Experimental Observation of Single Bubble Rise Characteristics in Various Situations

2002 ◽  
Author(s):  
Tomio Okawa ◽  
Tomoe Tanaka ◽  
Kazuhiro Torimoto ◽  
Masanori Nishiura ◽  
Isao Kataoka
Keyword(s):  
Bubble Formation ◽  
Experimental Information ◽  
Single Bubble ◽  
Phase Flow ◽  
Rise Velocity ◽  
Liquid Temperature ◽  
Two Phase ◽  
Bubble Rise ◽  
High Temperature Water ◽  
Temperature Water

The effects of liquid temperature and injection method on single bubble rise characteristics in clean still water were experimentally investigated. It was confirmed that the shape and rise velocity of a bubble strongly depend on the method of bubble formation. For the rise velocity in high temperature water, the correlation for fully contaminated liquid might be appropriate even in the clean water. Because of the importance in the numerical simulation of bubbly two-phase flow, the experimental information on rise path oscillation such as amplitude and frequency was also reported.

Numerical Simulation of Single Bubble Moving in Stagnant Solid-Liquid Mixture Pool Using Finite Volume Particle Method

2013 ◽  
Author(s):  
Yuki Aramaki ◽  
Takahito Suzuki ◽  
Ichiro Miya ◽  
Liancheng Guo ◽  
Koji Morita
Keyword(s):  
Liquid Mixture ◽  
Single Bubble ◽  
Phase Flow ◽  
Bubble Shape ◽  
Rise Velocity ◽  
Bubble Rise ◽  
Bubble Rise Velocity ◽  
Three Phase ◽  
Three Phase Flow ◽  
Fluid Interactions

Three-phase flow formed in a disrupted core of nuclear reactors is one of the key phenomena to be simulated in reactor safety analysis. Particle-based simulation could be a powerful CFD tool to understand and clarify local thermal-hydraulic behaviors involved in such three-phase flows. In the present study, to develop a computational framework for three-phase flow simulations, a single bubble moving in a stagnant solid particle-liquid mixture pool was simulated using the finite volume particle (FVP) method. The simulations were carried out in a two dimensional system. The bubble shape change and the bubble rise velocity were compared with the newly performed experiments, which used solid particulate glasses of 0.9 mm in diameter, liquid silicone and air. The two-phase flow simulation of a single bubble rising in a stagnant liquid pool reproduced measured bubble shape and bubble rise velocity reasonably. On the other hand, the bubble rise velocity in a stagnant particle-liquid mixture pool was overestimated in comparison with the measurement. This result suggests that particle-particle and particle-fluid interactions would have dominant influence on bubble motion behavior in the particle-liquid mixture pool under the present multiphase conditions. To evaluate such interactions in the simulations, the particle-particle interactions were modeled by the distinct element method (DEM), while two models were applied to represent particle-fluid interactions. One is the theoretical model for apparent viscosity of particle-liquid mixture, which describes the viscosity increase of liquid mixed with solids based on the Frankel-Acrivos equation. The other is the drag force model for solid-fluid interactions. In the present study, we took the Gidaspow drag correlation, which is a combination of the Ergun equation and Wen-Yu equation. A comparison of both the transient bubble shape and bubble rise velocity between the results of experiment and simulation demonstrates that the present computational framework based on the FVP method and solid-phase interaction models is useful for numerical simulations of a single bubble moving in a stagnant solid particle-liquid mixture pool.

Aerosol Decontamination Behavior in Two Phase Flow During Pool Scrubbing

2020 ◽  
Author(s):  
Kohei Yoshida ◽  
Kota Fujiwara ◽  
Yuki Nakamura ◽  
Akiko Kaneko ◽  
Yutaka Abe
Keyword(s):  
Flow Structure ◽  
Two Phase Flow ◽  
Bubble Diameter ◽  
Wire Mesh ◽  
Single Bubble ◽  
Dominant Factor ◽  
Large Bubble ◽  
Phase Flow ◽  
Rise Velocity ◽  
Two Phase

Abstract In some scenarios in severe accidents (SAs) of nuclear power plants (NPPs), non-condensable gas containing vapor and small particles of fission products (FPs) will be released from the reactor vessel, pass through the wet well of a suppression chamber. In these conditions, water inside the wet well will trap FPs before released to the atmosphere. This trapping effect is called pool scrubbing. Since pool scrubbing is assumed to have a good decontamination effect, researches about the pool scrubbing are important from the viewpoints of NPPs safety. Therefore, it is necessary to understand the two-phase flow behavior in pool scrubbing. The mechanism of the FPs removal behavior in pool scrubbing is not clearly understood due to the complicated hydrodynamic phenomena. In addition, the evaluation of the validity of physical models used in pre-existing SA analysis codes are not enough. Therefore, a reliable model to evaluate particle decontamination efficiency by pool scrubbing is highly regarded. Currently, decontamination factor (DF) of pool scrubbing is calculated by analysis code such as MELCOR. In the MELCOR code, some assumptions and empirical formula are used, e.g. bubble diameter and rising velocity. However, the correlation between DF and flow structure characteristics are not understood, and dominant factor of decontamination behavior in two phase flow is required. Therefore, the aim of this study is to elucidate the dominant factor of decontamination by measuring DF and flow structure of bubbly plume. As to understand two phase flow characteristics during pool scrubbing, we focus on bubble diameter and swarm rise velocity. In Air-particle mixture flow injected into the experimental facility gas velocity, void fraction and bubble diameter distribution were measured by a wire mesh sensor (WMS) in each height. In addition, DF by pool scrubbing was derived from aerosol measurements by an aerosol spectrometer. The measured warm rise velocity were compared with equation of single bubble terminal velocity. The swarm rise velocity is higher than single bubble velocity. Furthermore, Large bubble are identified to be still remained at swarm region defined in MELCOR. In addition, dominant factor of decontamination behavior is defined as particle diameter, neither aerosol solubility nor particle density.

Mixing Characteristics of a Two-Phase Flow (Gas-Liquid) Microchannel Mixer

2011 ◽  
Author(s):  
Tarek Abdel-Salam ◽  
Srikanth Pidugu
Keyword(s):  
Reynolds Number ◽  
Two Phase Flow ◽  
Bubble Formation ◽  
Width Ratio ◽  
Phase Flow ◽  
Two Phase ◽  
Bubble Generation ◽  
Air Bubble ◽  
And Performance ◽  
Actual Shape

Multiphase phase flows occur in many engineering and bio-medical applications. Bubble formation in microchannels can be beneficial or harmful depending upon their influence on the operation and performance of microfludic devices. Potential uses of bubble generation found in many applications such as microreactors, micropump, and micromixers. In the present work the flow and mixing process in a passive microchannel mixer were numerically investigated. Effects of velocity, and inlet width ratio (Dgas/Dliquid) on the two phase flow were studied. Numerical results are obtained for 2-dimensional and 3-dimesional cases with a finite volume CFD code and using structured grids. Different liquid-gas Reynolds number ratios (Reliquid/Regas) were used ranging from 4 to 42. In addition, three values of the inlet width ratio (Dgas/Dliquid) were used. Results for the 3-D cases capture the actual shape of the air bubble with the thin film between the bubble and the walls. Also, increasing Reliquid increases the rate of the development of the air bubble. The bubble length increases with the increase of Dgas/Dliquid. For the same values of Re, the rate of growth of the bubble increases with the increase of Dgas/Dliquid. Finally, a correlation is provided to predict the length of the bubble with liquid-gas Reynolds number ratio (Reliquid/Regas) and tube width.

Two-Phase Flow Patterns During Microchannel Vaporization of CO2 at Near-Critical Pressures

2003 ◽  
Author(s):  
Jostein Pettersen
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Bubble Formation ◽  
Glass Tube ◽  
Flow Patterns ◽  
High Mass ◽  
Phase Flow ◽  
Two Phase

Carbon dioxide (CO2 / R-744) is receiving renewed interest as a refrigerant, in many cases based on systems with microchannel heat exchangers that have high pressure capability, efficient heat transfer, and compact design. A good understanding of two-phase flow of evaporating CO2 in microchannels is needed to analyze and predict heat transfer. A special test rig was built in order to observe two-phase flow patterns, using a horizontal quartz glass tube with ID 0.98 mm, externally coated by a transparent resistive film. Heat flux was obtained by applying DC power to the film, and flow patterns were recorded at 4000 or 8000 frames per second by a digital video camera. Flow patterns were recorded for temperatures 20°C and 0°C, and for mass flux ranging from 100 to 580 kgm−2s−1. The observations showed a dominance of intermittent (slug) flow at low x, and wavy annular flow with entrainment of droplets at higher x. At high mass flux, the annular/entrained flow pattern could be described as dispersed. The aggravated dryout problem reported from heat transfer experiments at high mass flux could be explained by increased entrainment. Stratified flow was not observed in the tests with heat load. Bubble formation and growth could be observed in the liquid film, and the presence of bubbles gave differences in flow pattern compared to adiabatic flow. The flow pattern observations did not fit generalized maps or transition lines showed in the literature.

Vibration Behavior of a Channel Subjected to an Internal Two-Phase Flow

2007 ◽  
Author(s):  
Ming Ming Zhang ◽  
Joseph Katz
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Bubble Formation ◽  
Normal Modes ◽  
Acoustic Mode ◽  
Phase Flow ◽  
Two Phase ◽  
Square Channel ◽  
Bubble Cloud ◽  
The Past

Vibrations of a channel wall subjected to an external two-phase flow have been widely investigated in the past. However, there is very little information on the effect of internal two-phase flows on the vibrations. To this end, this paper presents results of an experimental investigation of changes to wall vibrations in a vertical square channel, which are caused by introducing a uniform bubble cloud into the flow. The effects of void fraction, characteristic bubble size and flow velocity on wall vibrations are measured. Results show that wall vibrations are greatly enhanced, by up to 25 dB, compared with the same flow without bubbles. The enhancement and spectra of the vibration are mainly dependent on the bubble void fraction. To understand the physics behind the results, evolution of the spectra along the streamwise direction are examined. The primary mechanisms for increased vibrations are: the lateral fundamental acoustic mode excitation of a bubble cloud whose frequency decreases due to change in sonic speed and normal modes of the bubble cloud. The fundamental mode of a bubble cloud persists along the entire channel and its harmonics enhance the vibrations over a broad frequency range. The cloud normal modes are generated due to the process of bubble formation, and they decay with increasing distance from the source.

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