• 조명전기설비학회논문지
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• 제21권4호
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• pp.115-121
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• 2007

This paper describes experiments of the breakdown characteristics by temperature change of $SF_6$ gas and Imitation Air(I-Air) in model GIS(Gas Insulated Switchgear). From the results of the experiments, the breakdown characteristics classify the vapor stage of $SF_6$ according to Paschen's law, in which the stage of coexistence for gas & liquid of the voltage value increases. This results in large deviation and the breakdown of the voltage(VB) low stage as the interior of the chamber is filled with a mixture of $SF_6$ that is not liquefacted and remaining air that can not be ventilated. The ability of $SF_6$ liquid($LSF_6$) insulation is higher than high-pressurize $SF_6$ gas. The VB of the I-Air decreases as the temperature drops and the VB also drops. It is considered that the results of this paper are fundamental data for the electric insulation design of superconductor and cryogenic equipment that will be studied and developed in the future.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.51-57
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• 2012

Performance evaluation of a compressor is conducted to develop 500W class ultra-micro gas turbine (UMGT) for power generation. The performance evaluation is essential to check the performance of the components of UMGT, a radial turbine, a centrifugal compressor, an angular combustor and a shaft, which have been already designed in previous researches. The purpose of this study is to introduce the development process of the performance testing equipments of the UMGT and to present the results of compressor performance test. For the performance evaluation of the compressor, two test equipments are developed and the initial test equipment uses commercial static air bearings with long shaft. In the improved test equipment, static air bearing is improved to increase rotating speed and compressed nitrogen gas is used for utility gas of the static air bearing to supply compressed air in a stable and steady way. To increase rotating speed to 320,000 rpm, 80% speed of design speed, compressed air is provided to the turbine. The performance map of the compressor with the 50%, 60%, 70%, 80% speed of design point is presented. The results of the performance test of compressor show a good agreement with the results of 3D CFD.

• 제어로봇시스템학회논문지
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• 제12권6호
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• pp.539-546
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• 2006

The Air Quality Sensor(AQS), located near the fresh air inlet, serves to reduce the amount of pollution entering the vehicle cabin through the HVAC(heating, ventilating, and air conditioning) system by sending a signal to close the fresh air inlet door/ventilation flap when the vehicle enters a high pollution area. The sensor module which includes two independent sensing elements for responding to diesel and gasoline exhaust gases, and temperature sensor and humidity sensor was designed for intelligent AQS in automobile. With this sensor module, AVR microcontroller was designed with back propagation neural network to a powerful gas/vapor pattern recognition when the motor vehicles pass a pollution area. Momentum back propagation algorithm was used in this study instead of normal backpropagation to reduce the teaming time of neural network. The signal from neural network was modified to control the inlet of automobile and display the result or alarm the situation in this study. One chip microcontroller, ATmega 128L(ATmega Ltd., USA) was used for the control and display. And our developed system can intelligently reduce the malfunction of AQS from the dampness of air or dense fog with the backpropagation neural network and the input sensor module with four sensing elements such as reducing gas sensing element, oxidizing gas sensing element, temperature sensing element and humidity sensing element.

• Journal of Welding and Joining
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• 제5권2호
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• pp.17-26
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• 1987

In this study, the experiments were carried out for the purpose of establishment of the arc sparing method which reducing oxides or oxide film by using the inert gas as the carrier gas of atomizing particles. Main results obtained are as follows; 1. Oxides and oxide film which lower the adhesion strength are largely reduced by using the inert gas as the carrier gas of atomizing particles, and adhesion strength of coating film are improved. 2. The coating film characteristics appear to be no difference between the inert gas arc spraying in air environment and that in argon gas environment. 3. Inert gas arc spraying using argon as the carrie gas has higher reduction rate of composition element in coating film than compressed air spraying does.

• 한국기계가공학회지
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• 제8권2호
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• pp.83-89
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• 2009

An air-fuel ratio control is essential in reducing hazardous exhaust emissions from a compressed natural gas(CNG) engine, and can be accomplished by accurate control of gas injection flow. In this study, theoretical research was conducted on injection characteristics of a solenoid gas injector, and injection experiments for calibration and analysis were performed. Various factors for gas injection flow such as injection pressure, gas temperature, and supply voltage are studied. A dynamic flow equation of the natural gas was proposed on the basis of flow dynamics theories and results of the injection experiment. The verification of the dynamic flow equation of the solenoid injector was carried out with a large CNG-engine applied to an urban bus. Air-fuel ratio control experiments were conducted in both steady and transient state. Results of injection experiments for the solenoid injector and the CNG-engine was proved the control method proposed herein to be effective.

• 설비공학논문집
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• 제15권8호
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• pp.674-682
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• 2003

Natural gas hydrate typically contains 85 wt.% water and 15 wt.% natural gas, and commonly belongs to cubic structure I and II. Also, 1m$^3$ hydrate of natural gas can be decomposed to 200 m$^3$ natural gas at standard condition. If this characteristic of hydrate is reversely utilized, natural gas is fixed into water and produced to hydrate. Therefore the hydrate is great as a means to transport and store natural gas. So, the tests were performed on the formation of natural gas hydrate is governed by the pressure, temperature, gas composition etc. The results show that the equilibrium pressure of structure II is approximately 65% lower and the solubility is about 3 times higher than structure I. Also if the subcoolings of structure I and structure II are more than 9 K and 11 K respectively, the hydrates are rapidly formed.

• 설비공학논문집
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• 제3권2호
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• pp.131-141
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• 1991

A method of optimum design of an axial rotary sensible heat exchanger for the heat recovery of exhaust gas from the air conditioning space was developed in consideration of economics of investment cost and profit according to the installation of heat exchangers. Leakage rate of exhaust gas was calculated and the correlation for the pressure drop due to leakage of exhaust gas was proposed. Heat transfer between the matrix and exhaust and intake gas was analysed to calculate the effectiveness of heat exchanger, which was used for the optimum design of rotary heat exchanger. The results show that optimum rotational speed increases as the length of rotor increases and there exists optimum NTU which maximizes the gain of total cost according to the installation of rotary heat exchanger.

• 한국대기환경학회지
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• 제7권1호
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• pp.31-40
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• 1991

This study shows the correlation between $NO_x$ emission in the exhaust gas and various operation factors of dual fuel engine for Co-generation system. General tendency was shown that the thermal efficiency was lowered by the change of operation factors. However these were not confirmed on this experiment. Increasing T4 temperature (exhaust gas temperature at turbo-charger inlet) reduces $NO_x$ emission rate. The higher T4 temperature requires lower excess air as the excess air ratio is controlled by T4 temperature on gas mode operation. Another tendency was that $NO_x$ emission rate is reduced in case of increasing boost air temperature, quantity of pilot oil or bypassing flue gas through the exhaust gas boiler. The diameter of the fuel injection nozzle was changed smaller than design value and the injection timing was readjusted. Thus $NO_x$ emission rate could be reduced as retarding injection timing and changing hole diameter of fuel injection nozzle, however maxium engine out-put was decreased by changing fuel nozzle on the diesel mode operation.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.153-156
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• 2008

MILD combustion has been successfully applied to gaseous fuels and few commercial systems are now in operation. Extending MILD combustion applicability to solid fuel of sawdust is the focus of the present work. The MILD combustion furnace at the University of Adelaide in Australia was used in this study. A measurement of $O_2$ and CO emissions have been carried out in parallel with consideration of NOx emission and compared in each modes of conventional natural gas combustion, natural gas MILD combustion, NOx emission in natural gas MILD combustion mode can be reduced to 20% in comparison with conventional combustion. Emission in cases of air carrying sawdust combustion and $CO_2$ carrying sawdust combustion were also compared. Air and $CO_2$ were sued as a carry gas for the sawdust. It was found that MILD conditions are possible for sawdust particles of less than $355{\mu}m$ without additional air pre-heating. It was also found that when using $CO_2$ as the carry gas the flame inside the furnace was not visible anymore and that NOx emission dropped to less than two folds.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1819-1823
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• 1997

When flammable gases are mixed with air or oxygen in the explosion concentration range and are ignited by sufficiently large electrostatic discharge energy, they may explode causing severe disaster in workplaces. The minimum ignition energy (MIE) of single gas-air mixtures has been already investigated by many researchers, but the MIE of mixtures of more than three substances is not examined yet. The purpose of this study is to investigate the MIE of several three-component gas mixtures experimentally. The result of our experiment shows that the MIE of some gas mixtures is quite different from that we expected based on the characteristics of individual gas-air mixture.