• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
• /
• pp.813-814
• /
• 2006

The squirrel case induction motor has widely used in the driving of the blowers but it is low efficiency and hard to control. So, the damper is used for the control of a flow and it cause to low the driving efficiency. Our laboratory has proposed the single-phase SRM(switched reluctance motor) for driving blowers. It has salient pole structure and can be reduced a number of semiconductors than three-phase SRM. But it can not be starting by itself and has heavier torque ripple than three-phase SRM. For self-starting the single-phase SRM is required the starting device which place the rotor at the rising inductance slope. On this paper, the electromagnet starting device is designed to generate the starting torque and to fix the rotating direction of the single-phase SRM which is fabricaed to use a blower.

• Geomechanics and Engineering
• /
• 제13권1호
• /
• pp.1-23
• /
• 2017

A coupled liquid-gas-solid three-phase model, linking two numerical codes (TOUGH2/EOS3 and $FLAC^{3D}$), was firstly established and validated by simulating an in-situ air flow test in Essen. Then the coupled model was employed to investigate responses of multiphase flow and soil skeleton deformation to compressed air or freshwater injection using the same simulation conditions in an aquifer of Tianjin, China. The simulation results show that with injecting pressurized fluids, the vertical effective stress in some area decreases owing to the pore pressure increasing, an expansion of soil skeleton appears, and land uplift occurs due to support actions from lower deformed soils. After fluids injection stops, soil deformation decreases overall due to injecting fluids dissipating. With the same applied pressure, changes in multiphase flow and geo-mechanical deformation caused by compressed air injection are relatively greater than those by freshwater injection. Furthermore, the expansion of soil skeleton induced by compressed air injection transfers upward and laterally continuously with time, while during and after freshwater injection, this expansion reaches rapidly a quasi-steady state. These differences induced by two fluids injection are mainly because air could spread upward and laterally easily for its lower density and phase state transition appears for compressed air injection.

• 대한기계학회논문집B
• /
• 제24권2호
• /
• pp.306-315
• /
• 2000

An experimental study was conducted to examine the internal flow patterns inside the mixing chamber of effervescent atomizers. The mixing chamber has the rectangular cross section ($8mm{\times}2mm$) and made of transparent acrylic plate for flow visualization. The parameters tested were the air/liquid ratio (ALR), injection. pressure, and the nozzle orifice diameter. Three different flow regimes were observed; bubbly, annular, and intermittent flows. In the bubbly flow regime, the discharged mixture was disintegrated into drops through the bubble expansion and the ligament breakup. On the other hand, in the annular flow regime, the liquid annulus was disintegrated into small drops by the aerodynamic interaction between the phases due to the high relative velocities between the gas and the liquid. In the intermittent flow regime, the bubble-expansion/ligament-disintegration mode and the annulus-disintegration mode appeared alternatively. The correlations representing the transition criteria between the two-phase flow patterns within the mixing chamber were proposed based on the drift-flux models.

• 한국추진공학회지
• /
• 제21권5호
• /
• pp.71-79
• /
• 2017

액체-기체의 2상 유동에 대한 수치해석 기법을 연구하였다. 비압축성 방정식에는 가상 압축성 기법을 적용하였으며 LS와 VOF를 합친 CLSVOF 기법을 적용하여 액체-기체 경계면을 추적하였다. CLSVOF의 격자 의존도를 파악하기 위해 h=1/64, 1/128, 1/128, 그리고 1/160의 격자로 Zalesak's disk 문제와 액체의 3차원 변형 문제의 수치해석을 실시했으며 격자가 최대 보존 오차에 미치는 영향을 조사하였다. 비압축성 2상 유동 방정식을 적용하여 Rayleigh-Taylor 불안정성에 대한 수치해석을 실시하였고 밀도 차에 의한 액체 표면 불안정성이 나타난다는 것을 알 수 있었다.

• 한국전산유체공학회지
• /
• 제13권4호
• /
• pp.126-134
• /
• 2008

We developed a three dimensional Navier-Stokes code based on the level set method to simulate two phase flows with high density ratio. The Navier-Stokes equations with consideration of the surface tension effects are solved by using SIMPLE algorithm on a non-staggered grid. The present code is validated by simulating two test problems. First one is to simulate a rising bubble inside a cube. The thickness of the interface of the bubble is shown to affect the pressure distribution around the interface. As the thickness decreases, the pressure field around the interface becomes more oscillatory. As the bubble rises, a ring vortex is shown to form around the interface and the bubble eventually develops into an ellipsoidal shape. Merge of two bubbles inside a container is secondly tested to show the robustness of the present code for two phase flow simulation. Numerical results show stable and reliable behavior during the process of merging of two bubbles. The velocity and pressure fields around the interface of bubbles are shown oscillation free during the merging of two bubbles.

• 센서학회지
• /
• 제25권1호
• /
• pp.57-64
• /
• 2016

To understand a two-phase flow, a liquid film thickness is one of the important factors. A lot of researches have been performed to measure liquid film thickness with various approaches. Recently, an electrical conductance method which uses the conductivity of the liquid film has been widely applied on measuring the liquid film thickness. Though the electrical method has an advantage in high spatial resolution, as the conductivity of liquid can be affected by its temperature variation, the conventional electrical conductance methods have a limitation in being applied on varying temperature conditions where a heat transfer is involved. The purpose of this study is to develop a three-ring liquid film sensor that overcomes the limitation of the conventional method. The three-ring conductance method can measure the film thickness regardless of temperature variation by compensating the change of liquid conductivity. Considering its application on a wide range of conditions such as high temperature or curved surfaces, the sensor was fabricated on flexible printed circuit board (FPCB) in this study. This paper presents the concept of the measurement method, design procedure, prototype sensor fabrication and calibration results.

• 전력전자학회논문지
• /
• 제7권4호
• /
• pp.322-331
• /
• 2002

본 논문은 단상 반파 PWM 정류기와 3상 2-leg 인버터를 결합한 단상-삼상 컨버터 회로에서 전원전압의 센서를 제거하여 3상 유도전동기를 저가형으로 구동하는 방법을 제안하고자 한다. 전원전압의 센서를 제거하기 위해 전원 전류의 실측치와 제어기 내의 모델전류가 일치하도록 관측기를 구성하여 전원전압을 추정한다. 본 논문에서 제안한 기법을 사용할 경우 스위칭 소자와 센서 수를 줄이면서 직류전압 일정제어, 입력전류의 정현제어 및 단위 역률 제어가 가능하고 VVVF 교류전압을 얻을 수 있다는 장점이 있다. 3[Hp]의 3상 유도전동기의 V/f 구동에 적용한 실험결과로 제시된 알고리즘의 타당성을 검증한다.

• 대한기계학회논문집
• /
• 제12권3호
• /
• pp.599-606
• /
• 1988

본 연구에서는 공기와 물을 사용한 근사수평 반류성층유동에서의 계면파 구조 를 측정하였다. 3차원파 영역내의 유동조건하에서 탐침접촉법을 이용하여 계면파의 액막분포도를 구하였으며 Gauss 모델과 비교분석하였다. 또 이 분포도에서 파의 구 조와 관련된 통계치, 즉 평균액막두께, 파진폭, 파고 교란강도등을 계산하여 유동조건 에 따른 경향을 분석하였다. 본 연구와 병행하여 계면전단응력과 계면마찰계수에 관 한 실험을 수행하였는데 이 결과와 계면파 구조와의 상호연관성도 고찰하였다.

• 한국유체기계학회 논문집
• /
• 제5권3호
• /
• pp.15-24
• /
• 2002

This paper presents an experimental study on the unsteady flow phenomena such as leakage flow and rotating stall which have influences on the performance and stability of an axial flow fan. For this study, unsteady pressure were measured using high frequency pressure transducers mounted on the easing wall of rotor passage and analyzed by Double Phase-Locked Averaging Technique. As the flow rate was reduced to near stall point, the pressure difference between the pressure and the suction side of the blade was increased especially new the leading edge and the lowest pressure zone of suction side was gradually developed. From the result of unsteady pressure field on the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail.

• International Journal of Fluid Machinery and Systems
• /
• 제3권3호
• /
• pp.211-220
• /
• 2010

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.