developed in this study will be greatly helpful to design and verify the optimum operating condition of MCFC stack.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1349-1355
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• 2015

It is difficult to calculate the magnetic force of an object of magnetic material in contact with other objects using the existing methods, such as Maxwell stress tensor method, magnetic charge method, or magnetizing current method. These methods are applicable for force computation only when the object is surrounded by air. The virtual air-gap concept has been proposed for calculating the contact force. However, its application is limited to magneto-static system. In this paper, we present the virtual air-gap concept for contact surface force in the eddy-current system. Its validity and usefulness are shown by comparison between numerical and experimental examples.

• KIEAE Journal
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• v.8 no.5
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• pp.11-16
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• 2008

This research has established CFD model on pit's cool-tube system through heat and air movement simulations, of which data was based on experimental and verification. This research work verified the effectiveness of the cool-tube system by analysing temperature, humidity and air current of the actually installed case. Also, we analysed heat transfer through air current simulation and the results are as followings. Firstly, we experiment on temperature, humidity and speed of air currents of the cool tube system with pit space during the month of May (spring). The average exterior temperature was $16.1^{\circ}C$, and $18.2^{\circ}C$ for the pit, $24.7^{\circ}C$ for the compressor room. Secondly, based on measured data of real case, we have analysed heat transfer through air current simulation and verified our proposed model. The actual measurement of average temperature of exhaust air of the pit's area is $19.7^{\circ}C$ with tolerance of $-0.33^{\circ}C{\sim}-0.6^{\circ}C$ compared to above simulations. Thirdly, having verified air current simulation model with formation of 260,000 and 1,000,000 cells, we could get reasonable near values with 260,000 cells. Lastly, the next step of research would be focused on proposing the best possible pit's cool-tube system after analysis of heat transfer of the air current simulation based on verified CFD model.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.3
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• pp.210-215
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• 2016

The transient characteristics of the Mg/Air fuel cell were ascribed to the load current, electrolyte concentrations, air electrode area and electrode distance. It was found that transient phenomena occurred in the load current, which is due to activate of the oxidation and reduction reaction process. The transient time increase with the load current increase. The transient characteristics were investigated with regard to internal resistance. The maximum power output analysis was employed in order to explain the delayed action under various experimental conditions. The internal resistances had a significant effect on the transient characteristics. The transient curves thus obtained were in almost agreement with internal resistance characteristics.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.2
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• pp.77-81
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• 2009

Air-gap was introduced to suppress the saturation of the iron core comprising the flux-lock type superconducting fault current limiter (SFCL) with parallel connection of two coils. However, the air-gap makes the impedance of this SFCL decreased and can result in unusefulness of the SFCL. To analyze the current limiting characteristics of the SFCL with the air-gap, the experimental circuit for short-circuit test was constructed. Through the comparison with the current limiting characteristics of the SFCL without air-gap, the merit and the demerit of the flux-lock type SFCL with the air-gap were discussed.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.325-328
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• 1988

Until now to analysis of LIM first winding current distribution is assumed to be finite sinusoidal current. But this method have demerits to learn the difference of LIM's characteristics which is produced by difference of winding method. So in this paper amodel of which period is the length core and air gap mmf of this winding current developed to fourier series, then mmf which contain air gap mmf is obtained this mmf is transformed to current sheet and the analysis result which are obtained by using sinusoidal first current and proposed method are compared.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.119-122
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• 2005

A study on motor current signature analysis has been executed for monitoring the fault of journal bearing due to wear. The air gap eccentricity of motor produces specific frequencies in motor current, the supplied current frequency plus and minus rotational rotor frequency. The air gap eccentricity is simulated by the clearance of Journal bearing. The amplitudes of the specific frequencies increase with the increasing clearances. The amplitudes of the specific frequencies continue to increase over the wear limit that is used in the manufacturer of the test motor. Though clear relations between the amplitudes of the specific frequencies and the clearances are not obtained in this paper, the specific frequencies can be used as an indicator of a journal bearing fault. Further study is necessary to make out the quantitative relations between the specific frequencies and the clearances.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.1
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• pp.56-62
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• 2020

The purpose of this study is to observe the visualization of the flow field for air flow distributed in the car from the ventilation fan installed in the ceiling of the passenger elevator car through the numerical analysis using computational fluid dynamics. STAR-CCM+, which is a code used for the numerical analysis, was used to predict the airflow distribution inside the elevator car. The numerical analysis of the distribution of the air current in the elevator was carried out. As a result, the analysis results for each point and the visualization of the air current distribution and the temperature distribution in the elevator car and were obtained. It was found that heat transfer was actively occurring inside the car due to the influence of the flow field discharged from the ventilation vent installed in the ceiling in the elevator car, and especially the convection heat transfer of Model-2 was more active than that of Model-1. As a result, the temperature distribution inside the car was found to be relatively low. In addition, the temperature distribution at a cross-section of 1700mm height in the elevator car shows that Model-2 is the location of the ventilation vent which makes people feel more comfortable.

• Journal of Power Electronics
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• v.15 no.2
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• pp.530-543
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• 2015

Air-cooling method is adopted on the basis of the requirements for the thermal stability and convenient field use of an electrical source transmitter. The power losses of the transmitter are determined after calculating the losses of the alternating current (AC)-direct current (DC) power supply, the constant-current circuit, and the output circuit. According to the analysis of the characteristics of a heat sink with striped fins and a fan, the engineering calculation expression of the Nusselt number and the design process for air-cooled dissipation are proposed. Experimental results verify that the error between calculated and measured values of the transmitter losses is 12.2%, which meets the error design requirements of less than 25%. Steady-state average temperature rise of the heat sink of the AC-DC power supply is $22^{\circ}C$, which meets the design requirements of a temperature rise between $20^{\circ}C$ and $40^{\circ}C$. The transmitter has favorable thermal stability with 40 kW output power.