• 한국정밀공학회지
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• 제26권8호
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• pp.112-118
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• 2009

A pressure rise is generated while air bearing stages are moving in high vacuum environment. This study analyzed this pressure rise phenomenon theoretically and verified it experimentally using two different kinds of stages - linear and rotary air bearing stages. Results indicate that the pressure rise was caused by additional leakage resulting from stage velocity, along with adsorption and outgassing of gas molecules from the guide rail surface. Though tilting of the stage due to acceleration and deceleration reached several micrometers, it had a negligible effect on pressure rise because the tilting time was very short. Therefore, a rotary air bearing stage showed much less pressure rise than a linear stage because the rotary stage theoretically has nothing to do with the above causes. Additional leakage caused by stage velocity was inevitable if the stage had movements, but pressure rise caused by adsorption and outgassing could be suppressed by improving the surface quality to reduce real surface area, and by coating the guide rail surface with titanium nitride (TiN) which has less adhesion probability of gas molecules. The results also indicate that the pressure rise increased when the air bearing stage operated under high vacuum conditions.

• Journal of Mechanical Science and Technology
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• 제19권12호
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• pp.2303-2311
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• 2005

Super low temperature has many applications nowadays, from the chemical processing, automotives manufacturing, plastic recycling, etc. Considering of its wide application in the present and the future, study of the super-low temperature refrigeration system should be actively carried out. Super low state temperature can be achieved by using multi-stage refrigeration system. This paper present the development and testing of cascade refrigerator system for achieving super-low temperature. On this experiment, two different types of HCFCs refrigerants are utilized, R-22 and R-23 were applied for the high stage and the low-pressure stage respectively. The lowest temperature in the low-pressure evaporator that can be achieved by this cascade refrigeration system is down to $-85^{\circ}C$. This experiment is aimed to study the effect of inlet pressure of the low-pressure stage evaporator and low-pressure stage compressors inlet pressure characteristics to the overall temperature characteristics of cascade refrigeration system.

• Journal of Mechanical Science and Technology
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• 제20권4호
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• pp.482-493
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• 2006

The carbody structure of a high speed train passing through a tunnel is subjected to pressure fluctuation. Fatigue strength of the carbody structure against the fluctuating pressure loading should be proved in the design stage for safety. In this study, to get the useful information on the pressure fluctuation in the tunnel, measurement has been conducted during test running of KHST on the high speed line for two years. The measured results were analyzed and arranged to be used for carbody design. A prediction method for the magnitude and frequency of pressure change was proposed and the propagating characteristics of pressure wave was investigated. By statistical analysis for the measured results, a pressure loading spectrum for the high speed train was given. The proposed method can also be used to estimate the pressure loading spectrum for new high speed line at design stage combined with the results of train performance simulation.

• International Journal of Fluid Machinery and Systems
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• 제6권3호
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• pp.160-169
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• 2013

Two-stage turbocharging is an important way to raise engine power density, to realize energy saving and emission reducing. At present, turbine matching of two-stage turbocharger is based on MAP of turbine. The matching method does not take the effect of turbines' interaction into consideration, assuming that flow at high pressure turbine outlet and low pressure turbine inlet is uniform. Actually, there is swirl flow at outlet of high pressure turbine, and the swirl flow will influence performance of low pressure turbine which influencing performance of engine further. Three-dimension models of turbines with two-stage turbocharger were built in this paper. Based on the turbine models, mechanism of swirl flow at high pressure turbine outlet influencing low pressure turbine performance was studied and a two-stage radial counter-rotation turbine system was raised. Mechanisms of the influence of counter-rotation turbine system acting on low-pressure turbine were studied using simulation method. The research result proved that in condition of small turbine flow rate corresponding to engine low-speed working condition, counter-rotation turbine system can effectively decrease the influence of swirl flow at high pressure turbine outlet imposing on low pressure turbine and increases efficiency of the low-pressure turbine, furthermore increases the low-speed performance of the engine.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1238-1247
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• 2003

Simplified thermodynamic analysis of high pressure 4-stage reciprocating compressors with 4 inter-coolers has been investigated to predict a behavior of a compressor system for NGV(natural gas vehicles). A computer program has been developed to predict and estimate the performance of high pressure 4-stage reciprocating compressor system. Thermodynamic properties of compressed natural gas(CNG) were calculated by ideal gas theory and compression cycle was assumed as reversible adiabatic compression and expansion processes, and isobaric intake and discharge processes. Comparison between results predicted by calculation model and measured by experimental tests is presented.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.345-348
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• 2010

Two-stage light-gas gun은 고압실, 압축실 그리고 발사관으로 비교적 간단한 구조로 구성되며, 짧은 시간동안 초고압을 발생시키기 용이함으로 현재까지 고속충격역학, 발사체 공기역학, 재료역학 등 다양한 공학 분야에서 적용되어왔다. 본 연구는 초고압 액체 제트 분사에 적용하기 위한 기초적 연구로서, 고압실 하류에 설치된 제1격막의 파막 압력의 변화에 따른 발사체의 속도 변화 및 관내 압력 거동을 조사하기위하여, 다양한 격막을 적용하여 실험을 수행하였다. 제1격막의 파막 압력은 발사체의 속도에 지배적인 영향을 미치게 되며, 약 14 Bar이상일 경우 발사관의 압력이 압축튜브의 압력보다 크게 증가하였다.

• 한국유체기계학회 논문집
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• 제16권1호
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• pp.32-39
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• 2013

The multi-stage control valve is one of the devices which controls cavitation and high pressure drop. To attain the high pressure drop, the conventional control valves adopted the multi-stage trim to avoid the occurrence of local cavitation in valves. This work studied the effect of divergence angle on the characteristics of multi-stage trim. Pressure drop and flow characteristics was calculated for the 1 passage of multi-staged trim by using the FLUENT 6.3.26. The result showed that the pressure drop is significantly influenced by the divergence angle of multi-stage trim. In addition, the pressure drop increased consistently as the Reynolds number and divergence angle increases.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.592-596
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• 2012

This paper presents numerical analysis result of rotor-bearing system of a multi-stage high pressure pump. Especially resonance possibility, stability and damping factor are estimated for a selected commercial multi-stage high pressure pump. The result shows that it is not easy to avoid resonance of rotor-bearing system against main excitation forces which are residual unbalance force and pressure pulsation. This makes damping effect be more important.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.373-376
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• 2008

Industrial Steam Turbine first stage shell pressure is related to throttle flow. Theoretically, first stage shell pressure could, therefore, be measured and used as an index of turbine throttle flow. However, accurate flow measurements show that this pressure is not a reliable index of the actual flow. Data analysis of steam turbinessubjected to ASME acceptance tests shows that the use of first stage shell pressure as an index of throttle flow produced errors as large as 9.6 %. The mean of the errors was +2.2% with a standard deviation of ${\pm}$2.8 %. Applications that require an accuratedetermination of turbine steam flow, such as turbine acceptance testing, should, therefore, not rely on this method. Therefore, First stage shell pressure measurement serves as a valid and economical indicator of turbine throttle flow in cases where a high degree of accuracy in throttle flow measurement is not required but repeatability is desired, such as for boiler control. Generally speaking, Steam turbine first stage shell pressure may also be a very useful monitor of turbine performance when used with certain other turbine measurements.

• 플랜트 저널
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• 제4권3호
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• pp.60-65
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• 2008

Power plant industry has been developed at high-capacity, high-technology, and innovation. Steam turbine became the most useful equipment that dominate more than 50% of all the world electricity production. And developed new materials of the turbine blade and extended length of the turbine last blade brought reform in steam turbine performance upgrade. In this paper, when do partial load driving in high-capacity steam turbine, optimum driving method found whether there is something. In operating steam turbine, there is a lot of loss from secondary wake and throttle of the 1st stage nozzle by the biggest leading factor that load fluctuation affects in high-pressure steam turbine performance. Effect of internal efficiency by 1 stage nozzle is the biggest here, but here fluid flow and flow analysis were not yet examined closely definitely. So, Analyzed design data and acceptance performance test result to applying subcritical pressure drum type 560 MW, supercritical-pressure once through type 500 MW, and 800 MW steam turbines actually. In conclusion, at partial load driving, partial arc admission(PAA) is more efficient than full arc admission(FAA) efficiency. This is judged by because increase being proportional with gross energy of stream that is pressure - available energy if pressure of stream that is flowed in to the turbine increases, available energy becomes maximum and turbine efficiency improves. Therefore, turbine performance is that preview that first stage performance fell if decline is serious in partial load because first stage performance changes according to load.