• Nuclear Engineering and Technology
• /
• 제36권1호
• /
• pp.12-23
• /
• 2004

In the present study a new measurement technique has been developed, which uses an ultrasonic transmission signal in order to identify the vertical two phase flow pattern. The ultrasonic measurement system developed in the present study not only provides the information required for the identification of vertical two phase flow patterns but also makes real time identification possible. Various vertical two phase flow patterns such as bubbly, slug, churn, annular flow etc. have been accurately identified with the present ultrasonic measurement system under atmospheric condition. In addition, the present test apparatus can practically simulate the ultrasonic propagation characteristics under high temperature and high pressure systems. Therefore, it is expected that the present ultrasonic flow pattern identification technique could be applicable to the vertical two phase flow systems under high temperature and high pressure conditions.

• Journal of Advanced Marine Engineering and Technology
• /
• 제27권3호
• /
• pp.460-465
• /
• 2003

Microgravity experiments were conducted to determine the effect of liquid and gas superficial velocities on flow behaviors. Flow behaviors observed under microgravity conditions can be classified into five flow patterns: bubble. Taylor bubble, slug, semi-annular and annular flows. Transition boundary between four flow patterns could be determined by drift-flux model. It was also found that the effect of gravity and pipe inclination on flow pattern transition was not significant in the inertia dominant region.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.767-772
• /
• 2006

The SWTR(Surface Water Treatment Rule) requires achieving removal 99.9% Giardia and 99.99% Virus. To remove Giardia and Virus, disinfection process is essential process. CT is important index for Disinfection performance. CT value is expressed by CXT. C is represented by disinfection concentration and T is represented by $T_{10}$ which means 90% contact time in clearwell. To improve Disinfection performance, it is desirable to increase $T_{10}$. Primary factor affected $T_{10}$ is flow Pattern. Because guide wall change that flow pattern is uniform, we have installed guide wall to increase $T_{10}$. In this paper, we have performed numerical analysis for clearwell installed symmetric guide wall and center divided guide wall using CFD. We have analyzed flow pattern and $T_{10}$ in each clearwell. And. we compare symmetric guide wall with center divided guide wall in flow pattern and $T_{10}$.

• Journal of Mechanical Science and Technology
• /
• 제17권5호
• /
• pp.758-765
• /
• 2003

An experimental investigation on the flow pattern and pressure drop was carried out for both an adiabatic and a diabatic two-phase flow in a horizontal tube with pure refrigerants R134a and R123 and their mixtures as test fluids. The observed flow patterns were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire regions of mass velocity in this study. The measured frictional pressure drop in the adiabatic experiments increased with an increase in vapor quality and mass velocity These data were compared to various correlations proposed in the past for the frictional pressure drop. The Chisholm correlation underpredicted the present data both for pure fluids and their mixtures in the entire mass velocity range of 150 to 600 kg/m$^2$s covered in the measurements, white the Friedel correlation was found to overpredict the present data in the stratified and stratified-wavy flow region, and to underpredict in the annular flow region.

• 한국산학기술학회논문지
• /
• 제8권6호
• /
• pp.1307-1312
• /
• 2007

본 논문은 세관내 R-134a의 유동특성을 실험적으로 조사한 것이다. 이에 대한 실험장치는 마그네틱 기어 펌프, 증발기, 수액기, 사이트 글라스, 응축기 계측기로 구성된다. 유동양식을 관찰하기 위한 사이트 글라스는 증발기 입출구에 설치하였다. 실험은 세관내 R-22와 R-134a의 유동특성을 살펴보기 위해서 수행되었다. 이에 대한 실험변수인 냉매질량 유속은 100에서 1000 $kg/m^2s$이고, 포화온도는 $30^{\circ}C$이다. 증발과정 중의 유동양식에서 2 mm의 세관내 환상유동은 8 mm관의 대구경관에 비해 저건도와 저질량유속에서 발생하였다. 본 실헐 결과와 종래의 유동양식 선도와 비교한 결과, 2 mm의 세관내 증발 유동양식은 Baker, Mandhane, Taitel-Dukler의 유동양식 선도와는 큰 차이를 보였지만, Dobson의 유동양식 선도와는 좋은 일치를 보였다.

• 대한설비공학회지:설비저널
• /
• 제17권3호
• /
• pp.238-248
• /
• 1988

The flow pattern inside the power condenser is generally known to be very complicated due to the phase change and turbulence effects as well as the effect of condenser geometry. In the present study, the flow pattern inside the power condenser was numerically simulated with a personal computer. The widely known CHAMPION 2/E/FIX(Concentration, Heat and Momentum Program Instruction Outfit, 2D/Elliptic/Fixed grid) computer code was modified for this purpose. The flow was asssumed to be two-dimensional and steady-state, and the tube bank was considered to be homogeneous porous medium. Simple turbulent diffusion coefficients based on the appropriate experiments were obtained for the computation. Through this analytical approach, the flow pattern could be predicted fairly well. The computational results also show that the location of the air vent plays an important key role in determining the efficiency of the condenser.

• 한국해양공학회지
• /
• 제7권1호
• /
• pp.81-91
• /
• 1993

Studies on the flow pattern due to reclamation in the Myunggi-Nocksan region are carried out based on field observations and numerical experiments. Serial time series measurement of current, temperature and salinity were conducted for 1 tidal period at intervals of 1 hour from surface to bottom on station located at 128.deg. 54' 44" E, 35.deg. 01' 04" N in April and June 1992. Surface current opposite to the subsurface current causes turbulent mixing to make homogeneous salinity pattern in vertical section. Reclamation has little effect on the wave pattern and flow patterns are also nearly similar except on the nearby region of reclamation where flow speed somewhat weakened.

• 연구논문집
• /
• 통권31호
• /
• pp.53-63
• /
• 2001

Numerical investigation based on the control-volume using finite-difference method has been made by the development of computer program in order to figure out the pattern of the flow field inside screw decanter. The typical flow pattern inside screw decanter is characterized by the two strong recirculation zones separated by the main stream from slurry discharge hole to exit. These recirculation regions and flow pattern are strongly influenced by the centrifugal force and the change of the value of slurry viscosities, that is,500, 1,000 and 3,000cp respectively. The wear of screw decanter appeared experimentally in two spots; one is near the circumferential area of the slurry discharge hole and the other is on the decanter blades at a certain height from the bottom to a different degree after the continuous long-term operation. These wears are partly explained by the flow pattern and the strong turbulence intensity near the recirculation attachment region.

• 대한기계학회논문집B
• /
• 제28권4호
• /
• pp.395-405
• /
• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Using the proposed numerical technique, the collapse of a water dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions with respect to time have been compared with the reported experimental results.

• 로봇학회논문지
• /
• 제3권2호
• /
• pp.91-98
• /
• 2008

This paper describes the recognition method of moving objects in mobile robot with an omnidirectional camera. The moving object is detected using the specific pattern of an optical flow in omnidirectional image. This paper consists of two parts. In the first part, the pattern of an optical flow is investigated in omnidirectional image. The optical flow in omnidirectional image is influenced on the geometry characteristic of an omnidirectional camera. The pattern of an optical flow is theoretically and experimentally investigated. In the second part, the detection of moving objects is presented from the estimated optical flow. The moving object is extracted through the relative evaluation of optical flows which is derived from the pattern of optical flow. In particular, Focus-Of-Expansion (FOE) and Focus-Of-Contraction (FOC) vectors are defined from the estimated optical flow. They are used as reference vectors for the relative evaluation of optical flows. The proposed algorithm is performed in four motions of a mobile robot such as straight forward, left turn, right turn and rotation. Experimental results using real movie show the effectiveness of the proposed method.