• The Korean Journal of Rheology
• /
• v.7 no.3
• /
• pp.181-191
• /
• 1995

점탄성유체의 물성치들 중 정압열팽창계수 및 밀도는 자연대류 열전달 연구에 전단 속도 0에서의 점도는 점탄성유체에 대한 모델들 사용 시 필요하다. 본 연구에서는 점탄성유 체이며 마찰 감소 첨가제, 유전자 분리용액동으로 사용하는 Separan AP-273 용액의 정압열 팽창계수, 밀도 및 전단속도 0에서의 점도에대한 농도 및 온도의 영향을 조사하였다. 작동유 체의 물성치들은 10~6$0^{\circ}C$의 온도범위와 100~20,000wppm의 농도범위에서 측정되었다. 작 동유체의 물성치들에 미치는 열주기와 노화의 영향을 조사하기 위해서 정압열팽창계수와 전 단속도 0에서의 점도를 교대로 두 번씩 측정했다. 정압열팽창계수 및 밀도를 측정하는 장치 의 측정 정밀도는 증류수에 대한 측정치와 문헌에 나타난 자료를 비교하여 얻었고 이는 $\pm$ 2%이내였다. Separan AP-273용액의 정압열팽창계수 및 밀도는 증류수의 값들로 대치될수 있다. 작동유체의 정압열팽창계수와 밀도는 열주기와 노화의 영향을 받지 않았다. 낙하식 점 도계를 사용해 측정한 겉보기점도 값들을 나타내느 flow curve에서 전단속도가 0이 되는방 향으로 겉보기점도를 외삽시켜 Separan AP-273용액에 대한 전단속도0에서의 점도를 얻었 다. 정압열팽창계수 측정 전후에 측정한 작동유체에 대한 전단속도 0에서의 점도는 열주기 와 노화로 인해 퇴화되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.4
• /
• pp.47-56
• /
• 2005

In GPS/INS/barometer navigation system for UAV, vertical channel damping loop was introduced to suppress divergence of the vertical axis error of INS, which could be reduced to the level of accuracy of pressure altitude measured by a pitot-static tube. Because static pressure measured by the pitot-static tube depends on the speed and attitude of the vehicle, static pressure error models, based on aerodynamic data from wind tunnel test, CFD analysis, and flight test, were applied to reduce the error of pressure altitude. Through flight tests and sensitivity analyses, the error model using the ratio of differential pressure and static pressure turned out to be superior to the model using only differential pressure, especially in case of high altitude flight. Both models were proposed to compensate the effect of vehicle speed change and used differential and static pressure which could be obtained directly from the output of pressure transducer.

• Journal of the KSME
• /
• v.29 no.5
• /
• pp.525-537
• /
• 1989

본교에서는 정압 공기베어링의 특성 및 다공질 정압 공기베어링의 현황, 문제점등에 대한 개괄적 인 소개를 하였다. 이상에서와 살펴본 바와 같이 정압 공기베어링은 고속, 고정도를 요하는 각종 산업용기기의 부품으로써 연구개발, 응용되어 왔으며 결과적으로 기술한계극복에 많은 기여를 하 였다. 앞으로의 첨단기술을 위주로 한 각종 가공, 측정분야에 있어서도 공기베어링은 많은 역할을 할 것이며 특히 다공질베어링을 중심으로 한 고강성 정압 공기베어링에 대한 기대는 매우 크다고 할 수 있다.

• Journal of Biosystems Engineering
• /
• v.15 no.4
• /
• pp.339-345
• /
• 1990

공기통풍 건조시 공기흐름(airflow)에 대한 곡물저항(grain resistance)은 송풍시스템에서 fan의 선정시 매우 중요하다. 지금까지는 공기흐름에 대한 곡물저항은 주로 Shedd의 curve에 준하여 정해졌다. 그러나 실제의 경우 곡물수확 또는 건조시 기계적 원인에 의하여 미세립자(fine material)가 생성된다. 이에 본 연구에서 밀(red hard winter wheat)을 대상으로 송풍량, 함수율, 미세립자량이 정압강하(static pressure drop)에 미치는 영향을 규명하였고, 이러한 변수가 포함된 수학적 모델을 개발하였다. 독립변수는 0.051로부터 $0.203m^3/m^2.sec$에 이르는 7단계의 각각 다른 송풍량과 3단계의 함수율 (11, 13, 15%w.b), 4단계의 미세립자량(0, 2, 4, 8%)이고, 종속변수는 정압강하이다. 정압강하와 test bed에서의 송풍량은 micromanometer를 사용하여 측정하였다. 결과는 독립변수(송풍량, 함수율, 미세립자량)는 모두 정압강하에 significant하게 영향을 미치는 것으로 나타났다. 규정된 범위내에서 함수율이 증가함에 따라 정압강하는 최고 45% 까지 감소되었고, 반면 미세립자량이 증가함에 따라 정압강하는 최고 195%까지 증가되었다. 수집된 data로서 다음과 같은 regression equation이 개발되었다($P=AV+BV^2+C(MO)V+D(FM)V$). 본 연구의 결과는 공기송풍시스팀에서 송풍량, 함수율, 미세립자량이 정압강하에 미치는 영향을 규명하였고, 에너지 절약적 송풍시스템을 설계하는 데 도움이 될 수 있을 것이다.

• Aerospace Engineering and Technology
• /
• v.7 no.2
• /
• pp.46-52
• /
• 2008

The instrumentation was studied in order to measure aerodynamic performance and efficiency of a compressor as a component of a 5MW-class gas turbine for power generation. In case of an axial compressor, the distributions of static pressure on a casing can be obtained by averaging at each stage and those of total pressure and temperature in the flow field of the compressor can be measured with a Kiel temperature probe. In case of a centrifugal compressor, the static pressures at the hub and the tip, respectively, of an impeller exit are considerably different, so the pressures need to be measured at both positions and thereafter averaged. The distributions of static pressures in a diffuser and a deswirler are measured at ten positions along five streamlines in one pitch. In addition the flow field can be measured in detail by 5-hole Pitot tube in order to analyze the flow characteristics of the core flow region and wake region and the rotor-stator interaction of the compressor.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.03a
• /
• pp.131-136
• /
• 2006

일면전단시험은 전단면의 응력을 직접 측정하므로 평면변형시 강도를 파악할 수 있는 등의 많은 장점을 가지고 있으며, 시험조작이 간편하기 때문에 실용적으로도 우수한 것으로 판단된다. 그러나 사질토의 경우에 의한, Dilatancy에 의한 체적변화과정에서 공시체와 전단상자의 주면마찰력이 전단면의 수직 응력을 증감시키기 때문에 구해지는 강도가 과대 또는 과소하게 나타나는 것으로 알려져 있다. 그러나 반력판측에 장착한 하중계를 통해 전단면의 수직응력을 직접 측정 제어하는 형식으로 개선되어 주면마찰력의 영향을 해소하였다. 따라서 본 연구는 반력판측에 하중계를 장착한 개량형 다단식 단순전단시험기를 개발하여 사질토의 정압(CD)조건 전단시험을 수행하여 강도특성과 전단강도에 미치는 영향을 개량형 일면전단시험의 결과와 비교하였다. 그 결과 정압조건의 일면전단시험과 단순전단시험에 의한 강도정수는 조밀한 모래의 경우는 거의 비슷하게 나타나며, 느슨한 모래의 경우는 일면전단이 다소 크게 나타났다. 그리고 단순전단과 일면전단시험에서의 Dilatancy거동에는 큰 차이가 나타나지 않았다.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.17 no.4
• /
• pp.418-425
• /
• 1988

Since conventional computer program is workable only with velocity boundary condition, in practical fluid passage such as clean room which usually have wide inlets and outlets, it is not easy to measure velocity itself because of its vector property. Furthermore a certain assumption of velocity at boundaries may lead to physically unreasonable results. From this motivation, we have developed a computer program to predict whole flow field imposed on pressure-based boundary condition which can be measured by relatively simple method. The only additional velocity boundary condition that should be imposed on to make the problem unique, are no slip condition at all walls and zero cross stream velocity at inlet. The result of present study was compared with that by Bernoulli equation being used practically. They were coincident well each other within 5%, therefore the validity of the present method is proved. In the present work, the flow field in a clean room subject to pressure-based boundary conditions at an inlet and two exits was predicted numerically. The pressure difference between the inlet and the left exit which keeps relatively low pressure among two exits is fixed as 150[Pa] and the pressure at the right exit is varied from zero to 150[Pa] by the increment of 25[Pa]. For each cases the flow characteristics in the clean room, the velocity profile at the inlet, and the flow rate through the two exits was predicted. The flow rate through the right exit imposed on relatively higher pressure than the left exit decreased linearly according to the increase of pressure of the right exit. When the pressure of the right exit is increased enough to cause back flow at the exit, the flow rate is rapidly decreased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2012.05a
• /
• pp.65-69
• /
• 2012

An oxygen rich preburner was tested and the responses from the pressure sensors were studied with FFT analysis. Since the limited capability of the static sensor, less than 250 Hz frequency domain was investigated and compared to the results of the dynamic sensors. As a result, 60 Hz harmonics were presented dominant in the combustion pressure and oxygen inlet pressure. While similar harmonics were shown with the dynamic sensor, it indicated that harmonics less than 60 Hz were very minor and the high frequency is more important.

• Nuclear Engineering and Technology
• /
• v.8 no.2
• /
• pp.81-88
• /
• 1976

A flash method for measuring the unknown thermal property (the density, specific heat, or thermal diffusivity could be chosen as unknown) is described. The thermal diffusivity of UO$_2$ fuel samples is obtained from room temperature (300 K) to high temperature (1400 K). The specific heat is measured using a commercially available differential scanning calorimeter from room temperature to 500 K. The thermal conductivity of UO$_2$ fuel samples is calculated from the density, thermal diffusivity, and specific heat at constant pressure. The present results are in complete agreement with the usual trends for the thermal conductivity of dielectric materials, in which impurity levels are very important at low temperatures but become relatively unimportant at high temperatures. In addition, the thermal diffusivity values at room temperature are reexamined by measuring the thermal diffusivity of several UO$_2$ fuel samples with same level of doped Gd$_2$O$_3$.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.7 no.5
• /
• pp.1026-1031
• /
• 2003

Automatic feed pumps are operated and stopped by a pressure switch. Thus, because of repeated operations and stops of the pumps according to fluctuations of water volume, operation with constant rate and pressure is impossible. Moreover, because of repeated running of the pump, keeping up of constant pressure is impossible and damage and energy loss are weak points of the pimps. To make up for defects of an automatic feed pump, this paper designed and made a static pressure feed system which was composed of a feed water control valve, a flow sensor and a control system. The valve device plays an important part in reducing load of pumps by constant water supply regardless of outflow of water. Outflow of water is determined by infrared diode of the flow sensor. The control system is made of a 8 bit micro-processor and the pump was controled by a specific control algorithm. With the constant pressure feed system, discharge pressure was kept at fixed pressure, accurate operations and stops were smoothly accomplished and the pump was operated with constant pressure. Thus, the constant pressure feed system can be considered as an advanced system which made up for the weak points in the current automatic feed systems.