• Title, Summary, Keyword: bubble-point

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Phase Behavior of Ternary Mixture of Poly(ethylene-co-octene) - Ethylene - 1-Octene (Poly(ethylene-co-octene) - Ethylene - 1-Octene 3성분계 혼합물의 상거동)

  • Lee, Sang-Ho;Sohn, Jin-Eun;Chung, Sung-Yoon;Han, Sang-Hoon
    • Elastomers and Composites
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    • v.41 no.2
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    • pp.116-124
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    • 2006
  • Cloud-point data to $160^{\circ}C$ and 1,000 bar are presented with poly(ethylene-co-15.3 mole% octene) copolymers ($PEO_{15}$) in pure 1-octene and mixtures of ethylene - 1-octene. The cloud-point curves for $PEO_{15}$ - ethylene - 1-octene mixture dramatically increase in pressure to as high as 1,000 bar with an increasing ethylene concentration. At ethylene concentrations less than 18 wt%, the ternary mixture has bubble- and cloud-point curves. As the ethylene concentration of the ternary mixture increases, the bubble-point curve and the single-phase region reduce. The reduction in the single phase region with increasing ethylene concentrations is the result of reduced dispersion interactions between $PEO_{15}$ and the mixed solvent. The single-phase region decreases with increasing temperatures when ethylene concentrations are lower than 36 wt%, whereas the single-phase region increases with temperatures at ethylene concentrations greater than 50 wt%. At ethylene concentrations greater than 50 wt% the effect of the polar interactions of the mixed solvent, which is unfavorable to dissolve PEO, is greater than the effect of the density of the mixed solvent. Therefore, the cloud-point pressures increase with a decreasing temperature. However, at ethylene concentrations less than 50 wt%, the cloud-point pressures decrease with temperature, because the effect of the polar interactions is less than the density effect.

Operating Characteristics of a Bubble Pump for Diffusion-Absorption Refrigerator (확산형 흡수식 냉동기용 기포펌프의 운전특성에 관한 연구)

  • 이현경;김선창;이재헌
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.9
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    • pp.878-887
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    • 2001
  • Experimental investigation has been carried out to examine the operating characteristics of a bubble pump for diffusion absorption refrigerator. The effects of heat input and delivery height on generation rate of refrigerant vapor and circulation rate of solution have been investigated. as a result heat input and delivery height increase, circulation rate of solution increases. And the smaller the tube diameter, the larger the circulation rate of solution. Pumping ratio increases to a critical point and then decrease with the increase of heat input, and it increases with the increase in delivery height. In this paper, Marcus's analytical theory was also examined. It was found that the Marcus\`s analytical theory of a bubble pump was not appropriate for a bubble pump using ammonia aqueous solution as a working fluid.

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Discrete Vortex Simulation of Turbulent Separated and Reattaching Flow With Local Perturbation (국소교란이 있는 난류박리 재부착유동의 이산와류 수치해석)

  • 정용만;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.2
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    • pp.479-491
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    • 1994
  • Discrete vortex method was applied for simulating an active control of turbulent leading- edge separation bubble. The leading-edge separation zone was perturbed by a time-dependent sinusoidal perturbation of different frequencies and levels. In order to describe the local sinusoidal perturbation at the separation point, a source pulsation vortex technique was proposed. The present two-dimensional vortex simulations were qualitatively compared with the experimental results for a blunt circular cylinder, where perturbation was introduced along the square-cut leading edge of the cylinder $(Kiya et al.^{(6,7)}).$ It was found that the reattachment length attained a minimum point at low levels of perturbation and two minima at a moderate higher perturbation frequency. The effects of local perturbation on the evolution of leading-edge separation bubble were scrutinized by comparing the perturbed flow with the natural flow. These comparisons were made for the distributions of mean velocity and its velocity fluctuations, intermittency and wall velocity. The motions of instantaneous reattachment in the space-time domain were demonstrated, which were also compared with the experimental findings. In order to investigate the reduction mehanism of reattachment length in the separation bubble, various cross-correlations for velocity and pressure and the relevant convection velocities were evaluated. It was observed that the convection velocity was closely associated with its corresponding pulsationg frequency.

A Study of Heat Transfer Phenomena due to a Formed Gas Bubble under Heat-Conduction Domain in A Closed Square Cavity (TLC 를 이용한 사각공동내의 열전도 영역에 기포의 형성으로 인한 열전달 현상 구명)

  • Eom, Young-Kyoon;You, Jae-Bong
    • Proceedings of the KSME Conference
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    • pp.85-89
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    • 2003
  • In a closed square cavity filled with a liquid, a cooled the upper horizontal wall and a heated the lower horizontal wall, the flow isn't generated under the ground-based condition when Rayleigh number is lower than 1700. In such case the flow phenomena near an air bubble under a cooled horizontal wall were investigated. The temperature and the flow fields were studied by using the Thermo-sensitive Liquid-Crystal and the image processing. The qualitative analysis for the temperature and the flow fields were carried out by applying the image processing technique to the original data. Injecting bubble at the center point of upper cooled wall, the symmetry shape of two vortexes near an air bubble was observed. The bubble size increased, the size of velocity and the magnitude of velocity increased. In spite of elapsed time, a pair of two vortexes was the unique and steady-state flow in a square cavity and wasn't induce to the other flow in the surround region.

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On the Measurement Technique of Void Fraction by Single Camera Two Phase PIV (단일 카메라 입자영상유속계를 이용한 이상유동 기포율 측정방법)

  • Choi, Dong-Whan;Sung, Jae-Yong;Yoo, Jung-Yul
    • Proceedings of the KSME Conference
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    • pp.1558-1563
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    • 2004
  • A measurement technique for the void fraction and the bubble dynamics in gas-liquid two-phase flows has been proposed using a time-resolved two-phase PIV system. For the three-dimensional evaluation of the bubble information, both the images from the front and side views are simultaneously recorded into a high speed CCD camera by reflecting the side image into the front view with the help of a $45^{\circ}$ oriented mirror. Then, a stereo-matching technique is applied to calculate the void fraction, bubble size and shape. To obtain the rising bubble velocities, the 2-frame PTV method was applied. Consequently, the present technique shows good feasibility for the measurements of the volume fractions, mean diameters, aspect ratios and velocities of the bubbles at the three-dimensional point of view.

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Numerical Simulation of Cavitating Flows on a Foil by Using Bubble Size Distribution Model

  • Ito, Yutaka;Nagasaki, Takao
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.216-227
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    • 2004
  • A new cavitating model by using bubble size distribution based on bubbles-mass has been proposed. Both liquid and vapor phases are treated with Eulerian framework as a mixture containing minute cavitating bubbles. In addition vapor phase consists of various sizes of vapor bubbles, which are distributed to classes based on their mass. The bubble number-density for each class was solved by considering the change of the bubble-mass due to phase change as well as generation of new bubbles due to heterogeneous nucleation. In this method, the bubble-mass is treated as an independent variable, and the other dependent variables are solved in spatial coordinates and bubble-mass coordinate. Firstly, we employed this method to calculate bubble nucleation and growth in stationary super-heated liquid nitrogen, and bubble collapse in stationary sub-cooled one. In the case of bubble growth in super-heated liquid, bubble number-density of the smallest class based on its mass is increased due to the nucleation. These new bubbles grow with time, and the bubbles shift to larger class. Therefore void fraction of each class is increased due to the growth in the whole class. On the other hand, in the case of bubble collapse in sub-cooled liquid, the existing bubbles are contracted, and then they shift to smaller class. It finally becomes extinct at the smallest one. Secondly, the present method is applied to a cavitating flow around NACA00l5 foil. Liquid nitrogen and liquid oxygen are employed as working fluids. Cavitation number, $\sigma$, is fixed at 0.15, inlet velocities are changed at 5, 10, 20 and 50m/s. Inlet temperatures are 90K in case of liquid nitrogen, and 90K and 1l0K in case of liquid oxygen. 110K of oxygen is corresponding to the 90K of nitrogen because of the same relative temperature to the critical one, $T_{r}$=$T/T_c^{+}$. Cavitating flow around the NACA0015 foils was properly analyzed by using bubble size distribution. Finally, the method is applied to a cavitating flow in an inducer of the LE-7A hydrogen turbo-pump. This inducer has 3 spiral foils. However, for simplicity, 2D calculation was carried out in an unrolled channel at 0.9R cross-section. The channel moves against the fluid at a peripheral velocity corresponding to the inducer revolutions. Total inlet pressure, $Pt_{in}$, is set at l00KPa, because cavitation is not generated at a design point, $Pt_{in}$=260KPa. The bubbles occur upstream of the foils and collapse between them. Cavitating flow in the inducer was successfully predicted by using the bubble size distribution.

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A Measurement of Temperature by TLC without Contact and A Study of Thermocapillary Flow under Ground-based Conditions (TLC 비접촉 온도측정과 중력장에서 열모세관 현상 구명)

  • 엄용균;유재봉
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.1071-1075
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    • 2003
  • In a closed square cavity filled with a liquid, a cooled the upper horizontal wail and a heated the lower horizontal wall, the flow isn't generated under the ground-based condition when Rayleigh number is lower than 1700. In such case the flow phenomena near an air bubble under a cooled horizontal wall were investigated. The temperature and the flow fields were studied by using the Thermo-sensitive Liquid-Crystal and the image processing. The qualitative analysis for the temperature and the flow fields were carried out by applying the image processing technique to the original data. Injecting bubble at the center point of upper cooled wall, the symmetry shape of two vortexes near an air bubble was observed. The bubble size increased, the size of velocity and the magnitude of velocity increased. In spite of elapsed time, a pair of two vortexes was the unique and steady-state flow in a square cavity and wasn't induce to the other flow in the surround region.

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Multiphase turbulence mechanisms identification from consistent analysis of direct numerical simulation data

  • Magolan, Ben;Baglietto, Emilio;Brown, Cameron;Bolotnov, Igor A.;Tryggvason, Gretar;Lu, Jiacai
    • Nuclear Engineering and Technology
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    • v.49 no.6
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    • pp.1318-1325
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    • 2017
  • Direct Numerical Simulation (DNS) serves as an irreplaceable tool to probe the complexities of multiphase flow and identify turbulent mechanisms that elude conventional experimental measurement techniques. The insights unlocked via its careful analysis can be used to guide the formulation and development of turbulence models used in multiphase computational fluid dynamics simulations of nuclear reactor applications. Here, we perform statistical analyses of DNS bubbly flow data generated by Bolotnov ($Re_{\tau}=400$) and LueTryggvason ($Re_{\tau}=150$), examining single-point statistics of mean and turbulent liquid properties, turbulent kinetic energy budgets, and two-point correlations in space and time. Deformability of the bubble interface is shown to have a dramatic impact on the liquid turbulent stresses and energy budgets. A reduction in temporal and spatial correlations for the streamwise turbulent stress (uu) is also observed at wall-normal distances of $y^+=15$, $y/{\delta}=0.5$, and $y/{\delta}=1.0$. These observations motivate the need for adaptation of length and time scales for bubble-induced turbulence models and serve as guidelines for future analyses of DNS bubbly flow data.

Mesh Generation Methodology for FE Analysis of 3D Structures Using Fuzzy Knowledge and Bubble Method (피지이론과 버블기법을 이용한 3차원 구조물의 유한요소해석을 위한 요소생성기법)

  • Lee, Joon-Seong;Lee, Eun-Chul
    • Journal of the Korean Institute of Intelligent Systems
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    • v.19 no.2
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    • pp.230-235
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    • 2009
  • This paper describes an automatic finite element mesh generation for finite element analysis of three-dimensional structures. It is consisting of fuzzy knowledge processing, bubble meshing and solid geometry modeler. This novel mesh generation process consists of three subprocesses: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The bubble spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Automatic generation of finite element for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for 3D geometry.

Automatic Mesh Generation System for FE Analysis of 3D Crack (3차원 균열의 유한요소해석을 위한 자동요소분할 시스템)

  • Lee, Ho-Jeong;Lee, Joon-Seong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.9
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    • pp.2183-2188
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    • 2009
  • This paper describes an automatic mesh generation system for finite element analysis of three-dimensional cracks. It is consisting of fuzzy knowledge processing, bubble meshing and solid geometry modeler. This novel mesh generation process consists of three sub-processes: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional crack structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The bubble spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Practical performances of the present system are demonstrated through several mesh generations for 3D cracks.