Behavior of Bubbles Separated by a Cross-Shaped Obstacle Placed in a Circular Flow Channel

2017 ◽  
Author(s):  
Kazuyuki Takase ◽  
Hiep H. Nguyen ◽  
Gaku Takase ◽  
Yoshihisa Hiraki
Keyword(s):  
High Speed ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Flow Direction ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Wire Mesh ◽  
Phase Flow ◽  
Two Phase ◽  
Validation Data

Clarifying two-phase flow characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. Moreover, bubbly flow data in subchannels with spacers are needed as validation data for current CFD codes like a direct two-phase flow analysis code. In order to investigate the spacer effect on the bubbly flow behavior in a subchannel of the nuclear reactor, bubble dynamics around the simply simulated spacer was visually observed by a high speed camera. Furthermore, the void fraction and interfacial velocity distributions just behind the simulated spacer were measured quantitatively by using a wire-mesh sensor system with three wire-layers in the flow direction. From the present study, bubble separation behavior dependence upon the spacer shape was clarified.

Image Based Bubbly Flow Feature Identification Using Deep Learning

2021 ◽  
Author(s):  
Takashi Furuhashi ◽  
Takuro Sasaki ◽  
Shuichiro Miwa
Keyword(s):  
High Speed ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Fluid Model ◽  
Bubbly Flow ◽  
Interfacial Area ◽  
Liquid Interface ◽  
Phase Flow ◽  
Two Phase ◽  
Interfacial Area Concentration

Abstract Gas-liquid two-phase flow has high potential in heat transfer and mixing capabilities, and therefore it is utilized in various technologies such as nuclear reactor and chemical plants. There are several flow regimes since the gas-liquid interface transforms constantly. For the sake of safety and optimization in operating plants, it is crucial to understand the behavior of the gas-liquid interface. We have focused on extracting the bubble features in the bubbly flow by filming the bubbly flow with a high-speed camera and training convolutional neural network (CNN) for feature extraction. The assumption made was bubbles in the bubbly flow being ellipsoids. Since void fraction and interfacial area concentration are one of the geometric parameters in the two-phase flow models, like two-fluid model, it becomes possible to evaluate the flow field of the two-phase flow quickly and quantitively by calculating these parameters from the extracted features. We have compared two-phase flow parameters with the conventional object detection method using bounding boxes, and the new ellipse fitting method to identify the best region proposal shape. As a result, the conventional method showed higher accuracy in extracting bubble features under our flow conditions.

Measurement of Two-Dimensional Void Fraction Distributions of Rising Bubbles in a Simulated Sub-Channel by Wire-Mesh Sensors at Conditions of Forced Convective and Stagnant Flows

2017 ◽  
Author(s):  
Yota Suzuki ◽  
Yusei Tanaka ◽  
Taku Sakka ◽  
Akinori Sato ◽  
Kazuyuki Takase ◽  
...  
Keyword(s):  
Flow Condition ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Wire Mesh ◽  
Phase Flow ◽  
Two Dimensional ◽  
Two Phase ◽  
Fuel Rods ◽  
Fuel Rod ◽  
Stagnant Flow

Clarifying thermal-hydraulic characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. Spacers installed in subchannels of fuel assemblies have the role of keeping the interval between adjacent fuel rods constantly. Similarly, in case of PWR the spacer has also the role as the turbulence promoter. When the transient event occurs, two-phase flow is generated by boiling of water due to heating of fuel rods. Therefore, it is important to confirm the two-phase flow behavior around the spacer. So, the effect of the spacer affecting the two-phase flow was investigated experimentally at forced convective flow condition. Furthermore, in order to improve the thermal safety of current light water reactors, it is necessary to clarify the two-phase flow behavior in the subchannels at the stagnant flow condition. So, the bubbly flow data around a simulated fuel rod were obtained experimentally at the stagnant flow condition. A wire-mesh sensor was used to obtain a detailed two-dimensional void fraction distribution around the simulated spacer and fuel rod. As a result of this research, the bubbly behavior around the simulated spacer and fuel rod was qualitatively revealed and also bubble dynamics in the sub-channels at the conditions of forced convective and stagnant flows were evaluated. The present experimental data are very useful for verifying the detailed three-dimensional two-phase flow analysis codes.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (12) Bubble Motion Along the Flow in Structure Vibration

2014 ◽  
Author(s):  
Yuki Kato ◽  
Rie Arai ◽  
Akiko Kaneko ◽  
Hideaki Monji ◽  
Yutaka Abe ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Velocity Field ◽  
Test Section ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Experimental Results ◽  
Phase Flow ◽  
Bubble Motion ◽  
Two Phase

In a nuclear power plant, one of the important issues is an evaluation of the safety of the reactor core and its pipes when an earthquake occurs. Many researchers have conducted studies on constructions of plants. Consequently, there is some knowledge about earthquake-resisting designs. However the influence of an earthquake vibration on thermal fluid inside a nuclear reactor plant is not fully understood. Especially, there is little knowledge how coolant in a core response when large earthquake acceleration is added. Some studies about the response of fluid to the vibration were carried out. And it is supposed that the void fraction and/or the power of core are fluctuated with the oscillation by the experiments and numerical analysis. However the detailed mechanism about a kinetic response of gas and liquid phases is not enough investigated, therefore the aim of this study is to clarify the influence of vibration of construction on bubbly flow behavior. In order to investigate the influence of vibration of construction on bubbly flow behavior, we visualized bubbly flow in pipeline on which sine wave was applied. In a test section, bubbly flow was produced by injecting gas into liquid flow through a horizontal circular pipe. In order to vibrate the test section, an oscillating table was used. The frequency and acceleration of vibration added from the oscillating table was from 1.0 Hz to 10 Hz and . 0.4 G (1 G=9.8 m/s2) at each frequency. The test section and a high speed video camera were fixed on the oscillating table. Thus the relative velocity between the camera and the test section was ignored. PIV measurement was also conducted to investigate interaction between bubble motion and surround in flow structure. Liquid pressure was also measured at upstream and downstream of the test section. The effects of oscillation on bubbly flow were quantitatively evaluated by these pressure measurements and the velocity field. In the results, it was observed that the difference of bubble motion by changing oscillation frequency. Moreover it was suggested that the bubble deformation is correlated with the fluctuation of liquid velocity field around the bubble and the pressure gradient in the flow area. In addition, these experimental results were compared with numerical simulation by a detailed two-phase flow simulation code with an advanced interface tracking method, TPFIT. Numerical simulation was qualitatively agreed with experimental results.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (13) Rising Bubble Motion Under Horizontal Vibration

2014 ◽  
Author(s):  
Rie Arai ◽  
Akiko Kaneko ◽  
Hideaki Monji ◽  
Yutaka Abe ◽  
Hiroyuki Yoshida ◽  
...  
Keyword(s):  
Void Fraction ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Nuclear Reactors ◽  
Bubbly Flow ◽  
Structural Safety ◽  
Phase Flow ◽  
Two Phase ◽  
Safety Operation

An earthquake is one of the most serious phenomena for the safety of a nuclear reactor in Japan. Therefore, structural safety of nuclear reactors has been studied and nuclear reactors ware contracted with structural safety for a big earthquake. However, it is not enough for safety operation of nuclear reactors because thermal-fluid safety is not confirmed under the earthquake. For instance, behavior of gas-liquid two-phase flow is unknown under the earthquake conditions. Especially, fluctuation of void fraction is an important factor for the safety operation of the nuclear reactor. In the previous work, fluctuation of void faction in bubbly flow was studied experimentally and theoretically, to investigate the stability of the bubbly flow. In such studies, flow rate or void fraction fluctuations were given to the steady bubbly flow. In the case of the earthquake, the fluctuation is not only the flow rate, but also a body force on the two-phase flow and a shear force through a pipe wall. Interactions of gas and liquid through their interface also act on the behavior of the two-phase flow. The fluctuation of the void fraction is not clear for such complicated situation under the earthquake. Therefore, in this research project, the behavior of gas-liquid two-phase flow is investigated experimentally and numerically in the series of study. In this study, to investigate the effects of vibration on bubbly flow in the components and construct an experimental database for validation, we performed visualization experiments of vertical bubbly flow in a rectangular water tank on which a sine wave vibration was applied. In this paper, results of visualized experiment evaluated by the visualization techniques, including positions of bubbles, shapes of bubbles and liquid velocity distributions around bubbles, were shown. And liquid velocity distribution around bubbles by the PIV measurement was also shown. In the results, bubble behaviors were affected by oscillation. And the cycle of the bubble tilt angle was almost same as the cycle of oscillation table velocity.

scholarly journals Experimental Investigations on the Inner Flow Behavior of Centrifugal Pumps under Inlet Air-Water Two-Phase Conditions

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4377 ◽  
Author(s):  
Si ◽  
Zhang ◽  
Bois ◽  
Zhang ◽  
Cui ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Performance Degradation ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Impeller Blade ◽  
Pump Performance ◽  
Starting Point

Centrifugal pumps are widely used and are known to be sensitive to inlet air-water two-phase flow conditions. The pump performance degradation mainly depends on the changes in the two-phase flow behavior inside the pump. In the present paper, experimental overall pump performance tests were performed for two different rotational speeds and several inlet air void fractions (αi) up to pump shut-off condition. Visualizations were also performed on the flow patterns of a whole impeller passage and the volute tongue area to physically understand pump performance degradation. The results showed that liquid flow modification does not follow head modification as described by affinity laws, which are only valid for homogeneous bubbly flow regimes. Three-dimensional effects were more pronounced when inlet void fraction increased up to 3%. Bubbly flow with low mean velocities were observed close to the volute tongue for all αi, and returned back to the impeller blade passages. The starting point of pump break down was related to a strong inward reverse flow that occurred in the vicinity of the shroud gap between the impeller and volute tongue area.

Effects of Curved Section on Gas-Liquid Two-Phase Flow in Milli-Channel

2013 ◽  
Author(s):  
Kazuki Takeda ◽  
Shinpei Okamoto ◽  
Kenji Yoshida ◽  
Isao Kataoka
Keyword(s):  
Pressure Loss ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Narrow Channel ◽  
Phase Flow ◽  
Straight Section ◽  
Industrial Products ◽  
Two Phase ◽  
Curved Section

In recent years, we can easily find the gas-liquid two-phase flow in narrow channel which has straight section and curved section in many industrial products. In order to improve the performance of these industrial products, it is important to clarify the effects of curved section on gas-liquid two-phase flow behavior in narrow channel. In this study, we have measured the pressure loss precisely on straight section and curved section in milli-channel respectively. From the measured pressure loss, we evaluated the mean pressure loss and its intensity. Flow visualization by using high-speed video camera was additionally performed to make clear the relation between modification of pressure loss and flow pattern in curved section. As a result, effects of curved section on gas-liquid two-phase flow in narrow channel were evaluated.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (11) Bubble Motion Under the Flow Vibration

2014 ◽  
Author(s):  
Ryotaro Yokoyama ◽  
Jun-ichi Takano ◽  
Hideaki Monji ◽  
Akiko Kaneko ◽  
Yutaka Abe ◽  
...  
Keyword(s):  
Flow Rate ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Plug Flow ◽  
Flow Simulation ◽  
Phase Flow ◽  
Bubble Behavior ◽  
Two Phase ◽  
Rate Fluctuation

Earthquake is one of the most serious phenomena for safety of a nuclear power plant. Therefore, nuclear reactors were contracted considering structural safety for a big earthquake. In a nuclear reactor, the gas-liquid two-phase flow is the one of primary factor of the property and bubbly or plug flow behavior is important issue to evaluate of safety. However, the influence of an earthquake vibration on the gas-liquid two-phase flow inside the nuclear power plant is not understood enough. For example, the bubbly flow behavior under the flow rate fluctuation caused by the earthquake acceleration is not clear. It is necessary to clear the two-phase flow behavior under the earthquake conditions. To develop the prediction technology of two-phase flow dynamics under the earthquake acceleration, the detailed two-phase flow simulation code with an advanced interface tracking method, TPFIT was expanded to the two-phase flow simulation under earthquake accelerating conditions. In the present study, the objective is to clarify the behavior of the gas-liquid two-phase flow under the earthquake conditions. Especially, the bubble behavior in the two-phase flow, a diameter, shape and velocity of bubbles which are expected to be influenced by the oscillation of the earthquake is investigated. In this experiment, the flow was bubbly flow and/or plug flow in a horizontal circular pipe. The working fluids were water and nitrogen gas. The nitrogen gas from gas cylinder was injected into the water through a nozzle and bubbly flow was generated at a mixer. The water was driven by a pump and the flow rate fluctuation was given by a reciprocating piston attached to the main flow loop. Main frequency of earthquakes is generally between 0.5Hz and 10Hz. Thus the frequency of the flow rate fluctuation in the experiment also was taken between 0.5Hz and 10Hz. The behavior of horizontal gas-liquid two-phase flow under the flow rate fluctuation was investigated by image processing using a high-speed video camera and PIV at test section. The pressure sensors were installed at the inlet of the mixer and the outlet of the test section. As the result, the bubble behavior mechanism under the flow rate fluctuation was obtained. In addition, the acceleration of a bubble and the pressure gradient in the pipe was synchronized under all frequency conditions. The prediction results by TPFIT were compared with the experimental results. They show good agreement on the flow field around a bubble and the bubble behavior.

Experimental Visualization of Two Phase Flow Inside an Electrical Submersible Pump Stage

2009 ◽  
Author(s):  
Lissett Barrios ◽  
Mauricio Gargaglione Prado
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubble Diameter ◽  
Phase Flow ◽  
Submersible Pump ◽  
Bubble Behavior ◽  
Two Phase ◽  
Operational Conditions ◽  
Electrical Submersible Pump

Dynamic multiphase flow behavior inside a mixed flow Electrical Submersible Pump (ESP) has been studied experimentally and theoretically for the first time. The overall objectives of this study are to determine the flow patterns and bubble behavior inside the ESP and to predict the operational conditions that cause surging. An experimental facility has been designed and constructed to enable flow pattern visualization inside the second stage of a real ESP. Special high speed instrumentation was selected to acquire visual flow dynamics and bubble size measurements inside the impeller channel. Experimental data was acquired utilizing two types of tests (surging test and bubble diameter measurement test) to completely evaluate the pump behavior at different operational conditions. A similarity analysis performed for single-phase flow inside the pump concluded that viscosity effects are negligible compared to the centrifugal field effects for rotational speeds higher than 600 rpm. Therefore, the two-phase flow tests were performed for rotational speeds of 600, 900, 1200, and 1500 rpm. Results showed formation of a large gas pocket at the pump intake during surging conditions.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration (6) Numerical Simulation of Bubble Deformation Near Wall Under Accelerating Condition

2012 ◽  
Author(s):  
Hiroyuki Yoshida ◽  
Taku Nagatake ◽  
Kazuyuki Takase ◽  
Akiko Kaneko ◽  
Hideaki Monji ◽  
...  
Keyword(s):  
Flow Rate ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Nuclear Reactors ◽  
Bubbly Flow ◽  
Flow Simulation ◽  
Structural Safety ◽  
Phase Flow ◽  
Two Phase ◽  
Safety Operation

Earthquake is one of the most serious phenomena for safety of a nuclear reactor in Japan. Therefore, structural safety of nuclear reactors has been studied and nuclear reactors were contracted with structural safety for a big earthquake. However, it is not enough for safety operation of nuclear reactors because thermal-fluid safety is not confirmed under the earthquake. For instance, behavior of gas-liquid two-phase flow is unknown under the earthquake conditions. Especially, fluctuation of void faction is an important factor for the safety operation of the nuclear reactor. In the previous work, fluctuation of void faction in bubbly flow was studied experimentally and theoretically to investigate the stability of the bubbly flow. In such studies, flow rate or void fraction fluctuations were given to the steady bubbly flow. In case of the earthquake, the fluctuation is not only the flow rate, but also body force on the two-phase flow and shear force through a pipe wall. Interactions of gas and liquid through their interface also act on the behavior of the two-phase flow. The fluctuation of the void fraction is not clear for such complicated situation under the earthquake. Therefore, the behavior of gas-liquid two-phase flow is investigated experimentally and numerically in a series of study. In this study, to develop the prediction technology of two-phase flow dynamics under earthquake acceleration, a detailed two-phase flow simulation code with an advanced interface tracking method TPFIT was expanded to two-phase flow simulation under earthquake conditions. In this paper, outline of expansion of the TPFIT to simulate detailed two-phase flow behavior under the earthquake condition was shown. And the bubbly flow in a horizontal pipe excited by oscillation acceleration and under the fluctuation of the liquid flow was simulated by using expanded TPFIT. Predicted deformation of bubbles near wall was compared with measured results under flow rate fluctuation and structural vibration.

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