• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1320-1325
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• 1995

For hydrogen-cooled large turbine generators, partial discharges in ground wall insulations are suppressed by high hydrogen pressure. The first goal of the experiment is to investigate the effect of hydrogen pressure on partial discharge activity and aging rate in turbine generator winding insulations. A series of tests have been performed on two groups of the accelerated aging experiments. The first group of stator windings was aged under hydrogen pressure of 4 atm while the second group of stator windings was aged under air atmosphere. The stator windings aged under air atmosphere suffer from larger partial discharge magnitude with larger voids at high electrical stress than those under hydrogen pressure. The second goal of the experiment is to evaluate the validity of on-line measurement technique which is normally measured under hydrogen environment. The test results show that further experiments are needed to apply the on-line scheme to turbine generator being under high hydrogen pressure.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.590-591
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• 2005

Hydrodynamic pressure fluctuations and their roles on the design of hydraulic structures has been the subject of many investigations. The studies showed that turbulent pressure fluctuations may cause serious damages to hydraulic structures. In case of high velocity flows, separation of flow from the boundary also causes the local pressure to drop and as a result, the resultant pressure fluctuations may trigger cavitation. Sever hydrodynamic pressures are also associated with the vibration of structures. Therefore, in this work, experiments were performed to determine the intensity of pressure fluctuations and their distribution along the bed of a ski-jump flip bucket. Experiments were completed on a physical model at the Institution of Water Research of Iran. The results consist of the statistical characteristics of pressure fluctuations, its maximum, minimum, and r.m.s values along the bed of the bucket. The spectral analysis of pressure fluctuations which is useful for the instability analysis of such structures is also provided. It is hoped that the present results will help the designer of such structures.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.459-462
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• 2008

The fact that the major cases of life casualties are from smoke in the fire accidents and the expected steep increase of skyscrapers, huge spaces, multiplexes and huge scaled underground spaces demand establishment of efficient smoke countermeasure. The architectural factors affecting the pressure field of building should be examined for the successful design and operation of smoke management system and the stack effect is one of the important factors. The field experiments on stack effect in stairwells of high-rise building with regard to open/close condition of door are carried out to evaluate the features of pressure applied to door between each compartments, i.e, stair, lobby and accommodation. The procedures and results of experiments are presented.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.154-165
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• 2024

Acetic acid and acetonitrile produced in the chemical process of petrochemical plants are used at high temperatures and pressures. They are exposed to harsh corrosive environments. The present investigation aimed to evaluate corrosion characteristics of metals with excellent corrosion resistance by performing immersion and electrochemical experiments with different composition ratios of acetic acid and acetonitrile in a high-temperature and high-pressure environment. Results of immersion experiment revealed that as acetic acid concentration increased, surface damage and corrosion also increased. In immersion experiments under all conditions, super austenitic stainless steel (UNS N08367) had the best corrosion resistance among various metals. The maximum damage depth under the most severe immersion conditions was observed to be 4.19 ㎛, which was approximately 25.25 ㎛ smaller than that of highly damaged stainless steel (UNS S31804). As a result of electrochemical experiments, electrochemical characteristics of various metals presented some differences with different composition ratios of acetic acid and acetonitrile. However, super austenitic stainless steel (UNS N08367) had the best corrosion resistance at a high pressure condition with a high concentration of acetic acid.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.6 no.3
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• pp.33-42
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• 1992

This paper presented time dependent high-pressure arc discharge model considering the axial convection and verified the pertinence with application to the high pressure mercury lamp. Using this model, this paper xmaminse the effect of the axial convection and arc contraction of lower electrode region. This model consisted with the results of experiments in few [%] error, and showed the arc contraction of lower electrode region.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.1
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• pp.69-78
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• 1999

In this study a new pattern of pressure control of hydraulic cylinder using high speed On-Off solenoid valve in the electro-hydraulic system has been suggested. The control valve is 3-way high speed On-Off solenoid valve which is operated by PWM(Pulse Width Modulation)control signal. The high speed On-Off solenoid valve has a tendency to induce severe pressure fluctuation in the hydraulic actuator so it has not been used for the purpose of closed loop control with direct pres-sure feedback. In this study closed loop control with direct pressure feedback is enabled by using a digital filter which has linear minimum mean square filter algorithm. Through some experiments it is confirmed that stable pressure control can be realized by the proposed control technique.

• Journal of ILASS-Korea
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• v.18 no.4
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• pp.188-195
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• 2013

An investigation on spray characteristics of fuels which diesel and di-methyl ether (DME) with change of injection pressure used the multi-injection in constant volume combustion chamber (CVCC). Diesel was already used famous fuel which we could use. DME showed similar features with diesel like as cetane number, auto-ignition temperature. High cetane number of diesel and DME could make possible to compression ignition. DME showed different atomization from diesel due to evaporating pressures and boiling points. Experiments were carried out in CVCC equipped with Delphi solenoid 6-hole type injector and the spray characteristics of diesel and DME were tested the various pre and pilot injection. Terms of injections and a number of injections in multi-injection has been controlled. Experiments were performed in 2 types that 1500 rpm, 2000 rpm and under the condition of injection ranging from 100 bar to 500 bar. From the results of this experiment diesel showed longer spray penetration than DME. That result showed different of atomization speed DME and diesel. Result of high injection pressure condition showed similar spray characteristics diesel and DME. After this investigation, new conditions and experiments using laser light to go forward and add the fuels like as the biodiesel and diesel and DME blend.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.204-209
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• 2008

The interest in the mechanical behavior of materials at high strain rates has increased in recent years, and by now it is well known that mechanical properties can be strongly influenced by the speed of applied load. The split Hopkinson pressure bar (SHPB) has been widely used to determine mechanical properties of materials at high loading rates. However, to ensure test reliability, measurement error source must be accounted for and eliminated. During experiment, the specimens were located between the incident and the transmit bar. The presence of contact frictions between the test bars and specimen may cause errors. In this work, numerical experiments were carried out to investigate the effect of friction on test results. In SHPB test, the measured stress by the transmitted bar is assumed to be flow stress of the test specimen. Through the numerical experiments, however, it is shown that the measured stress by the transmit bar is axial stress components. When, the contact surface is frictionless, the flow stress and the axial stress of the specimen are about the same. When the contact surface is not frictionless, however, the flow stress and the axial stress are not the same anymore. Therefore, the measured stress by the transmitted bar is not flow stress. The effect of friction on the difference between flow stress and axial stress is investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.159-165
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• 2008

This paper deals with the optimum high pressure control algorithm for a transcritical $CO_2$ mobile air-conditioning system with belt-driven compressor to achieve the maximum COP. The experiments were performed to find out the maximum COP conditions with various operating conditions. The experimental results showed that the COP was increased and then decreased with increase of the refrigerant high pressure for the system. Therefore the value of high pressure which has maximum COP could be selected. Furthermore, the strong (linear) relation between the optimum high pressure and the gas cooler outlet temperature was revealed, which suggests the use of a simple controller with only one parameter for the transcritical $CO_2$ cycle.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.57-64
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• 2003

The characteristics of fuel spray have an important effect on engine performance such as power, specific fuel consumption and emission because fuel spray controls the mixing and combustion process in an engine. Therefore, if the characteristics of fuel spray can be measured, they can be effectively used for improving engine performance. The major factors controlling fuel spray are injection pressure, ambient pressure and engine speed. In this study, the experiment is performed in a high temperature and high pressure chamber. In experiments, spray tip penetration, spray angle and spray tip velocity are measured at various injection pressure (10 and 14 MPa), ambient pressure(3,4 and 5 MPa), fuel pump speed(500, 700 and 900 rpm). Experimental results are useful for deriving an experimental spray equation and design an optimal engine. The results showed that injection pressure, ambient pressure and fuel pump speed are important factors influencing on the characteristics of spray. 1) Injection pressure influences on the characteristics of spray. That is, as injection pressure is increased, spray angle is decreased but spray penetration and spray tip velocity is increased. 2) Spray angle and spray penetration are increased as fuel pump speed is increased.